Jeffrey M. Weinberg, MD

When COVID-19 emerged in March 2020, physicians were forced to evaluate the potential impacts of the pandemic on our patients and the conditions that we treat. For dermatologists, psoriasis came into particular focus, as many patients were being treated with biologic therapies. The initial concern was that these biologics might render our patients more susceptible to both COVID-19 infection and/or a more severe disease course.

In early 2020, the National Psoriasis Foundation (NPF) presented its own recommendations for treating patients with psoriatic disease during the pandemic.¹ Some highlights included the following¹:

• At the time, it was stipulated that patients with COVID-19 infection should stop taking a biologic.

• Psoriasis patients in high-risk groups (eg, concomitant systemic disease) should discuss with their dermatologist if their therapeutic regimen should be continued or altered.

• Patients taking oral immunosuppressive therapy may be at greater risk for COVID-19 infection, though there is no strong COVID-19–related evidence to provide specific guidelines or risk level.

In May 2020, the NPF COVID-19 Task Force was formed. This group—chaired by dermatologist Joel M. Gelfand, MD, MSCE (Philadelphia, Pennsylvania), and rheumatologist Christopher T. Ritchlin, MD, MPH (Rochester, New York)—was comprised of members from both the NPF Medical Board and Scientific Advisory Committee in dermatology, rheumatology, infectious disease, and critical care. The NPF COVID-19 Task Force has been critical in keeping the dermatology community apprised of the latest scientific thinking related to COVID-19 and publishing guidance statements that are updated and amended on a regular basis as new data becomes available.² Key recommendations most relevant to the daily care of patients with psoriatic disease included the following²:

• Patients with psoriasis and/or psoriatic arthritis have similar rates of SARS-CoV-2 infection and COVID-19 outcomes as the general population based on existing data, with some exceptions.

• Therapies for psoriasis and/or psoriatic arthritis do not meaningfully alter the risk for acquiring SARS-CoV-2 infection or having worse COVID-19 outcomes.

• Patients should continue their biologic or oral therapies for psoriasis and/or psoriatic arthritis in most cases, unless they become infected with SARS-CoV-2.

• Chronic systemic steroid use for psoriatic disease in the setting of acute infection with COVID-19 may be associated with worse outcomes; however, steroids may improve outcomes for COVID-19 when initiated in hospitalized patients who require oxygen therapy.

• When local restrictions or pandemic conditions limit the ability for in-person visits, offer telemedicine to manage patients.

• Patients with psoriatic disease who do not have contraindications to vaccination should receive a messenger RNA (mRNA)–based COVID-19 vaccine and boosters, based on federal, state, and local guidance. Systemic medications for psoriasis or psoriatic arthritis are not a contraindication to the mRNA-based COVID-19 vaccine. 

• Patients who are to receive an mRNA-based COVID-19 vaccine should continue their biologic or oral therapies for psoriasis and/or psoriatic arthritis in most cases.

• The use of hydroxychloroquine, chloroquine, and ivermectin is not suggested for the prevention or treatment of COVID-19 disease.

These guidelines have been critical in addressing some of the most pressing issues in psoriasis patient care, particularly the susceptibility to COVID-19, the role of psoriasis therapies in initial infection and health outcomes, and issues related to the administration of vaccines in those on systemic therapies. Based on these recommendations, we have been given a solid foundation that our current standard of care can (for the most part) continue with the continued presence of COVID-19 in our society. I encourage all providers to familiarize themselves with the NPF COVID-19 Task Force guidelines and keep abreast of updates as they become available (https://www.psoriasis.org/covid-19-task-force-guidance-statements/).

When COVID-19 emerged in March 2020, physicians were forced to evaluate the potential impacts of the pandemic on our patients and the conditions that we treat. For dermatologists, psoriasis came into particular focus, as many patients were being treated with biologic therapies. The initial concern was that these biologics might render our patients more susceptible to both COVID-19 infection and/or a more severe disease course.

In early 2020, the National Psoriasis Foundation (NPF) presented its own recommendations for treating patients with psoriatic disease during the pandemic.¹ Some highlights included the following¹:

• At the time, it was stipulated that patients with COVID-19 infection should stop taking a biologic.

• Psoriasis patients in high-risk groups (eg, concomitant systemic disease) should discuss with their dermatologist if their therapeutic regimen should be continued or altered.

• Patients taking oral immunosuppressive therapy may be at greater risk for COVID-19 infection, though there is no strong COVID-19–related evidence to provide specific guidelines or risk level.

In May 2020, the NPF COVID-19 Task Force was formed. This group—chaired by dermatologist Joel M. Gelfand, MD, MSCE (Philadelphia, Pennsylvania), and rheumatologist Christopher T. Ritchlin, MD, MPH (Rochester, New York)—was comprised of members from both the NPF Medical Board and Scientific Advisory Committee in dermatology, rheumatology, infectious disease, and critical care. The NPF COVID-19 Task Force has been critical in keeping the dermatology community apprised of the latest scientific thinking related to COVID-19 and publishing guidance statements that are updated and amended on a regular basis as new data becomes available.² Key recommendations most relevant to the daily care of patients with psoriatic disease included the following²:

• Patients with psoriasis and/or psoriatic arthritis have similar rates of SARS-CoV-2 infection and COVID-19 outcomes as the general population based on existing data, with some exceptions.

• Therapies for psoriasis and/or psoriatic arthritis do not meaningfully alter the risk for acquiring SARS-CoV-2 infection or having worse COVID-19 outcomes.

• Patients should continue their biologic or oral therapies for psoriasis and/or psoriatic arthritis in most cases, unless they become infected with SARS-CoV-2.

• Chronic systemic steroid use for psoriatic disease in the setting of acute infection with COVID-19 may be associated with worse outcomes; however, steroids may improve outcomes for COVID-19 when initiated in hospitalized patients who require oxygen therapy.

• When local restrictions or pandemic conditions limit the ability for in-person visits, offer telemedicine to manage patients.

• Patients with psoriatic disease who do not have contraindications to vaccination should receive a messenger RNA (mRNA)–based COVID-19 vaccine and boosters, based on federal, state, and local guidance. Systemic medications for psoriasis or psoriatic arthritis are not a contraindication to the mRNA-based COVID-19 vaccine. 

• Patients who are to receive an mRNA-based COVID-19 vaccine should continue their biologic or oral therapies for psoriasis and/or psoriatic arthritis in most cases.

• The use of hydroxychloroquine, chloroquine, and ivermectin is not suggested for the prevention or treatment of COVID-19 disease.

These guidelines have been critical in addressing some of the most pressing issues in psoriasis patient care, particularly the susceptibility to COVID-19, the role of psoriasis therapies in initial infection and health outcomes, and issues related to the administration of vaccines in those on systemic therapies. Based on these recommendations, we have been given a solid foundation that our current standard of care can (for the most part) continue with the continued presence of COVID-19 in our society. I encourage all providers to familiarize themselves with the NPF COVID-19 Task Force guidelines and keep abreast of updates as they become available (https://www.psoriasis.org/covid-19-task-force-guidance-statements/).

When COVID-19 emerged in March 2020, physicians were forced to evaluate the potential impacts of the pandemic on our patients and the conditions that we treat. For dermatologists, psoriasis came into particular focus, as many patients were being treated with biologic therapies. The initial concern was that these biologics might render our patients more susceptible to both COVID-19 infection and/or a more severe disease course.

In early 2020, the National Psoriasis Foundation (NPF) presented its own recommendations for treating patients with psoriatic disease during the pandemic.¹ Some highlights included the following¹:

• At the time, it was stipulated that patients with COVID-19 infection should stop taking a biologic.

• Psoriasis patients in high-risk groups (eg, concomitant systemic disease) should discuss with their dermatologist if their therapeutic regimen should be continued or altered.

• Patients taking oral immunosuppressive therapy may be at greater risk for COVID-19 infection, though there is no strong COVID-19–related evidence to provide specific guidelines or risk level.

In May 2020, the NPF COVID-19 Task Force was formed. This group—chaired by dermatologist Joel M. Gelfand, MD, MSCE (Philadelphia, Pennsylvania), and rheumatologist Christopher T. Ritchlin, MD, MPH (Rochester, New York)—was comprised of members from both the NPF Medical Board and Scientific Advisory Committee in dermatology, rheumatology, infectious disease, and critical care. The NPF COVID-19 Task Force has been critical in keeping the dermatology community apprised of the latest scientific thinking related to COVID-19 and publishing guidance statements that are updated and amended on a regular basis as new data becomes available.² Key recommendations most relevant to the daily care of patients with psoriatic disease included the following²:

• Patients with psoriasis and/or psoriatic arthritis have similar rates of SARS-CoV-2 infection and COVID-19 outcomes as the general population based on existing data, with some exceptions.

• Therapies for psoriasis and/or psoriatic arthritis do not meaningfully alter the risk for acquiring SARS-CoV-2 infection or having worse COVID-19 outcomes.

• Patients should continue their biologic or oral therapies for psoriasis and/or psoriatic arthritis in most cases, unless they become infected with SARS-CoV-2.

• Chronic systemic steroid use for psoriatic disease in the setting of acute infection with COVID-19 may be associated with worse outcomes; however, steroids may improve outcomes for COVID-19 when initiated in hospitalized patients who require oxygen therapy.

• When local restrictions or pandemic conditions limit the ability for in-person visits, offer telemedicine to manage patients.

• Patients with psoriatic disease who do not have contraindications to vaccination should receive a messenger RNA (mRNA)–based COVID-19 vaccine and boosters, based on federal, state, and local guidance. Systemic medications for psoriasis or psoriatic arthritis are not a contraindication to the mRNA-based COVID-19 vaccine. 

• Patients who are to receive an mRNA-based COVID-19 vaccine should continue their biologic or oral therapies for psoriasis and/or psoriatic arthritis in most cases.

• The use of hydroxychloroquine, chloroquine, and ivermectin is not suggested for the prevention or treatment of COVID-19 disease.

These guidelines have been critical in addressing some of the most pressing issues in psoriasis patient care, particularly the susceptibility to COVID-19, the role of psoriasis therapies in initial infection and health outcomes, and issues related to the administration of vaccines in those on systemic therapies. Based on these recommendations, we have been given a solid foundation that our current standard of care can (for the most part) continue with the continued presence of COVID-19 in our society. I encourage all providers to familiarize themselves with the NPF COVID-19 Task Force guidelines and keep abreast of updates as they become available (https://www.psoriasis.org/covid-19-task-force-guidance-statements/).

After learning about coronavirus disease 2019 (COVID-19) on the news, we were all aware that it would eventually affect our lives and our dermatology practices. However, once the COVID-19 pandemic arrived in the United States, we were under a shelter-in-place order, schools were shut, and most businesses were closed within a few weeks.

As dermatologists, we were considered essential workers, and our offices could remain open. However, as the numbers of cases accelerated in New York City—the global epicenter of the pandemic—and we approached our peak, I closed down my practice, except for emergencies.

One of the first medical challenges dermatologists faced in the early days of the COVID-19 pandemic was the proper management of our psoriasis patients. The major concern was that patients on biologics and other immunomodulatory therapies might be at an increased risk for COVID-19 infection and increased morbidity if affected. I received a multitude of telephone calls from patients taking these therapies who expressed high levels of concern and anxiety and were looking for direction as to whether they should continue their medications.

Early on, several of our professional societies provided guidelines regarding the use of systemic immunosuppressive agents during the COVID-19 pandemic. On April 15, 2020, the American Academy of Dermatology (AAD) advised, “Dermatologists must delicately balance the risk of immunosuppression with the risk of disease flare requiring urgent intervention with patient-specific risks.”¹ The AAD strongly recommended that patients should not stop their ongoing systemic immunosuppressive therapy without consulting their physicians. The AAD’s guidance provided specific recommendations for the following groups: (1) patients on systemic immunosuppressive agents who have not tested positive or exhibited signs/symptoms of COVID-19, (2) patients on systemic immunosuppressive agents who have tested positive for COVID-19 or exhibit signs/symptoms of COVID-19, (3) patients who have halted systemic immunosuppressive therapy after testing positive for COVID-19 (in whom it recommended physicians could reinitiate treatment), and (4) patients being considered for systemic immunosuppressive agents.¹

The National Psoriasis Foundation (NPF) also recognized the need for additional guidelines for health care providers and patients on managing psoriatic disease during the COVID-19 pandemic. In June 2020, the NPF formed a COVID-19 Task Force, which released its own recommendations for adult and pediatric patients with psoriatic disease.² Similar to the AAD, the NPF COVID-19 Task Force recommended that patients do not stop biologic or oral therapies for psoriasis during the current health crisis, stating the following: “While some uncertainties remain, initial data suggest that the benefit of continuing treatments for psoriatic diseases outweighs the hypothetical risks associated with immune modulating treatment of poor COVID-19–related outcomes for most patients.” Individuals in high-risk groups were advised to consult their health care providers regarding whether they should continue or alter therapy during the pandemic, and the clinical decision would be guided by the specific treatment regimen; the patient’s age, disease characteristics, and underlying medical conditions; or any particular concerns. Additionally, the task force emphasized that patients with psoriatic disease should continue to follow common sense measures to lower the risk of becoming infected with COVID-19, including practicing physical distancing, wearing face coverings in public settings, and washing their hands regularly.²

We remain in the midst of the COVID-19 pandemic with no true guidance as to the future course and impact of the infection. It is important to realize that our understanding of the coronavirus and its impact on our patients is constantly evolving. I encourage all providers to stay current with updates on clinical guidelines. In addition, we should pay attention to the myriad of clinical trials and registries now underway, as they may provide more insight into optimal clinical management in these challenging times.

Most importantly, stay safe!

After learning about coronavirus disease 2019 (COVID-19) on the news, we were all aware that it would eventually affect our lives and our dermatology practices. However, once the COVID-19 pandemic arrived in the United States, we were under a shelter-in-place order, schools were shut, and most businesses were closed within a few weeks.

As dermatologists, we were considered essential workers, and our offices could remain open. However, as the numbers of cases accelerated in New York City—the global epicenter of the pandemic—and we approached our peak, I closed down my practice, except for emergencies.

One of the first medical challenges dermatologists faced in the early days of the COVID-19 pandemic was the proper management of our psoriasis patients. The major concern was that patients on biologics and other immunomodulatory therapies might be at an increased risk for COVID-19 infection and increased morbidity if affected. I received a multitude of telephone calls from patients taking these therapies who expressed high levels of concern and anxiety and were looking for direction as to whether they should continue their medications.

Early on, several of our professional societies provided guidelines regarding the use of systemic immunosuppressive agents during the COVID-19 pandemic. On April 15, 2020, the American Academy of Dermatology (AAD) advised, “Dermatologists must delicately balance the risk of immunosuppression with the risk of disease flare requiring urgent intervention with patient-specific risks.”¹ The AAD strongly recommended that patients should not stop their ongoing systemic immunosuppressive therapy without consulting their physicians. The AAD’s guidance provided specific recommendations for the following groups: (1) patients on systemic immunosuppressive agents who have not tested positive or exhibited signs/symptoms of COVID-19, (2) patients on systemic immunosuppressive agents who have tested positive for COVID-19 or exhibit signs/symptoms of COVID-19, (3) patients who have halted systemic immunosuppressive therapy after testing positive for COVID-19 (in whom it recommended physicians could reinitiate treatment), and (4) patients being considered for systemic immunosuppressive agents.¹

The National Psoriasis Foundation (NPF) also recognized the need for additional guidelines for health care providers and patients on managing psoriatic disease during the COVID-19 pandemic. In June 2020, the NPF formed a COVID-19 Task Force, which released its own recommendations for adult and pediatric patients with psoriatic disease.² Similar to the AAD, the NPF COVID-19 Task Force recommended that patients do not stop biologic or oral therapies for psoriasis during the current health crisis, stating the following: “While some uncertainties remain, initial data suggest that the benefit of continuing treatments for psoriatic diseases outweighs the hypothetical risks associated with immune modulating treatment of poor COVID-19–related outcomes for most patients.” Individuals in high-risk groups were advised to consult their health care providers regarding whether they should continue or alter therapy during the pandemic, and the clinical decision would be guided by the specific treatment regimen; the patient’s age, disease characteristics, and underlying medical conditions; or any particular concerns. Additionally, the task force emphasized that patients with psoriatic disease should continue to follow common sense measures to lower the risk of becoming infected with COVID-19, including practicing physical distancing, wearing face coverings in public settings, and washing their hands regularly.²

We remain in the midst of the COVID-19 pandemic with no true guidance as to the future course and impact of the infection. It is important to realize that our understanding of the coronavirus and its impact on our patients is constantly evolving. I encourage all providers to stay current with updates on clinical guidelines. In addition, we should pay attention to the myriad of clinical trials and registries now underway, as they may provide more insight into optimal clinical management in these challenging times.

Most importantly, stay safe!

After learning about coronavirus disease 2019 (COVID-19) on the news, we were all aware that it would eventually affect our lives and our dermatology practices. However, once the COVID-19 pandemic arrived in the United States, we were under a shelter-in-place order, schools were shut, and most businesses were closed within a few weeks.

As dermatologists, we were considered essential workers, and our offices could remain open. However, as the numbers of cases accelerated in New York City—the global epicenter of the pandemic—and we approached our peak, I closed down my practice, except for emergencies.

One of the first medical challenges dermatologists faced in the early days of the COVID-19 pandemic was the proper management of our psoriasis patients. The major concern was that patients on biologics and other immunomodulatory therapies might be at an increased risk for COVID-19 infection and increased morbidity if affected. I received a multitude of telephone calls from patients taking these therapies who expressed high levels of concern and anxiety and were looking for direction as to whether they should continue their medications.

Early on, several of our professional societies provided guidelines regarding the use of systemic immunosuppressive agents during the COVID-19 pandemic. On April 15, 2020, the American Academy of Dermatology (AAD) advised, “Dermatologists must delicately balance the risk of immunosuppression with the risk of disease flare requiring urgent intervention with patient-specific risks.”¹ The AAD strongly recommended that patients should not stop their ongoing systemic immunosuppressive therapy without consulting their physicians. The AAD’s guidance provided specific recommendations for the following groups: (1) patients on systemic immunosuppressive agents who have not tested positive or exhibited signs/symptoms of COVID-19, (2) patients on systemic immunosuppressive agents who have tested positive for COVID-19 or exhibit signs/symptoms of COVID-19, (3) patients who have halted systemic immunosuppressive therapy after testing positive for COVID-19 (in whom it recommended physicians could reinitiate treatment), and (4) patients being considered for systemic immunosuppressive agents.¹

The National Psoriasis Foundation (NPF) also recognized the need for additional guidelines for health care providers and patients on managing psoriatic disease during the COVID-19 pandemic. In June 2020, the NPF formed a COVID-19 Task Force, which released its own recommendations for adult and pediatric patients with psoriatic disease.² Similar to the AAD, the NPF COVID-19 Task Force recommended that patients do not stop biologic or oral therapies for psoriasis during the current health crisis, stating the following: “While some uncertainties remain, initial data suggest that the benefit of continuing treatments for psoriatic diseases outweighs the hypothetical risks associated with immune modulating treatment of poor COVID-19–related outcomes for most patients.” Individuals in high-risk groups were advised to consult their health care providers regarding whether they should continue or alter therapy during the pandemic, and the clinical decision would be guided by the specific treatment regimen; the patient’s age, disease characteristics, and underlying medical conditions; or any particular concerns. Additionally, the task force emphasized that patients with psoriatic disease should continue to follow common sense measures to lower the risk of becoming infected with COVID-19, including practicing physical distancing, wearing face coverings in public settings, and washing their hands regularly.²

We remain in the midst of the COVID-19 pandemic with no true guidance as to the future course and impact of the infection. It is important to realize that our understanding of the coronavirus and its impact on our patients is constantly evolving. I encourage all providers to stay current with updates on clinical guidelines. In addition, we should pay attention to the myriad of clinical trials and registries now underway, as they may provide more insight into optimal clinical management in these challenging times.

Most importantly, stay safe!

During the last year, the field of psoriasis has continued to expand, with new therapies, new guidelines, and further understanding of the impact of treatment on associated comorbidities. 

One of the most exciting prospects of the treatment of psoriasis with biologics is the potential for the reduction in major adverse cardiovascular events (MACEs). It has been well established that psoriasis is associated with increased cardiovascular risk.^1,2 Ahlehoff et al¹ conducted a cohort study of the entire Danish population 18 years and older followed from 1997 to 2006 by individual-level linkage of nationwide registers. They concluded that psoriasis is associated with increased risk for adverse cardiovascular events and all-cause mortality. Young age, severe skin affection, and/or psoriatic arthritis (PsA) carry the most risk. They suggested that patients with psoriasis may be candidates for early cardiovascular risk factor modification.¹  

Ogdie et al² endeavored to quantify the risk for MACE among patients with PsA, rheumatoid arthritis (RA), and psoriasis without known PsA compared to the general population after adjusting for traditional cardiovascular risk factors. Patients with PsA (N=8706), RA (N=41,752), psoriasis (N=138,424), and unexposed controls (N=81,573) were identified. After adjustment for traditional risk factors, the risk for MACE was higher in patients with PsA not prescribed a disease-modifying antirheumatic drug (DMARD)(hazard ratio [HR], 1.24; 95% confidence interval [CI], 1.03-1.49), patients with RA (no DMARD: HR, 1.39; 95% CI, 1.28-1.50; DMARD: HR, 1.58; 95% CI, 1.46-1.70), patients with psoriasis not prescribed a DMARD (HR, 1.08; 95% CI, 1.02-1.15), and patients with severe psoriasis (DMARD: HR, 1.42; 95% CI, 1.17-1.73).² These data are one aspect of our increasing insight into the management of psoriasis. 

To expand on the new guidelines and new therapies presented in 2019, this issue includes review articles looking at these facets. Wu and Weinberg3 review the impact of diet on psoriasis. Pithadia et al⁴ explain the American Academy of Dermatology and National Psoriasis Foundation guidelines of care for the management of psoriasis with biologics for the prescribing dermatologist, with an emphasis on the most clinically significant considerations during each step of treatment with biologic therapies (ie, choosing a biologic, initiating therapy, assessing treatment response, switching biologics). Havnaer et al⁵ provide an update on the newly approved and pipeline systemic agents for psoriasis.  

We hope that you find this issue enjoyable and informative. 

During the last year, the field of psoriasis has continued to expand, with new therapies, new guidelines, and further understanding of the impact of treatment on associated comorbidities. 

One of the most exciting prospects of the treatment of psoriasis with biologics is the potential for the reduction in major adverse cardiovascular events (MACEs). It has been well established that psoriasis is associated with increased cardiovascular risk.^1,2 Ahlehoff et al¹ conducted a cohort study of the entire Danish population 18 years and older followed from 1997 to 2006 by individual-level linkage of nationwide registers. They concluded that psoriasis is associated with increased risk for adverse cardiovascular events and all-cause mortality. Young age, severe skin affection, and/or psoriatic arthritis (PsA) carry the most risk. They suggested that patients with psoriasis may be candidates for early cardiovascular risk factor modification.¹  

Ogdie et al² endeavored to quantify the risk for MACE among patients with PsA, rheumatoid arthritis (RA), and psoriasis without known PsA compared to the general population after adjusting for traditional cardiovascular risk factors. Patients with PsA (N=8706), RA (N=41,752), psoriasis (N=138,424), and unexposed controls (N=81,573) were identified. After adjustment for traditional risk factors, the risk for MACE was higher in patients with PsA not prescribed a disease-modifying antirheumatic drug (DMARD)(hazard ratio [HR], 1.24; 95% confidence interval [CI], 1.03-1.49), patients with RA (no DMARD: HR, 1.39; 95% CI, 1.28-1.50; DMARD: HR, 1.58; 95% CI, 1.46-1.70), patients with psoriasis not prescribed a DMARD (HR, 1.08; 95% CI, 1.02-1.15), and patients with severe psoriasis (DMARD: HR, 1.42; 95% CI, 1.17-1.73).² These data are one aspect of our increasing insight into the management of psoriasis. 

To expand on the new guidelines and new therapies presented in 2019, this issue includes review articles looking at these facets. Wu and Weinberg3 review the impact of diet on psoriasis. Pithadia et al⁴ explain the American Academy of Dermatology and National Psoriasis Foundation guidelines of care for the management of psoriasis with biologics for the prescribing dermatologist, with an emphasis on the most clinically significant considerations during each step of treatment with biologic therapies (ie, choosing a biologic, initiating therapy, assessing treatment response, switching biologics). Havnaer et al⁵ provide an update on the newly approved and pipeline systemic agents for psoriasis.  

We hope that you find this issue enjoyable and informative. 

During the last year, the field of psoriasis has continued to expand, with new therapies, new guidelines, and further understanding of the impact of treatment on associated comorbidities. 

One of the most exciting prospects of the treatment of psoriasis with biologics is the potential for the reduction in major adverse cardiovascular events (MACEs). It has been well established that psoriasis is associated with increased cardiovascular risk.^1,2 Ahlehoff et al¹ conducted a cohort study of the entire Danish population 18 years and older followed from 1997 to 2006 by individual-level linkage of nationwide registers. They concluded that psoriasis is associated with increased risk for adverse cardiovascular events and all-cause mortality. Young age, severe skin affection, and/or psoriatic arthritis (PsA) carry the most risk. They suggested that patients with psoriasis may be candidates for early cardiovascular risk factor modification.¹  

Ogdie et al² endeavored to quantify the risk for MACE among patients with PsA, rheumatoid arthritis (RA), and psoriasis without known PsA compared to the general population after adjusting for traditional cardiovascular risk factors. Patients with PsA (N=8706), RA (N=41,752), psoriasis (N=138,424), and unexposed controls (N=81,573) were identified. After adjustment for traditional risk factors, the risk for MACE was higher in patients with PsA not prescribed a disease-modifying antirheumatic drug (DMARD)(hazard ratio [HR], 1.24; 95% confidence interval [CI], 1.03-1.49), patients with RA (no DMARD: HR, 1.39; 95% CI, 1.28-1.50; DMARD: HR, 1.58; 95% CI, 1.46-1.70), patients with psoriasis not prescribed a DMARD (HR, 1.08; 95% CI, 1.02-1.15), and patients with severe psoriasis (DMARD: HR, 1.42; 95% CI, 1.17-1.73).² These data are one aspect of our increasing insight into the management of psoriasis. 

To expand on the new guidelines and new therapies presented in 2019, this issue includes review articles looking at these facets. Wu and Weinberg3 review the impact of diet on psoriasis. Pithadia et al⁴ explain the American Academy of Dermatology and National Psoriasis Foundation guidelines of care for the management of psoriasis with biologics for the prescribing dermatologist, with an emphasis on the most clinically significant considerations during each step of treatment with biologic therapies (ie, choosing a biologic, initiating therapy, assessing treatment response, switching biologics). Havnaer et al⁵ provide an update on the newly approved and pipeline systemic agents for psoriasis.  

We hope that you find this issue enjoyable and informative. 

Psoriasis is a chronic cutaneous disease associated with immune-mediated inflammation. The disease has a complex etiology, with factors such as genetics, smoking, alcohol use, diet, and stress all believed to be implicated in its appearance and severity. Specific factors, including increased body mass index and weight gain, have been associated with a higher prevalence of psoriasis and are risk factors for the disease. Because psoriasis varies in severity and incidence, patients often can experience a substantial negative impact on their quality of life, with increased incidences of anxiety and depression.¹ Because diet is an accessible and controllable variable, many patients choose to alter their diets to help relieve symptoms of the disease. This article aims to review and summarize the existing literature for possible relationships and correlations between diet and psoriasis.

Because diet is a factor contributing to psoriasis, it is a lifestyle change that patients often make. In a 2017 survey of 1206 patients with psoriasis, 86% reported modifying their diets.² Furthermore, when patients were compared with control individuals of the same sex and of similar age, it was shown that those with psoriasis consumed statistically significant lower amounts of sugar, whole-grain fiber, dairy products, and calcium (P<.001). The survey also found that patient diets included significantly more fruits, vegetables, and legumes (P<.01). Although no single diet was adhered to by patients, 40% did report attempting a specialized diet to improve their psoriasis. The most common diets were gluten free (35.6%), low carbohydrate/high protein (16.6%), and Paleolithic (11.6%). In addition to these diets, the Mediterranean diet and a vegetarian diet were both among those reported to improve psoriatic symptoms. Finally, certain foods stood out as more frequently reported to affect symptoms, particularly fish oil, fruits, vegetables, and water, which were all reported by at least 10% of respondents to positively affect their psoriasis. Reductions in consumption of alcohol, gluten, nightshades, and junk foods were associated with skin improvements in at least 50% of patients.² These baseline differences in diet informed our search of the literature and showed that dietary changes can serve as an important adjunct to treatment for many patients.

Mediterranean Diet

The Mediterranean diet consists of a high amount of fruits, vegetables, nuts and legumes, cereals, and olive oil, while restricting consumption of red meats, dairy products, and alcohol (besides red wine) at meals.³ Adherence to the diet has been associated with a reduced risk for cardiovascular diseases,⁴ rheumatoid arthritis, and Crohn disease,³ among others, possibly because the diet contains a high proportion and variety of foods that contain antioxidants and anti-inflammatory compounds, including the monounsaturated fatty acids (MUFAs) in olive oil and the polyphenols in fruits and vegetables. Consumption of both MUFAs and highly anti-inflammatory nutrients has been associated with reduced prevalence of risk factors for chronic inflammatory diseases, and consumption levels of MUFAs in particular have been reported to be a predictive factor in psoriasis severity.³

Recent studies have tried to quantify an association between consumption of the Mediterranean diet and psoriasis. One cross-sectional study in 2015 evaluated 62 patients with psoriasis for their adherence to the Mediterranean diet and psoriasis severity.⁴ Utilizing a 14-question evaluation, the study found that patients with a higher severity of psoriasis, as evaluated by a psoriasis area and severity index (PASI) score and C-reactive protein levels, had a lower adherence to the diet. Notably, consumption of extra-virgin olive oil was found to be an independent predictor of PASI score, and consumption of fish was an independent predictor of C-reactive protein levels.⁴

A second cross-sectional questionnaire study found similar results in a larger population of 3557 patients. The same association between patients with severe psoriasis and low levels of adherence to the Mediterranean diet was reported.³ Although neither study showed a causal relationship between the diet and psoriasis severity, both did report the potential impacts of proinflammatory and anti-inflammatory foods. General foods and nutrients listed by the studies as having anti-inflammatory properties include MUFAs; fish; vitamins A, C, D, and E; and omega-3 fatty acids.³ Because of the large number of confounding factors in dietary studies that rely on questionnaires, it is hard to definitively label the Mediterranean diet as beneficial topsoriasis. However, individual components of the diet may be used as predictors of psoriasis severity, and the diet itself may be used in tandem with other treatments for psoriasis.

Gluten-Free Diet

Celiac disease is an inflammatory enteropathy caused by an immune reaction to the protein gliadin, which is found in foods containing gluten, such as wheat.⁵ Immune system assault on the intestinal enterocytes leads to the stripping away of villi, negatively affecting nutrient absorption. Multiple studies have reported an association between having psoriasis and having celiac disease as well as the reverse, including a 3-fold increased risk of celiac disease for patients with psoriasis in a 2017 meta-analysis.⁶ Even if patients with psoriasis did not have celiac disease, studies have found that a notable percentage of patients with psoriasis have elevated antigliadin IgA antibody levels.⁷ Many hypotheses have been proposed to explain this association. One article suggested that the malabsorption associated with celiac disease predisposes patients to vitamin D deficiency, which is a contributing risk factor for psoriasis.⁸ Other explanations involve common immune cells involved in the response to both diseases and a shared genetic background between the 2 diseases.⁸ As a gluten-free diet is standard for patients with celiac disease, it stands to reason that IgA could be used as a serum biomarker for patients who also could see improvements by adopting the diet.

This result could help explain the proportion of respondents to the 2017 survey who experienced improvements to their psoriasis if the gluten-free diet was in fact not triggering the inflammatory effects that a regular diet would, which also may help to explain the mixed results that the gluten-free diet has had as a treatment for psoriasis. One 3-month study of patients who were positive for antigliadin antibodies found that the majority (82%) experienced a decrease in antibody levels and affected skin area after following a gluten-free diet. Only half the patients had been diagnosed with celiac disease prior to the study, lending credibility to the idea that antigliadin antibody could be used as a marker for patients with psoriasis who would benefit from a gluten-free diet.⁹ Other case studies have reported no improvement of psoriasis following implementation of a gluten-free diet,¹⁰ despite the patients having elevated gliadin antibodies or celiac disease. More studies are required to discern the exact nature of the benefits of a gluten-free diet on psoriasis; however, it does serve as a promising option for patients with both psoriasis and celiac disease.

Ketogenic Diet

As obesity and weight gain are factors associated with psoriasis, some patients turn to diets that restrict calories with the goal of losing weight to improve their symptoms. One 2015 case report studied a patient who restored her response to systemic treatment of psoriasis following an intensive 4-week, calorie-restricted ketogenic diet.¹¹ The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet. Animal studies have shown the diet to have anti-inflammatory effects, including lowering levels of proinflammatory cytokines and reduced fever.¹² In the 2015 case report, the rapid and consistent weight loss experienced by the patient because of the ketogenic diet was thought to be the cause of the restoration of treatment effectiveness,¹¹ which is interesting, since the role of the ketogenic diet was not to supplement any deficiencies but to move the patient to a physiologic state that was once again receptive to treatment. This finding suggests that a variety of diets could improve psoriasis symptoms, so long as they do not cause inflammation or reduce overall body mass. One study of patients on a calorie-restricted diet over 8 weeks did see a trend of patients on the diet showing improvement in both their PASI scores and Dermatology Life Quality Index, though the improvement was not statistically significant.¹³ To determine if the ketogenic diet has a significant association with psoriasis improvement, controlled, large-population studies should be performed in the future with age, sex, and weight-matched controls, which may be difficult to do. Further studies looking at the association between weight loss and psoriasis also could be another direction.

Vegetarian Diet

Both vegetarian and vegan diets have been evaluated for their efficacy in relieving symptoms of chronic inflammatory disorders. Although the 2 diets are similar in avoiding consumption of meat, fish, and poultry, vegan diets often have additional food restrictions, including avoiding eggs, honey, and dairy products. One study noted the impact of these diets on patients with a variety of skin conditions following a period of fasting. It was observed that some patients with psoriasis saw an improvement in their symptoms during the period when they were eating a vegetarian or vegan diet, which was attributed to a return to normal levels of activity of neutrophils, extrapolated from serum levels of lactoferrin.¹⁴ Vegetarian diets have been shown to be associated with higher ratios of anti-inflammatory to proinflammatory adipokines compared to omnivorous diets,¹⁵ as well as lower expression levels of proinflammatory genes in the gut microbiota and lower expression levels of IgE.¹⁶ Perhaps the anti-inflammatory impacts of the diet affected the symptoms of psoriasis. The benefits of a vegetarian diet also have been attributed to the high amount of potassium consumed,¹⁷ which is used in the body to synthesize cortisol, a common treatment for psoriasis. Potassium supplementation has been shown to raise serum cortisol levels in patients.⁶ Although additional studies are needed to discern the significance of potassium in the vegetarian diet, both hypotheses are reasonable explanations for the observations seen in these studies.

Vitamin D and Other Nutritional Supplements

Because it is not always feasible for patients to alter their diets, many have turned to dietary supplements as an alternative method of treatment and lifestyle change. Two of the more prominently represented nutritional additives in the literature are fish oils and vitamin D.¹⁸ Supplemental vitamin D is a prohormone that can be endogenously converted to its active 1,25-dihydroxyvitamin D.¹⁹ Vitamin D plays important roles in the regulation of calcium and magnesium in the bones as well as the maturation and differentiation of keratinocytes in the skin.¹⁶ Topical vitamin D analogues are standard treatments for psoriasis, as they are used to modulate the immune system to great effect.²⁰ Some patients with psoriasis present with vitamin D insufficiency,²¹ and it stands to reason that oral supplementation may be a treatment option. There have been multiple studies assessing the efficacy of oral vitamin D for the treatment of psoriasis; however, in the only randomized and placebo-controlled trial, there was only a slight nonsignificant improvement in the group supplemented with vitamin D.²⁰ Another small, open-label study reported remarkably improved PASI scores in 9 vitamin D–supplemented, dietary calcium–restricted patients.²² The lack of recent, large-sample studies makes it hard to draw notable conclusions from these studies.

The polyunsaturated fatty acids found in fish oils also have been considered as a treatment option for psoriasis.²³ Millsop et al²⁰ conducted an analysis of the literature reviewing the efficacy of fish oil in the treatment of psoriasis. Twelve of 15 compiled trials showed an improvement in psoriasis, ranging from slight improvements from baseline levels of the disease to statistically significant decreases in PASI scores (P<.05). It is notable that the amount of fish oil given in these studies varied widely, but the amount given did not necessarily correlate with strength of impact.²⁰ For example, Mayser et al,²⁴ Bittiner et al,²⁵ and Grimminger et al²⁶ each performed prospective, double-blind studies with docosahexaenoic acid and eicosapentaenoic acid (the omega-3 fatty acids found in fish oils), and all 3 studies saw improvements in the omega-3–treated group vs the control group. The doses of the oils, however, ranged from as low as 1.2 and 1.8 g daily of docosahexaenoic acid and eicosapentaenoic acid, respectively, to 4.2 g daily of each fatty acid.^24-26

Studies also have shown little to no improvement in the use of fish oil to treat psoriasis. One such study was conducted by Soyland et al²⁷ in 1993 in Norway. Utilizing a prospective, double-blind, placebo-controlled design over 4 months on 145 patients with moderate to severe psoriasis, researchers evaluated the treatment effectiveness via PASI scores; subjective reports from the patients; clinical manifestations; and factors such as cellular infiltration, desquamation, and redness. The results were mixed, with the placebo (corn oil) group having less redness and cellular desquamation and the fish oil group showing less cellular infiltration. In the other categories, there was no significant difference between the 2 groups, and researchers concluded there was no significant benefit to treating psoriasis using fish oil vs corn oil.²⁷ As with many of the other diets, there have been no recent, large-scale studies performed on the effect of fish oil supplementation on psoriasis; however, of the studies we reviewed, none showed fish oil supplementation to have a significant negative impact on psoriasis.

Conclusion

Dietary modifications have a complex multifactorial effect on psoriasis, often dependent on the variations of psoriasis and the lifestyle of the patient, including level of exercise, activities such as smoking and drinking, and genetic susceptibilities to conditions such as obesity. Thus, it is difficult for one diet to have a significant impact on psoriasis symptoms that applies to the majority of individuals. However, it appears that certain foods or nutritional supplements can be modified from all diets for general improvement. Foods with systemic anti-inflammatory effects, such as olive oil and fish oil, seem to be beneficial in treating psoriasis. As an extension, a gluten-free diet may help psoriasis patients with celiac disease by reducing the inflammatory environment of the body. On the opposite side of the spectrum, proinflammatory foods such as dietary fat and alcohol should be avoided.²⁸

In general, larger and more recent population-based studies are needed to add to the literature on this subject. Nationwide voluntary web-based surveys such as the NutriNet-Santé study in France may be one way to quickly amass large quantities of data (ClinicalTrials.gov Identifier NCT03335644). Participants are recruited through multimedia campaigns and return online questionnaires annually for 1 decade. A subset of participants also contributes biologic samples and participates in clinical examinations. This type of data gathering would capture many variables, provide a large sample size, and perhaps shed light on regional differences in diet and lifestyle that could then be targeted with treatments.

Psoriasis is a chronic cutaneous disease associated with immune-mediated inflammation. The disease has a complex etiology, with factors such as genetics, smoking, alcohol use, diet, and stress all believed to be implicated in its appearance and severity. Specific factors, including increased body mass index and weight gain, have been associated with a higher prevalence of psoriasis and are risk factors for the disease. Because psoriasis varies in severity and incidence, patients often can experience a substantial negative impact on their quality of life, with increased incidences of anxiety and depression.¹ Because diet is an accessible and controllable variable, many patients choose to alter their diets to help relieve symptoms of the disease. This article aims to review and summarize the existing literature for possible relationships and correlations between diet and psoriasis.

Because diet is a factor contributing to psoriasis, it is a lifestyle change that patients often make. In a 2017 survey of 1206 patients with psoriasis, 86% reported modifying their diets.² Furthermore, when patients were compared with control individuals of the same sex and of similar age, it was shown that those with psoriasis consumed statistically significant lower amounts of sugar, whole-grain fiber, dairy products, and calcium (P<.001). The survey also found that patient diets included significantly more fruits, vegetables, and legumes (P<.01). Although no single diet was adhered to by patients, 40% did report attempting a specialized diet to improve their psoriasis. The most common diets were gluten free (35.6%), low carbohydrate/high protein (16.6%), and Paleolithic (11.6%). In addition to these diets, the Mediterranean diet and a vegetarian diet were both among those reported to improve psoriatic symptoms. Finally, certain foods stood out as more frequently reported to affect symptoms, particularly fish oil, fruits, vegetables, and water, which were all reported by at least 10% of respondents to positively affect their psoriasis. Reductions in consumption of alcohol, gluten, nightshades, and junk foods were associated with skin improvements in at least 50% of patients.² These baseline differences in diet informed our search of the literature and showed that dietary changes can serve as an important adjunct to treatment for many patients.

Mediterranean Diet

The Mediterranean diet consists of a high amount of fruits, vegetables, nuts and legumes, cereals, and olive oil, while restricting consumption of red meats, dairy products, and alcohol (besides red wine) at meals.³ Adherence to the diet has been associated with a reduced risk for cardiovascular diseases,⁴ rheumatoid arthritis, and Crohn disease,³ among others, possibly because the diet contains a high proportion and variety of foods that contain antioxidants and anti-inflammatory compounds, including the monounsaturated fatty acids (MUFAs) in olive oil and the polyphenols in fruits and vegetables. Consumption of both MUFAs and highly anti-inflammatory nutrients has been associated with reduced prevalence of risk factors for chronic inflammatory diseases, and consumption levels of MUFAs in particular have been reported to be a predictive factor in psoriasis severity.³

Recent studies have tried to quantify an association between consumption of the Mediterranean diet and psoriasis. One cross-sectional study in 2015 evaluated 62 patients with psoriasis for their adherence to the Mediterranean diet and psoriasis severity.⁴ Utilizing a 14-question evaluation, the study found that patients with a higher severity of psoriasis, as evaluated by a psoriasis area and severity index (PASI) score and C-reactive protein levels, had a lower adherence to the diet. Notably, consumption of extra-virgin olive oil was found to be an independent predictor of PASI score, and consumption of fish was an independent predictor of C-reactive protein levels.⁴

A second cross-sectional questionnaire study found similar results in a larger population of 3557 patients. The same association between patients with severe psoriasis and low levels of adherence to the Mediterranean diet was reported.³ Although neither study showed a causal relationship between the diet and psoriasis severity, both did report the potential impacts of proinflammatory and anti-inflammatory foods. General foods and nutrients listed by the studies as having anti-inflammatory properties include MUFAs; fish; vitamins A, C, D, and E; and omega-3 fatty acids.³ Because of the large number of confounding factors in dietary studies that rely on questionnaires, it is hard to definitively label the Mediterranean diet as beneficial topsoriasis. However, individual components of the diet may be used as predictors of psoriasis severity, and the diet itself may be used in tandem with other treatments for psoriasis.

Gluten-Free Diet

Celiac disease is an inflammatory enteropathy caused by an immune reaction to the protein gliadin, which is found in foods containing gluten, such as wheat.⁵ Immune system assault on the intestinal enterocytes leads to the stripping away of villi, negatively affecting nutrient absorption. Multiple studies have reported an association between having psoriasis and having celiac disease as well as the reverse, including a 3-fold increased risk of celiac disease for patients with psoriasis in a 2017 meta-analysis.⁶ Even if patients with psoriasis did not have celiac disease, studies have found that a notable percentage of patients with psoriasis have elevated antigliadin IgA antibody levels.⁷ Many hypotheses have been proposed to explain this association. One article suggested that the malabsorption associated with celiac disease predisposes patients to vitamin D deficiency, which is a contributing risk factor for psoriasis.⁸ Other explanations involve common immune cells involved in the response to both diseases and a shared genetic background between the 2 diseases.⁸ As a gluten-free diet is standard for patients with celiac disease, it stands to reason that IgA could be used as a serum biomarker for patients who also could see improvements by adopting the diet.

This result could help explain the proportion of respondents to the 2017 survey who experienced improvements to their psoriasis if the gluten-free diet was in fact not triggering the inflammatory effects that a regular diet would, which also may help to explain the mixed results that the gluten-free diet has had as a treatment for psoriasis. One 3-month study of patients who were positive for antigliadin antibodies found that the majority (82%) experienced a decrease in antibody levels and affected skin area after following a gluten-free diet. Only half the patients had been diagnosed with celiac disease prior to the study, lending credibility to the idea that antigliadin antibody could be used as a marker for patients with psoriasis who would benefit from a gluten-free diet.⁹ Other case studies have reported no improvement of psoriasis following implementation of a gluten-free diet,¹⁰ despite the patients having elevated gliadin antibodies or celiac disease. More studies are required to discern the exact nature of the benefits of a gluten-free diet on psoriasis; however, it does serve as a promising option for patients with both psoriasis and celiac disease.

Ketogenic Diet

As obesity and weight gain are factors associated with psoriasis, some patients turn to diets that restrict calories with the goal of losing weight to improve their symptoms. One 2015 case report studied a patient who restored her response to systemic treatment of psoriasis following an intensive 4-week, calorie-restricted ketogenic diet.¹¹ The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet. Animal studies have shown the diet to have anti-inflammatory effects, including lowering levels of proinflammatory cytokines and reduced fever.¹² In the 2015 case report, the rapid and consistent weight loss experienced by the patient because of the ketogenic diet was thought to be the cause of the restoration of treatment effectiveness,¹¹ which is interesting, since the role of the ketogenic diet was not to supplement any deficiencies but to move the patient to a physiologic state that was once again receptive to treatment. This finding suggests that a variety of diets could improve psoriasis symptoms, so long as they do not cause inflammation or reduce overall body mass. One study of patients on a calorie-restricted diet over 8 weeks did see a trend of patients on the diet showing improvement in both their PASI scores and Dermatology Life Quality Index, though the improvement was not statistically significant.¹³ To determine if the ketogenic diet has a significant association with psoriasis improvement, controlled, large-population studies should be performed in the future with age, sex, and weight-matched controls, which may be difficult to do. Further studies looking at the association between weight loss and psoriasis also could be another direction.

Vegetarian Diet

Both vegetarian and vegan diets have been evaluated for their efficacy in relieving symptoms of chronic inflammatory disorders. Although the 2 diets are similar in avoiding consumption of meat, fish, and poultry, vegan diets often have additional food restrictions, including avoiding eggs, honey, and dairy products. One study noted the impact of these diets on patients with a variety of skin conditions following a period of fasting. It was observed that some patients with psoriasis saw an improvement in their symptoms during the period when they were eating a vegetarian or vegan diet, which was attributed to a return to normal levels of activity of neutrophils, extrapolated from serum levels of lactoferrin.¹⁴ Vegetarian diets have been shown to be associated with higher ratios of anti-inflammatory to proinflammatory adipokines compared to omnivorous diets,¹⁵ as well as lower expression levels of proinflammatory genes in the gut microbiota and lower expression levels of IgE.¹⁶ Perhaps the anti-inflammatory impacts of the diet affected the symptoms of psoriasis. The benefits of a vegetarian diet also have been attributed to the high amount of potassium consumed,¹⁷ which is used in the body to synthesize cortisol, a common treatment for psoriasis. Potassium supplementation has been shown to raise serum cortisol levels in patients.⁶ Although additional studies are needed to discern the significance of potassium in the vegetarian diet, both hypotheses are reasonable explanations for the observations seen in these studies.

Vitamin D and Other Nutritional Supplements

Because it is not always feasible for patients to alter their diets, many have turned to dietary supplements as an alternative method of treatment and lifestyle change. Two of the more prominently represented nutritional additives in the literature are fish oils and vitamin D.¹⁸ Supplemental vitamin D is a prohormone that can be endogenously converted to its active 1,25-dihydroxyvitamin D.¹⁹ Vitamin D plays important roles in the regulation of calcium and magnesium in the bones as well as the maturation and differentiation of keratinocytes in the skin.¹⁶ Topical vitamin D analogues are standard treatments for psoriasis, as they are used to modulate the immune system to great effect.²⁰ Some patients with psoriasis present with vitamin D insufficiency,²¹ and it stands to reason that oral supplementation may be a treatment option. There have been multiple studies assessing the efficacy of oral vitamin D for the treatment of psoriasis; however, in the only randomized and placebo-controlled trial, there was only a slight nonsignificant improvement in the group supplemented with vitamin D.²⁰ Another small, open-label study reported remarkably improved PASI scores in 9 vitamin D–supplemented, dietary calcium–restricted patients.²² The lack of recent, large-sample studies makes it hard to draw notable conclusions from these studies.

The polyunsaturated fatty acids found in fish oils also have been considered as a treatment option for psoriasis.²³ Millsop et al²⁰ conducted an analysis of the literature reviewing the efficacy of fish oil in the treatment of psoriasis. Twelve of 15 compiled trials showed an improvement in psoriasis, ranging from slight improvements from baseline levels of the disease to statistically significant decreases in PASI scores (P<.05). It is notable that the amount of fish oil given in these studies varied widely, but the amount given did not necessarily correlate with strength of impact.²⁰ For example, Mayser et al,²⁴ Bittiner et al,²⁵ and Grimminger et al²⁶ each performed prospective, double-blind studies with docosahexaenoic acid and eicosapentaenoic acid (the omega-3 fatty acids found in fish oils), and all 3 studies saw improvements in the omega-3–treated group vs the control group. The doses of the oils, however, ranged from as low as 1.2 and 1.8 g daily of docosahexaenoic acid and eicosapentaenoic acid, respectively, to 4.2 g daily of each fatty acid.^24-26

Studies also have shown little to no improvement in the use of fish oil to treat psoriasis. One such study was conducted by Soyland et al²⁷ in 1993 in Norway. Utilizing a prospective, double-blind, placebo-controlled design over 4 months on 145 patients with moderate to severe psoriasis, researchers evaluated the treatment effectiveness via PASI scores; subjective reports from the patients; clinical manifestations; and factors such as cellular infiltration, desquamation, and redness. The results were mixed, with the placebo (corn oil) group having less redness and cellular desquamation and the fish oil group showing less cellular infiltration. In the other categories, there was no significant difference between the 2 groups, and researchers concluded there was no significant benefit to treating psoriasis using fish oil vs corn oil.²⁷ As with many of the other diets, there have been no recent, large-scale studies performed on the effect of fish oil supplementation on psoriasis; however, of the studies we reviewed, none showed fish oil supplementation to have a significant negative impact on psoriasis.

Conclusion

Dietary modifications have a complex multifactorial effect on psoriasis, often dependent on the variations of psoriasis and the lifestyle of the patient, including level of exercise, activities such as smoking and drinking, and genetic susceptibilities to conditions such as obesity. Thus, it is difficult for one diet to have a significant impact on psoriasis symptoms that applies to the majority of individuals. However, it appears that certain foods or nutritional supplements can be modified from all diets for general improvement. Foods with systemic anti-inflammatory effects, such as olive oil and fish oil, seem to be beneficial in treating psoriasis. As an extension, a gluten-free diet may help psoriasis patients with celiac disease by reducing the inflammatory environment of the body. On the opposite side of the spectrum, proinflammatory foods such as dietary fat and alcohol should be avoided.²⁸

In general, larger and more recent population-based studies are needed to add to the literature on this subject. Nationwide voluntary web-based surveys such as the NutriNet-Santé study in France may be one way to quickly amass large quantities of data (ClinicalTrials.gov Identifier NCT03335644). Participants are recruited through multimedia campaigns and return online questionnaires annually for 1 decade. A subset of participants also contributes biologic samples and participates in clinical examinations. This type of data gathering would capture many variables, provide a large sample size, and perhaps shed light on regional differences in diet and lifestyle that could then be targeted with treatments.

Psoriasis is a chronic cutaneous disease associated with immune-mediated inflammation. The disease has a complex etiology, with factors such as genetics, smoking, alcohol use, diet, and stress all believed to be implicated in its appearance and severity. Specific factors, including increased body mass index and weight gain, have been associated with a higher prevalence of psoriasis and are risk factors for the disease. Because psoriasis varies in severity and incidence, patients often can experience a substantial negative impact on their quality of life, with increased incidences of anxiety and depression.¹ Because diet is an accessible and controllable variable, many patients choose to alter their diets to help relieve symptoms of the disease. This article aims to review and summarize the existing literature for possible relationships and correlations between diet and psoriasis.

Because diet is a factor contributing to psoriasis, it is a lifestyle change that patients often make. In a 2017 survey of 1206 patients with psoriasis, 86% reported modifying their diets.² Furthermore, when patients were compared with control individuals of the same sex and of similar age, it was shown that those with psoriasis consumed statistically significant lower amounts of sugar, whole-grain fiber, dairy products, and calcium (P<.001). The survey also found that patient diets included significantly more fruits, vegetables, and legumes (P<.01). Although no single diet was adhered to by patients, 40% did report attempting a specialized diet to improve their psoriasis. The most common diets were gluten free (35.6%), low carbohydrate/high protein (16.6%), and Paleolithic (11.6%). In addition to these diets, the Mediterranean diet and a vegetarian diet were both among those reported to improve psoriatic symptoms. Finally, certain foods stood out as more frequently reported to affect symptoms, particularly fish oil, fruits, vegetables, and water, which were all reported by at least 10% of respondents to positively affect their psoriasis. Reductions in consumption of alcohol, gluten, nightshades, and junk foods were associated with skin improvements in at least 50% of patients.² These baseline differences in diet informed our search of the literature and showed that dietary changes can serve as an important adjunct to treatment for many patients.

Mediterranean Diet

The Mediterranean diet consists of a high amount of fruits, vegetables, nuts and legumes, cereals, and olive oil, while restricting consumption of red meats, dairy products, and alcohol (besides red wine) at meals.³ Adherence to the diet has been associated with a reduced risk for cardiovascular diseases,⁴ rheumatoid arthritis, and Crohn disease,³ among others, possibly because the diet contains a high proportion and variety of foods that contain antioxidants and anti-inflammatory compounds, including the monounsaturated fatty acids (MUFAs) in olive oil and the polyphenols in fruits and vegetables. Consumption of both MUFAs and highly anti-inflammatory nutrients has been associated with reduced prevalence of risk factors for chronic inflammatory diseases, and consumption levels of MUFAs in particular have been reported to be a predictive factor in psoriasis severity.³

Recent studies have tried to quantify an association between consumption of the Mediterranean diet and psoriasis. One cross-sectional study in 2015 evaluated 62 patients with psoriasis for their adherence to the Mediterranean diet and psoriasis severity.⁴ Utilizing a 14-question evaluation, the study found that patients with a higher severity of psoriasis, as evaluated by a psoriasis area and severity index (PASI) score and C-reactive protein levels, had a lower adherence to the diet. Notably, consumption of extra-virgin olive oil was found to be an independent predictor of PASI score, and consumption of fish was an independent predictor of C-reactive protein levels.⁴

A second cross-sectional questionnaire study found similar results in a larger population of 3557 patients. The same association between patients with severe psoriasis and low levels of adherence to the Mediterranean diet was reported.³ Although neither study showed a causal relationship between the diet and psoriasis severity, both did report the potential impacts of proinflammatory and anti-inflammatory foods. General foods and nutrients listed by the studies as having anti-inflammatory properties include MUFAs; fish; vitamins A, C, D, and E; and omega-3 fatty acids.³ Because of the large number of confounding factors in dietary studies that rely on questionnaires, it is hard to definitively label the Mediterranean diet as beneficial topsoriasis. However, individual components of the diet may be used as predictors of psoriasis severity, and the diet itself may be used in tandem with other treatments for psoriasis.

Gluten-Free Diet

Celiac disease is an inflammatory enteropathy caused by an immune reaction to the protein gliadin, which is found in foods containing gluten, such as wheat.⁵ Immune system assault on the intestinal enterocytes leads to the stripping away of villi, negatively affecting nutrient absorption. Multiple studies have reported an association between having psoriasis and having celiac disease as well as the reverse, including a 3-fold increased risk of celiac disease for patients with psoriasis in a 2017 meta-analysis.⁶ Even if patients with psoriasis did not have celiac disease, studies have found that a notable percentage of patients with psoriasis have elevated antigliadin IgA antibody levels.⁷ Many hypotheses have been proposed to explain this association. One article suggested that the malabsorption associated with celiac disease predisposes patients to vitamin D deficiency, which is a contributing risk factor for psoriasis.⁸ Other explanations involve common immune cells involved in the response to both diseases and a shared genetic background between the 2 diseases.⁸ As a gluten-free diet is standard for patients with celiac disease, it stands to reason that IgA could be used as a serum biomarker for patients who also could see improvements by adopting the diet.

This result could help explain the proportion of respondents to the 2017 survey who experienced improvements to their psoriasis if the gluten-free diet was in fact not triggering the inflammatory effects that a regular diet would, which also may help to explain the mixed results that the gluten-free diet has had as a treatment for psoriasis. One 3-month study of patients who were positive for antigliadin antibodies found that the majority (82%) experienced a decrease in antibody levels and affected skin area after following a gluten-free diet. Only half the patients had been diagnosed with celiac disease prior to the study, lending credibility to the idea that antigliadin antibody could be used as a marker for patients with psoriasis who would benefit from a gluten-free diet.⁹ Other case studies have reported no improvement of psoriasis following implementation of a gluten-free diet,¹⁰ despite the patients having elevated gliadin antibodies or celiac disease. More studies are required to discern the exact nature of the benefits of a gluten-free diet on psoriasis; however, it does serve as a promising option for patients with both psoriasis and celiac disease.

Ketogenic Diet

As obesity and weight gain are factors associated with psoriasis, some patients turn to diets that restrict calories with the goal of losing weight to improve their symptoms. One 2015 case report studied a patient who restored her response to systemic treatment of psoriasis following an intensive 4-week, calorie-restricted ketogenic diet.¹¹ The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet. Animal studies have shown the diet to have anti-inflammatory effects, including lowering levels of proinflammatory cytokines and reduced fever.¹² In the 2015 case report, the rapid and consistent weight loss experienced by the patient because of the ketogenic diet was thought to be the cause of the restoration of treatment effectiveness,¹¹ which is interesting, since the role of the ketogenic diet was not to supplement any deficiencies but to move the patient to a physiologic state that was once again receptive to treatment. This finding suggests that a variety of diets could improve psoriasis symptoms, so long as they do not cause inflammation or reduce overall body mass. One study of patients on a calorie-restricted diet over 8 weeks did see a trend of patients on the diet showing improvement in both their PASI scores and Dermatology Life Quality Index, though the improvement was not statistically significant.¹³ To determine if the ketogenic diet has a significant association with psoriasis improvement, controlled, large-population studies should be performed in the future with age, sex, and weight-matched controls, which may be difficult to do. Further studies looking at the association between weight loss and psoriasis also could be another direction.

Vegetarian Diet

Both vegetarian and vegan diets have been evaluated for their efficacy in relieving symptoms of chronic inflammatory disorders. Although the 2 diets are similar in avoiding consumption of meat, fish, and poultry, vegan diets often have additional food restrictions, including avoiding eggs, honey, and dairy products. One study noted the impact of these diets on patients with a variety of skin conditions following a period of fasting. It was observed that some patients with psoriasis saw an improvement in their symptoms during the period when they were eating a vegetarian or vegan diet, which was attributed to a return to normal levels of activity of neutrophils, extrapolated from serum levels of lactoferrin.¹⁴ Vegetarian diets have been shown to be associated with higher ratios of anti-inflammatory to proinflammatory adipokines compared to omnivorous diets,¹⁵ as well as lower expression levels of proinflammatory genes in the gut microbiota and lower expression levels of IgE.¹⁶ Perhaps the anti-inflammatory impacts of the diet affected the symptoms of psoriasis. The benefits of a vegetarian diet also have been attributed to the high amount of potassium consumed,¹⁷ which is used in the body to synthesize cortisol, a common treatment for psoriasis. Potassium supplementation has been shown to raise serum cortisol levels in patients.⁶ Although additional studies are needed to discern the significance of potassium in the vegetarian diet, both hypotheses are reasonable explanations for the observations seen in these studies.

Vitamin D and Other Nutritional Supplements

Because it is not always feasible for patients to alter their diets, many have turned to dietary supplements as an alternative method of treatment and lifestyle change. Two of the more prominently represented nutritional additives in the literature are fish oils and vitamin D.¹⁸ Supplemental vitamin D is a prohormone that can be endogenously converted to its active 1,25-dihydroxyvitamin D.¹⁹ Vitamin D plays important roles in the regulation of calcium and magnesium in the bones as well as the maturation and differentiation of keratinocytes in the skin.¹⁶ Topical vitamin D analogues are standard treatments for psoriasis, as they are used to modulate the immune system to great effect.²⁰ Some patients with psoriasis present with vitamin D insufficiency,²¹ and it stands to reason that oral supplementation may be a treatment option. There have been multiple studies assessing the efficacy of oral vitamin D for the treatment of psoriasis; however, in the only randomized and placebo-controlled trial, there was only a slight nonsignificant improvement in the group supplemented with vitamin D.²⁰ Another small, open-label study reported remarkably improved PASI scores in 9 vitamin D–supplemented, dietary calcium–restricted patients.²² The lack of recent, large-sample studies makes it hard to draw notable conclusions from these studies.

The polyunsaturated fatty acids found in fish oils also have been considered as a treatment option for psoriasis.²³ Millsop et al²⁰ conducted an analysis of the literature reviewing the efficacy of fish oil in the treatment of psoriasis. Twelve of 15 compiled trials showed an improvement in psoriasis, ranging from slight improvements from baseline levels of the disease to statistically significant decreases in PASI scores (P<.05). It is notable that the amount of fish oil given in these studies varied widely, but the amount given did not necessarily correlate with strength of impact.²⁰ For example, Mayser et al,²⁴ Bittiner et al,²⁵ and Grimminger et al²⁶ each performed prospective, double-blind studies with docosahexaenoic acid and eicosapentaenoic acid (the omega-3 fatty acids found in fish oils), and all 3 studies saw improvements in the omega-3–treated group vs the control group. The doses of the oils, however, ranged from as low as 1.2 and 1.8 g daily of docosahexaenoic acid and eicosapentaenoic acid, respectively, to 4.2 g daily of each fatty acid.^24-26

Studies also have shown little to no improvement in the use of fish oil to treat psoriasis. One such study was conducted by Soyland et al²⁷ in 1993 in Norway. Utilizing a prospective, double-blind, placebo-controlled design over 4 months on 145 patients with moderate to severe psoriasis, researchers evaluated the treatment effectiveness via PASI scores; subjective reports from the patients; clinical manifestations; and factors such as cellular infiltration, desquamation, and redness. The results were mixed, with the placebo (corn oil) group having less redness and cellular desquamation and the fish oil group showing less cellular infiltration. In the other categories, there was no significant difference between the 2 groups, and researchers concluded there was no significant benefit to treating psoriasis using fish oil vs corn oil.²⁷ As with many of the other diets, there have been no recent, large-scale studies performed on the effect of fish oil supplementation on psoriasis; however, of the studies we reviewed, none showed fish oil supplementation to have a significant negative impact on psoriasis.

Conclusion

Dietary modifications have a complex multifactorial effect on psoriasis, often dependent on the variations of psoriasis and the lifestyle of the patient, including level of exercise, activities such as smoking and drinking, and genetic susceptibilities to conditions such as obesity. Thus, it is difficult for one diet to have a significant impact on psoriasis symptoms that applies to the majority of individuals. However, it appears that certain foods or nutritional supplements can be modified from all diets for general improvement. Foods with systemic anti-inflammatory effects, such as olive oil and fish oil, seem to be beneficial in treating psoriasis. As an extension, a gluten-free diet may help psoriasis patients with celiac disease by reducing the inflammatory environment of the body. On the opposite side of the spectrum, proinflammatory foods such as dietary fat and alcohol should be avoided.²⁸

In general, larger and more recent population-based studies are needed to add to the literature on this subject. Nationwide voluntary web-based surveys such as the NutriNet-Santé study in France may be one way to quickly amass large quantities of data (ClinicalTrials.gov Identifier NCT03335644). Participants are recruited through multimedia campaigns and return online questionnaires annually for 1 decade. A subset of participants also contributes biologic samples and participates in clinical examinations. This type of data gathering would capture many variables, provide a large sample size, and perhaps shed light on regional differences in diet and lifestyle that could then be targeted with treatments.

Recent advances in our understanding of psoriatic immune pathways have led to new generations of targeted therapies developed over the last 5 years. Although the pathogenesis of psoriasis remains to be fully elucidated, the success of these targeted therapies has confirmed a critical role of the IL-23/helper T cell (T_H17) axis in maintaining the psoriatic immune cascade, a positive feedback loop in which IL-17, IL-12, and IL-23 released from myeloid dendritic cells lead to activation of helperT cells. Activated helper T cells—namely T_H1, T_H17, and T_H22—release IL-17, IL-22, and other proinflammatory cytokines, amplifying the immune response and leading to keratinocyte proliferation and immune cell migration to psoriatic lesions. Inhibition of IL-17 and IL-23 by several biologics disrupts this aberrant inflammatory cascade and has led to dramatic improvements in outcomes, particularly among patients with moderate to severe disease.

Numerous biologics targeting these pathways and several oral treatments have been approved by the US Food and Drug Administration (FDA) for the treatment of psoriasis; in addition, a number of promising therapies are on the horizon, and knowledge of these medications might help guide our treatment approach to the patient with psoriasis. This article provides an update on the most recent (as of 2019) approved therapies and medications in the pipeline for moderate to severe plaque psoriasis, with a focus on systemic agents in phase 3 clinical trials. (Medications targeting psoriatic arthritis, biosimilars, and existing medications approved by the FDA prior to 2019 will not be discussed.)

Risankizumab

Risankizumab-rzaa (formerly BI 655066) is a humanized IgG1 monoclonal antibody that targets the p19 subunit of IL-23, selectively inhibiting the role of this critical cytokine in psoriatic inflammation.

Phase 1 Trial
In a phase 1 proof-of-concept study, 39 patients with moderate to severe plaque psoriasis received varying dosages of intravenous or subcutaneous risankizumab or placebo.¹ At week 12, the percentage of risankizumab-treated patients achieving reduction in the psoriasis area and severity index (PASI) score by 75% (PASI 75), 90% (PASI 90), and 100% (PASI 100) was 87% (27/31; P<.001 vs placebo), 58% (18/31; P=.007 vs placebo), and 16% (5/31; P=.590 vs placebo), respectively. Improvements in PASI scores were observed as early as week 2. Adverse events (AEs) were reported by 65% of the risankizumab group and 88% of the placebo group. Serious AEs were reported in 4 patients receiving risankizumab, none of which were considered related to the study medication.¹

Phase 2 Trial
A phase 2 comparator trial demonstrated noninferiority at higher dosages of risankizumab in comparison to the IL-12/IL-23 inhibitor ustekinumab.² Among 166 participants with moderate to severe plaque psoriasis, PASI 90 at week 12 was met by 77% of participants receiving 90 or 180 mg of risankizumab compared to 40% receiving ustekinumab (P<.001). Onset of activity with risankizumab was faster and the duration of effect longer vs ustekinumab; by week 8, at least PASI 75 was achieved by approximately 80% of participants in the 90-mg and 180-mg risankizumab groups compared to 60% in the ustekinumab group; PASI score reductions generally were maintained for as long as 20 weeks after the final dose of risankizumab was administered.²

Phase 3 Trials
The 52-week UltIMMa-1 and UltIMMa-2 phase 3 trials compared subcutaneous risankizumab (150 mg) to ustekinumab (45 or 90 mg [weight-based dosing]) or placebo administered at weeks 0, 4, 16, 28, and 40 in approximately 1000 patients with moderate to severe plaque psoriasis.³ Patients initially assigned to placebo switched to risankizumab 150 mg at week 16. At week 16, PASI 90 was achieved by 75.3% of risankizumab-treated patients, 42.0% of ustekinumab-treated patients, and 4.9% of placebo-treated patients in UltIMMa-1, and by 74.8% of risankizumab-treated patients, 47.5% of ustekinumab-treated patients, and 2.0% of placebo-treated patients in UltIMMa-2 (P<.0001 vs placebo and ustekinumab for both studies). Achievement of a static physician’s global assessment (sPGA) score of 0 or 1 at week 16 similarly favored risankizumab, with 87.8%, 63.0%, and 7.8% of patients in UltIMMa-1 meeting an sPGA score of 0 or 1 in the risankizumab, ustekinumab, and placebo groups, respectively, and 83.7%, 61.6%, and 5.1% in UltIMMa-2 meeting an sPGA score of 0 or 1 in the risankizumab, ustekinumab, and placebo groups, respectively (P<.0001 vs placebo and ustekinumab for both studies). Among patients initially assigned to risankizumab, improvements in PASI and sPGA continued to increase until week 52, with 81.9% achieving PASI 90 at week 52 compared to 44.0% on ustekinumab in UltIMMa-1, and 80.6% achieving PASI 90 at week 52 compared to 50.5% on ustekinumab in UltIMMa-2 (P<.0001 vs ustekinumab for both studies). Treatment-emergent AE profiles were similar for risankizumab and ustekinumab in both studies, and there were no unexpected safety findings.³

Risankizumab received FDA approval for the treatment of moderate to severe plaque psoriasis in April 2019.

Bimekizumab

Bimekizumab (UCB4940), a humanized IgG1 monoclonal antibody, selectively neutralizes the biologic functions of IL-17A and IL-17F, the latter of which has only recently been implicated in contributing to the psoriatic immune cascade.⁴

First-in-Human Study
Thirty-nine participants with mild psoriasis demonstrated efficacy after single-dose intravenous bimekizumab, with maximal improvements in all measures of disease activity observed between weeks 8 and 12 in participants receiving 160 to 640 mg.⁵

Proof-of-Concept Phase 1b Study
A subsequent trial of 53 participants with psoriatic arthritis demonstrated sustained efficacy to week 20 with varying dosages of intravenous bimekizumab.⁶ At week 8, PASI 100 was met by 86.7% of participants receiving the top 3 dosages of bimekizumab compared to none of the placebo-treated participants. Treatment-emergent AEs, including neutropenia and elevation of liver transaminases, were mostly mild to moderate and resolved spontaneously. There were 3 severe AEs and 3 serious AEs, none of which were related to treatment.⁶

Importantly, bimekizumab was shown in this small study to have the potential to be highly effective at treating psoriatic arthritis. American College of Rheumatology ACR20, ACR50, and ACR70 response criteria were very high, with an ACR20 of 80% and an ACR50 of 40%.⁶ Further trials are necessary to gather more data and confirm these findings; however, these levels of response are higher than those of any other biologic on the market.

Phase 2b Dose-Ranging Study
In this trial, 250 participants with moderate to severe plaque psoriasis received either 64 mg, 160 mg with a 320-mg loading dose, 320 mg, or 480 mg of subcutaneous bimekizumab or placebo at weeks 0, 4, and 8.⁷ At week 12, PASI 90 was achieved by significantly more patients in all bimekizumab-treated groups compared to the placebo group (46.2%–79.1% vs 0%; P<.0001 for all dosages); PASI 100 also was achieved by significantly more bimekizumab-treated patients (27.9%–60.0% vs 0%; P<.0002). Improvement began as early as week 4, with clinically meaningful responses observed in all bimekizumab groups across all measures of disease activity. Treatment-emergent AEs occurred more frequently in bimekizumab-treated participants (61%) than in placebo-treated participants (36%); the most common AEs were nasopharyngitis and upper respiratory tract infection. Of note, fungal infections were reported by 4.3% of participants receiving bimekizumab; all cases were localized superficial infection, and none led to discontinuation. Three serious AEs were reported, none of which were considered related to the study treatment.⁷

Mirikizumab

Mirikizumab (LY3074828) is a humanized IgG4 monoclonal antibody that selectively binds and inhibits the p19 subunit of IL-23, with no action on IL-12.

Phase 1 Trial
Mirikizumab was shown to improve PASI scores in patients with plaque psoriasis.⁸

Phase 2 Trial
Subsequently, a trial of 205 participants with moderate to severe plaque psoriasis compared 3 dosing regimens of subcutaneous mirikizumab—30, 100, or 300 mg—at weeks 0 and 8 compared to placebo.⁹ Primary end point results at week 16 demonstrated PASI 90 response rates of 0%, 29% (P=.009), 59% (P<.001), and 67% (P<.001) in the placebo, 30-mg, 100-mg, and 300-mg mirikizumab groups, respectively. Complete clearance of psoriasis, measured by PASI 100 and sPGA 0, was achieved by 0%, 16%, 31%, and 31%, respectively (P=.039 for 30 mg vs placebo; P=.007 for the higher dosage groups vs placebo). Response rates for all efficacy outcomes were statistically significantly higher for all mirikizumab treatment groups compared to placebo and were highest in the 100-mg and 300-mg treatment groups. Frequencies of participants reporting AEs were similar across treatment and placebo groups.⁹

Oral Medications

Only a few small-molecule, orally bioavailable therapies are on the market for the treatment of psoriasis, some of which are associated with unfavorable side-effect profiles that preclude long-term therapy.

BMS-986165
The intracellular signaling enzyme tyrosine kinase 2 is involved in functional responses of IL-12 and IL-23. BMS-986165, a potent oral inhibitor of tyrosine kinase 2 with greater selectivity than other tyrosine kinase inhibitors, demonstrated efficacy in a phase 2 trial of 267 participants with moderate to severe plaque psoriasis receiving any of 5 dosing regimens—3 mg every other day, 3 mg daily, 3 mg twice daily, 6 mg twice daily, and 12 mg daily—compared to placebo.¹⁰ At week 12, the percentage of patients with a 75% or greater reduction in PASI was 7% with placebo, 9% with 3 mg every other day (P=.49 vs placebo), 39% with 3 mg daily (P<.001 vs placebo), 69% with 3 mg twice daily (P<.001 vs placebo), 67% with 6 mg twice daily (P<.001 vs placebo), and 75% with 12 mg once daily (P<.001 vs placebo). Adverse events occurred in 51% of patients in the placebo group and in 55% to 80% of BMS-986165–treated patients; the most common AEs were nasopharyngitis, headache, diarrhea, nausea, and upper respiratory tract infection.¹⁰

A phase 3 trial comparing BMS-986165 with placebo and apremilast is underway (ClinicalTrials.gov Identifier NCT03611751).

Piclidenoson (CF101)
A novel small molecule that binds the Gi protein–associated A₃ adenosine receptor piclidenoson induces an anti-inflammatory response via deregulation of the Wnt and nuclear factor κB signal transduction pathways, leading to downregulation of proinflammatory cytokines, including IL-17 and IL-23.¹¹

In a phase 2 dose-ranging study, 75 patients with moderate to severe plaque psoriasis received varying dosages—1, 2, or 4 mg—of oral piclidenoson or placebo twice daily for 12 weeks.¹² Progressive improvement in the mean change from baseline PASI score was observed in the 2-mg group, with statistically significant differences at weeks 8 and 12 compared to placebo (P=.047 and P=.031, respectively). At week 12, 35.3% of the 2-mg group achieved at least PASI 50. Improvements in PASI were less pronounced in the 4-mg group, and no therapeutic benefit was observed in the 1-mg group. Of the 20 AEs reported, 15 possibly were related to the study drug; 1 AE was severe.¹²

In a subsequent phase 2/3 trial, patients with moderate to severe plaque psoriasis received piclidenoson—1 or 2 mg—or placebo twice daily.¹³ At week 12, PASI 75 was achieved by 8.5% of patients in the 2-mg group and by 6.9% of patients receiving placebo (P=.621), thereby not meeting the primary study end point. Results at week 32 were more encouraging. In the 2-mg group, PASI mean percentage improvement was 57% (P<.002) compared to baseline, with linear improvements observed in PASI 50 (63.5%), PASI 75 (35.5%), PASI 90 (24.7%), and PASI 100 (10.6%).¹³

A phase 3 trial comparing piclidenoson 2 and 3 mg to apremilast and placebo is in progress (ClinicalTrials.gov Identifier NCT03168256).

Future Directions

Despite abundant options for treating moderate to severe plaque psoriasis and psoriatic arthritis, the pipeline remains rich. Novel treatments might have improved efficacy, favorable safety profiles, and different modes of administration compared to current medications. In addition to the novel therapeutics covered here, several treatments are in development further down the pipeline, with only phase 1 or 2 data available. Remtolumab (ABT-122), a tumor necrosis factor α– and IL-17A–targeted immunoglobulin, is unique among biologics, given its dual inhibition of tumor necrosis factor α and IL-17A.¹⁴ M1095 (ALX-0761), a novel trivalent bispecific nanobody, is another intriguing candidate. This dual inhibitor of IL-17A/F might exhibit a number of advantages over conventional antibodies, including better tissue penetration, reduced immunogenicity, and a longer half-life (ClinicalTrials.gov Identifier NCT03384745).^15,16

As always with drug development, numerous medications that were under development failed to meet primary end points in phase 2 trials and have therefore been discontinued, including namilumab and prurisol. It is reassuring that the pace of drug discovery and development in psoriasis does not seem to be slowing; to our patients’ benefit, we will have an array of treatments available to tailor therapy to the individual.

Recent advances in our understanding of psoriatic immune pathways have led to new generations of targeted therapies developed over the last 5 years. Although the pathogenesis of psoriasis remains to be fully elucidated, the success of these targeted therapies has confirmed a critical role of the IL-23/helper T cell (T_H17) axis in maintaining the psoriatic immune cascade, a positive feedback loop in which IL-17, IL-12, and IL-23 released from myeloid dendritic cells lead to activation of helperT cells. Activated helper T cells—namely T_H1, T_H17, and T_H22—release IL-17, IL-22, and other proinflammatory cytokines, amplifying the immune response and leading to keratinocyte proliferation and immune cell migration to psoriatic lesions. Inhibition of IL-17 and IL-23 by several biologics disrupts this aberrant inflammatory cascade and has led to dramatic improvements in outcomes, particularly among patients with moderate to severe disease.

Numerous biologics targeting these pathways and several oral treatments have been approved by the US Food and Drug Administration (FDA) for the treatment of psoriasis; in addition, a number of promising therapies are on the horizon, and knowledge of these medications might help guide our treatment approach to the patient with psoriasis. This article provides an update on the most recent (as of 2019) approved therapies and medications in the pipeline for moderate to severe plaque psoriasis, with a focus on systemic agents in phase 3 clinical trials. (Medications targeting psoriatic arthritis, biosimilars, and existing medications approved by the FDA prior to 2019 will not be discussed.)

Risankizumab

Risankizumab-rzaa (formerly BI 655066) is a humanized IgG1 monoclonal antibody that targets the p19 subunit of IL-23, selectively inhibiting the role of this critical cytokine in psoriatic inflammation.

Phase 1 Trial
In a phase 1 proof-of-concept study, 39 patients with moderate to severe plaque psoriasis received varying dosages of intravenous or subcutaneous risankizumab or placebo.¹ At week 12, the percentage of risankizumab-treated patients achieving reduction in the psoriasis area and severity index (PASI) score by 75% (PASI 75), 90% (PASI 90), and 100% (PASI 100) was 87% (27/31; P<.001 vs placebo), 58% (18/31; P=.007 vs placebo), and 16% (5/31; P=.590 vs placebo), respectively. Improvements in PASI scores were observed as early as week 2. Adverse events (AEs) were reported by 65% of the risankizumab group and 88% of the placebo group. Serious AEs were reported in 4 patients receiving risankizumab, none of which were considered related to the study medication.¹

Phase 2 Trial
A phase 2 comparator trial demonstrated noninferiority at higher dosages of risankizumab in comparison to the IL-12/IL-23 inhibitor ustekinumab.² Among 166 participants with moderate to severe plaque psoriasis, PASI 90 at week 12 was met by 77% of participants receiving 90 or 180 mg of risankizumab compared to 40% receiving ustekinumab (P<.001). Onset of activity with risankizumab was faster and the duration of effect longer vs ustekinumab; by week 8, at least PASI 75 was achieved by approximately 80% of participants in the 90-mg and 180-mg risankizumab groups compared to 60% in the ustekinumab group; PASI score reductions generally were maintained for as long as 20 weeks after the final dose of risankizumab was administered.²

Phase 3 Trials
The 52-week UltIMMa-1 and UltIMMa-2 phase 3 trials compared subcutaneous risankizumab (150 mg) to ustekinumab (45 or 90 mg [weight-based dosing]) or placebo administered at weeks 0, 4, 16, 28, and 40 in approximately 1000 patients with moderate to severe plaque psoriasis.³ Patients initially assigned to placebo switched to risankizumab 150 mg at week 16. At week 16, PASI 90 was achieved by 75.3% of risankizumab-treated patients, 42.0% of ustekinumab-treated patients, and 4.9% of placebo-treated patients in UltIMMa-1, and by 74.8% of risankizumab-treated patients, 47.5% of ustekinumab-treated patients, and 2.0% of placebo-treated patients in UltIMMa-2 (P<.0001 vs placebo and ustekinumab for both studies). Achievement of a static physician’s global assessment (sPGA) score of 0 or 1 at week 16 similarly favored risankizumab, with 87.8%, 63.0%, and 7.8% of patients in UltIMMa-1 meeting an sPGA score of 0 or 1 in the risankizumab, ustekinumab, and placebo groups, respectively, and 83.7%, 61.6%, and 5.1% in UltIMMa-2 meeting an sPGA score of 0 or 1 in the risankizumab, ustekinumab, and placebo groups, respectively (P<.0001 vs placebo and ustekinumab for both studies). Among patients initially assigned to risankizumab, improvements in PASI and sPGA continued to increase until week 52, with 81.9% achieving PASI 90 at week 52 compared to 44.0% on ustekinumab in UltIMMa-1, and 80.6% achieving PASI 90 at week 52 compared to 50.5% on ustekinumab in UltIMMa-2 (P<.0001 vs ustekinumab for both studies). Treatment-emergent AE profiles were similar for risankizumab and ustekinumab in both studies, and there were no unexpected safety findings.³

Risankizumab received FDA approval for the treatment of moderate to severe plaque psoriasis in April 2019.

Bimekizumab

Bimekizumab (UCB4940), a humanized IgG1 monoclonal antibody, selectively neutralizes the biologic functions of IL-17A and IL-17F, the latter of which has only recently been implicated in contributing to the psoriatic immune cascade.⁴

First-in-Human Study
Thirty-nine participants with mild psoriasis demonstrated efficacy after single-dose intravenous bimekizumab, with maximal improvements in all measures of disease activity observed between weeks 8 and 12 in participants receiving 160 to 640 mg.⁵

Proof-of-Concept Phase 1b Study
A subsequent trial of 53 participants with psoriatic arthritis demonstrated sustained efficacy to week 20 with varying dosages of intravenous bimekizumab.⁶ At week 8, PASI 100 was met by 86.7% of participants receiving the top 3 dosages of bimekizumab compared to none of the placebo-treated participants. Treatment-emergent AEs, including neutropenia and elevation of liver transaminases, were mostly mild to moderate and resolved spontaneously. There were 3 severe AEs and 3 serious AEs, none of which were related to treatment.⁶

Importantly, bimekizumab was shown in this small study to have the potential to be highly effective at treating psoriatic arthritis. American College of Rheumatology ACR20, ACR50, and ACR70 response criteria were very high, with an ACR20 of 80% and an ACR50 of 40%.⁶ Further trials are necessary to gather more data and confirm these findings; however, these levels of response are higher than those of any other biologic on the market.

Phase 2b Dose-Ranging Study
In this trial, 250 participants with moderate to severe plaque psoriasis received either 64 mg, 160 mg with a 320-mg loading dose, 320 mg, or 480 mg of subcutaneous bimekizumab or placebo at weeks 0, 4, and 8.⁷ At week 12, PASI 90 was achieved by significantly more patients in all bimekizumab-treated groups compared to the placebo group (46.2%–79.1% vs 0%; P<.0001 for all dosages); PASI 100 also was achieved by significantly more bimekizumab-treated patients (27.9%–60.0% vs 0%; P<.0002). Improvement began as early as week 4, with clinically meaningful responses observed in all bimekizumab groups across all measures of disease activity. Treatment-emergent AEs occurred more frequently in bimekizumab-treated participants (61%) than in placebo-treated participants (36%); the most common AEs were nasopharyngitis and upper respiratory tract infection. Of note, fungal infections were reported by 4.3% of participants receiving bimekizumab; all cases were localized superficial infection, and none led to discontinuation. Three serious AEs were reported, none of which were considered related to the study treatment.⁷

Mirikizumab

Mirikizumab (LY3074828) is a humanized IgG4 monoclonal antibody that selectively binds and inhibits the p19 subunit of IL-23, with no action on IL-12.

Phase 1 Trial
Mirikizumab was shown to improve PASI scores in patients with plaque psoriasis.⁸

Phase 2 Trial
Subsequently, a trial of 205 participants with moderate to severe plaque psoriasis compared 3 dosing regimens of subcutaneous mirikizumab—30, 100, or 300 mg—at weeks 0 and 8 compared to placebo.⁹ Primary end point results at week 16 demonstrated PASI 90 response rates of 0%, 29% (P=.009), 59% (P<.001), and 67% (P<.001) in the placebo, 30-mg, 100-mg, and 300-mg mirikizumab groups, respectively. Complete clearance of psoriasis, measured by PASI 100 and sPGA 0, was achieved by 0%, 16%, 31%, and 31%, respectively (P=.039 for 30 mg vs placebo; P=.007 for the higher dosage groups vs placebo). Response rates for all efficacy outcomes were statistically significantly higher for all mirikizumab treatment groups compared to placebo and were highest in the 100-mg and 300-mg treatment groups. Frequencies of participants reporting AEs were similar across treatment and placebo groups.⁹

Oral Medications

Only a few small-molecule, orally bioavailable therapies are on the market for the treatment of psoriasis, some of which are associated with unfavorable side-effect profiles that preclude long-term therapy.

BMS-986165
The intracellular signaling enzyme tyrosine kinase 2 is involved in functional responses of IL-12 and IL-23. BMS-986165, a potent oral inhibitor of tyrosine kinase 2 with greater selectivity than other tyrosine kinase inhibitors, demonstrated efficacy in a phase 2 trial of 267 participants with moderate to severe plaque psoriasis receiving any of 5 dosing regimens—3 mg every other day, 3 mg daily, 3 mg twice daily, 6 mg twice daily, and 12 mg daily—compared to placebo.¹⁰ At week 12, the percentage of patients with a 75% or greater reduction in PASI was 7% with placebo, 9% with 3 mg every other day (P=.49 vs placebo), 39% with 3 mg daily (P<.001 vs placebo), 69% with 3 mg twice daily (P<.001 vs placebo), 67% with 6 mg twice daily (P<.001 vs placebo), and 75% with 12 mg once daily (P<.001 vs placebo). Adverse events occurred in 51% of patients in the placebo group and in 55% to 80% of BMS-986165–treated patients; the most common AEs were nasopharyngitis, headache, diarrhea, nausea, and upper respiratory tract infection.¹⁰

A phase 3 trial comparing BMS-986165 with placebo and apremilast is underway (ClinicalTrials.gov Identifier NCT03611751).

Piclidenoson (CF101)
A novel small molecule that binds the Gi protein–associated A₃ adenosine receptor piclidenoson induces an anti-inflammatory response via deregulation of the Wnt and nuclear factor κB signal transduction pathways, leading to downregulation of proinflammatory cytokines, including IL-17 and IL-23.¹¹

In a phase 2 dose-ranging study, 75 patients with moderate to severe plaque psoriasis received varying dosages—1, 2, or 4 mg—of oral piclidenoson or placebo twice daily for 12 weeks.¹² Progressive improvement in the mean change from baseline PASI score was observed in the 2-mg group, with statistically significant differences at weeks 8 and 12 compared to placebo (P=.047 and P=.031, respectively). At week 12, 35.3% of the 2-mg group achieved at least PASI 50. Improvements in PASI were less pronounced in the 4-mg group, and no therapeutic benefit was observed in the 1-mg group. Of the 20 AEs reported, 15 possibly were related to the study drug; 1 AE was severe.¹²

In a subsequent phase 2/3 trial, patients with moderate to severe plaque psoriasis received piclidenoson—1 or 2 mg—or placebo twice daily.¹³ At week 12, PASI 75 was achieved by 8.5% of patients in the 2-mg group and by 6.9% of patients receiving placebo (P=.621), thereby not meeting the primary study end point. Results at week 32 were more encouraging. In the 2-mg group, PASI mean percentage improvement was 57% (P<.002) compared to baseline, with linear improvements observed in PASI 50 (63.5%), PASI 75 (35.5%), PASI 90 (24.7%), and PASI 100 (10.6%).¹³

A phase 3 trial comparing piclidenoson 2 and 3 mg to apremilast and placebo is in progress (ClinicalTrials.gov Identifier NCT03168256).

Future Directions

Despite abundant options for treating moderate to severe plaque psoriasis and psoriatic arthritis, the pipeline remains rich. Novel treatments might have improved efficacy, favorable safety profiles, and different modes of administration compared to current medications. In addition to the novel therapeutics covered here, several treatments are in development further down the pipeline, with only phase 1 or 2 data available. Remtolumab (ABT-122), a tumor necrosis factor α– and IL-17A–targeted immunoglobulin, is unique among biologics, given its dual inhibition of tumor necrosis factor α and IL-17A.¹⁴ M1095 (ALX-0761), a novel trivalent bispecific nanobody, is another intriguing candidate. This dual inhibitor of IL-17A/F might exhibit a number of advantages over conventional antibodies, including better tissue penetration, reduced immunogenicity, and a longer half-life (ClinicalTrials.gov Identifier NCT03384745).^15,16

As always with drug development, numerous medications that were under development failed to meet primary end points in phase 2 trials and have therefore been discontinued, including namilumab and prurisol. It is reassuring that the pace of drug discovery and development in psoriasis does not seem to be slowing; to our patients’ benefit, we will have an array of treatments available to tailor therapy to the individual.

Recent advances in our understanding of psoriatic immune pathways have led to new generations of targeted therapies developed over the last 5 years. Although the pathogenesis of psoriasis remains to be fully elucidated, the success of these targeted therapies has confirmed a critical role of the IL-23/helper T cell (T_H17) axis in maintaining the psoriatic immune cascade, a positive feedback loop in which IL-17, IL-12, and IL-23 released from myeloid dendritic cells lead to activation of helperT cells. Activated helper T cells—namely T_H1, T_H17, and T_H22—release IL-17, IL-22, and other proinflammatory cytokines, amplifying the immune response and leading to keratinocyte proliferation and immune cell migration to psoriatic lesions. Inhibition of IL-17 and IL-23 by several biologics disrupts this aberrant inflammatory cascade and has led to dramatic improvements in outcomes, particularly among patients with moderate to severe disease.

Numerous biologics targeting these pathways and several oral treatments have been approved by the US Food and Drug Administration (FDA) for the treatment of psoriasis; in addition, a number of promising therapies are on the horizon, and knowledge of these medications might help guide our treatment approach to the patient with psoriasis. This article provides an update on the most recent (as of 2019) approved therapies and medications in the pipeline for moderate to severe plaque psoriasis, with a focus on systemic agents in phase 3 clinical trials. (Medications targeting psoriatic arthritis, biosimilars, and existing medications approved by the FDA prior to 2019 will not be discussed.)

Risankizumab

Risankizumab-rzaa (formerly BI 655066) is a humanized IgG1 monoclonal antibody that targets the p19 subunit of IL-23, selectively inhibiting the role of this critical cytokine in psoriatic inflammation.

Phase 1 Trial
In a phase 1 proof-of-concept study, 39 patients with moderate to severe plaque psoriasis received varying dosages of intravenous or subcutaneous risankizumab or placebo.¹ At week 12, the percentage of risankizumab-treated patients achieving reduction in the psoriasis area and severity index (PASI) score by 75% (PASI 75), 90% (PASI 90), and 100% (PASI 100) was 87% (27/31; P<.001 vs placebo), 58% (18/31; P=.007 vs placebo), and 16% (5/31; P=.590 vs placebo), respectively. Improvements in PASI scores were observed as early as week 2. Adverse events (AEs) were reported by 65% of the risankizumab group and 88% of the placebo group. Serious AEs were reported in 4 patients receiving risankizumab, none of which were considered related to the study medication.¹

Phase 2 Trial
A phase 2 comparator trial demonstrated noninferiority at higher dosages of risankizumab in comparison to the IL-12/IL-23 inhibitor ustekinumab.² Among 166 participants with moderate to severe plaque psoriasis, PASI 90 at week 12 was met by 77% of participants receiving 90 or 180 mg of risankizumab compared to 40% receiving ustekinumab (P<.001). Onset of activity with risankizumab was faster and the duration of effect longer vs ustekinumab; by week 8, at least PASI 75 was achieved by approximately 80% of participants in the 90-mg and 180-mg risankizumab groups compared to 60% in the ustekinumab group; PASI score reductions generally were maintained for as long as 20 weeks after the final dose of risankizumab was administered.²

Phase 3 Trials
The 52-week UltIMMa-1 and UltIMMa-2 phase 3 trials compared subcutaneous risankizumab (150 mg) to ustekinumab (45 or 90 mg [weight-based dosing]) or placebo administered at weeks 0, 4, 16, 28, and 40 in approximately 1000 patients with moderate to severe plaque psoriasis.³ Patients initially assigned to placebo switched to risankizumab 150 mg at week 16. At week 16, PASI 90 was achieved by 75.3% of risankizumab-treated patients, 42.0% of ustekinumab-treated patients, and 4.9% of placebo-treated patients in UltIMMa-1, and by 74.8% of risankizumab-treated patients, 47.5% of ustekinumab-treated patients, and 2.0% of placebo-treated patients in UltIMMa-2 (P<.0001 vs placebo and ustekinumab for both studies). Achievement of a static physician’s global assessment (sPGA) score of 0 or 1 at week 16 similarly favored risankizumab, with 87.8%, 63.0%, and 7.8% of patients in UltIMMa-1 meeting an sPGA score of 0 or 1 in the risankizumab, ustekinumab, and placebo groups, respectively, and 83.7%, 61.6%, and 5.1% in UltIMMa-2 meeting an sPGA score of 0 or 1 in the risankizumab, ustekinumab, and placebo groups, respectively (P<.0001 vs placebo and ustekinumab for both studies). Among patients initially assigned to risankizumab, improvements in PASI and sPGA continued to increase until week 52, with 81.9% achieving PASI 90 at week 52 compared to 44.0% on ustekinumab in UltIMMa-1, and 80.6% achieving PASI 90 at week 52 compared to 50.5% on ustekinumab in UltIMMa-2 (P<.0001 vs ustekinumab for both studies). Treatment-emergent AE profiles were similar for risankizumab and ustekinumab in both studies, and there were no unexpected safety findings.³

Risankizumab received FDA approval for the treatment of moderate to severe plaque psoriasis in April 2019.

Bimekizumab

Bimekizumab (UCB4940), a humanized IgG1 monoclonal antibody, selectively neutralizes the biologic functions of IL-17A and IL-17F, the latter of which has only recently been implicated in contributing to the psoriatic immune cascade.⁴

First-in-Human Study
Thirty-nine participants with mild psoriasis demonstrated efficacy after single-dose intravenous bimekizumab, with maximal improvements in all measures of disease activity observed between weeks 8 and 12 in participants receiving 160 to 640 mg.⁵

Proof-of-Concept Phase 1b Study
A subsequent trial of 53 participants with psoriatic arthritis demonstrated sustained efficacy to week 20 with varying dosages of intravenous bimekizumab.⁶ At week 8, PASI 100 was met by 86.7% of participants receiving the top 3 dosages of bimekizumab compared to none of the placebo-treated participants. Treatment-emergent AEs, including neutropenia and elevation of liver transaminases, were mostly mild to moderate and resolved spontaneously. There were 3 severe AEs and 3 serious AEs, none of which were related to treatment.⁶

Importantly, bimekizumab was shown in this small study to have the potential to be highly effective at treating psoriatic arthritis. American College of Rheumatology ACR20, ACR50, and ACR70 response criteria were very high, with an ACR20 of 80% and an ACR50 of 40%.⁶ Further trials are necessary to gather more data and confirm these findings; however, these levels of response are higher than those of any other biologic on the market.

Phase 2b Dose-Ranging Study
In this trial, 250 participants with moderate to severe plaque psoriasis received either 64 mg, 160 mg with a 320-mg loading dose, 320 mg, or 480 mg of subcutaneous bimekizumab or placebo at weeks 0, 4, and 8.⁷ At week 12, PASI 90 was achieved by significantly more patients in all bimekizumab-treated groups compared to the placebo group (46.2%–79.1% vs 0%; P<.0001 for all dosages); PASI 100 also was achieved by significantly more bimekizumab-treated patients (27.9%–60.0% vs 0%; P<.0002). Improvement began as early as week 4, with clinically meaningful responses observed in all bimekizumab groups across all measures of disease activity. Treatment-emergent AEs occurred more frequently in bimekizumab-treated participants (61%) than in placebo-treated participants (36%); the most common AEs were nasopharyngitis and upper respiratory tract infection. Of note, fungal infections were reported by 4.3% of participants receiving bimekizumab; all cases were localized superficial infection, and none led to discontinuation. Three serious AEs were reported, none of which were considered related to the study treatment.⁷

Mirikizumab

Mirikizumab (LY3074828) is a humanized IgG4 monoclonal antibody that selectively binds and inhibits the p19 subunit of IL-23, with no action on IL-12.

Phase 1 Trial
Mirikizumab was shown to improve PASI scores in patients with plaque psoriasis.⁸

Phase 2 Trial
Subsequently, a trial of 205 participants with moderate to severe plaque psoriasis compared 3 dosing regimens of subcutaneous mirikizumab—30, 100, or 300 mg—at weeks 0 and 8 compared to placebo.⁹ Primary end point results at week 16 demonstrated PASI 90 response rates of 0%, 29% (P=.009), 59% (P<.001), and 67% (P<.001) in the placebo, 30-mg, 100-mg, and 300-mg mirikizumab groups, respectively. Complete clearance of psoriasis, measured by PASI 100 and sPGA 0, was achieved by 0%, 16%, 31%, and 31%, respectively (P=.039 for 30 mg vs placebo; P=.007 for the higher dosage groups vs placebo). Response rates for all efficacy outcomes were statistically significantly higher for all mirikizumab treatment groups compared to placebo and were highest in the 100-mg and 300-mg treatment groups. Frequencies of participants reporting AEs were similar across treatment and placebo groups.⁹

Oral Medications

Only a few small-molecule, orally bioavailable therapies are on the market for the treatment of psoriasis, some of which are associated with unfavorable side-effect profiles that preclude long-term therapy.

BMS-986165
The intracellular signaling enzyme tyrosine kinase 2 is involved in functional responses of IL-12 and IL-23. BMS-986165, a potent oral inhibitor of tyrosine kinase 2 with greater selectivity than other tyrosine kinase inhibitors, demonstrated efficacy in a phase 2 trial of 267 participants with moderate to severe plaque psoriasis receiving any of 5 dosing regimens—3 mg every other day, 3 mg daily, 3 mg twice daily, 6 mg twice daily, and 12 mg daily—compared to placebo.¹⁰ At week 12, the percentage of patients with a 75% or greater reduction in PASI was 7% with placebo, 9% with 3 mg every other day (P=.49 vs placebo), 39% with 3 mg daily (P<.001 vs placebo), 69% with 3 mg twice daily (P<.001 vs placebo), 67% with 6 mg twice daily (P<.001 vs placebo), and 75% with 12 mg once daily (P<.001 vs placebo). Adverse events occurred in 51% of patients in the placebo group and in 55% to 80% of BMS-986165–treated patients; the most common AEs were nasopharyngitis, headache, diarrhea, nausea, and upper respiratory tract infection.¹⁰

A phase 3 trial comparing BMS-986165 with placebo and apremilast is underway (ClinicalTrials.gov Identifier NCT03611751).

Piclidenoson (CF101)
A novel small molecule that binds the Gi protein–associated A₃ adenosine receptor piclidenoson induces an anti-inflammatory response via deregulation of the Wnt and nuclear factor κB signal transduction pathways, leading to downregulation of proinflammatory cytokines, including IL-17 and IL-23.¹¹

In a phase 2 dose-ranging study, 75 patients with moderate to severe plaque psoriasis received varying dosages—1, 2, or 4 mg—of oral piclidenoson or placebo twice daily for 12 weeks.¹² Progressive improvement in the mean change from baseline PASI score was observed in the 2-mg group, with statistically significant differences at weeks 8 and 12 compared to placebo (P=.047 and P=.031, respectively). At week 12, 35.3% of the 2-mg group achieved at least PASI 50. Improvements in PASI were less pronounced in the 4-mg group, and no therapeutic benefit was observed in the 1-mg group. Of the 20 AEs reported, 15 possibly were related to the study drug; 1 AE was severe.¹²

In a subsequent phase 2/3 trial, patients with moderate to severe plaque psoriasis received piclidenoson—1 or 2 mg—or placebo twice daily.¹³ At week 12, PASI 75 was achieved by 8.5% of patients in the 2-mg group and by 6.9% of patients receiving placebo (P=.621), thereby not meeting the primary study end point. Results at week 32 were more encouraging. In the 2-mg group, PASI mean percentage improvement was 57% (P<.002) compared to baseline, with linear improvements observed in PASI 50 (63.5%), PASI 75 (35.5%), PASI 90 (24.7%), and PASI 100 (10.6%).¹³

A phase 3 trial comparing piclidenoson 2 and 3 mg to apremilast and placebo is in progress (ClinicalTrials.gov Identifier NCT03168256).

Future Directions

Despite abundant options for treating moderate to severe plaque psoriasis and psoriatic arthritis, the pipeline remains rich. Novel treatments might have improved efficacy, favorable safety profiles, and different modes of administration compared to current medications. In addition to the novel therapeutics covered here, several treatments are in development further down the pipeline, with only phase 1 or 2 data available. Remtolumab (ABT-122), a tumor necrosis factor α– and IL-17A–targeted immunoglobulin, is unique among biologics, given its dual inhibition of tumor necrosis factor α and IL-17A.¹⁴ M1095 (ALX-0761), a novel trivalent bispecific nanobody, is another intriguing candidate. This dual inhibitor of IL-17A/F might exhibit a number of advantages over conventional antibodies, including better tissue penetration, reduced immunogenicity, and a longer half-life (ClinicalTrials.gov Identifier NCT03384745).^15,16

As always with drug development, numerous medications that were under development failed to meet primary end points in phase 2 trials and have therefore been discontinued, including namilumab and prurisol. It is reassuring that the pace of drug discovery and development in psoriasis does not seem to be slowing; to our patients’ benefit, we will have an array of treatments available to tailor therapy to the individual.

What does your patient need to know at the first visit?

Patient education is important initially. There are several causes for nail dystrophy. Oftentimes, when patients present, they believe that they have onychomycosis. Therefore, it is important to counsel individuals with potential nail psoriasis (Figure) and to discuss the differential diagnosis of the condition.

The presence of psoriasis on other areas of the body and the absence of fungal infection on the soles of the feet and in between the toes increases the likelihood of nail psoriasis. The most accurate test to perform is a nail clipping with subsequent periodic acid–Schiff stain. It is important to remember, however, that nail psoriasis and fungal infection of the nail can coexist.

Once the diagnosis of nail psoriasis is established, it is important to review gentle care of the nails. A thorough discussion of therapeutic options is helpful. Patients also should be advised that the presence of nail psoriasis can increase the likelihood of the development of
psoriatic arthritis.

What are your go-to treatments?

Prior to the development of biologic therapies, topical treatments were the mainstay of treatment. Topical corticosteroid preparations can be used around and under the nail. Other therapeutic options include topical calcipotriene and topical retinoids.

Intralesional injection is another therapeutic option. Injection into the nail bed is useful for the treatment of nail bed symptoms of nail psoriasis such as onycholysis. Injection into the proximal nail fold can ameliorate signs of nail matrix psoriasis such as nail pitting. Although injection can be effective, it also can be painful; therefore, many patients do not opt to have this therapy performed.

Systemic therapy has been shown to be highly effective in improving nail psoriasis. There has been a good amount of data from studies specifically done in nail psoriasis and nail data that have been taken from larger phase 3 trials (Elewski et al; van de Kerkhof et al). Therefore, several of the biologics on the market as well apremilast are good options for the treatment of nail psoriasis. When using a systemic agent, it is important to carefully review the benefits and risks of each therapy with patients. Because the nail grows slowly, improvement can be gradual and take several months to peak.

How do you keep patients compliant with treatment?

Because nail psoriasis causes distress among patients, it generally is not too hard for them to be compliant. Of course, it is important to have regular follow-up to monitor progress and to reinforce the importance of continued therapy. At the end of the day, however, treatment success is the best asset to encourage continued compliance.

Resources for Patients
Managing nail psoriasis
http://www.psoriasis.org/about-psoriasis/specific-locations/hands-feet-nails/managing-nail-psoriasis

What is nail psoriasis, and how can I treat it?
http://www.aad.org/public/diseases/scaly-skin/psoriasis/diagnosis-and-treatment-of-psoriasis/what-is-nail-psoriasis-and-how-can-i-treat-it

Suggested Readings
Elewski BE, Okun MM, Papp K, et al. Adalimumab for nail psoriasis: efficacy and safety from the first 26 weeks of phase 3, randomized, placebo controlled trial. J Am Acad Dermatol. 2018;78:90.e1-99.e1.

Van de Kerkhof P, Guenther L, Gottlieb AB, et al. Ixekizumab treatment improves fingernail psoriasis in patients with moderate-to-severe psoriasis: results from the randomized, controlled, and open-label phases of UNCOVER-3. J Eur Acad Dermatol Venereol. 2017;31:477-482.

Yin N, Choudhary S, Nouri K. Pulsed dye laser for the treatment of nail psoriasis. Cutis. 2013;92:129-135.

What does your patient need to know at the first visit?

Patient education is important initially. There are several causes for nail dystrophy. Oftentimes, when patients present, they believe that they have onychomycosis. Therefore, it is important to counsel individuals with potential nail psoriasis (Figure) and to discuss the differential diagnosis of the condition.

The presence of psoriasis on other areas of the body and the absence of fungal infection on the soles of the feet and in between the toes increases the likelihood of nail psoriasis. The most accurate test to perform is a nail clipping with subsequent periodic acid–Schiff stain. It is important to remember, however, that nail psoriasis and fungal infection of the nail can coexist.

Once the diagnosis of nail psoriasis is established, it is important to review gentle care of the nails. A thorough discussion of therapeutic options is helpful. Patients also should be advised that the presence of nail psoriasis can increase the likelihood of the development of
psoriatic arthritis.

What are your go-to treatments?

Prior to the development of biologic therapies, topical treatments were the mainstay of treatment. Topical corticosteroid preparations can be used around and under the nail. Other therapeutic options include topical calcipotriene and topical retinoids.

Intralesional injection is another therapeutic option. Injection into the nail bed is useful for the treatment of nail bed symptoms of nail psoriasis such as onycholysis. Injection into the proximal nail fold can ameliorate signs of nail matrix psoriasis such as nail pitting. Although injection can be effective, it also can be painful; therefore, many patients do not opt to have this therapy performed.

Systemic therapy has been shown to be highly effective in improving nail psoriasis. There has been a good amount of data from studies specifically done in nail psoriasis and nail data that have been taken from larger phase 3 trials (Elewski et al; van de Kerkhof et al). Therefore, several of the biologics on the market as well apremilast are good options for the treatment of nail psoriasis. When using a systemic agent, it is important to carefully review the benefits and risks of each therapy with patients. Because the nail grows slowly, improvement can be gradual and take several months to peak.

How do you keep patients compliant with treatment?

Because nail psoriasis causes distress among patients, it generally is not too hard for them to be compliant. Of course, it is important to have regular follow-up to monitor progress and to reinforce the importance of continued therapy. At the end of the day, however, treatment success is the best asset to encourage continued compliance.

Resources for Patients
Managing nail psoriasis
http://www.psoriasis.org/about-psoriasis/specific-locations/hands-feet-nails/managing-nail-psoriasis

What is nail psoriasis, and how can I treat it?
http://www.aad.org/public/diseases/scaly-skin/psoriasis/diagnosis-and-treatment-of-psoriasis/what-is-nail-psoriasis-and-how-can-i-treat-it

Suggested Readings
Elewski BE, Okun MM, Papp K, et al. Adalimumab for nail psoriasis: efficacy and safety from the first 26 weeks of phase 3, randomized, placebo controlled trial. J Am Acad Dermatol. 2018;78:90.e1-99.e1.

Van de Kerkhof P, Guenther L, Gottlieb AB, et al. Ixekizumab treatment improves fingernail psoriasis in patients with moderate-to-severe psoriasis: results from the randomized, controlled, and open-label phases of UNCOVER-3. J Eur Acad Dermatol Venereol. 2017;31:477-482.

Yin N, Choudhary S, Nouri K. Pulsed dye laser for the treatment of nail psoriasis. Cutis. 2013;92:129-135.

What does your patient need to know at the first visit?

Patient education is important initially. There are several causes for nail dystrophy. Oftentimes, when patients present, they believe that they have onychomycosis. Therefore, it is important to counsel individuals with potential nail psoriasis (Figure) and to discuss the differential diagnosis of the condition.

The presence of psoriasis on other areas of the body and the absence of fungal infection on the soles of the feet and in between the toes increases the likelihood of nail psoriasis. The most accurate test to perform is a nail clipping with subsequent periodic acid–Schiff stain. It is important to remember, however, that nail psoriasis and fungal infection of the nail can coexist.

Once the diagnosis of nail psoriasis is established, it is important to review gentle care of the nails. A thorough discussion of therapeutic options is helpful. Patients also should be advised that the presence of nail psoriasis can increase the likelihood of the development of
psoriatic arthritis.

What are your go-to treatments?

Prior to the development of biologic therapies, topical treatments were the mainstay of treatment. Topical corticosteroid preparations can be used around and under the nail. Other therapeutic options include topical calcipotriene and topical retinoids.

Intralesional injection is another therapeutic option. Injection into the nail bed is useful for the treatment of nail bed symptoms of nail psoriasis such as onycholysis. Injection into the proximal nail fold can ameliorate signs of nail matrix psoriasis such as nail pitting. Although injection can be effective, it also can be painful; therefore, many patients do not opt to have this therapy performed.

Systemic therapy has been shown to be highly effective in improving nail psoriasis. There has been a good amount of data from studies specifically done in nail psoriasis and nail data that have been taken from larger phase 3 trials (Elewski et al; van de Kerkhof et al). Therefore, several of the biologics on the market as well apremilast are good options for the treatment of nail psoriasis. When using a systemic agent, it is important to carefully review the benefits and risks of each therapy with patients. Because the nail grows slowly, improvement can be gradual and take several months to peak.

How do you keep patients compliant with treatment?

Because nail psoriasis causes distress among patients, it generally is not too hard for them to be compliant. Of course, it is important to have regular follow-up to monitor progress and to reinforce the importance of continued therapy. At the end of the day, however, treatment success is the best asset to encourage continued compliance.

Resources for Patients
Managing nail psoriasis
http://www.psoriasis.org/about-psoriasis/specific-locations/hands-feet-nails/managing-nail-psoriasis

What is nail psoriasis, and how can I treat it?
http://www.aad.org/public/diseases/scaly-skin/psoriasis/diagnosis-and-treatment-of-psoriasis/what-is-nail-psoriasis-and-how-can-i-treat-it

Suggested Readings
Elewski BE, Okun MM, Papp K, et al. Adalimumab for nail psoriasis: efficacy and safety from the first 26 weeks of phase 3, randomized, placebo controlled trial. J Am Acad Dermatol. 2018;78:90.e1-99.e1.

Van de Kerkhof P, Guenther L, Gottlieb AB, et al. Ixekizumab treatment improves fingernail psoriasis in patients with moderate-to-severe psoriasis: results from the randomized, controlled, and open-label phases of UNCOVER-3. J Eur Acad Dermatol Venereol. 2017;31:477-482.

Yin N, Choudhary S, Nouri K. Pulsed dye laser for the treatment of nail psoriasis. Cutis. 2013;92:129-135.

Increased understanding of the pathophysiology of psoriasis has been one of the driving forces in the development of new therapies. An understanding of the processes involved is important in the optimal management of the disease. The last 30 years of research and clinical practice have revolutionized our understanding of the pathogenesis of psoriasis as the dysregulation of immunity triggered by environmental and genetic stimuli. Psoriasis was originally regarded as a primary disorder of epidermal hyperproliferation. However, experimental models and clinical results from immunomodulating therapies have refined this perspective in conceptualizing psoriasis as a genetically programmed pathologic interaction among resident skin cells; infiltrating immunocytes; and a host of proinflammatory cytokines, chemokines, and growth factors produced by these immunocytes. Two populations of immunocytes and their respective signaling molecules collaborate in the pathogenesis: (1) innate immunocytes, mediated by antigen-presenting cells (APCs)(including natural killer [NK] T lymphocytes, Langerhans cells, and neutrophils), and (2) acquired or adaptive immunocytes, mediated by mature CD4⁺ and CD8⁺ T lymphocytes in the skin. Such dysregulation of immunity and subsequent inflammation is responsible for the development and perpetuation of the clinical plaques and histological inflammatory infiltrate characteristic of psoriasis.

Although psoriasis is considered to be an immune-mediated disease in which intralesional T lymphocytes and their proinflammatory signals trigger primed basal layer keratinocytes to rapidly proliferate, debate and research focus on the stimulus that incites this inflammatory process. Our current understanding considers psoriasis to be triggered by exogenous or endogenous environmental stimuli in genetically susceptible individuals. Such stimuli include group A streptococcal pharyngitis, viremia, allergic drug reactions, antimalarial drugs, lithium, beta-blockers, IFN-α, withdrawal of systemic corticosteroids, local trauma (Köbner phenomenon), and emotional stress. These stimuli correlate with the onset or flares of psoriatic lesions. Psoriasis genetics centers on susceptibility loci and corresponding candidate genes, particularly the psoriasis susceptibility (PSORS) 1 locus on the major histocompatibility complex (MHC) class I region. Current research on the pathogenesis of psoriasis examines the complex interactions among immunologic mechanisms, environmental stimuli, and genetic susceptibility. After discussing the clinical presentation and histopathologic features of psoriasis, we will review the pathophysiology of psoriasis through noteworthy developments, including serendipitous observations, reactions to therapies, clinical trials, and animal model systems that have shaped our view of the disease process. In addition to the classic skin lesions, approximately 23% of psoriasis patients develop psoriatic arthritis, with a 10-year latency after diagnosis of psoriasis.¹

Principles of Immunity

The immune system, intended to protect its host from foreign invaders and unregulated cell growth, employs 2 main effector pathways—the innate and the acquired (or adaptive) immune responses—both of which contribute to the pathophysiology of psoriasis.² Innate immunity responses occur within minutes to hours of antigen exposure but fail to develop memory for when the antigen is encountered again. However, adaptive immunity responses take days to weeks to respond after challenged with an antigen. The adaptive immune cells have the capacity to respond to a greater range of antigens and develop immunologic memory via rearrangement of antigen receptors on B and T cells. These specialized B and T cells can then be promptly mobilized and differentiated into mature effector cells that protect the host from a foreign pathogen.

Innate and adaptive immune responses are highly intertwined; they can initiate, perpetuate, and terminate the immune mechanisms responsible for inflammation. They can modify the nature of the immune response by altering the relative proportions of type 1 (T_H1), type 2 (T_H2), and the more recently discovered type 17 (T_H17) subset of helper T cells and their respective signaling molecules. A T_H1 response is essential for a cellular immunologic reaction to intracellular bacteria and viruses or cellular immunity. A T_H2 response promotes IgE synthesis, eosinophilia, and mast cell maturation for extracellular parasites and helminthes as well as humoral immunity, while a T_H17 response is important for cell-mediated immunity to extracellular bacteria and plays a role in autoimmunity.³ The innate and adaptive immune responses employ common effector molecules such as chemokines and cytokines, which are essential in mediating an immune response.

Implicating Dysregulation of Immunity

Our present appreciation of the pathogenesis of psoriasis is based on the history of trial-and-error therapies; serendipitous discoveries; and the current immune targeting drugs used in a variety of chronic inflammatory conditions, including rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease. Before the mid-1980s, research focused on the hyperproliferative epidermal cells as the primary pathology because a markedly thickened epidermis was indeed demonstrated on histologic specimens. Altered cell-cycle kinetics were thought to be the culprit behind the hyperkeratotic plaques. Thus, initial treatments centered on oncologic and antimitotic therapies used to arrest keratinocyte proliferation with agents such as arsenic, ammoniated mercury, and methotrexate.⁴

However, a paradigm shift from targeting epidermal keratinocytes to immunocyte populations was recognized when a patient receiving cyclosporine to prevent transplant rejection noted clearing of psoriatic lesions in the 1980s.⁵ Cyclosporine was observed to inhibit messenger RNA transcription of T-cell cytokines, thereby implicating immunologic dysregulation, specifically T-cell hyperactivity, in the pathogenesis of psoriasis.⁶ However, the concentrations of oral cyclosporine reached in the epidermis exerted direct effects on keratinocyte proliferation and lymphocyte function in these patients.⁷ Thus, the question was raised as to whether the keratinocytes or the lymphocytes drove the psoriatic plaques. The use of an IL-2 diphtheria toxin-fusion protein, denileukin diftitox, specific for activated T cells with high-affinity IL-2 receptors and nonreactive with keratinocytes, distinguished which cell type was responsible. This targeted T-cell toxin provided clinical and histological clearing of psoriatic plaques. Thus, T lymphocytes rather than keratinocytes were recognized as the definitive driver behind the psoriatic plaques.⁸

Additional studies have demonstrated that treatments that induce prolonged clearing of psoriatic lesions without continuous therapy, such as psoralen plus UVA irradiation, decreased the numbers of T cells in plaques by at least 90%.⁹ However, treatments that require continual therapy for satisfactory clinical results, such as cyclosporine and etretinate, simply suppress T-cell activity and proliferation.^10,11 Further evidence has linked cellular immunity with the pathogenesis of psoriasis, defining it as a T_H1-type disease. Natural killer T cells were shown to be involved through the use of a severe combined immunodeficient mouse model. They were injected into prepsoriatic skin grafted on immunodeficient mice, creating a psoriatic plaque with an immune response showing cytokines from T_H1 cells rather than T_H2 cells.¹² When psoriatic plaques were treated topically with the toll-like receptor 7 agonist imiquimod, aggravation and spreading of the plaques were noted. The exacerbation of psoriasis was accompanied by an induction of lesional T_H1-type interferon produced by plasmacytoid dendritic cell (DC) precursors. Plasmacytoid DCs were observed to compose up to 16% of the total dermal infiltrate in psoriatic skin lesions based on their coexpression of BDCA2 and CD123.¹³ Additionally, cancer patients being treated with interferon alfa experienced induction of psoriasis.¹⁴ Moreover, patients being treated for warts with intralesional interferon alfa developed psoriatic plaques in neighboring prior asymptomatic skin.¹⁵ Patients with psoriasis who were treated with interferon gamma, a T_H1 cytokine type, also developed new plaques correlating with the sites of injection.¹⁶

Intralesional T Lymphocytes

Psoriatic lesions contain a host of innate immunocytes, such as APCs, NK cells, and neutrophils, as well as adaptive T cells and an inflammatory infiltrate. These cells include CD4 and CD8 subtypes in which the CD8⁺ cells predominate in the epidermis, while CD4⁺ cells show preference for the dermis.¹⁷ There are 2 groups of CD8⁺ cells: one group migrates to the epidermis, expressing the integrin CD103, while the other group is found in the dermis but may be headed to or from the epidermis. The CD8⁺ cells residing in the epidermis that express the integrin CD103 are capable of interacting with E-cadherin, which enables these cells to travel to the epidermis and bind resident cells. Immunophenotyping reveals that these mature T cells represent chiefly activated memory cells, including CD2⁺, CD3⁺, CD5⁺, CLA, CD28, and CD45RO⁺.¹⁸ Many of these cells express activation markers such as HLA-DR, CD25, and CD27, in addition to the T-cell receptor (TCR).

T-Lymphocyte Stimulation

Both mature CD4⁺ and CD8⁺ T cells can respond to the peptides presented by APCs. Although the specific antigen that these T cells are reacting to has not yet been elucidated, several antigenic stimuli have been proposed, including self-proteins, microbial pathogens, and microbial superantigens. The premise that self-reactive T lymphocytes may contribute to the disease process is derived from the molecular mimicry theory in which an exuberant immune response to a pathogen produces cross-reactivity with self-antigens.¹⁹ Considering that infections have been associated with the onset of psoriasis, this theory merits consideration. However, it also has been observed that T cells can be activated without antigens or superantigens but rather with direct contact with accessory cells.²⁰ No single theory has clearly emerged. Researchers continue to search for the inciting stimulus that triggers the T lymphocyte and attempt to determine whether T cells are reacting to a self-derived or non–self-derived antigen.

T-Lymphocyte Signaling

T-cell signaling is a highly coordinated process in which T lymphocytes recognize antigens via presentation by mature APCs in the skin rather than the lymphoid tissues. Such APCs expose antigenic peptides via class I or II MHC molecules for which receptors are present on the T-cell surface. The antigen recognition complex at the T-cell and APC interface, in concert with a host of antigen-independent co-stimulatory signals, regulates T-cell signaling and is referred to as the immunologic synapse. The antigen presentation and network of co-stimulatory and adhesion molecules optimize T-cell activation, and dermal DCs release IL-12 and IL-23 to promote a T_H1 and T_H17 response, respectively. The growth factors released by these helper T cells sustain neoangiogenesis, stimulate epidermal hyperproliferation, alter epidermal differentiation, and decrease susceptibility to apoptosis that characterizes the erythematous hypertrophic scaling lesions of psoriasis.²¹ Furthermore, the cytokines produced from the immunologic response, such as tumor necrosis factor (TNF) α, IFN-γ, and IL-2, correspond to cytokines that are upregulated in psoriatic plaques.²²

Integral components of the immunologic synapse complex include co-stimulatory signals such as CD28, CD40, CD80, and CD86, as well as adhesion molecules such as cytotoxic T-lymphocyte antigen 4 and lymphocyte function-associated antigen (LFA) 1, which possess corresponding receptors on the T cell. These molecules play a key role in T-cell signaling, as their disruption has been shown to decrease T-cell responsiveness and associated inflammation. The B7 family of molecules routinely interacts with CD28 T cells to co-stimulate T-cell activation. Cytotoxic T-lymphocyte antigen 4 immunoglobulin, an antibody on the T-cell surface, targets B7 and interferes with signaling between B7 and CD28. In psoriatic patients, this blockade was demonstrated to attenuate the T-cell response and correlated with a clinical and histological decrease in psoriasiform hyperplasia.²³ Biologic therapies that disrupt the LFA-1 component of the immunologic synapse also have demonstrated efficacy in the treatment of psoriasis. Alefacept is a human LFA-3 fusion protein that binds CD2 on T cells and blocks the interaction between LFA-3 on APCs and CD2 on memory CD45RO⁺ T cells and induces apoptosis of such T cells. Efalizumab is a human monoclonal antibody to the CD11 chain of LFA-1 that blocks the interaction between LFA-1 on the T cell and intercellular adhesion molecule 1 on an APC or endothelial cell. Both alefacept and efalizumab, 2 formerly marketed biologic therapies, demonstrated remarkable clinical reduction of psoriatic lesions, and alefacept has been shown to produce disease remission for up to 18 months after discontinuation of therapy.^24-26

NK T Cells

Natural killer T cells represent a subset of CD3⁺ T cells present in psoriatic plaques. Although NK T cells possess a TCR, they differ from T cells by displaying NK receptors comprised of lectin and immunoglobulin families. These cells exhibit remarkable specificity and are activated upon recognition of glycolipids presented by CD1d molecules. This process occurs in contrast to CD4⁺ and CD8⁺ T cells, which, due to their TCR diversity, respond to peptides processed by APCs and displayed on MHC molecules. Natural killer T cells can be classified into 2 subsets: (1) one group that expresses CD4 and preferentially produces T_H1- versus T_H2-type cytokines, and (2) another group that lacks CD4 and CD8 that only produces T_H1-type cytokines. The innate immune system employs NK T cells early in the immune response because of their direct cytotoxicity and rapid production of cytokines such as IFN-γ, which promotes a T_H1 inflammatory response, and IL-4, which promotes the development of T_H2 cells. Excessive or dysfunctional NK T cells have been associated with autoimmune diseases such as multiple sclerosis and inflammatory bowel disease as well as allergic contact dermatitis.^27-29

In psoriasis, NK T cells are located in the epidermis, closely situated to epidermal keratinocytes, which suggests a role for direct antigen presentation. Furthermore, CD1d is overexpressed throughout the epidermis of psoriatic plaques, whereas normally CD1d expression is confined to terminally differentiated keratinocytes. An in vitro study examining cytokine-based inflammation demonstrative of psoriasis treated cultured CD1d-positive keratinocytes with interferon gamma in the presence of alpha-galactosylceramide of the lectin family.³⁰ Interferon gamma was observed to enhance keratinocyte CD1d expression, and subsequently, CD1d-positive keratinocytes were found to activate NK T cells to produce high levels of IFN-γ, while levels of IL-4 remained undetectable. The preferential production of IFN-γ supports a T_H1-mediated mechanism regulated by NK T cells in the immunopathogenesis of psoriasis.

Dendritic Cells

Dendritic cells are APCs that process antigens in the tissues in which they reside, after which they migrate to local lymph nodes where they present their native antigens to T cells. This process allows the T-cell response to be tailored to the appropriate antigens in the corresponding tissues. Immature DCs that capture antigens mature by migrating to the T-cell center of the lymph node where they present their antigens to either MHC molecules or the CD1 family. This presentation results in T-cell proliferation and differentiation that correlates with the required type of T-cell response. Multiple subsets of APCs, including myeloid and plasmacytoid DCs, are highly represented in the epidermis and dermis of psoriatic plaques as compared with normal skin.³¹ Dermal DCs are thought to be responsible for activating both the T_H1 and T_H17 infiltrate by secreting IL-12 and IL-23, respectively. This mixed cellular response secretes cytokines and leads to a cascade of events involving keratinocytes, fibroblasts, endothelial cells, and neutrophils that create the cutaneous lesions seen in psoriasis.³

Although DCs play a pivotal role in eliciting an immune response against a foreign invader, they also contribute to the establishment of tolerance. Throughout their maturation, DCs are continuously sensing their environment, which shapes their production of T_H1- versus T_H2-type cytokines and subsequently the nature of the T-cell response. When challenged with a virus, bacteria, or unchecked cell growth, DCs mature into APCs. However, in the absence of a strong stimulus, DCs fail to mature into APCs and present self-peptides with MHC molecules, thereby creating regulatory T cells involved in peripheral tolerance.³² If this balance between immunogenic APCs and housekeeping T cells is upset, inflammatory conditions such as psoriasis can result.

Cytokines

Cytokines are low-molecular-weight glycoproteins that function as signals to produce inflammation, defense, tissue repair and remodeling, fibrosis, angiogenesis, and restriction of neoplastic growth.³³ Cytokines are produced by immunocytes such as lymphocytes and macrophages as well as nonimmunocytes such as endothelial cells and keratinocytes. Proinflammatory cytokines include IL-1, IL-2, the IL-17 family, IFN-γ, and TNF-α, while anti-inflammatory cytokines include IL-4 and IL-10. A relative preponderance of T_H1 proinflammatory cytokines or an insufficiency of T_H2 anti-inflammatory cytokines induces local inflammation and recruitment of additional immunocyte populations, which produce added cytokines.³⁴ A vicious cycle of inflammation occurs that results in cutaneous manifestations such as a plaque. Psoriatic lesions are characterized by a relative increase of T_H1-type (eg, IL-2, IFN-γ, TNF-α, TNF-β) to T_H2-type (eg, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13) cytokines and an increase in T_H17-type cytokines. Natural killer T cells stimulated by CD1d-overexpressing keratinocytes increase production of proinflammatory IFN-γ without effect on the anti-inflammatory IL-4. In addition to the cytokines produced by T cells, APCs produce IL-18, IL-23, and TNF-α found in the inflammatory infiltrate of psoriatic plaques. Both IL-18 and IL-23 stimulate T_H1 cells to produce IFN-γ, and IL-23 stimulates T_H17 cells. Clearly, a T_H1- and T_H17-type pattern governs the immune effector cells and their respective cytokines present in psoriatic skin.

Tumor Necrosis Factor α

Although a network of cytokines is responsible for the inflammation of psoriasis, TNF-α has been implicated as a master proinflammatory cytokine of the innate immune response due to its widespread targets and sources. Tumor necrosis factor α is produced by activated T cells, keratinocytes, NK cells, macrophages, monocytes, Langerhans APCs, and endothelial cells. Psoriatic lesions demonstrate high concentrations of TNF-α, while the synovial fluid of psoriatic arthritis patients demonstrates elevated concentrations of TNF-α, IL-1, IL-6, and IL-8.³⁴ In psoriasis, TNF-α supports the expression of adhesion molecules (intercellular adhesion molecule 1 and P- and E-selectin), angiogenesis via vascular endothelial growth factor, the synthesis of proinflammatory molecules (IL-1, IL-6, IL-8, and nuclear factor κβ), and keratinocyte hyperproliferation via vasoactive intestinal peptide.³⁵

A role for TNF-α in psoriasis treatment was serendipitously discovered in a trial for Crohn disease in which infliximab, a mouse-human IgG1 anti–TNF-α monoclonal antibody, was observed to clear psoriatic plaques in a patient with both Crohn disease and psoriasis.³⁶ Immunotherapies that target TNF-α, including infliximab, etanercept, and adalimumab, demonstrate notable efficacy in the treatment of psoriasis.^37-39 Tumor necrosis factor α is regarded as the driver of the inflammatory cycle of psoriasis due to its numerous modes of production, capability to amplify other proinflammatory signals, and the efficacy and rapidity with which it produces clinical improvements in psoriasis.

IL-23/T_H17 Axis

A new distinct population of helper T cells has been shown to play an important role in psoriasis. These cells develop with the help of IL-23 (secreted by dermal DCs) and subsequently secrete cytokines such as IL-17; they are, therefore, named T_H17 cells. CD161 is considered a surface marker for these cells.⁴⁰ Strong evidence for this IL-23/T_H17 axis has been shown in mouse and human models as well as in genetic studies.

IL-23 is a cytokine that shares the p40 subunit with IL-12 and has been linked to autoimmune diseases in both mice and humans.³ It is required for optimal development of T_H17 cells⁴¹ from a committed CD4⁺ T-cell population after exposure to transforming growth factor β1 in combination with other proinflammatory cytokines.^42,43 IL-23 messenger RNA is produced at higher levels in inflammatory psoriatic skin lesions versus uninvolved skin,⁴⁴ and intradermal IL-23 injections in mice produced lesions resembling psoriasis macroscopically and microscopically.⁴⁵ Furthermore, several systemic therapies have been shown to modulate IL-23 levels and correlate with clinical benefit.³ Alterations in the gene for the IL-23 receptor have been shown to be protective for psoriasis,^46-48 and the gene coding for the p40 subunit is associated with psoriasis.^46,47

Type 17 helper T cells produce a number of cytokines, such as IL-22, IL-17A, IL-17F, and IL-26; the latter 3 are considered to be specific to this lineage.⁴² IL-22 acts on outer body barrier tissues, such as the skin, and has antimicrobial activity. Blocking the activity of IL-22 in mice prevented the development of skin lesions,⁴⁹ and psoriasis patients have elevated levels of IL-22 in the skin and blood.^50,51 The IL-17 cytokines induce the expression of proinflammatory cytokines, colony-stimulating factors, and chemokines, and they recruit, mobilize, and activate neutrophils.⁵² IL-17 messenger RNA was found in lesional psoriatic skin but not unaffected skin,⁵³ and cells isolated from the dermis of psoriatic skin have been shown to produce IL-17.⁵⁴ IL-17A is not elevated in the serum of psoriatic patients (unlike other autoimmune diseases),⁵⁵ and it is, therefore, thought that T_H17 cells and IL-17A production are localized to the affected psoriatic skin. Consistent with this concept is the finding that treatments such as cyclosporin A and anti-TNF agents decrease proinflammatory cytokines in lesional skin but not in the periphery.^56-58 These cytokines released by T_H17 cells in addition to those released by T_H1 cells act on keratinocytes and produce epidermal hyperproliferation, acanthosis, and hyperparakeratosis characteristic of psoriasis.³

New therapies have been developed to target the IL-23/T_H17 axis. Ustekinumab is approved for moderate to severe plaque psoriasis. This treatment’s effect may be sustained for up to 3 years, it is generally well tolerated, and it may be useful for patients refractory to anti-TNF therapy such as etanercept.⁵⁹ Briakinumab, another blocker of IL-12 and IL-23, was studied in phase 3 clinical trials, but its development was discontinued due to safety concerns.⁶⁰ Newer drugs targeting the IL-23/T_H17 axis include secukinumab, ixekizumab, brodalumab, guselkumab, and tildrakizumab.

Genetic Basis of Psoriasis

Psoriasis is a disease of overactive immunity in genetically susceptible individuals. Because patients exhibit varying skin phenotypes, extracutaneous manifestations, and disease courses, multiple genes resulting from linkage disequilibrium are believed to be involved in the pathogenesis of psoriasis. A decade of genome-wide linkage scans have established that PSORS1 is the strongest susceptibility locus demonstrable through family linkage studies; PSORS1 is responsible for up to 50% of the genetic component of psoriasis.⁶¹ More recently, HLA-Cw6 has received the most attention as a candidate gene of the PSORS1 susceptibility locus on the MHC class I region on chromosome 6p21.3.⁶² This gene may function in antigen presentation via MHC class I, which aids in the activation of the overactive T cells characteristic of psoriatic inflammation.

Studies involving the IL-23/T_H17 axis have shown genetics to play a role. Individuals may be protected from psoriasis with a nonsynonymous nucleotide substitution in the IL23R gene,^47-49 and certain haplotypes of the IL23R gene are associated with the disease^47,49 in addition to other autoimmune conditions.

Genomic scans have shown additional susceptibility loci for psoriasis on chromosomes 1q21, 3q21, 4q32-35, 16q12, and 17q25. Two regions on chromosome 17q were recently localized via mapping, which demonstrated a 6 megabase pairs separation, thereby indicating independent linkage factors. Genes SLC9A3R1 and NAT9 are present in the first region, while RAPTOR is demonstrated in the second region.⁶³SLC9A3R1 and NAT9 are players that regulate signal transduction, the immunologic synapse, and T-cell growth. RAPTOR is involved in T-cell function and growth pathways. Using these genes as an example, we can predict that the alterations of regulatory genes, even those yet undetermined, can enhance T-cell proliferation and inflammation manifested in psoriasis.

Conclusion

Psoriasis is a complex disease whereby multiple exogenous and endogenous stimuli incite already heightened innate immune responses in genetically predetermined individuals. The disease process is a result of a network of cell types, including T cells, DCs, and keratinocytes that, with the production of cytokines, generate a chronic inflammatory state. Our understanding of these cellular interactions and cytokines originates from developments, some meticulously planned, others serendipitous, in the fields of immunology, cell and molecular biology, and genetics. Such progress has fostered the creation of targeted immune therapy that has demonstrated remarkable efficacy in psoriasis treatment. Further study of the underlying pathophysiology of psoriasis may provide additional targets for therapy.

Increased understanding of the pathophysiology of psoriasis has been one of the driving forces in the development of new therapies. An understanding of the processes involved is important in the optimal management of the disease. The last 30 years of research and clinical practice have revolutionized our understanding of the pathogenesis of psoriasis as the dysregulation of immunity triggered by environmental and genetic stimuli. Psoriasis was originally regarded as a primary disorder of epidermal hyperproliferation. However, experimental models and clinical results from immunomodulating therapies have refined this perspective in conceptualizing psoriasis as a genetically programmed pathologic interaction among resident skin cells; infiltrating immunocytes; and a host of proinflammatory cytokines, chemokines, and growth factors produced by these immunocytes. Two populations of immunocytes and their respective signaling molecules collaborate in the pathogenesis: (1) innate immunocytes, mediated by antigen-presenting cells (APCs)(including natural killer [NK] T lymphocytes, Langerhans cells, and neutrophils), and (2) acquired or adaptive immunocytes, mediated by mature CD4⁺ and CD8⁺ T lymphocytes in the skin. Such dysregulation of immunity and subsequent inflammation is responsible for the development and perpetuation of the clinical plaques and histological inflammatory infiltrate characteristic of psoriasis.

Although psoriasis is considered to be an immune-mediated disease in which intralesional T lymphocytes and their proinflammatory signals trigger primed basal layer keratinocytes to rapidly proliferate, debate and research focus on the stimulus that incites this inflammatory process. Our current understanding considers psoriasis to be triggered by exogenous or endogenous environmental stimuli in genetically susceptible individuals. Such stimuli include group A streptococcal pharyngitis, viremia, allergic drug reactions, antimalarial drugs, lithium, beta-blockers, IFN-α, withdrawal of systemic corticosteroids, local trauma (Köbner phenomenon), and emotional stress. These stimuli correlate with the onset or flares of psoriatic lesions. Psoriasis genetics centers on susceptibility loci and corresponding candidate genes, particularly the psoriasis susceptibility (PSORS) 1 locus on the major histocompatibility complex (MHC) class I region. Current research on the pathogenesis of psoriasis examines the complex interactions among immunologic mechanisms, environmental stimuli, and genetic susceptibility. After discussing the clinical presentation and histopathologic features of psoriasis, we will review the pathophysiology of psoriasis through noteworthy developments, including serendipitous observations, reactions to therapies, clinical trials, and animal model systems that have shaped our view of the disease process. In addition to the classic skin lesions, approximately 23% of psoriasis patients develop psoriatic arthritis, with a 10-year latency after diagnosis of psoriasis.¹

Principles of Immunity

The immune system, intended to protect its host from foreign invaders and unregulated cell growth, employs 2 main effector pathways—the innate and the acquired (or adaptive) immune responses—both of which contribute to the pathophysiology of psoriasis.² Innate immunity responses occur within minutes to hours of antigen exposure but fail to develop memory for when the antigen is encountered again. However, adaptive immunity responses take days to weeks to respond after challenged with an antigen. The adaptive immune cells have the capacity to respond to a greater range of antigens and develop immunologic memory via rearrangement of antigen receptors on B and T cells. These specialized B and T cells can then be promptly mobilized and differentiated into mature effector cells that protect the host from a foreign pathogen.

Innate and adaptive immune responses are highly intertwined; they can initiate, perpetuate, and terminate the immune mechanisms responsible for inflammation. They can modify the nature of the immune response by altering the relative proportions of type 1 (T_H1), type 2 (T_H2), and the more recently discovered type 17 (T_H17) subset of helper T cells and their respective signaling molecules. A T_H1 response is essential for a cellular immunologic reaction to intracellular bacteria and viruses or cellular immunity. A T_H2 response promotes IgE synthesis, eosinophilia, and mast cell maturation for extracellular parasites and helminthes as well as humoral immunity, while a T_H17 response is important for cell-mediated immunity to extracellular bacteria and plays a role in autoimmunity.³ The innate and adaptive immune responses employ common effector molecules such as chemokines and cytokines, which are essential in mediating an immune response.

Implicating Dysregulation of Immunity

Our present appreciation of the pathogenesis of psoriasis is based on the history of trial-and-error therapies; serendipitous discoveries; and the current immune targeting drugs used in a variety of chronic inflammatory conditions, including rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease. Before the mid-1980s, research focused on the hyperproliferative epidermal cells as the primary pathology because a markedly thickened epidermis was indeed demonstrated on histologic specimens. Altered cell-cycle kinetics were thought to be the culprit behind the hyperkeratotic plaques. Thus, initial treatments centered on oncologic and antimitotic therapies used to arrest keratinocyte proliferation with agents such as arsenic, ammoniated mercury, and methotrexate.⁴

However, a paradigm shift from targeting epidermal keratinocytes to immunocyte populations was recognized when a patient receiving cyclosporine to prevent transplant rejection noted clearing of psoriatic lesions in the 1980s.⁵ Cyclosporine was observed to inhibit messenger RNA transcription of T-cell cytokines, thereby implicating immunologic dysregulation, specifically T-cell hyperactivity, in the pathogenesis of psoriasis.⁶ However, the concentrations of oral cyclosporine reached in the epidermis exerted direct effects on keratinocyte proliferation and lymphocyte function in these patients.⁷ Thus, the question was raised as to whether the keratinocytes or the lymphocytes drove the psoriatic plaques. The use of an IL-2 diphtheria toxin-fusion protein, denileukin diftitox, specific for activated T cells with high-affinity IL-2 receptors and nonreactive with keratinocytes, distinguished which cell type was responsible. This targeted T-cell toxin provided clinical and histological clearing of psoriatic plaques. Thus, T lymphocytes rather than keratinocytes were recognized as the definitive driver behind the psoriatic plaques.⁸

Additional studies have demonstrated that treatments that induce prolonged clearing of psoriatic lesions without continuous therapy, such as psoralen plus UVA irradiation, decreased the numbers of T cells in plaques by at least 90%.⁹ However, treatments that require continual therapy for satisfactory clinical results, such as cyclosporine and etretinate, simply suppress T-cell activity and proliferation.^10,11 Further evidence has linked cellular immunity with the pathogenesis of psoriasis, defining it as a T_H1-type disease. Natural killer T cells were shown to be involved through the use of a severe combined immunodeficient mouse model. They were injected into prepsoriatic skin grafted on immunodeficient mice, creating a psoriatic plaque with an immune response showing cytokines from T_H1 cells rather than T_H2 cells.¹² When psoriatic plaques were treated topically with the toll-like receptor 7 agonist imiquimod, aggravation and spreading of the plaques were noted. The exacerbation of psoriasis was accompanied by an induction of lesional T_H1-type interferon produced by plasmacytoid dendritic cell (DC) precursors. Plasmacytoid DCs were observed to compose up to 16% of the total dermal infiltrate in psoriatic skin lesions based on their coexpression of BDCA2 and CD123.¹³ Additionally, cancer patients being treated with interferon alfa experienced induction of psoriasis.¹⁴ Moreover, patients being treated for warts with intralesional interferon alfa developed psoriatic plaques in neighboring prior asymptomatic skin.¹⁵ Patients with psoriasis who were treated with interferon gamma, a T_H1 cytokine type, also developed new plaques correlating with the sites of injection.¹⁶

Intralesional T Lymphocytes

Psoriatic lesions contain a host of innate immunocytes, such as APCs, NK cells, and neutrophils, as well as adaptive T cells and an inflammatory infiltrate. These cells include CD4 and CD8 subtypes in which the CD8⁺ cells predominate in the epidermis, while CD4⁺ cells show preference for the dermis.¹⁷ There are 2 groups of CD8⁺ cells: one group migrates to the epidermis, expressing the integrin CD103, while the other group is found in the dermis but may be headed to or from the epidermis. The CD8⁺ cells residing in the epidermis that express the integrin CD103 are capable of interacting with E-cadherin, which enables these cells to travel to the epidermis and bind resident cells. Immunophenotyping reveals that these mature T cells represent chiefly activated memory cells, including CD2⁺, CD3⁺, CD5⁺, CLA, CD28, and CD45RO⁺.¹⁸ Many of these cells express activation markers such as HLA-DR, CD25, and CD27, in addition to the T-cell receptor (TCR).

T-Lymphocyte Stimulation

Both mature CD4⁺ and CD8⁺ T cells can respond to the peptides presented by APCs. Although the specific antigen that these T cells are reacting to has not yet been elucidated, several antigenic stimuli have been proposed, including self-proteins, microbial pathogens, and microbial superantigens. The premise that self-reactive T lymphocytes may contribute to the disease process is derived from the molecular mimicry theory in which an exuberant immune response to a pathogen produces cross-reactivity with self-antigens.¹⁹ Considering that infections have been associated with the onset of psoriasis, this theory merits consideration. However, it also has been observed that T cells can be activated without antigens or superantigens but rather with direct contact with accessory cells.²⁰ No single theory has clearly emerged. Researchers continue to search for the inciting stimulus that triggers the T lymphocyte and attempt to determine whether T cells are reacting to a self-derived or non–self-derived antigen.

T-Lymphocyte Signaling

T-cell signaling is a highly coordinated process in which T lymphocytes recognize antigens via presentation by mature APCs in the skin rather than the lymphoid tissues. Such APCs expose antigenic peptides via class I or II MHC molecules for which receptors are present on the T-cell surface. The antigen recognition complex at the T-cell and APC interface, in concert with a host of antigen-independent co-stimulatory signals, regulates T-cell signaling and is referred to as the immunologic synapse. The antigen presentation and network of co-stimulatory and adhesion molecules optimize T-cell activation, and dermal DCs release IL-12 and IL-23 to promote a T_H1 and T_H17 response, respectively. The growth factors released by these helper T cells sustain neoangiogenesis, stimulate epidermal hyperproliferation, alter epidermal differentiation, and decrease susceptibility to apoptosis that characterizes the erythematous hypertrophic scaling lesions of psoriasis.²¹ Furthermore, the cytokines produced from the immunologic response, such as tumor necrosis factor (TNF) α, IFN-γ, and IL-2, correspond to cytokines that are upregulated in psoriatic plaques.²²

Integral components of the immunologic synapse complex include co-stimulatory signals such as CD28, CD40, CD80, and CD86, as well as adhesion molecules such as cytotoxic T-lymphocyte antigen 4 and lymphocyte function-associated antigen (LFA) 1, which possess corresponding receptors on the T cell. These molecules play a key role in T-cell signaling, as their disruption has been shown to decrease T-cell responsiveness and associated inflammation. The B7 family of molecules routinely interacts with CD28 T cells to co-stimulate T-cell activation. Cytotoxic T-lymphocyte antigen 4 immunoglobulin, an antibody on the T-cell surface, targets B7 and interferes with signaling between B7 and CD28. In psoriatic patients, this blockade was demonstrated to attenuate the T-cell response and correlated with a clinical and histological decrease in psoriasiform hyperplasia.²³ Biologic therapies that disrupt the LFA-1 component of the immunologic synapse also have demonstrated efficacy in the treatment of psoriasis. Alefacept is a human LFA-3 fusion protein that binds CD2 on T cells and blocks the interaction between LFA-3 on APCs and CD2 on memory CD45RO⁺ T cells and induces apoptosis of such T cells. Efalizumab is a human monoclonal antibody to the CD11 chain of LFA-1 that blocks the interaction between LFA-1 on the T cell and intercellular adhesion molecule 1 on an APC or endothelial cell. Both alefacept and efalizumab, 2 formerly marketed biologic therapies, demonstrated remarkable clinical reduction of psoriatic lesions, and alefacept has been shown to produce disease remission for up to 18 months after discontinuation of therapy.^24-26

NK T Cells

Natural killer T cells represent a subset of CD3⁺ T cells present in psoriatic plaques. Although NK T cells possess a TCR, they differ from T cells by displaying NK receptors comprised of lectin and immunoglobulin families. These cells exhibit remarkable specificity and are activated upon recognition of glycolipids presented by CD1d molecules. This process occurs in contrast to CD4⁺ and CD8⁺ T cells, which, due to their TCR diversity, respond to peptides processed by APCs and displayed on MHC molecules. Natural killer T cells can be classified into 2 subsets: (1) one group that expresses CD4 and preferentially produces T_H1- versus T_H2-type cytokines, and (2) another group that lacks CD4 and CD8 that only produces T_H1-type cytokines. The innate immune system employs NK T cells early in the immune response because of their direct cytotoxicity and rapid production of cytokines such as IFN-γ, which promotes a T_H1 inflammatory response, and IL-4, which promotes the development of T_H2 cells. Excessive or dysfunctional NK T cells have been associated with autoimmune diseases such as multiple sclerosis and inflammatory bowel disease as well as allergic contact dermatitis.^27-29

In psoriasis, NK T cells are located in the epidermis, closely situated to epidermal keratinocytes, which suggests a role for direct antigen presentation. Furthermore, CD1d is overexpressed throughout the epidermis of psoriatic plaques, whereas normally CD1d expression is confined to terminally differentiated keratinocytes. An in vitro study examining cytokine-based inflammation demonstrative of psoriasis treated cultured CD1d-positive keratinocytes with interferon gamma in the presence of alpha-galactosylceramide of the lectin family.³⁰ Interferon gamma was observed to enhance keratinocyte CD1d expression, and subsequently, CD1d-positive keratinocytes were found to activate NK T cells to produce high levels of IFN-γ, while levels of IL-4 remained undetectable. The preferential production of IFN-γ supports a T_H1-mediated mechanism regulated by NK T cells in the immunopathogenesis of psoriasis.

Dendritic Cells

Dendritic cells are APCs that process antigens in the tissues in which they reside, after which they migrate to local lymph nodes where they present their native antigens to T cells. This process allows the T-cell response to be tailored to the appropriate antigens in the corresponding tissues. Immature DCs that capture antigens mature by migrating to the T-cell center of the lymph node where they present their antigens to either MHC molecules or the CD1 family. This presentation results in T-cell proliferation and differentiation that correlates with the required type of T-cell response. Multiple subsets of APCs, including myeloid and plasmacytoid DCs, are highly represented in the epidermis and dermis of psoriatic plaques as compared with normal skin.³¹ Dermal DCs are thought to be responsible for activating both the T_H1 and T_H17 infiltrate by secreting IL-12 and IL-23, respectively. This mixed cellular response secretes cytokines and leads to a cascade of events involving keratinocytes, fibroblasts, endothelial cells, and neutrophils that create the cutaneous lesions seen in psoriasis.³

Although DCs play a pivotal role in eliciting an immune response against a foreign invader, they also contribute to the establishment of tolerance. Throughout their maturation, DCs are continuously sensing their environment, which shapes their production of T_H1- versus T_H2-type cytokines and subsequently the nature of the T-cell response. When challenged with a virus, bacteria, or unchecked cell growth, DCs mature into APCs. However, in the absence of a strong stimulus, DCs fail to mature into APCs and present self-peptides with MHC molecules, thereby creating regulatory T cells involved in peripheral tolerance.³² If this balance between immunogenic APCs and housekeeping T cells is upset, inflammatory conditions such as psoriasis can result.

Cytokines

Cytokines are low-molecular-weight glycoproteins that function as signals to produce inflammation, defense, tissue repair and remodeling, fibrosis, angiogenesis, and restriction of neoplastic growth.³³ Cytokines are produced by immunocytes such as lymphocytes and macrophages as well as nonimmunocytes such as endothelial cells and keratinocytes. Proinflammatory cytokines include IL-1, IL-2, the IL-17 family, IFN-γ, and TNF-α, while anti-inflammatory cytokines include IL-4 and IL-10. A relative preponderance of T_H1 proinflammatory cytokines or an insufficiency of T_H2 anti-inflammatory cytokines induces local inflammation and recruitment of additional immunocyte populations, which produce added cytokines.³⁴ A vicious cycle of inflammation occurs that results in cutaneous manifestations such as a plaque. Psoriatic lesions are characterized by a relative increase of T_H1-type (eg, IL-2, IFN-γ, TNF-α, TNF-β) to T_H2-type (eg, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13) cytokines and an increase in T_H17-type cytokines. Natural killer T cells stimulated by CD1d-overexpressing keratinocytes increase production of proinflammatory IFN-γ without effect on the anti-inflammatory IL-4. In addition to the cytokines produced by T cells, APCs produce IL-18, IL-23, and TNF-α found in the inflammatory infiltrate of psoriatic plaques. Both IL-18 and IL-23 stimulate T_H1 cells to produce IFN-γ, and IL-23 stimulates T_H17 cells. Clearly, a T_H1- and T_H17-type pattern governs the immune effector cells and their respective cytokines present in psoriatic skin.

Tumor Necrosis Factor α

Although a network of cytokines is responsible for the inflammation of psoriasis, TNF-α has been implicated as a master proinflammatory cytokine of the innate immune response due to its widespread targets and sources. Tumor necrosis factor α is produced by activated T cells, keratinocytes, NK cells, macrophages, monocytes, Langerhans APCs, and endothelial cells. Psoriatic lesions demonstrate high concentrations of TNF-α, while the synovial fluid of psoriatic arthritis patients demonstrates elevated concentrations of TNF-α, IL-1, IL-6, and IL-8.³⁴ In psoriasis, TNF-α supports the expression of adhesion molecules (intercellular adhesion molecule 1 and P- and E-selectin), angiogenesis via vascular endothelial growth factor, the synthesis of proinflammatory molecules (IL-1, IL-6, IL-8, and nuclear factor κβ), and keratinocyte hyperproliferation via vasoactive intestinal peptide.³⁵

A role for TNF-α in psoriasis treatment was serendipitously discovered in a trial for Crohn disease in which infliximab, a mouse-human IgG1 anti–TNF-α monoclonal antibody, was observed to clear psoriatic plaques in a patient with both Crohn disease and psoriasis.³⁶ Immunotherapies that target TNF-α, including infliximab, etanercept, and adalimumab, demonstrate notable efficacy in the treatment of psoriasis.^37-39 Tumor necrosis factor α is regarded as the driver of the inflammatory cycle of psoriasis due to its numerous modes of production, capability to amplify other proinflammatory signals, and the efficacy and rapidity with which it produces clinical improvements in psoriasis.

IL-23/T_H17 Axis

A new distinct population of helper T cells has been shown to play an important role in psoriasis. These cells develop with the help of IL-23 (secreted by dermal DCs) and subsequently secrete cytokines such as IL-17; they are, therefore, named T_H17 cells. CD161 is considered a surface marker for these cells.⁴⁰ Strong evidence for this IL-23/T_H17 axis has been shown in mouse and human models as well as in genetic studies.

IL-23 is a cytokine that shares the p40 subunit with IL-12 and has been linked to autoimmune diseases in both mice and humans.³ It is required for optimal development of T_H17 cells⁴¹ from a committed CD4⁺ T-cell population after exposure to transforming growth factor β1 in combination with other proinflammatory cytokines.^42,43 IL-23 messenger RNA is produced at higher levels in inflammatory psoriatic skin lesions versus uninvolved skin,⁴⁴ and intradermal IL-23 injections in mice produced lesions resembling psoriasis macroscopically and microscopically.⁴⁵ Furthermore, several systemic therapies have been shown to modulate IL-23 levels and correlate with clinical benefit.³ Alterations in the gene for the IL-23 receptor have been shown to be protective for psoriasis,^46-48 and the gene coding for the p40 subunit is associated with psoriasis.^46,47

Type 17 helper T cells produce a number of cytokines, such as IL-22, IL-17A, IL-17F, and IL-26; the latter 3 are considered to be specific to this lineage.⁴² IL-22 acts on outer body barrier tissues, such as the skin, and has antimicrobial activity. Blocking the activity of IL-22 in mice prevented the development of skin lesions,⁴⁹ and psoriasis patients have elevated levels of IL-22 in the skin and blood.^50,51 The IL-17 cytokines induce the expression of proinflammatory cytokines, colony-stimulating factors, and chemokines, and they recruit, mobilize, and activate neutrophils.⁵² IL-17 messenger RNA was found in lesional psoriatic skin but not unaffected skin,⁵³ and cells isolated from the dermis of psoriatic skin have been shown to produce IL-17.⁵⁴ IL-17A is not elevated in the serum of psoriatic patients (unlike other autoimmune diseases),⁵⁵ and it is, therefore, thought that T_H17 cells and IL-17A production are localized to the affected psoriatic skin. Consistent with this concept is the finding that treatments such as cyclosporin A and anti-TNF agents decrease proinflammatory cytokines in lesional skin but not in the periphery.^56-58 These cytokines released by T_H17 cells in addition to those released by T_H1 cells act on keratinocytes and produce epidermal hyperproliferation, acanthosis, and hyperparakeratosis characteristic of psoriasis.³

New therapies have been developed to target the IL-23/T_H17 axis. Ustekinumab is approved for moderate to severe plaque psoriasis. This treatment’s effect may be sustained for up to 3 years, it is generally well tolerated, and it may be useful for patients refractory to anti-TNF therapy such as etanercept.⁵⁹ Briakinumab, another blocker of IL-12 and IL-23, was studied in phase 3 clinical trials, but its development was discontinued due to safety concerns.⁶⁰ Newer drugs targeting the IL-23/T_H17 axis include secukinumab, ixekizumab, brodalumab, guselkumab, and tildrakizumab.

Genetic Basis of Psoriasis

Psoriasis is a disease of overactive immunity in genetically susceptible individuals. Because patients exhibit varying skin phenotypes, extracutaneous manifestations, and disease courses, multiple genes resulting from linkage disequilibrium are believed to be involved in the pathogenesis of psoriasis. A decade of genome-wide linkage scans have established that PSORS1 is the strongest susceptibility locus demonstrable through family linkage studies; PSORS1 is responsible for up to 50% of the genetic component of psoriasis.⁶¹ More recently, HLA-Cw6 has received the most attention as a candidate gene of the PSORS1 susceptibility locus on the MHC class I region on chromosome 6p21.3.⁶² This gene may function in antigen presentation via MHC class I, which aids in the activation of the overactive T cells characteristic of psoriatic inflammation.

Studies involving the IL-23/T_H17 axis have shown genetics to play a role. Individuals may be protected from psoriasis with a nonsynonymous nucleotide substitution in the IL23R gene,^47-49 and certain haplotypes of the IL23R gene are associated with the disease^47,49 in addition to other autoimmune conditions.

Genomic scans have shown additional susceptibility loci for psoriasis on chromosomes 1q21, 3q21, 4q32-35, 16q12, and 17q25. Two regions on chromosome 17q were recently localized via mapping, which demonstrated a 6 megabase pairs separation, thereby indicating independent linkage factors. Genes SLC9A3R1 and NAT9 are present in the first region, while RAPTOR is demonstrated in the second region.⁶³SLC9A3R1 and NAT9 are players that regulate signal transduction, the immunologic synapse, and T-cell growth. RAPTOR is involved in T-cell function and growth pathways. Using these genes as an example, we can predict that the alterations of regulatory genes, even those yet undetermined, can enhance T-cell proliferation and inflammation manifested in psoriasis.

Conclusion

Psoriasis is a complex disease whereby multiple exogenous and endogenous stimuli incite already heightened innate immune responses in genetically predetermined individuals. The disease process is a result of a network of cell types, including T cells, DCs, and keratinocytes that, with the production of cytokines, generate a chronic inflammatory state. Our understanding of these cellular interactions and cytokines originates from developments, some meticulously planned, others serendipitous, in the fields of immunology, cell and molecular biology, and genetics. Such progress has fostered the creation of targeted immune therapy that has demonstrated remarkable efficacy in psoriasis treatment. Further study of the underlying pathophysiology of psoriasis may provide additional targets for therapy.

Increased understanding of the pathophysiology of psoriasis has been one of the driving forces in the development of new therapies. An understanding of the processes involved is important in the optimal management of the disease. The last 30 years of research and clinical practice have revolutionized our understanding of the pathogenesis of psoriasis as the dysregulation of immunity triggered by environmental and genetic stimuli. Psoriasis was originally regarded as a primary disorder of epidermal hyperproliferation. However, experimental models and clinical results from immunomodulating therapies have refined this perspective in conceptualizing psoriasis as a genetically programmed pathologic interaction among resident skin cells; infiltrating immunocytes; and a host of proinflammatory cytokines, chemokines, and growth factors produced by these immunocytes. Two populations of immunocytes and their respective signaling molecules collaborate in the pathogenesis: (1) innate immunocytes, mediated by antigen-presenting cells (APCs)(including natural killer [NK] T lymphocytes, Langerhans cells, and neutrophils), and (2) acquired or adaptive immunocytes, mediated by mature CD4⁺ and CD8⁺ T lymphocytes in the skin. Such dysregulation of immunity and subsequent inflammation is responsible for the development and perpetuation of the clinical plaques and histological inflammatory infiltrate characteristic of psoriasis.

Although psoriasis is considered to be an immune-mediated disease in which intralesional T lymphocytes and their proinflammatory signals trigger primed basal layer keratinocytes to rapidly proliferate, debate and research focus on the stimulus that incites this inflammatory process. Our current understanding considers psoriasis to be triggered by exogenous or endogenous environmental stimuli in genetically susceptible individuals. Such stimuli include group A streptococcal pharyngitis, viremia, allergic drug reactions, antimalarial drugs, lithium, beta-blockers, IFN-α, withdrawal of systemic corticosteroids, local trauma (Köbner phenomenon), and emotional stress. These stimuli correlate with the onset or flares of psoriatic lesions. Psoriasis genetics centers on susceptibility loci and corresponding candidate genes, particularly the psoriasis susceptibility (PSORS) 1 locus on the major histocompatibility complex (MHC) class I region. Current research on the pathogenesis of psoriasis examines the complex interactions among immunologic mechanisms, environmental stimuli, and genetic susceptibility. After discussing the clinical presentation and histopathologic features of psoriasis, we will review the pathophysiology of psoriasis through noteworthy developments, including serendipitous observations, reactions to therapies, clinical trials, and animal model systems that have shaped our view of the disease process. In addition to the classic skin lesions, approximately 23% of psoriasis patients develop psoriatic arthritis, with a 10-year latency after diagnosis of psoriasis.¹

Principles of Immunity

The immune system, intended to protect its host from foreign invaders and unregulated cell growth, employs 2 main effector pathways—the innate and the acquired (or adaptive) immune responses—both of which contribute to the pathophysiology of psoriasis.² Innate immunity responses occur within minutes to hours of antigen exposure but fail to develop memory for when the antigen is encountered again. However, adaptive immunity responses take days to weeks to respond after challenged with an antigen. The adaptive immune cells have the capacity to respond to a greater range of antigens and develop immunologic memory via rearrangement of antigen receptors on B and T cells. These specialized B and T cells can then be promptly mobilized and differentiated into mature effector cells that protect the host from a foreign pathogen.

Innate and adaptive immune responses are highly intertwined; they can initiate, perpetuate, and terminate the immune mechanisms responsible for inflammation. They can modify the nature of the immune response by altering the relative proportions of type 1 (T_H1), type 2 (T_H2), and the more recently discovered type 17 (T_H17) subset of helper T cells and their respective signaling molecules. A T_H1 response is essential for a cellular immunologic reaction to intracellular bacteria and viruses or cellular immunity. A T_H2 response promotes IgE synthesis, eosinophilia, and mast cell maturation for extracellular parasites and helminthes as well as humoral immunity, while a T_H17 response is important for cell-mediated immunity to extracellular bacteria and plays a role in autoimmunity.³ The innate and adaptive immune responses employ common effector molecules such as chemokines and cytokines, which are essential in mediating an immune response.

Implicating Dysregulation of Immunity

Our present appreciation of the pathogenesis of psoriasis is based on the history of trial-and-error therapies; serendipitous discoveries; and the current immune targeting drugs used in a variety of chronic inflammatory conditions, including rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease. Before the mid-1980s, research focused on the hyperproliferative epidermal cells as the primary pathology because a markedly thickened epidermis was indeed demonstrated on histologic specimens. Altered cell-cycle kinetics were thought to be the culprit behind the hyperkeratotic plaques. Thus, initial treatments centered on oncologic and antimitotic therapies used to arrest keratinocyte proliferation with agents such as arsenic, ammoniated mercury, and methotrexate.⁴

However, a paradigm shift from targeting epidermal keratinocytes to immunocyte populations was recognized when a patient receiving cyclosporine to prevent transplant rejection noted clearing of psoriatic lesions in the 1980s.⁵ Cyclosporine was observed to inhibit messenger RNA transcription of T-cell cytokines, thereby implicating immunologic dysregulation, specifically T-cell hyperactivity, in the pathogenesis of psoriasis.⁶ However, the concentrations of oral cyclosporine reached in the epidermis exerted direct effects on keratinocyte proliferation and lymphocyte function in these patients.⁷ Thus, the question was raised as to whether the keratinocytes or the lymphocytes drove the psoriatic plaques. The use of an IL-2 diphtheria toxin-fusion protein, denileukin diftitox, specific for activated T cells with high-affinity IL-2 receptors and nonreactive with keratinocytes, distinguished which cell type was responsible. This targeted T-cell toxin provided clinical and histological clearing of psoriatic plaques. Thus, T lymphocytes rather than keratinocytes were recognized as the definitive driver behind the psoriatic plaques.⁸

Additional studies have demonstrated that treatments that induce prolonged clearing of psoriatic lesions without continuous therapy, such as psoralen plus UVA irradiation, decreased the numbers of T cells in plaques by at least 90%.⁹ However, treatments that require continual therapy for satisfactory clinical results, such as cyclosporine and etretinate, simply suppress T-cell activity and proliferation.^10,11 Further evidence has linked cellular immunity with the pathogenesis of psoriasis, defining it as a T_H1-type disease. Natural killer T cells were shown to be involved through the use of a severe combined immunodeficient mouse model. They were injected into prepsoriatic skin grafted on immunodeficient mice, creating a psoriatic plaque with an immune response showing cytokines from T_H1 cells rather than T_H2 cells.¹² When psoriatic plaques were treated topically with the toll-like receptor 7 agonist imiquimod, aggravation and spreading of the plaques were noted. The exacerbation of psoriasis was accompanied by an induction of lesional T_H1-type interferon produced by plasmacytoid dendritic cell (DC) precursors. Plasmacytoid DCs were observed to compose up to 16% of the total dermal infiltrate in psoriatic skin lesions based on their coexpression of BDCA2 and CD123.¹³ Additionally, cancer patients being treated with interferon alfa experienced induction of psoriasis.¹⁴ Moreover, patients being treated for warts with intralesional interferon alfa developed psoriatic plaques in neighboring prior asymptomatic skin.¹⁵ Patients with psoriasis who were treated with interferon gamma, a T_H1 cytokine type, also developed new plaques correlating with the sites of injection.¹⁶

Intralesional T Lymphocytes

Psoriatic lesions contain a host of innate immunocytes, such as APCs, NK cells, and neutrophils, as well as adaptive T cells and an inflammatory infiltrate. These cells include CD4 and CD8 subtypes in which the CD8⁺ cells predominate in the epidermis, while CD4⁺ cells show preference for the dermis.¹⁷ There are 2 groups of CD8⁺ cells: one group migrates to the epidermis, expressing the integrin CD103, while the other group is found in the dermis but may be headed to or from the epidermis. The CD8⁺ cells residing in the epidermis that express the integrin CD103 are capable of interacting with E-cadherin, which enables these cells to travel to the epidermis and bind resident cells. Immunophenotyping reveals that these mature T cells represent chiefly activated memory cells, including CD2⁺, CD3⁺, CD5⁺, CLA, CD28, and CD45RO⁺.¹⁸ Many of these cells express activation markers such as HLA-DR, CD25, and CD27, in addition to the T-cell receptor (TCR).

T-Lymphocyte Stimulation

Both mature CD4⁺ and CD8⁺ T cells can respond to the peptides presented by APCs. Although the specific antigen that these T cells are reacting to has not yet been elucidated, several antigenic stimuli have been proposed, including self-proteins, microbial pathogens, and microbial superantigens. The premise that self-reactive T lymphocytes may contribute to the disease process is derived from the molecular mimicry theory in which an exuberant immune response to a pathogen produces cross-reactivity with self-antigens.¹⁹ Considering that infections have been associated with the onset of psoriasis, this theory merits consideration. However, it also has been observed that T cells can be activated without antigens or superantigens but rather with direct contact with accessory cells.²⁰ No single theory has clearly emerged. Researchers continue to search for the inciting stimulus that triggers the T lymphocyte and attempt to determine whether T cells are reacting to a self-derived or non–self-derived antigen.

T-Lymphocyte Signaling

T-cell signaling is a highly coordinated process in which T lymphocytes recognize antigens via presentation by mature APCs in the skin rather than the lymphoid tissues. Such APCs expose antigenic peptides via class I or II MHC molecules for which receptors are present on the T-cell surface. The antigen recognition complex at the T-cell and APC interface, in concert with a host of antigen-independent co-stimulatory signals, regulates T-cell signaling and is referred to as the immunologic synapse. The antigen presentation and network of co-stimulatory and adhesion molecules optimize T-cell activation, and dermal DCs release IL-12 and IL-23 to promote a T_H1 and T_H17 response, respectively. The growth factors released by these helper T cells sustain neoangiogenesis, stimulate epidermal hyperproliferation, alter epidermal differentiation, and decrease susceptibility to apoptosis that characterizes the erythematous hypertrophic scaling lesions of psoriasis.²¹ Furthermore, the cytokines produced from the immunologic response, such as tumor necrosis factor (TNF) α, IFN-γ, and IL-2, correspond to cytokines that are upregulated in psoriatic plaques.²²

Integral components of the immunologic synapse complex include co-stimulatory signals such as CD28, CD40, CD80, and CD86, as well as adhesion molecules such as cytotoxic T-lymphocyte antigen 4 and lymphocyte function-associated antigen (LFA) 1, which possess corresponding receptors on the T cell. These molecules play a key role in T-cell signaling, as their disruption has been shown to decrease T-cell responsiveness and associated inflammation. The B7 family of molecules routinely interacts with CD28 T cells to co-stimulate T-cell activation. Cytotoxic T-lymphocyte antigen 4 immunoglobulin, an antibody on the T-cell surface, targets B7 and interferes with signaling between B7 and CD28. In psoriatic patients, this blockade was demonstrated to attenuate the T-cell response and correlated with a clinical and histological decrease in psoriasiform hyperplasia.²³ Biologic therapies that disrupt the LFA-1 component of the immunologic synapse also have demonstrated efficacy in the treatment of psoriasis. Alefacept is a human LFA-3 fusion protein that binds CD2 on T cells and blocks the interaction between LFA-3 on APCs and CD2 on memory CD45RO⁺ T cells and induces apoptosis of such T cells. Efalizumab is a human monoclonal antibody to the CD11 chain of LFA-1 that blocks the interaction between LFA-1 on the T cell and intercellular adhesion molecule 1 on an APC or endothelial cell. Both alefacept and efalizumab, 2 formerly marketed biologic therapies, demonstrated remarkable clinical reduction of psoriatic lesions, and alefacept has been shown to produce disease remission for up to 18 months after discontinuation of therapy.^24-26

NK T Cells

Natural killer T cells represent a subset of CD3⁺ T cells present in psoriatic plaques. Although NK T cells possess a TCR, they differ from T cells by displaying NK receptors comprised of lectin and immunoglobulin families. These cells exhibit remarkable specificity and are activated upon recognition of glycolipids presented by CD1d molecules. This process occurs in contrast to CD4⁺ and CD8⁺ T cells, which, due to their TCR diversity, respond to peptides processed by APCs and displayed on MHC molecules. Natural killer T cells can be classified into 2 subsets: (1) one group that expresses CD4 and preferentially produces T_H1- versus T_H2-type cytokines, and (2) another group that lacks CD4 and CD8 that only produces T_H1-type cytokines. The innate immune system employs NK T cells early in the immune response because of their direct cytotoxicity and rapid production of cytokines such as IFN-γ, which promotes a T_H1 inflammatory response, and IL-4, which promotes the development of T_H2 cells. Excessive or dysfunctional NK T cells have been associated with autoimmune diseases such as multiple sclerosis and inflammatory bowel disease as well as allergic contact dermatitis.^27-29

In psoriasis, NK T cells are located in the epidermis, closely situated to epidermal keratinocytes, which suggests a role for direct antigen presentation. Furthermore, CD1d is overexpressed throughout the epidermis of psoriatic plaques, whereas normally CD1d expression is confined to terminally differentiated keratinocytes. An in vitro study examining cytokine-based inflammation demonstrative of psoriasis treated cultured CD1d-positive keratinocytes with interferon gamma in the presence of alpha-galactosylceramide of the lectin family.³⁰ Interferon gamma was observed to enhance keratinocyte CD1d expression, and subsequently, CD1d-positive keratinocytes were found to activate NK T cells to produce high levels of IFN-γ, while levels of IL-4 remained undetectable. The preferential production of IFN-γ supports a T_H1-mediated mechanism regulated by NK T cells in the immunopathogenesis of psoriasis.

Dendritic Cells

Dendritic cells are APCs that process antigens in the tissues in which they reside, after which they migrate to local lymph nodes where they present their native antigens to T cells. This process allows the T-cell response to be tailored to the appropriate antigens in the corresponding tissues. Immature DCs that capture antigens mature by migrating to the T-cell center of the lymph node where they present their antigens to either MHC molecules or the CD1 family. This presentation results in T-cell proliferation and differentiation that correlates with the required type of T-cell response. Multiple subsets of APCs, including myeloid and plasmacytoid DCs, are highly represented in the epidermis and dermis of psoriatic plaques as compared with normal skin.³¹ Dermal DCs are thought to be responsible for activating both the T_H1 and T_H17 infiltrate by secreting IL-12 and IL-23, respectively. This mixed cellular response secretes cytokines and leads to a cascade of events involving keratinocytes, fibroblasts, endothelial cells, and neutrophils that create the cutaneous lesions seen in psoriasis.³

Although DCs play a pivotal role in eliciting an immune response against a foreign invader, they also contribute to the establishment of tolerance. Throughout their maturation, DCs are continuously sensing their environment, which shapes their production of T_H1- versus T_H2-type cytokines and subsequently the nature of the T-cell response. When challenged with a virus, bacteria, or unchecked cell growth, DCs mature into APCs. However, in the absence of a strong stimulus, DCs fail to mature into APCs and present self-peptides with MHC molecules, thereby creating regulatory T cells involved in peripheral tolerance.³² If this balance between immunogenic APCs and housekeeping T cells is upset, inflammatory conditions such as psoriasis can result.

Cytokines

Cytokines are low-molecular-weight glycoproteins that function as signals to produce inflammation, defense, tissue repair and remodeling, fibrosis, angiogenesis, and restriction of neoplastic growth.³³ Cytokines are produced by immunocytes such as lymphocytes and macrophages as well as nonimmunocytes such as endothelial cells and keratinocytes. Proinflammatory cytokines include IL-1, IL-2, the IL-17 family, IFN-γ, and TNF-α, while anti-inflammatory cytokines include IL-4 and IL-10. A relative preponderance of T_H1 proinflammatory cytokines or an insufficiency of T_H2 anti-inflammatory cytokines induces local inflammation and recruitment of additional immunocyte populations, which produce added cytokines.³⁴ A vicious cycle of inflammation occurs that results in cutaneous manifestations such as a plaque. Psoriatic lesions are characterized by a relative increase of T_H1-type (eg, IL-2, IFN-γ, TNF-α, TNF-β) to T_H2-type (eg, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13) cytokines and an increase in T_H17-type cytokines. Natural killer T cells stimulated by CD1d-overexpressing keratinocytes increase production of proinflammatory IFN-γ without effect on the anti-inflammatory IL-4. In addition to the cytokines produced by T cells, APCs produce IL-18, IL-23, and TNF-α found in the inflammatory infiltrate of psoriatic plaques. Both IL-18 and IL-23 stimulate T_H1 cells to produce IFN-γ, and IL-23 stimulates T_H17 cells. Clearly, a T_H1- and T_H17-type pattern governs the immune effector cells and their respective cytokines present in psoriatic skin.

Tumor Necrosis Factor α

Although a network of cytokines is responsible for the inflammation of psoriasis, TNF-α has been implicated as a master proinflammatory cytokine of the innate immune response due to its widespread targets and sources. Tumor necrosis factor α is produced by activated T cells, keratinocytes, NK cells, macrophages, monocytes, Langerhans APCs, and endothelial cells. Psoriatic lesions demonstrate high concentrations of TNF-α, while the synovial fluid of psoriatic arthritis patients demonstrates elevated concentrations of TNF-α, IL-1, IL-6, and IL-8.³⁴ In psoriasis, TNF-α supports the expression of adhesion molecules (intercellular adhesion molecule 1 and P- and E-selectin), angiogenesis via vascular endothelial growth factor, the synthesis of proinflammatory molecules (IL-1, IL-6, IL-8, and nuclear factor κβ), and keratinocyte hyperproliferation via vasoactive intestinal peptide.³⁵

A role for TNF-α in psoriasis treatment was serendipitously discovered in a trial for Crohn disease in which infliximab, a mouse-human IgG1 anti–TNF-α monoclonal antibody, was observed to clear psoriatic plaques in a patient with both Crohn disease and psoriasis.³⁶ Immunotherapies that target TNF-α, including infliximab, etanercept, and adalimumab, demonstrate notable efficacy in the treatment of psoriasis.^37-39 Tumor necrosis factor α is regarded as the driver of the inflammatory cycle of psoriasis due to its numerous modes of production, capability to amplify other proinflammatory signals, and the efficacy and rapidity with which it produces clinical improvements in psoriasis.

IL-23/T_H17 Axis

A new distinct population of helper T cells has been shown to play an important role in psoriasis. These cells develop with the help of IL-23 (secreted by dermal DCs) and subsequently secrete cytokines such as IL-17; they are, therefore, named T_H17 cells. CD161 is considered a surface marker for these cells.⁴⁰ Strong evidence for this IL-23/T_H17 axis has been shown in mouse and human models as well as in genetic studies.

IL-23 is a cytokine that shares the p40 subunit with IL-12 and has been linked to autoimmune diseases in both mice and humans.³ It is required for optimal development of T_H17 cells⁴¹ from a committed CD4⁺ T-cell population after exposure to transforming growth factor β1 in combination with other proinflammatory cytokines.^42,43 IL-23 messenger RNA is produced at higher levels in inflammatory psoriatic skin lesions versus uninvolved skin,⁴⁴ and intradermal IL-23 injections in mice produced lesions resembling psoriasis macroscopically and microscopically.⁴⁵ Furthermore, several systemic therapies have been shown to modulate IL-23 levels and correlate with clinical benefit.³ Alterations in the gene for the IL-23 receptor have been shown to be protective for psoriasis,^46-48 and the gene coding for the p40 subunit is associated with psoriasis.^46,47

Type 17 helper T cells produce a number of cytokines, such as IL-22, IL-17A, IL-17F, and IL-26; the latter 3 are considered to be specific to this lineage.⁴² IL-22 acts on outer body barrier tissues, such as the skin, and has antimicrobial activity. Blocking the activity of IL-22 in mice prevented the development of skin lesions,⁴⁹ and psoriasis patients have elevated levels of IL-22 in the skin and blood.^50,51 The IL-17 cytokines induce the expression of proinflammatory cytokines, colony-stimulating factors, and chemokines, and they recruit, mobilize, and activate neutrophils.⁵² IL-17 messenger RNA was found in lesional psoriatic skin but not unaffected skin,⁵³ and cells isolated from the dermis of psoriatic skin have been shown to produce IL-17.⁵⁴ IL-17A is not elevated in the serum of psoriatic patients (unlike other autoimmune diseases),⁵⁵ and it is, therefore, thought that T_H17 cells and IL-17A production are localized to the affected psoriatic skin. Consistent with this concept is the finding that treatments such as cyclosporin A and anti-TNF agents decrease proinflammatory cytokines in lesional skin but not in the periphery.^56-58 These cytokines released by T_H17 cells in addition to those released by T_H1 cells act on keratinocytes and produce epidermal hyperproliferation, acanthosis, and hyperparakeratosis characteristic of psoriasis.³

New therapies have been developed to target the IL-23/T_H17 axis. Ustekinumab is approved for moderate to severe plaque psoriasis. This treatment’s effect may be sustained for up to 3 years, it is generally well tolerated, and it may be useful for patients refractory to anti-TNF therapy such as etanercept.⁵⁹ Briakinumab, another blocker of IL-12 and IL-23, was studied in phase 3 clinical trials, but its development was discontinued due to safety concerns.⁶⁰ Newer drugs targeting the IL-23/T_H17 axis include secukinumab, ixekizumab, brodalumab, guselkumab, and tildrakizumab.

Genetic Basis of Psoriasis

Psoriasis is a disease of overactive immunity in genetically susceptible individuals. Because patients exhibit varying skin phenotypes, extracutaneous manifestations, and disease courses, multiple genes resulting from linkage disequilibrium are believed to be involved in the pathogenesis of psoriasis. A decade of genome-wide linkage scans have established that PSORS1 is the strongest susceptibility locus demonstrable through family linkage studies; PSORS1 is responsible for up to 50% of the genetic component of psoriasis.⁶¹ More recently, HLA-Cw6 has received the most attention as a candidate gene of the PSORS1 susceptibility locus on the MHC class I region on chromosome 6p21.3.⁶² This gene may function in antigen presentation via MHC class I, which aids in the activation of the overactive T cells characteristic of psoriatic inflammation.

Studies involving the IL-23/T_H17 axis have shown genetics to play a role. Individuals may be protected from psoriasis with a nonsynonymous nucleotide substitution in the IL23R gene,^47-49 and certain haplotypes of the IL23R gene are associated with the disease^47,49 in addition to other autoimmune conditions.

Genomic scans have shown additional susceptibility loci for psoriasis on chromosomes 1q21, 3q21, 4q32-35, 16q12, and 17q25. Two regions on chromosome 17q were recently localized via mapping, which demonstrated a 6 megabase pairs separation, thereby indicating independent linkage factors. Genes SLC9A3R1 and NAT9 are present in the first region, while RAPTOR is demonstrated in the second region.⁶³SLC9A3R1 and NAT9 are players that regulate signal transduction, the immunologic synapse, and T-cell growth. RAPTOR is involved in T-cell function and growth pathways. Using these genes as an example, we can predict that the alterations of regulatory genes, even those yet undetermined, can enhance T-cell proliferation and inflammation manifested in psoriasis.

Conclusion

Psoriasis is a complex disease whereby multiple exogenous and endogenous stimuli incite already heightened innate immune responses in genetically predetermined individuals. The disease process is a result of a network of cell types, including T cells, DCs, and keratinocytes that, with the production of cytokines, generate a chronic inflammatory state. Our understanding of these cellular interactions and cytokines originates from developments, some meticulously planned, others serendipitous, in the fields of immunology, cell and molecular biology, and genetics. Such progress has fostered the creation of targeted immune therapy that has demonstrated remarkable efficacy in psoriasis treatment. Further study of the underlying pathophysiology of psoriasis may provide additional targets for therapy.

This special issue is dedicated to resident education on psoriasis. With that in mind, we hope to address many topics of interest to those in training. Over the years, diet has been a hot topic among psoriasis patients. They want to know how diet affects psoriasis and what changes can be made to their diet to improve their condition. Although they have expected specific answers, my response has usually been that they should, of course, eat an overall healthy and balanced diet, and lose weight if necessary. I have continued, however, that no specific diet has been recommended. However, now we have some information that may start to give us some answers.

The Mediterranean diet has been regarded as a healthy regimen.¹ This diet emphasizes eating primarily plant-based foods, such as fruits and vegetables; whole grains; legumes; and nuts. Other recommendations include replacing butter with healthy fats such as olive oil and canola oil, using herbs and spices instead of salt to flavor foods, and limiting red meat to no more than a few times a month.¹

As we know, psoriasis is a chronic inflammatory disease. The Mediterranean diet has been shown to reduce chronic inflammation and has a positive effect on the risk for metabolic syndrome and cardiovascular events.¹ Phan et al¹ hypothesized a positive effect of the Mediterranean diet on psoriasis. They performed a study to assess the association between a score that reflects the adhesion to a Mediterranean diet (MEDI-LITE) and the onset and/or severity of psoriasis.¹

The NutriNet-Santé program is an ongoing, observational, web-based questionnaire cohort study launched in France in May 2009.¹ Data were collected and analyzed between April 2017 and June 2017. Individuals with psoriasis were identified utilizing a validated online questionnaire and then categorized by disease severity into 1 of 3 groups: severe psoriasis, nonsevere psoriasis, and psoriasis free.¹

During the initial 2 years of participation in the cohort, data on dietary intake (including alcohol) were gathered to calculate the MEDI-LITE score, ranging from 0 (no adherence) to 18 (maximum adherence).¹ Of the 158,361 total web-based participants, 35,735 (23%) replied to the psoriasis questionnaire.¹ Of the respondents, 3557 (10%) individuals reported having psoriasis. The condition was severe in 878 cases (24.7%), and 299 (8.4%) incident cases were recorded (cases occurring >2 years after participant inclusion in the cohort). After adjustment for confounding factors, the investigators found a significant inverse relationship between the MEDI-LITE score and having severe psoriasis (odds ratio [OR], 0.71; 95% CI, 0.55-0.92 for the MEDI-LITE score’s second tertile [score of 8 to 9]; and OR, 0.78; 95% CI, 0.59-1.01 for the third tertile [score of 10 to 18]).¹

The authors noted that patients with severe psoriasis displayed low levels of adherence to the Mediterranean diet.¹ They commented that this finding supports the hypothesis that the Mediterranean diet may slow the progression of psoriasis. If these findings are confirmed, adherence to a Mediterranean diet should be integrated into the routine management of moderate to severe psoriasis.¹ These findings are by no means definitive, but it is a first step in helping us define more specific dietary recommendations for psoriasis.

This issue includes several articles looking at various facets of psoriasis important to residents, including the pathophysiology of psoriasis,² treatment approach using biologic therapies,³ risk factors and triggers for psoriasis,⁴ and the psychosocial impact of psoriasis.⁵ We hope that you find this issue enjoyable and informative.

This special issue is dedicated to resident education on psoriasis. With that in mind, we hope to address many topics of interest to those in training. Over the years, diet has been a hot topic among psoriasis patients. They want to know how diet affects psoriasis and what changes can be made to their diet to improve their condition. Although they have expected specific answers, my response has usually been that they should, of course, eat an overall healthy and balanced diet, and lose weight if necessary. I have continued, however, that no specific diet has been recommended. However, now we have some information that may start to give us some answers.

The Mediterranean diet has been regarded as a healthy regimen.¹ This diet emphasizes eating primarily plant-based foods, such as fruits and vegetables; whole grains; legumes; and nuts. Other recommendations include replacing butter with healthy fats such as olive oil and canola oil, using herbs and spices instead of salt to flavor foods, and limiting red meat to no more than a few times a month.¹

As we know, psoriasis is a chronic inflammatory disease. The Mediterranean diet has been shown to reduce chronic inflammation and has a positive effect on the risk for metabolic syndrome and cardiovascular events.¹ Phan et al¹ hypothesized a positive effect of the Mediterranean diet on psoriasis. They performed a study to assess the association between a score that reflects the adhesion to a Mediterranean diet (MEDI-LITE) and the onset and/or severity of psoriasis.¹

The NutriNet-Santé program is an ongoing, observational, web-based questionnaire cohort study launched in France in May 2009.¹ Data were collected and analyzed between April 2017 and June 2017. Individuals with psoriasis were identified utilizing a validated online questionnaire and then categorized by disease severity into 1 of 3 groups: severe psoriasis, nonsevere psoriasis, and psoriasis free.¹

During the initial 2 years of participation in the cohort, data on dietary intake (including alcohol) were gathered to calculate the MEDI-LITE score, ranging from 0 (no adherence) to 18 (maximum adherence).¹ Of the 158,361 total web-based participants, 35,735 (23%) replied to the psoriasis questionnaire.¹ Of the respondents, 3557 (10%) individuals reported having psoriasis. The condition was severe in 878 cases (24.7%), and 299 (8.4%) incident cases were recorded (cases occurring >2 years after participant inclusion in the cohort). After adjustment for confounding factors, the investigators found a significant inverse relationship between the MEDI-LITE score and having severe psoriasis (odds ratio [OR], 0.71; 95% CI, 0.55-0.92 for the MEDI-LITE score’s second tertile [score of 8 to 9]; and OR, 0.78; 95% CI, 0.59-1.01 for the third tertile [score of 10 to 18]).¹

The authors noted that patients with severe psoriasis displayed low levels of adherence to the Mediterranean diet.¹ They commented that this finding supports the hypothesis that the Mediterranean diet may slow the progression of psoriasis. If these findings are confirmed, adherence to a Mediterranean diet should be integrated into the routine management of moderate to severe psoriasis.¹ These findings are by no means definitive, but it is a first step in helping us define more specific dietary recommendations for psoriasis.

This issue includes several articles looking at various facets of psoriasis important to residents, including the pathophysiology of psoriasis,² treatment approach using biologic therapies,³ risk factors and triggers for psoriasis,⁴ and the psychosocial impact of psoriasis.⁵ We hope that you find this issue enjoyable and informative.

This special issue is dedicated to resident education on psoriasis. With that in mind, we hope to address many topics of interest to those in training. Over the years, diet has been a hot topic among psoriasis patients. They want to know how diet affects psoriasis and what changes can be made to their diet to improve their condition. Although they have expected specific answers, my response has usually been that they should, of course, eat an overall healthy and balanced diet, and lose weight if necessary. I have continued, however, that no specific diet has been recommended. However, now we have some information that may start to give us some answers.

The Mediterranean diet has been regarded as a healthy regimen.¹ This diet emphasizes eating primarily plant-based foods, such as fruits and vegetables; whole grains; legumes; and nuts. Other recommendations include replacing butter with healthy fats such as olive oil and canola oil, using herbs and spices instead of salt to flavor foods, and limiting red meat to no more than a few times a month.¹

As we know, psoriasis is a chronic inflammatory disease. The Mediterranean diet has been shown to reduce chronic inflammation and has a positive effect on the risk for metabolic syndrome and cardiovascular events.¹ Phan et al¹ hypothesized a positive effect of the Mediterranean diet on psoriasis. They performed a study to assess the association between a score that reflects the adhesion to a Mediterranean diet (MEDI-LITE) and the onset and/or severity of psoriasis.¹

The NutriNet-Santé program is an ongoing, observational, web-based questionnaire cohort study launched in France in May 2009.¹ Data were collected and analyzed between April 2017 and June 2017. Individuals with psoriasis were identified utilizing a validated online questionnaire and then categorized by disease severity into 1 of 3 groups: severe psoriasis, nonsevere psoriasis, and psoriasis free.¹

During the initial 2 years of participation in the cohort, data on dietary intake (including alcohol) were gathered to calculate the MEDI-LITE score, ranging from 0 (no adherence) to 18 (maximum adherence).¹ Of the 158,361 total web-based participants, 35,735 (23%) replied to the psoriasis questionnaire.¹ Of the respondents, 3557 (10%) individuals reported having psoriasis. The condition was severe in 878 cases (24.7%), and 299 (8.4%) incident cases were recorded (cases occurring >2 years after participant inclusion in the cohort). After adjustment for confounding factors, the investigators found a significant inverse relationship between the MEDI-LITE score and having severe psoriasis (odds ratio [OR], 0.71; 95% CI, 0.55-0.92 for the MEDI-LITE score’s second tertile [score of 8 to 9]; and OR, 0.78; 95% CI, 0.59-1.01 for the third tertile [score of 10 to 18]).¹

The authors noted that patients with severe psoriasis displayed low levels of adherence to the Mediterranean diet.¹ They commented that this finding supports the hypothesis that the Mediterranean diet may slow the progression of psoriasis. If these findings are confirmed, adherence to a Mediterranean diet should be integrated into the routine management of moderate to severe psoriasis.¹ These findings are by no means definitive, but it is a first step in helping us define more specific dietary recommendations for psoriasis.

This issue includes several articles looking at various facets of psoriasis important to residents, including the pathophysiology of psoriasis,² treatment approach using biologic therapies,³ risk factors and triggers for psoriasis,⁴ and the psychosocial impact of psoriasis.⁵ We hope that you find this issue enjoyable and informative.

We are now in the midst of a second revolution in the care of patients with psoriasis. Since biologic therapies for psoriasis were first introduced in 2003 with the approval of alefacept, the psoriasis treatment paradigm has shifted and continues to evolve. Interestingly, the first 2 biologic agents approved for psoriasis, alefacept and efalizumab, are no longer on the market in the United States.

We certainly have made progress since the early days of psoriasis treatment. Over the years, we have come to understand the nature of psoriasis as a systemic inflammatory condition rather than as simply a skin disease. With this knowledge, we have continued to identify systemic comorbidities associated with psoriasis, including cardiovascular risk, diabetes, and metabolic syndrome. It is therefore the role of the dermatologist to serve as the gatekeeper for these individuals and help to screen for comorbidities of psoriasis, as well as provide appropriate counseling and referral.

Additionally, psoriasis therapies have been approved for new segments of the population. In 2016, the US Food and Drug Administration approved a supplemental biologics license application for use of etanercept in children aged 4 years and older with chronic moderate to severe plaque psoriasis who are candidates for systemic therapy or phototherapy. Last year, the US Food and Drug Administration also approved an expanded indication for ustekinumab for the treatment of adolescents (aged 12 years and older) with moderate to severe plaque psoriasis who are candidates for phototherapy or systemic therapy.

Another treatment development included the approval of apremilast as a new oral therapeutic option for psoriasis patients. This agent, which is approved for both psoriasis and psoriatic arthritis, has become an attractive therapy for many patients who are new to systemic treatment. Many patients prefer an oral medication and like the fact that no routine laboratory monitoring is required. Often patients leave their dermatologist’s office with 2- to 4-weeks’ worth of samples and can begin their course immediately.

A treat-to-target approach also has been established for psoriasis. In 2016, the Medical Board of the National Psoriasis Foundation¹ created specific treatment goals in order to make achieving clear or almost clear skin the new standard of care. A consensus-building study conducted among 25 psoriasis experts revealed that the most preferred instrument for evaluating disease severity was body surface area (BSA). The time at which most participants preferred to evaluate patient response after starting a new psoriasis therapy was 3 months, and an acceptable response at this timepoint was considered to be either BSA involvement of 3% or less or improvement in BSA involvement of 75% or more compared to baseline. The target response at 3 months after starting treatment was BSA involvement of 1% or less. During the maintenance period, evaluation every 6 months was most preferred, and the target response at every 6-month follow-up evaluation was BSA involvement of 1% or less.¹ These standards enable and encourage both clinicians and patients to maximize their treatment success.

Over the past several years, a variety of new biologic agents also have come to the market, including 3 IL-17 inhibitors (ixekizumab, brodalumab, and secukinumab) and one IL-23 inhibitor (guselkumab). All of these agents have added new options to the armamentarium for psoriasis treatment and are highly effective. Overall, the clinical improvement and safety profiles for these agents are promising, and these new drugs may be equal to or more efficacious than the currently available therapeutic options for psoriasis treatment; however, long-term studies are still needed to further establish the safety and efficacy profiles for these biologic agents. Even more novel therapies are in development, as will be discussed by Lee et al² in this issue.

It is the purpose of this special issue to review new standards of care for psoriasis in 2018. We hope that you find this issue enjoyable and informative.

We are now in the midst of a second revolution in the care of patients with psoriasis. Since biologic therapies for psoriasis were first introduced in 2003 with the approval of alefacept, the psoriasis treatment paradigm has shifted and continues to evolve. Interestingly, the first 2 biologic agents approved for psoriasis, alefacept and efalizumab, are no longer on the market in the United States.

We certainly have made progress since the early days of psoriasis treatment. Over the years, we have come to understand the nature of psoriasis as a systemic inflammatory condition rather than as simply a skin disease. With this knowledge, we have continued to identify systemic comorbidities associated with psoriasis, including cardiovascular risk, diabetes, and metabolic syndrome. It is therefore the role of the dermatologist to serve as the gatekeeper for these individuals and help to screen for comorbidities of psoriasis, as well as provide appropriate counseling and referral.

Additionally, psoriasis therapies have been approved for new segments of the population. In 2016, the US Food and Drug Administration approved a supplemental biologics license application for use of etanercept in children aged 4 years and older with chronic moderate to severe plaque psoriasis who are candidates for systemic therapy or phototherapy. Last year, the US Food and Drug Administration also approved an expanded indication for ustekinumab for the treatment of adolescents (aged 12 years and older) with moderate to severe plaque psoriasis who are candidates for phototherapy or systemic therapy.

Another treatment development included the approval of apremilast as a new oral therapeutic option for psoriasis patients. This agent, which is approved for both psoriasis and psoriatic arthritis, has become an attractive therapy for many patients who are new to systemic treatment. Many patients prefer an oral medication and like the fact that no routine laboratory monitoring is required. Often patients leave their dermatologist’s office with 2- to 4-weeks’ worth of samples and can begin their course immediately.

A treat-to-target approach also has been established for psoriasis. In 2016, the Medical Board of the National Psoriasis Foundation¹ created specific treatment goals in order to make achieving clear or almost clear skin the new standard of care. A consensus-building study conducted among 25 psoriasis experts revealed that the most preferred instrument for evaluating disease severity was body surface area (BSA). The time at which most participants preferred to evaluate patient response after starting a new psoriasis therapy was 3 months, and an acceptable response at this timepoint was considered to be either BSA involvement of 3% or less or improvement in BSA involvement of 75% or more compared to baseline. The target response at 3 months after starting treatment was BSA involvement of 1% or less. During the maintenance period, evaluation every 6 months was most preferred, and the target response at every 6-month follow-up evaluation was BSA involvement of 1% or less.¹ These standards enable and encourage both clinicians and patients to maximize their treatment success.

Over the past several years, a variety of new biologic agents also have come to the market, including 3 IL-17 inhibitors (ixekizumab, brodalumab, and secukinumab) and one IL-23 inhibitor (guselkumab). All of these agents have added new options to the armamentarium for psoriasis treatment and are highly effective. Overall, the clinical improvement and safety profiles for these agents are promising, and these new drugs may be equal to or more efficacious than the currently available therapeutic options for psoriasis treatment; however, long-term studies are still needed to further establish the safety and efficacy profiles for these biologic agents. Even more novel therapies are in development, as will be discussed by Lee et al² in this issue.

It is the purpose of this special issue to review new standards of care for psoriasis in 2018. We hope that you find this issue enjoyable and informative.

We are now in the midst of a second revolution in the care of patients with psoriasis. Since biologic therapies for psoriasis were first introduced in 2003 with the approval of alefacept, the psoriasis treatment paradigm has shifted and continues to evolve. Interestingly, the first 2 biologic agents approved for psoriasis, alefacept and efalizumab, are no longer on the market in the United States.

We certainly have made progress since the early days of psoriasis treatment. Over the years, we have come to understand the nature of psoriasis as a systemic inflammatory condition rather than as simply a skin disease. With this knowledge, we have continued to identify systemic comorbidities associated with psoriasis, including cardiovascular risk, diabetes, and metabolic syndrome. It is therefore the role of the dermatologist to serve as the gatekeeper for these individuals and help to screen for comorbidities of psoriasis, as well as provide appropriate counseling and referral.

Additionally, psoriasis therapies have been approved for new segments of the population. In 2016, the US Food and Drug Administration approved a supplemental biologics license application for use of etanercept in children aged 4 years and older with chronic moderate to severe plaque psoriasis who are candidates for systemic therapy or phototherapy. Last year, the US Food and Drug Administration also approved an expanded indication for ustekinumab for the treatment of adolescents (aged 12 years and older) with moderate to severe plaque psoriasis who are candidates for phototherapy or systemic therapy.

Another treatment development included the approval of apremilast as a new oral therapeutic option for psoriasis patients. This agent, which is approved for both psoriasis and psoriatic arthritis, has become an attractive therapy for many patients who are new to systemic treatment. Many patients prefer an oral medication and like the fact that no routine laboratory monitoring is required. Often patients leave their dermatologist’s office with 2- to 4-weeks’ worth of samples and can begin their course immediately.

A treat-to-target approach also has been established for psoriasis. In 2016, the Medical Board of the National Psoriasis Foundation¹ created specific treatment goals in order to make achieving clear or almost clear skin the new standard of care. A consensus-building study conducted among 25 psoriasis experts revealed that the most preferred instrument for evaluating disease severity was body surface area (BSA). The time at which most participants preferred to evaluate patient response after starting a new psoriasis therapy was 3 months, and an acceptable response at this timepoint was considered to be either BSA involvement of 3% or less or improvement in BSA involvement of 75% or more compared to baseline. The target response at 3 months after starting treatment was BSA involvement of 1% or less. During the maintenance period, evaluation every 6 months was most preferred, and the target response at every 6-month follow-up evaluation was BSA involvement of 1% or less.¹ These standards enable and encourage both clinicians and patients to maximize their treatment success.

Over the past several years, a variety of new biologic agents also have come to the market, including 3 IL-17 inhibitors (ixekizumab, brodalumab, and secukinumab) and one IL-23 inhibitor (guselkumab). All of these agents have added new options to the armamentarium for psoriasis treatment and are highly effective. Overall, the clinical improvement and safety profiles for these agents are promising, and these new drugs may be equal to or more efficacious than the currently available therapeutic options for psoriasis treatment; however, long-term studies are still needed to further establish the safety and efficacy profiles for these biologic agents. Even more novel therapies are in development, as will be discussed by Lee et al² in this issue.

It is the purpose of this special issue to review new standards of care for psoriasis in 2018. We hope that you find this issue enjoyable and informative.

Over the last decade we have come to understand the nature of psoriasis as a systemic inflammatory condition rather than as simply a skin disease. With this concept, we have continued to identify systemic comorbidities associated with psoriasis, including cardiovascular risk, diabetes mellitus, and metabolic syndrome. As dermatologists, we must serve as the gatekeeper for our patients with psoriasis and help to screen for comorbidities as well as provide appropriate counseling and referral.

Of the potential benefits of novel systemic therapies for psoriasis, the potential for addressing comorbid conditions with these treatments is critically important. Therefore, when I discuss psoriasis treatments, I always review and emphasize the anti-inflammatory effects of these agents. Although we know that psoriasis increases the risk for vascular inflammation and major adverse cardiovascular events (MACEs), it has been unclear if psoriasis duration affects these risks.

Egeberg et al¹ utilized 2 resources to understand the effect of psoriasis duration on vascular disease and cardiovascular events: a human imaging study and a population-based study of cardiovascular disease events. In the first part of the study, patients with psoriasis (N=190) underwent fludeoxyglucose F 18 positron emission tomography/computed tomography. Next, MACE risk was examined using nationwide registries (adjusted hazard ratio in patients with psoriasis [n=87,161] vs the general population [n=4,234,793]). In the imaging study, participants had low cardiovascular risk by traditional risk scores. The authors found that vascular inflammation as demonstrated by the imaging system was significantly associated with disease duration (β=.171; P=.002). In the population-based study, psoriasis duration had a strong relationship with MACE risk (1.0% per additional year of psoriasis duration [hazard ratio, 1.010; 95% confidence interval, 1.007-1.013]). The researchers reported that every standard deviation increase in disease duration increased the target-to-background ratio by 2.5%, which translated into an absolute increase of approximately 10% in future adverse events.¹

Therefore, the authors concluded that there were negative effects of psoriasis duration on vascular inflammation and MACEs,¹ which suggests that the cumulative duration of low-grade chronic inflammation may accelerate vascular disease development and MACEs. The authors therefore noted that providers should consider inquiring about duration of disease to counsel for heightened cardiovascular disease risk in psoriasis patients.¹

We have some evidence that therapeutic intervention may be useful. Wu et al² compared MACE risk in psoriasis patients receiving methotrexate or tumor necrosis factor α (TNF-α) inhibitors. They also assessed the impact of TNF-α inhibitor treatment duration on MACE risk. The authors concluded that psoriasis patients receiving TNF-α inhibitors had a lower MACE risk compared to those receiving methotrexate. Cumulative exposure to TNF-α inhibitors was associated with a reduced risk for MACEs.²

The findings of these studies are poignant and help to further emphasize the importance of proper identification and treatment of psoriasis and its comorbidities. This information also adds an element of urgency to the way we look at this disease and demonstrates that we must intervene as soon as possible in this process.

Over the last decade we have come to understand the nature of psoriasis as a systemic inflammatory condition rather than as simply a skin disease. With this concept, we have continued to identify systemic comorbidities associated with psoriasis, including cardiovascular risk, diabetes mellitus, and metabolic syndrome. As dermatologists, we must serve as the gatekeeper for our patients with psoriasis and help to screen for comorbidities as well as provide appropriate counseling and referral.

Of the potential benefits of novel systemic therapies for psoriasis, the potential for addressing comorbid conditions with these treatments is critically important. Therefore, when I discuss psoriasis treatments, I always review and emphasize the anti-inflammatory effects of these agents. Although we know that psoriasis increases the risk for vascular inflammation and major adverse cardiovascular events (MACEs), it has been unclear if psoriasis duration affects these risks.

Egeberg et al¹ utilized 2 resources to understand the effect of psoriasis duration on vascular disease and cardiovascular events: a human imaging study and a population-based study of cardiovascular disease events. In the first part of the study, patients with psoriasis (N=190) underwent fludeoxyglucose F 18 positron emission tomography/computed tomography. Next, MACE risk was examined using nationwide registries (adjusted hazard ratio in patients with psoriasis [n=87,161] vs the general population [n=4,234,793]). In the imaging study, participants had low cardiovascular risk by traditional risk scores. The authors found that vascular inflammation as demonstrated by the imaging system was significantly associated with disease duration (β=.171; P=.002). In the population-based study, psoriasis duration had a strong relationship with MACE risk (1.0% per additional year of psoriasis duration [hazard ratio, 1.010; 95% confidence interval, 1.007-1.013]). The researchers reported that every standard deviation increase in disease duration increased the target-to-background ratio by 2.5%, which translated into an absolute increase of approximately 10% in future adverse events.¹

Therefore, the authors concluded that there were negative effects of psoriasis duration on vascular inflammation and MACEs,¹ which suggests that the cumulative duration of low-grade chronic inflammation may accelerate vascular disease development and MACEs. The authors therefore noted that providers should consider inquiring about duration of disease to counsel for heightened cardiovascular disease risk in psoriasis patients.¹

We have some evidence that therapeutic intervention may be useful. Wu et al² compared MACE risk in psoriasis patients receiving methotrexate or tumor necrosis factor α (TNF-α) inhibitors. They also assessed the impact of TNF-α inhibitor treatment duration on MACE risk. The authors concluded that psoriasis patients receiving TNF-α inhibitors had a lower MACE risk compared to those receiving methotrexate. Cumulative exposure to TNF-α inhibitors was associated with a reduced risk for MACEs.²

The findings of these studies are poignant and help to further emphasize the importance of proper identification and treatment of psoriasis and its comorbidities. This information also adds an element of urgency to the way we look at this disease and demonstrates that we must intervene as soon as possible in this process.

Over the last decade we have come to understand the nature of psoriasis as a systemic inflammatory condition rather than as simply a skin disease. With this concept, we have continued to identify systemic comorbidities associated with psoriasis, including cardiovascular risk, diabetes mellitus, and metabolic syndrome. As dermatologists, we must serve as the gatekeeper for our patients with psoriasis and help to screen for comorbidities as well as provide appropriate counseling and referral.

Of the potential benefits of novel systemic therapies for psoriasis, the potential for addressing comorbid conditions with these treatments is critically important. Therefore, when I discuss psoriasis treatments, I always review and emphasize the anti-inflammatory effects of these agents. Although we know that psoriasis increases the risk for vascular inflammation and major adverse cardiovascular events (MACEs), it has been unclear if psoriasis duration affects these risks.

Egeberg et al¹ utilized 2 resources to understand the effect of psoriasis duration on vascular disease and cardiovascular events: a human imaging study and a population-based study of cardiovascular disease events. In the first part of the study, patients with psoriasis (N=190) underwent fludeoxyglucose F 18 positron emission tomography/computed tomography. Next, MACE risk was examined using nationwide registries (adjusted hazard ratio in patients with psoriasis [n=87,161] vs the general population [n=4,234,793]). In the imaging study, participants had low cardiovascular risk by traditional risk scores. The authors found that vascular inflammation as demonstrated by the imaging system was significantly associated with disease duration (β=.171; P=.002). In the population-based study, psoriasis duration had a strong relationship with MACE risk (1.0% per additional year of psoriasis duration [hazard ratio, 1.010; 95% confidence interval, 1.007-1.013]). The researchers reported that every standard deviation increase in disease duration increased the target-to-background ratio by 2.5%, which translated into an absolute increase of approximately 10% in future adverse events.¹

Therefore, the authors concluded that there were negative effects of psoriasis duration on vascular inflammation and MACEs,¹ which suggests that the cumulative duration of low-grade chronic inflammation may accelerate vascular disease development and MACEs. The authors therefore noted that providers should consider inquiring about duration of disease to counsel for heightened cardiovascular disease risk in psoriasis patients.¹

We have some evidence that therapeutic intervention may be useful. Wu et al² compared MACE risk in psoriasis patients receiving methotrexate or tumor necrosis factor α (TNF-α) inhibitors. They also assessed the impact of TNF-α inhibitor treatment duration on MACE risk. The authors concluded that psoriasis patients receiving TNF-α inhibitors had a lower MACE risk compared to those receiving methotrexate. Cumulative exposure to TNF-α inhibitors was associated with a reduced risk for MACEs.²

The findings of these studies are poignant and help to further emphasize the importance of proper identification and treatment of psoriasis and its comorbidities. This information also adds an element of urgency to the way we look at this disease and demonstrates that we must intervene as soon as possible in this process.