Cutis

The Comparison

A A 25-year-old man of Hispanic ethnicity with pink papules, pustules, and large keloidal tumors on the occipital scalp characteristic of acne keloidalis nuchae (AKN). There is hair loss and some tufting of remaining hairs.

B A 17-year-old adolescent boy of African descent with small papules on the occipital scalp and some hair loss from AKN.

C A 19-year-old man of African descent with extensive papules and keloidal tumors on the occipital scalp as well as scarring hair loss and tufting of hairs from AKN.

Acne keloidalis nuchae (AKN) is a chronic inflammatory condition commonly affecting the occipital scalp and posterior neck. It causes discrete or extensive fibrosing papules that may coalesce to form pronounced ­tumorlike masses^1,2 with scarring alopecia (Figure, A–C).³ Pustules, hair tufts, secondary bacterial infections, abscesses, and sinus tracts also may occur.¹ The pathogenesis of AKN has been characterized as varying stages of follicular inflammation at the infundibular and isthmus levels followed by fibrotic occlusion of the ­follicular lumen.⁴ Pruritus, pain, bleeding, oozing, and a feeling of scalp tightness may occur.^1,5

Umar et al⁶ performed a retrospective review of 108 men with AKN—58% of African descent, 37% Hispanic, 3% Asian, and 2% Middle Eastern—and proposed a 3-tier classification system for AKN. Tier 1 focused on the distribution and sagittal spread of AKN lesions between the clinical demarcation lines of the occipital notch and posterior hairline. Tier 2 focused on the type of lesions present—discrete papules or nodules, coalescing/abutting lesions, plaques (raised, atrophic, or indurated), or dome-shaped tumoral masses. Tier 3 focused on the presence or absence of co-existing dissecting cellulitis or folliculitis decalvans.⁶

Epidemiology

Acne keloidalis nuchae primarily manifests in adolescent and adult men of African or Afro-Caribbean descent.⁷ Among African American men, the prevalence of AKN ranges from 0.5% to 13.6%.⁸ Similar ranges have been reported among Nigerian, South African, and West African men.¹ Acne keloidalis nuchae also affects Asian and Hispanic men but rarely is seen in non-Hispanic White men or in women of any ethnicity.^9,10 The male to female ratio is 20:1.^1,11 Hair texture, hairstyling practices such as closely shaved or faded haircuts, and genetics likely contribute to development of AKN. Sports and occupations that require the use of headgear or a tight collar may increase the risk for AKN.¹²

Key clinical features in people with darker skin tones

• The lesions of AKN range in color from pink to dark brown or black. Postinflammatory hyperpigmentation or hyperchromia may be present around AKN lesions.
• Chronicity of AKN may lead to extended use of high-potency topical or intralesional corticosteroids, which causes transient or long-lasting hypopigmentation, especially in those with darker skin tones.

Worth noting

• Acne keloidalis nuchae can be disfiguring, which negatively impacts quality of life and self-esteem.¹²
• Some occupations (eg, military, police) have hair policies that may not be favorable to those with or at risk for AKN.
• Patients with AKN are 2 to 3 times more likely to present with metabolic syndrome, hypertension, type 2 diabetes mellitus, or obesity.¹³

Treatment

There are no treatments approved by the US Food and Drug Administration specifically for AKN. Treatment approaches are based on the pathophysiology, secondary impacts on the skin, and disease severity. Growing out the hair may prevent worsening and/or decrease the risk for new lesions.⁶

• Options include but are not limited to topical and systemic therapies (eg, topical corticosteroids, oral or topical antibiotics, isotretinoin, topical retinoids, imiquimod, pimecrolimus), light devices (eg, phototherapy, laser), ablative therapies (eg, laser, cryotherapy, radiotherapy), and surgery (eg, excision, follicular unit excision), often in combination.^6,14,15
• Intralesional triamcinolone injections are considered standard of care. Adotama et al¹⁶ found that injecting ­triamcinolone into the deep dermis in the area of flat or papular AKN yielded better control of inflammation and decreased appearance of lesions compared with injecting individual lesions.
• For extensive AKN lesions that do not respond to ­less-invasive therapies, consider surgical techniques,^6,17 such as follicular unit excision¹⁸ and more extensive surgical excisions building on approaches from pioneers Drs. John Kenney and Harold Pierce.¹⁹ An innovative surgical approach for removal of large AKNs is the bat excision technique—wound shape resembles a bat in a spread-eagled position—with secondary intention healing with or without debridement and/or tension sutures. The resulting linear scar acts as a new posterior hair line.²⁰

Health disparity highlights

Access to a dermatologic or plastic surgeon with expertise in the surgical treatment of large AKNs may be challenging but is needed to reduce risk for recurrence and adverse events.

Close-cropped haircuts on the occipital scalp, which are particularly popular among men of African descent, increase the risk for AKN.⁵ Although this grooming style may be a personal preference, other hairstyles commonly worn by those with tightly coiled hair may be deemed “unprofessional” in society or the workplace,²¹ which leads to hairstyling practices that may increase the risk for AKN.

Acne keloidalis nuchae remains an understudied entity that adversely affects patients with skin of color.

The Comparison

A A 25-year-old man of Hispanic ethnicity with pink papules, pustules, and large keloidal tumors on the occipital scalp characteristic of acne keloidalis nuchae (AKN). There is hair loss and some tufting of remaining hairs.

B A 17-year-old adolescent boy of African descent with small papules on the occipital scalp and some hair loss from AKN.

C A 19-year-old man of African descent with extensive papules and keloidal tumors on the occipital scalp as well as scarring hair loss and tufting of hairs from AKN.

Acne keloidalis nuchae (AKN) is a chronic inflammatory condition commonly affecting the occipital scalp and posterior neck. It causes discrete or extensive fibrosing papules that may coalesce to form pronounced ­tumorlike masses^1,2 with scarring alopecia (Figure, A–C).³ Pustules, hair tufts, secondary bacterial infections, abscesses, and sinus tracts also may occur.¹ The pathogenesis of AKN has been characterized as varying stages of follicular inflammation at the infundibular and isthmus levels followed by fibrotic occlusion of the ­follicular lumen.⁴ Pruritus, pain, bleeding, oozing, and a feeling of scalp tightness may occur.^1,5

Umar et al⁶ performed a retrospective review of 108 men with AKN—58% of African descent, 37% Hispanic, 3% Asian, and 2% Middle Eastern—and proposed a 3-tier classification system for AKN. Tier 1 focused on the distribution and sagittal spread of AKN lesions between the clinical demarcation lines of the occipital notch and posterior hairline. Tier 2 focused on the type of lesions present—discrete papules or nodules, coalescing/abutting lesions, plaques (raised, atrophic, or indurated), or dome-shaped tumoral masses. Tier 3 focused on the presence or absence of co-existing dissecting cellulitis or folliculitis decalvans.⁶

Epidemiology

Acne keloidalis nuchae primarily manifests in adolescent and adult men of African or Afro-Caribbean descent.⁷ Among African American men, the prevalence of AKN ranges from 0.5% to 13.6%.⁸ Similar ranges have been reported among Nigerian, South African, and West African men.¹ Acne keloidalis nuchae also affects Asian and Hispanic men but rarely is seen in non-Hispanic White men or in women of any ethnicity.^9,10 The male to female ratio is 20:1.^1,11 Hair texture, hairstyling practices such as closely shaved or faded haircuts, and genetics likely contribute to development of AKN. Sports and occupations that require the use of headgear or a tight collar may increase the risk for AKN.¹²

Key clinical features in people with darker skin tones

• The lesions of AKN range in color from pink to dark brown or black. Postinflammatory hyperpigmentation or hyperchromia may be present around AKN lesions.
• Chronicity of AKN may lead to extended use of high-potency topical or intralesional corticosteroids, which causes transient or long-lasting hypopigmentation, especially in those with darker skin tones.

Worth noting

• Acne keloidalis nuchae can be disfiguring, which negatively impacts quality of life and self-esteem.¹²
• Some occupations (eg, military, police) have hair policies that may not be favorable to those with or at risk for AKN.
• Patients with AKN are 2 to 3 times more likely to present with metabolic syndrome, hypertension, type 2 diabetes mellitus, or obesity.¹³

Treatment

There are no treatments approved by the US Food and Drug Administration specifically for AKN. Treatment approaches are based on the pathophysiology, secondary impacts on the skin, and disease severity. Growing out the hair may prevent worsening and/or decrease the risk for new lesions.⁶

• Options include but are not limited to topical and systemic therapies (eg, topical corticosteroids, oral or topical antibiotics, isotretinoin, topical retinoids, imiquimod, pimecrolimus), light devices (eg, phototherapy, laser), ablative therapies (eg, laser, cryotherapy, radiotherapy), and surgery (eg, excision, follicular unit excision), often in combination.^6,14,15
• Intralesional triamcinolone injections are considered standard of care. Adotama et al¹⁶ found that injecting ­triamcinolone into the deep dermis in the area of flat or papular AKN yielded better control of inflammation and decreased appearance of lesions compared with injecting individual lesions.
• For extensive AKN lesions that do not respond to ­less-invasive therapies, consider surgical techniques,^6,17 such as follicular unit excision¹⁸ and more extensive surgical excisions building on approaches from pioneers Drs. John Kenney and Harold Pierce.¹⁹ An innovative surgical approach for removal of large AKNs is the bat excision technique—wound shape resembles a bat in a spread-eagled position—with secondary intention healing with or without debridement and/or tension sutures. The resulting linear scar acts as a new posterior hair line.²⁰

Health disparity highlights

Access to a dermatologic or plastic surgeon with expertise in the surgical treatment of large AKNs may be challenging but is needed to reduce risk for recurrence and adverse events.

Close-cropped haircuts on the occipital scalp, which are particularly popular among men of African descent, increase the risk for AKN.⁵ Although this grooming style may be a personal preference, other hairstyles commonly worn by those with tightly coiled hair may be deemed “unprofessional” in society or the workplace,²¹ which leads to hairstyling practices that may increase the risk for AKN.

Acne keloidalis nuchae remains an understudied entity that adversely affects patients with skin of color.

The Comparison

A A 25-year-old man of Hispanic ethnicity with pink papules, pustules, and large keloidal tumors on the occipital scalp characteristic of acne keloidalis nuchae (AKN). There is hair loss and some tufting of remaining hairs.

B A 17-year-old adolescent boy of African descent with small papules on the occipital scalp and some hair loss from AKN.

C A 19-year-old man of African descent with extensive papules and keloidal tumors on the occipital scalp as well as scarring hair loss and tufting of hairs from AKN.

Acne keloidalis nuchae (AKN) is a chronic inflammatory condition commonly affecting the occipital scalp and posterior neck. It causes discrete or extensive fibrosing papules that may coalesce to form pronounced ­tumorlike masses^1,2 with scarring alopecia (Figure, A–C).³ Pustules, hair tufts, secondary bacterial infections, abscesses, and sinus tracts also may occur.¹ The pathogenesis of AKN has been characterized as varying stages of follicular inflammation at the infundibular and isthmus levels followed by fibrotic occlusion of the ­follicular lumen.⁴ Pruritus, pain, bleeding, oozing, and a feeling of scalp tightness may occur.^1,5

Umar et al⁶ performed a retrospective review of 108 men with AKN—58% of African descent, 37% Hispanic, 3% Asian, and 2% Middle Eastern—and proposed a 3-tier classification system for AKN. Tier 1 focused on the distribution and sagittal spread of AKN lesions between the clinical demarcation lines of the occipital notch and posterior hairline. Tier 2 focused on the type of lesions present—discrete papules or nodules, coalescing/abutting lesions, plaques (raised, atrophic, or indurated), or dome-shaped tumoral masses. Tier 3 focused on the presence or absence of co-existing dissecting cellulitis or folliculitis decalvans.⁶

Epidemiology

Acne keloidalis nuchae primarily manifests in adolescent and adult men of African or Afro-Caribbean descent.⁷ Among African American men, the prevalence of AKN ranges from 0.5% to 13.6%.⁸ Similar ranges have been reported among Nigerian, South African, and West African men.¹ Acne keloidalis nuchae also affects Asian and Hispanic men but rarely is seen in non-Hispanic White men or in women of any ethnicity.^9,10 The male to female ratio is 20:1.^1,11 Hair texture, hairstyling practices such as closely shaved or faded haircuts, and genetics likely contribute to development of AKN. Sports and occupations that require the use of headgear or a tight collar may increase the risk for AKN.¹²

Key clinical features in people with darker skin tones

• The lesions of AKN range in color from pink to dark brown or black. Postinflammatory hyperpigmentation or hyperchromia may be present around AKN lesions.
• Chronicity of AKN may lead to extended use of high-potency topical or intralesional corticosteroids, which causes transient or long-lasting hypopigmentation, especially in those with darker skin tones.

Worth noting

• Acne keloidalis nuchae can be disfiguring, which negatively impacts quality of life and self-esteem.¹²
• Some occupations (eg, military, police) have hair policies that may not be favorable to those with or at risk for AKN.
• Patients with AKN are 2 to 3 times more likely to present with metabolic syndrome, hypertension, type 2 diabetes mellitus, or obesity.¹³

Treatment

There are no treatments approved by the US Food and Drug Administration specifically for AKN. Treatment approaches are based on the pathophysiology, secondary impacts on the skin, and disease severity. Growing out the hair may prevent worsening and/or decrease the risk for new lesions.⁶

• Options include but are not limited to topical and systemic therapies (eg, topical corticosteroids, oral or topical antibiotics, isotretinoin, topical retinoids, imiquimod, pimecrolimus), light devices (eg, phototherapy, laser), ablative therapies (eg, laser, cryotherapy, radiotherapy), and surgery (eg, excision, follicular unit excision), often in combination.^6,14,15
• Intralesional triamcinolone injections are considered standard of care. Adotama et al¹⁶ found that injecting ­triamcinolone into the deep dermis in the area of flat or papular AKN yielded better control of inflammation and decreased appearance of lesions compared with injecting individual lesions.
• For extensive AKN lesions that do not respond to ­less-invasive therapies, consider surgical techniques,^6,17 such as follicular unit excision¹⁸ and more extensive surgical excisions building on approaches from pioneers Drs. John Kenney and Harold Pierce.¹⁹ An innovative surgical approach for removal of large AKNs is the bat excision technique—wound shape resembles a bat in a spread-eagled position—with secondary intention healing with or without debridement and/or tension sutures. The resulting linear scar acts as a new posterior hair line.²⁰

Health disparity highlights

Access to a dermatologic or plastic surgeon with expertise in the surgical treatment of large AKNs may be challenging but is needed to reduce risk for recurrence and adverse events.

Close-cropped haircuts on the occipital scalp, which are particularly popular among men of African descent, increase the risk for AKN.⁵ Although this grooming style may be a personal preference, other hairstyles commonly worn by those with tightly coiled hair may be deemed “unprofessional” in society or the workplace,²¹ which leads to hairstyling practices that may increase the risk for AKN.

Acne keloidalis nuchae remains an understudied entity that adversely affects patients with skin of color.

Vitamin D (VD) regulates keratinocyte proliferation and differentiation, modulates inflammatory pathways, and protects against cellular damage in the skin. ¹ In the setting of tissue injury and acute skin inflammation, active vitamin D—1,25(OH) ₂ D—suppresses signaling from pro-inflammatory chemokines and cytokines such as IFN- γ and IL-17. ^2,3 This suppression reduces proliferation of helper T cells (T _H 1, T _H 17) and B cells, decreasing tissue damage from reactive oxygen species release while enhancing secretion of the anti-inflammatory cytokine IL-10 by antigen-presenting cells. ^2-4

Suboptimal VD levels have been associated with numerous health consequences including malignancy, prompting interest in VD supplementation for improving cancer-related outcomes.⁵ Beyond disease prognosis, high-dose VD supplementation has been suggested as a potential therapy for adverse events (AEs) related to cancer treatments. In one study, mice that received oral vitamin D₃ supplementation of 11,500 IU/kg daily had fewer doxorubicin-induced cardiotoxic effects on ejection fraction (P<.0001) and stroke volume (P<.01) than mice that received VD supplementation of 1500 IU/kg daily.⁶

In this review, we examine the impact of chemoradiation on 25(OH)D levels—which more accurately reflects VD stores than 1,25(OH)₂D levels—and the impact of suboptimal VD on cutaneous toxicities related to chemoradiation. To define the suboptimal VD threshold, we used the Endocrine Society’s clinical practice guidelines, which characterize suboptimal 25(OH)D levels as insufficiency (21–29 ng/mL [52.5–72.5 nmol/L]) or deficiency (<20 ng/mL [50 nmol/L])⁷; deficiency can be further categorized as severe deficiency (<12 ng/mL [30 nmol/L]).⁸ This review also evaluates the evidence for vitamin D₃ supplementation to alleviate the cutaneous AEs of chemotherapy and radiation treatments.

Effects of Chemotherapy on Vitamin D Levels

A high prevalence of VD deficiency is seen in various cancers. In a retrospective review of 25(OH)D levels in 2098 adults with solid tumors of any stage (6% had metastatic disease [n=124]), suboptimal levels were found in 69% of patients with breast cancer (n=617), 75% with colorectal cancer (n=84), 72% with gynecologic cancer (n=65), 79% with kidney and bladder cancer (n=145), 83% with pancreatic and upper gastrointestinal tract cancer (n=178), 73% with lung cancer (n=73), 69% with prostate cancer (n=225), 61% with skin cancer (n=399), and 63% with thyroid cancer (n=172).⁵ Suboptimal VD also has been found in hematologic malignancies. In a prospective cohort study, mean serum 25(OH)D levels in 23 patients with recently diagnosed acute myeloid leukemia demonstrated VD deficiency (mean [SD], 18.6 [6.6] nmol/L).⁹ Given that many patients already exhibit a baseline VD deficiency at cancer diagnosis, it is important to understand the relationship between VD and cancer treatment modalities.⁵

In the United States, breast and colorectal cancers were estimated to be the first and fourth most common cancers, with 313,510 and 152,810 predicted new cases in 2024, respectively.¹⁰ This review will focus on breast and colorectal cancer when describing VD variation associated with chemotherapy exposure due to their high prevalence.

Effects of Chemotherapy on Vitamin D Levels in Breast Cancer—Breast cancer studies have shown suboptimal VD levels in 76% of females 75 years or younger with any T1, T2, or T3; N0 or N1; and M0 breast cancer, in which 38.5% (n=197) had insufficient and 37.5% (n=192) had deficient 25(OH)D levels.¹¹ In a study of female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), VD deficiency was seen in 60% of patients not receiving VD supplementation.^12,13 A systematic review that included 7 studies of different types of breast cancer suggested that circulating 25(OH)D may be associated with improved prognosis.¹⁴ Thus, studies have investigated risk factors associated with poor or worsening VD status in individuals with breast cancer, including exposure to chemotherapy and/or radiation treatment.^12,15-18

A prospective cohort study assessed 25(OH)D levels in 95 patients with any breast cancer (stages I, II, IIIA, IIIB) before and after initiating chemotherapy with docetaxel, doxorubicin, epirubicin, 5-fluorouracil, or cyclophosphamide, compared with a group of 52 females without cancer.¹⁷ In the breast cancer group, approximately 80% (76/95) had suboptimal and 50% (47/95) had deficient VD levels before chemotherapy initiation (mean [SD], 54.1 [22.8] nmol/L). In the comparison group, 60% (31/52) had suboptimal and 30% (15/52) had deficient VD at baseline (mean [SD], 66.1 [23.5] nmol/L), which was higher than the breast cancer group (P=.03). A subgroup analysis excluded participants who started, stopped, or lacked data on dietary supplements containing VD (n=39); in the remaining 56 participants, a significant decrease in 25(OH)D levels was observed shortly after finishing chemotherapy compared with the prechemotherapy baseline value (mean, −7.9 nmol/L; P=.004). Notably, 6 months after chemotherapy completion, 25(OH)D levels increased (mean, +12.8 nmol/L; P<.001). Vitamin D levels remained stable in the comparison group (P=.987).¹⁷

Consistent with these findings, a cross-sectional study assessing VD status in 394 female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), found that a history of chemotherapy was associated with increased odds of 25(OH)D levels less than 20 ng/mL compared with breast cancer patients with no prior chemotherapy (odds ratio, 1.86; 95% CI, 1.03-3.38).¹² Although the study data included chemotherapy history, no information was provided on specific chemotherapy agents or regimens used in this cohort, limiting the ability to detect the drugs most often implicated.

Both studies indicated a complex interplay between chemotherapy and VD levels in breast cancer patients. Although Kok et al¹⁷ suggested a transient decrease in VD levels during chemotherapy with a subsequent recovery after cessation, Fassio et al¹² highlighted the increased odds of VD deficiency associated with chemotherapy. Ultimately, larger randomized controlled trials are needed to better understand the relationship between chemotherapy and VD status in breast cancer patients.

Effects of Chemotherapy on Vitamin D Levels in Colorectal Cancer—Similar to patterns seen in breast cancer, a systematic review with 6 studies of different types of colorectal cancer suggested that circulating 25(OH)D levels may be associated with prognosis.¹⁴ Studies also have investigated the relationship between colorectal chemotherapy regimens and VD status.^15,16,18,19

A retrospective study assessed 25(OH)D levels in 315 patients with any colorectal cancer (stage I–IV).¹⁵ Patients were included in the analysis if they received less than 400 IU daily of VD supplementation at baseline. For the whole study sample, the mean (SD) VD level was 23.7 (13.71) ng/mL. Patients who had not received chemotherapy within 3 months of the VD level assessment were categorized as the no chemotherapy group, and the others were designated as the chemotherapy group; the latter group was exposed to various chemotherapy regimens, including combinations of irinotecan, oxaliplatin, 5-fluorouracil, leucovorin, bevacizumab, or cetuximab. Multivariate analysis showed that the chemotherapy group was 3.7 times more likely to have very low VD levels (≤15 ng/mL) compared with those in the no chemotherapy group (P<.0001).¹⁵

A separate cross-sectional study examined serum 25(OH)D concentrations in 1201 patients with any newly diagnosed colorectal carcinoma (stage I–III); 91% of cases were adenocarcinoma.¹⁸ In a multivariate analysis, chemotherapy plus surgery was associated with lower VD levels than surgery alone 6 months after diagnosis (mean, −8.74 nmol/L; 95% CI, −11.30 to −6.18 nmol/L), specifically decreasing by a mean of 6.7 nmol/L (95% CI, −9.8 to −3.8 nmol/L) after adjusting for demographic and lifestyle factors.¹⁸ However, a prospective cohort study demonstrated different findings.¹⁹ Comparing 58 patients with newly diagnosed colorectal adenocarcinoma (stages I–IV) who underwent chemotherapy and 36 patients who did not receive chemotherapy, there was no significant change in 25(OH)D levels from the time of diagnosis to 6 months later. Median VD levels decreased by 0.7 ng/mL in those who received chemotherapy, while a minimal (and not significant) increase of 1.6 ng/mL was observed in those without chemotherapy intervention (P=.26). Notably, supplementation was not restricted in this cohort, which may have resulted in higher VD levels in those taking supplements.¹⁹

Since time of year and geographic location can influence VD levels, one prospective cohort study controlled for differential sun exposure due to these factors in their analysis.¹⁶ Assessment of 25(OH)D levels was completed in 81 chemotherapy-naïve cancer patients immediately before beginning chemotherapy as well as 6 and 12 weeks into treatment. More than 8 primary cancer types were represented in this study, with breast (34% [29/81]) and colorectal (14% [12/81]) cancer being the most common, but the cancer stages of the participants were not detailed. Vitamin D levels decreased after commencing chemotherapy, with the largest drop occurring 6 weeks into treatment. From the 6- to 12-week end points, VD increased but remained below the original baseline level (baseline: mean [SD], 49.2 [22.3] nmol/L; 6 weeks: mean [SD], 40.9 [19.0] nmol/L; 12 weeks: mean [SD], 45.9 [19.7] nmol/L; P=.05).¹⁶

Although focused on breast and colorectal cancers, these studies suggest that various chemotherapy regimens may confer a higher risk for VD deficiency compared with VD status at diagnosis and/or prior to chemotherapy treatment. However, most of these studies only discussed stage-based differences, excluding analysis of the variety of cancer subtypes that comprise breast and colorectal malignancies, which may limit our ability to extrapolate from these data. Ultimately, larger randomized controlled trials are needed to better understand the relationship between chemotherapy and VD status across various primary cancer types.

Effects of Radiation Therapy on Vitamin D Levels

Unlike chemotherapy, studies on the association between radiation therapy and VD levels are minimal, with most reports in the literature discussing the use of VD to potentiate the effects of radiation therapy. In one cross-sectional analysis of 1201 patients with newly diagnosed stage I, II, or III colorectal cancer of any type (94% were adenocarcinoma), radiation plus surgery was associated with slightly lower 25(OH)D levels than surgery alone for tumor treatment 6 months after diagnosis (mean, −3.17; 95% CI, −6.07 to −0.28 nmol/L). However, after adjustment for demographic and lifestyle factors, this decrease in VD levels attributable to radiotherapy was not statistically significant compared with the surgery-only cohort (mean, −1.78; 95% CI, −5.07 to 1.52 nmol/L).¹⁸

Similarly, a cross-sectional study assessing VD status in 394 female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), found that a history of radiotherapy was not associated with a difference in serum 25(OH)D levels compared with those with breast cancer without prior radiotherapy (odds ratio, 0.90; 95% CI, 0.52-1.54).¹² From the limited existing literature specifically addressing variations of VD levels with radiation, radiation therapy does not appear to significantly impact VD levels.

Vitamin D Levels and the Severity of Chemotherapy- or Radiation Therapy–Induced AEs

A prospective cohort of 241 patients did not find an increase in the incidence or severity of chemotherapy-induced cutaneous toxicities in those with suboptimal 1,25(OH)₂D₃ levels (≤75 nmol/L).²⁰ Eight different primary cancer types were represented, including breast and colorectal cancer; the tumor stages of the participants were not detailed. Forty-one patients had normal 1,25(OH)₂D₃ levels, while the remaining 200 had suboptimal levels. There was no significant association between serum VD levels and the following dermatologic toxicities: desquamation (P=.26), xerosis (P=.15), mucositis (P=.30), or painful rash (P=.87). Surprisingly, nail changes and hand-foot reactions occurred with greater frequency in patients with normal VD levels (P=.01 and P=.03, respectively).²⁰ Hand-foot reaction is part of the toxic erythema of chemotherapy (TEC) spectrum, which is comprised of a range of cytotoxic skin injuries that typically manifest within 2 to 3 weeks of exposure to the offending chemotherapeutic agents, often characterized by erythema, pain, swelling, and blistering, particularly in intertriginous and acral areas.^21-23 Recovery from TEC generally takes at least 2 to 4 weeks and may necessitate cessation of the offending chemotherapeutic agent.^21,24 Notably, this study measured 1,25(OH)₂D₃ levels instead of 25(OH)D levels, which may not reliably indicate body stores of VD.^7,20 These results underscore the complex nature between chemotherapy and VD; however, VD levels alone do not appear to be a sufficient biomarker for predicting chemotherapy-associated cutaneous AEs.

Interestingly, radiation therapy–induced AEs may be associated with VD levels. A prospective cohort study of 98 patients with prostate, bladder, or gynecologic cancers (tumor stages were not detailed) undergoing pelvic radiotherapy found that females and males with 25(OH)D levels below a threshold of 35 and 40 nmol/L, respectively, were more likely to experience higher Radiation Therapy Oncology Group (RTOG) grade acute proctitis compared with those with VD above these thresholds.²⁵ Specifically, VD below these thresholds was associated with increased odds of RTOG grade 2 or higher radiation-induced proctitis (OR, 3.07; 95% CI, 1.27-7.50 [P=.013]). Additionally, a weak correlation was noted between VD below these thresholds and the RTOG grade, with a Spearman correlation value of −0.189 (P=.031).²⁵

One prospective cohort study included 28 patients with any cancer of the oral cavity, oropharynx, hypopharynx, or larynx stages II, III, or IVA; 93% (26/28) were stage III or IVA.²⁶ The 20 (71%) patients with suboptimal 25(OH)D levels (≤75 nmol/L) experienced a higher prevalence of grade II radiation dermatitis compared with the 8 (29%) patients with optimal VD levels (χ²₂=5.973; P=.0505). This pattern persisted with the severity of mucositis; patients from the suboptimal VD group presented with higher rates of grades II and III mucositis compared with the VD optimal group (χ²₂=13.627; P=.0011).²⁶ Recognizing the small cohort evaluated in the study, we highlight the importance of further studies to clarify these associations.

Chemotherapy-Induced Cutaneous Events Treated with High-Dose Vitamin D

Chemotherapeutic agents are known to induce cellular damage, resulting in a range of cutaneous AEs that can invoke discontinuation of otherwise effective chemotherapeutic interventions.^27,28 Recent research has explored the potential of high-dose vitamin D₃ as a therapeutic agent to mitigate cutaneous reactions.^29,30

A randomized, double-blind, placebo-controlled trial investigated the use of a single high dose of oral ­25(OH)D to treat topical nitrogen mustard (NM)–induced rash.²⁹ To characterize baseline inflammatory responses from NM injury without intervention, clinical measures, serum studies, and tissue analyses from skin biopsies were performed on 28 healthy adults after exposure to topical NM—a chemotherapeutic agent classified as a DNA alkylator. Two weeks later, participants were exposed to topical NM a second time and were split into 2 groups: 14 patients received a single 200,000-IU dose of oral 25(OH)D while the other 14 participants were given a placebo. Using the inflammatory markers induced from baseline exposure to NM alone, posttreatment analysis revealed that the punch biopsies from the 25(OH)D group expressed fewer NM-induced inflammatory markers compared with the placebo group at both 72 hours and 6 weeks following NM injury (72 hours: 12 vs 17 inflammatory markers; 6 weeks: 4 vs 11 inflammatory markers). Notably, NM inflammatory markers were enriched for IL-17 signaling pathways in the placebo biopsies but not in the 25(OH)D intervention group. This study also identified mild and severe patterns of inflammatory responses to NM that were independent of the 25(OH)D intervention. Biomarkers specific to skin biopsies from participants with the severe response included CCL20, CCL2, and CXCL8 (adjusted P<.05). At 6 weeks posttreatment, the 25(OH)D group showed a 67% reduction in NM injury markers compared with a 35% reduction in the placebo group. Despite a reduction in tissue inflammatory markers, there were no clinically significant changes observed in skin redness, swelling, or histologic structure when comparing the 25(OH)D- supplemented group to the placebo group at any time during the study, necessitating further research into the mechanistic roles of high doses VD supplementation.²⁹

Although Ernst et al²⁹ did not observe any clinically significant improvements with VD treatment, a case series of 6 patients with either glioblastoma multiforme, acute myeloid leukemia, or aplastic anemia did demonstrate clinical improvement of TEC after receiving high-dose vitamin D₃.³⁰ The mean time to onset of TEC was noted at 8.5 days following administration of the inciting chemotherapeutic agent, which included combinations of anthracycline, antimetabolite, kinase inhibitor, B-cell lymphoma 2 inhibitor, purine analogue, and alkylating agents. A combination of clinical and histologic findings was used to diagnose TEC. Baseline 25(OH)D levels were not established prior to treatment. The treatment regimen for 1 patient included 2 doses of 50,000 IU of VD spaced 1 week apart, totaling 100,000 IU, while the remaining 5 patients received a total of 200,000 IU, also split into 2 doses given 1 week apart. All patients received their first dose of VD within a week of the cutaneous eruption. Following the initial VD dose, there was a notable improvement in pain, pruritus, or swelling by the next day. Reduction in erythema also was observed within 1 to 4 days.³⁰

No AEs associated with VD supplementation were reported, suggesting a potential beneficial role of high-dose VD in accelerating recovery from chemotherapy-induced rashes without evident safety concerns.

Radiation Therapy–Induced Cutaneous Events Treated with High-Dose Vitamin D

Radiation dermatitis is a common and often severe complication of radiation therapy that affects more than 90% of patients undergoing treatment, with half of these individuals experiencing grade 2 toxicity, according to the National Cancer Institute’s Common Terminology Criteria for Adverse Events.^31,32 Radiation damage to basal keratinocytes and hair follicle stem cells disrupts the renewal of the skin’s outer layer, while a surge of free radicals causes irreversible DNA damage.³³ Symptoms of radiation dermatitis can vary from mild pink erythema to tissue ulceration and necrosis, typically within 1 to 4 weeks of radiation exposure.³⁴ The resulting dermatitis can take 2 to 4 weeks to heal, notably impacting patient quality of life and often necessitating modifications or interruptions in cancer therapy.³³

Prior studies have demonstrated the use of high-dose VD to improve the healing of UV-irradiated skin. A randomized controlled trial investigated high-dose vitamin D₃ to treat experimentally induced sunburn in 20 healthy adults. Compared with those who received a placebo, participants receiving the oral dose of 200,000 IU of vitamin D₃ demonstrated suppression of the pro-inflammatory mediators tumor necrosis factor α (P=.04) and inducible nitric oxide synthase (P=.02), while expression of tissue repair enhancer arginase 1 was increased (P<.005).³⁵ The mechanism of this enhanced tissue repair was investigated using a mouse model, in which intraperitoneal 25(OH)D was administered following severe UV-induced skin injury. On immunofluorescence microscopy, mice treated with VD showed enhanced autophagy within the macrophages infiltrating UV-irradiated skin.³⁶ The use of high-dose VD to treat UV-irradiated skin in these studies established a precedent for using VD to heal cutaneous injury caused by ionizing radiation therapy.

Some studies have focused on the role of VD for treating acute radiation dermatitis. A study of 23 patients with ductal carcinoma in situ or localized invasive ductal carcinoma breast cancer compared the effectiveness of topical calcipotriol to that of a standard hydrating ointment.³⁷ Participants were randomized to 1 of 2 treatments before starting adjuvant radiotherapy to evaluate their potential in preventing radiation dermatitis. In 87% (20/23) of these patients, no difference in skin reaction was observed between the 2 treatments, suggesting that topical VD application may not offer any advantage over the standard hydrating ointment for the prevention of radiation dermatitis.³⁷

Benefits of high-dose oral VD for treating radiation dermatitis also have been reported. Nguyen et al³⁸ documented 3 cases in which patients with neuroendocrine carcinoma of the pancreas, tonsillar carcinoma, and breast cancer received 200,000 IU of oral ergocalciferol distributed over 2 doses given 7 days apart for radiation dermatitis. These patients experienced substantial improvements in pain, swelling, and redness within a week of the initial dose. Additionally, a case of radiation recall dermatitis, which occurred a week after vinorelbine chemotherapy, was treated with 2 doses totaling 100,000 IU of oral ergocalciferol. This patient also had improvement in pain and swelling but continued to have tumor-related induration and ulceration.³⁹

Although topical VD did not show significant benefits over standard treatments for radiation dermatitis, high-dose oral VD appears promising in improving patient outcomes of pain and swelling more rapidly than current practices. Further research is needed to confirm these findings and establish standardized treatment protocols.

Final Thoughts

Suboptimal VD levels are prevalent in numerous cancer types. Chemotherapy often is associated with acute, potentially transient worsening of VD status in patients with breast and colorectal cancer. Although 25(OH)D levels have not corresponded with increased frequency of ­chemotherapy-related dermatologic AEs, suboptimal 25(OH)D levels appear to be associated with increased severity of radiation-induced mucositis and dermatitis.^20,25,26 The use of high-dose VD as a therapeutic agent shows promise in mitigating chemotherapy-induced and radiation therapy–induced rashes in multiple cancer types with reduction of inflammatory markers and a durable anti-inflammatory impact. Although the mechanisms of cellular injury vary among chemotherapeutic agents, the anti-inflammatory and tissue repair properties of VD may make it an effective treatment for chemotherapy-induced cutaneous damage regardless of injury mechanism.^2-4,35 However, reports of clinical improvement vary, and further objective studies to classify optimal dosing, administration, and outcome measures are needed. The absence of reported AEs associated with high-dose VD supplementation is encouraging, but selection of a safe and optimal dosing regimen can only occur with dedicated clinical trials.

Vitamin D (VD) regulates keratinocyte proliferation and differentiation, modulates inflammatory pathways, and protects against cellular damage in the skin. ¹ In the setting of tissue injury and acute skin inflammation, active vitamin D—1,25(OH) ₂ D—suppresses signaling from pro-inflammatory chemokines and cytokines such as IFN- γ and IL-17. ^2,3 This suppression reduces proliferation of helper T cells (T _H 1, T _H 17) and B cells, decreasing tissue damage from reactive oxygen species release while enhancing secretion of the anti-inflammatory cytokine IL-10 by antigen-presenting cells. ^2-4

Suboptimal VD levels have been associated with numerous health consequences including malignancy, prompting interest in VD supplementation for improving cancer-related outcomes.⁵ Beyond disease prognosis, high-dose VD supplementation has been suggested as a potential therapy for adverse events (AEs) related to cancer treatments. In one study, mice that received oral vitamin D₃ supplementation of 11,500 IU/kg daily had fewer doxorubicin-induced cardiotoxic effects on ejection fraction (P<.0001) and stroke volume (P<.01) than mice that received VD supplementation of 1500 IU/kg daily.⁶

In this review, we examine the impact of chemoradiation on 25(OH)D levels—which more accurately reflects VD stores than 1,25(OH)₂D levels—and the impact of suboptimal VD on cutaneous toxicities related to chemoradiation. To define the suboptimal VD threshold, we used the Endocrine Society’s clinical practice guidelines, which characterize suboptimal 25(OH)D levels as insufficiency (21–29 ng/mL [52.5–72.5 nmol/L]) or deficiency (<20 ng/mL [50 nmol/L])⁷; deficiency can be further categorized as severe deficiency (<12 ng/mL [30 nmol/L]).⁸ This review also evaluates the evidence for vitamin D₃ supplementation to alleviate the cutaneous AEs of chemotherapy and radiation treatments.

Effects of Chemotherapy on Vitamin D Levels

A high prevalence of VD deficiency is seen in various cancers. In a retrospective review of 25(OH)D levels in 2098 adults with solid tumors of any stage (6% had metastatic disease [n=124]), suboptimal levels were found in 69% of patients with breast cancer (n=617), 75% with colorectal cancer (n=84), 72% with gynecologic cancer (n=65), 79% with kidney and bladder cancer (n=145), 83% with pancreatic and upper gastrointestinal tract cancer (n=178), 73% with lung cancer (n=73), 69% with prostate cancer (n=225), 61% with skin cancer (n=399), and 63% with thyroid cancer (n=172).⁵ Suboptimal VD also has been found in hematologic malignancies. In a prospective cohort study, mean serum 25(OH)D levels in 23 patients with recently diagnosed acute myeloid leukemia demonstrated VD deficiency (mean [SD], 18.6 [6.6] nmol/L).⁹ Given that many patients already exhibit a baseline VD deficiency at cancer diagnosis, it is important to understand the relationship between VD and cancer treatment modalities.⁵

In the United States, breast and colorectal cancers were estimated to be the first and fourth most common cancers, with 313,510 and 152,810 predicted new cases in 2024, respectively.¹⁰ This review will focus on breast and colorectal cancer when describing VD variation associated with chemotherapy exposure due to their high prevalence.

Effects of Chemotherapy on Vitamin D Levels in Breast Cancer—Breast cancer studies have shown suboptimal VD levels in 76% of females 75 years or younger with any T1, T2, or T3; N0 or N1; and M0 breast cancer, in which 38.5% (n=197) had insufficient and 37.5% (n=192) had deficient 25(OH)D levels.¹¹ In a study of female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), VD deficiency was seen in 60% of patients not receiving VD supplementation.^12,13 A systematic review that included 7 studies of different types of breast cancer suggested that circulating 25(OH)D may be associated with improved prognosis.¹⁴ Thus, studies have investigated risk factors associated with poor or worsening VD status in individuals with breast cancer, including exposure to chemotherapy and/or radiation treatment.^12,15-18

A prospective cohort study assessed 25(OH)D levels in 95 patients with any breast cancer (stages I, II, IIIA, IIIB) before and after initiating chemotherapy with docetaxel, doxorubicin, epirubicin, 5-fluorouracil, or cyclophosphamide, compared with a group of 52 females without cancer.¹⁷ In the breast cancer group, approximately 80% (76/95) had suboptimal and 50% (47/95) had deficient VD levels before chemotherapy initiation (mean [SD], 54.1 [22.8] nmol/L). In the comparison group, 60% (31/52) had suboptimal and 30% (15/52) had deficient VD at baseline (mean [SD], 66.1 [23.5] nmol/L), which was higher than the breast cancer group (P=.03). A subgroup analysis excluded participants who started, stopped, or lacked data on dietary supplements containing VD (n=39); in the remaining 56 participants, a significant decrease in 25(OH)D levels was observed shortly after finishing chemotherapy compared with the prechemotherapy baseline value (mean, −7.9 nmol/L; P=.004). Notably, 6 months after chemotherapy completion, 25(OH)D levels increased (mean, +12.8 nmol/L; P<.001). Vitamin D levels remained stable in the comparison group (P=.987).¹⁷

Consistent with these findings, a cross-sectional study assessing VD status in 394 female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), found that a history of chemotherapy was associated with increased odds of 25(OH)D levels less than 20 ng/mL compared with breast cancer patients with no prior chemotherapy (odds ratio, 1.86; 95% CI, 1.03-3.38).¹² Although the study data included chemotherapy history, no information was provided on specific chemotherapy agents or regimens used in this cohort, limiting the ability to detect the drugs most often implicated.

Both studies indicated a complex interplay between chemotherapy and VD levels in breast cancer patients. Although Kok et al¹⁷ suggested a transient decrease in VD levels during chemotherapy with a subsequent recovery after cessation, Fassio et al¹² highlighted the increased odds of VD deficiency associated with chemotherapy. Ultimately, larger randomized controlled trials are needed to better understand the relationship between chemotherapy and VD status in breast cancer patients.

Effects of Chemotherapy on Vitamin D Levels in Colorectal Cancer—Similar to patterns seen in breast cancer, a systematic review with 6 studies of different types of colorectal cancer suggested that circulating 25(OH)D levels may be associated with prognosis.¹⁴ Studies also have investigated the relationship between colorectal chemotherapy regimens and VD status.^15,16,18,19

A retrospective study assessed 25(OH)D levels in 315 patients with any colorectal cancer (stage I–IV).¹⁵ Patients were included in the analysis if they received less than 400 IU daily of VD supplementation at baseline. For the whole study sample, the mean (SD) VD level was 23.7 (13.71) ng/mL. Patients who had not received chemotherapy within 3 months of the VD level assessment were categorized as the no chemotherapy group, and the others were designated as the chemotherapy group; the latter group was exposed to various chemotherapy regimens, including combinations of irinotecan, oxaliplatin, 5-fluorouracil, leucovorin, bevacizumab, or cetuximab. Multivariate analysis showed that the chemotherapy group was 3.7 times more likely to have very low VD levels (≤15 ng/mL) compared with those in the no chemotherapy group (P<.0001).¹⁵

A separate cross-sectional study examined serum 25(OH)D concentrations in 1201 patients with any newly diagnosed colorectal carcinoma (stage I–III); 91% of cases were adenocarcinoma.¹⁸ In a multivariate analysis, chemotherapy plus surgery was associated with lower VD levels than surgery alone 6 months after diagnosis (mean, −8.74 nmol/L; 95% CI, −11.30 to −6.18 nmol/L), specifically decreasing by a mean of 6.7 nmol/L (95% CI, −9.8 to −3.8 nmol/L) after adjusting for demographic and lifestyle factors.¹⁸ However, a prospective cohort study demonstrated different findings.¹⁹ Comparing 58 patients with newly diagnosed colorectal adenocarcinoma (stages I–IV) who underwent chemotherapy and 36 patients who did not receive chemotherapy, there was no significant change in 25(OH)D levels from the time of diagnosis to 6 months later. Median VD levels decreased by 0.7 ng/mL in those who received chemotherapy, while a minimal (and not significant) increase of 1.6 ng/mL was observed in those without chemotherapy intervention (P=.26). Notably, supplementation was not restricted in this cohort, which may have resulted in higher VD levels in those taking supplements.¹⁹

Since time of year and geographic location can influence VD levels, one prospective cohort study controlled for differential sun exposure due to these factors in their analysis.¹⁶ Assessment of 25(OH)D levels was completed in 81 chemotherapy-naïve cancer patients immediately before beginning chemotherapy as well as 6 and 12 weeks into treatment. More than 8 primary cancer types were represented in this study, with breast (34% [29/81]) and colorectal (14% [12/81]) cancer being the most common, but the cancer stages of the participants were not detailed. Vitamin D levels decreased after commencing chemotherapy, with the largest drop occurring 6 weeks into treatment. From the 6- to 12-week end points, VD increased but remained below the original baseline level (baseline: mean [SD], 49.2 [22.3] nmol/L; 6 weeks: mean [SD], 40.9 [19.0] nmol/L; 12 weeks: mean [SD], 45.9 [19.7] nmol/L; P=.05).¹⁶

Although focused on breast and colorectal cancers, these studies suggest that various chemotherapy regimens may confer a higher risk for VD deficiency compared with VD status at diagnosis and/or prior to chemotherapy treatment. However, most of these studies only discussed stage-based differences, excluding analysis of the variety of cancer subtypes that comprise breast and colorectal malignancies, which may limit our ability to extrapolate from these data. Ultimately, larger randomized controlled trials are needed to better understand the relationship between chemotherapy and VD status across various primary cancer types.

Effects of Radiation Therapy on Vitamin D Levels

Unlike chemotherapy, studies on the association between radiation therapy and VD levels are minimal, with most reports in the literature discussing the use of VD to potentiate the effects of radiation therapy. In one cross-sectional analysis of 1201 patients with newly diagnosed stage I, II, or III colorectal cancer of any type (94% were adenocarcinoma), radiation plus surgery was associated with slightly lower 25(OH)D levels than surgery alone for tumor treatment 6 months after diagnosis (mean, −3.17; 95% CI, −6.07 to −0.28 nmol/L). However, after adjustment for demographic and lifestyle factors, this decrease in VD levels attributable to radiotherapy was not statistically significant compared with the surgery-only cohort (mean, −1.78; 95% CI, −5.07 to 1.52 nmol/L).¹⁸

Similarly, a cross-sectional study assessing VD status in 394 female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), found that a history of radiotherapy was not associated with a difference in serum 25(OH)D levels compared with those with breast cancer without prior radiotherapy (odds ratio, 0.90; 95% CI, 0.52-1.54).¹² From the limited existing literature specifically addressing variations of VD levels with radiation, radiation therapy does not appear to significantly impact VD levels.

Vitamin D Levels and the Severity of Chemotherapy- or Radiation Therapy–Induced AEs

A prospective cohort of 241 patients did not find an increase in the incidence or severity of chemotherapy-induced cutaneous toxicities in those with suboptimal 1,25(OH)₂D₃ levels (≤75 nmol/L).²⁰ Eight different primary cancer types were represented, including breast and colorectal cancer; the tumor stages of the participants were not detailed. Forty-one patients had normal 1,25(OH)₂D₃ levels, while the remaining 200 had suboptimal levels. There was no significant association between serum VD levels and the following dermatologic toxicities: desquamation (P=.26), xerosis (P=.15), mucositis (P=.30), or painful rash (P=.87). Surprisingly, nail changes and hand-foot reactions occurred with greater frequency in patients with normal VD levels (P=.01 and P=.03, respectively).²⁰ Hand-foot reaction is part of the toxic erythema of chemotherapy (TEC) spectrum, which is comprised of a range of cytotoxic skin injuries that typically manifest within 2 to 3 weeks of exposure to the offending chemotherapeutic agents, often characterized by erythema, pain, swelling, and blistering, particularly in intertriginous and acral areas.^21-23 Recovery from TEC generally takes at least 2 to 4 weeks and may necessitate cessation of the offending chemotherapeutic agent.^21,24 Notably, this study measured 1,25(OH)₂D₃ levels instead of 25(OH)D levels, which may not reliably indicate body stores of VD.^7,20 These results underscore the complex nature between chemotherapy and VD; however, VD levels alone do not appear to be a sufficient biomarker for predicting chemotherapy-associated cutaneous AEs.

Interestingly, radiation therapy–induced AEs may be associated with VD levels. A prospective cohort study of 98 patients with prostate, bladder, or gynecologic cancers (tumor stages were not detailed) undergoing pelvic radiotherapy found that females and males with 25(OH)D levels below a threshold of 35 and 40 nmol/L, respectively, were more likely to experience higher Radiation Therapy Oncology Group (RTOG) grade acute proctitis compared with those with VD above these thresholds.²⁵ Specifically, VD below these thresholds was associated with increased odds of RTOG grade 2 or higher radiation-induced proctitis (OR, 3.07; 95% CI, 1.27-7.50 [P=.013]). Additionally, a weak correlation was noted between VD below these thresholds and the RTOG grade, with a Spearman correlation value of −0.189 (P=.031).²⁵

One prospective cohort study included 28 patients with any cancer of the oral cavity, oropharynx, hypopharynx, or larynx stages II, III, or IVA; 93% (26/28) were stage III or IVA.²⁶ The 20 (71%) patients with suboptimal 25(OH)D levels (≤75 nmol/L) experienced a higher prevalence of grade II radiation dermatitis compared with the 8 (29%) patients with optimal VD levels (χ²₂=5.973; P=.0505). This pattern persisted with the severity of mucositis; patients from the suboptimal VD group presented with higher rates of grades II and III mucositis compared with the VD optimal group (χ²₂=13.627; P=.0011).²⁶ Recognizing the small cohort evaluated in the study, we highlight the importance of further studies to clarify these associations.

Chemotherapy-Induced Cutaneous Events Treated with High-Dose Vitamin D

Chemotherapeutic agents are known to induce cellular damage, resulting in a range of cutaneous AEs that can invoke discontinuation of otherwise effective chemotherapeutic interventions.^27,28 Recent research has explored the potential of high-dose vitamin D₃ as a therapeutic agent to mitigate cutaneous reactions.^29,30

A randomized, double-blind, placebo-controlled trial investigated the use of a single high dose of oral ­25(OH)D to treat topical nitrogen mustard (NM)–induced rash.²⁹ To characterize baseline inflammatory responses from NM injury without intervention, clinical measures, serum studies, and tissue analyses from skin biopsies were performed on 28 healthy adults after exposure to topical NM—a chemotherapeutic agent classified as a DNA alkylator. Two weeks later, participants were exposed to topical NM a second time and were split into 2 groups: 14 patients received a single 200,000-IU dose of oral 25(OH)D while the other 14 participants were given a placebo. Using the inflammatory markers induced from baseline exposure to NM alone, posttreatment analysis revealed that the punch biopsies from the 25(OH)D group expressed fewer NM-induced inflammatory markers compared with the placebo group at both 72 hours and 6 weeks following NM injury (72 hours: 12 vs 17 inflammatory markers; 6 weeks: 4 vs 11 inflammatory markers). Notably, NM inflammatory markers were enriched for IL-17 signaling pathways in the placebo biopsies but not in the 25(OH)D intervention group. This study also identified mild and severe patterns of inflammatory responses to NM that were independent of the 25(OH)D intervention. Biomarkers specific to skin biopsies from participants with the severe response included CCL20, CCL2, and CXCL8 (adjusted P<.05). At 6 weeks posttreatment, the 25(OH)D group showed a 67% reduction in NM injury markers compared with a 35% reduction in the placebo group. Despite a reduction in tissue inflammatory markers, there were no clinically significant changes observed in skin redness, swelling, or histologic structure when comparing the 25(OH)D- supplemented group to the placebo group at any time during the study, necessitating further research into the mechanistic roles of high doses VD supplementation.²⁹

Although Ernst et al²⁹ did not observe any clinically significant improvements with VD treatment, a case series of 6 patients with either glioblastoma multiforme, acute myeloid leukemia, or aplastic anemia did demonstrate clinical improvement of TEC after receiving high-dose vitamin D₃.³⁰ The mean time to onset of TEC was noted at 8.5 days following administration of the inciting chemotherapeutic agent, which included combinations of anthracycline, antimetabolite, kinase inhibitor, B-cell lymphoma 2 inhibitor, purine analogue, and alkylating agents. A combination of clinical and histologic findings was used to diagnose TEC. Baseline 25(OH)D levels were not established prior to treatment. The treatment regimen for 1 patient included 2 doses of 50,000 IU of VD spaced 1 week apart, totaling 100,000 IU, while the remaining 5 patients received a total of 200,000 IU, also split into 2 doses given 1 week apart. All patients received their first dose of VD within a week of the cutaneous eruption. Following the initial VD dose, there was a notable improvement in pain, pruritus, or swelling by the next day. Reduction in erythema also was observed within 1 to 4 days.³⁰

No AEs associated with VD supplementation were reported, suggesting a potential beneficial role of high-dose VD in accelerating recovery from chemotherapy-induced rashes without evident safety concerns.

Radiation Therapy–Induced Cutaneous Events Treated with High-Dose Vitamin D

Radiation dermatitis is a common and often severe complication of radiation therapy that affects more than 90% of patients undergoing treatment, with half of these individuals experiencing grade 2 toxicity, according to the National Cancer Institute’s Common Terminology Criteria for Adverse Events.^31,32 Radiation damage to basal keratinocytes and hair follicle stem cells disrupts the renewal of the skin’s outer layer, while a surge of free radicals causes irreversible DNA damage.³³ Symptoms of radiation dermatitis can vary from mild pink erythema to tissue ulceration and necrosis, typically within 1 to 4 weeks of radiation exposure.³⁴ The resulting dermatitis can take 2 to 4 weeks to heal, notably impacting patient quality of life and often necessitating modifications or interruptions in cancer therapy.³³

Prior studies have demonstrated the use of high-dose VD to improve the healing of UV-irradiated skin. A randomized controlled trial investigated high-dose vitamin D₃ to treat experimentally induced sunburn in 20 healthy adults. Compared with those who received a placebo, participants receiving the oral dose of 200,000 IU of vitamin D₃ demonstrated suppression of the pro-inflammatory mediators tumor necrosis factor α (P=.04) and inducible nitric oxide synthase (P=.02), while expression of tissue repair enhancer arginase 1 was increased (P<.005).³⁵ The mechanism of this enhanced tissue repair was investigated using a mouse model, in which intraperitoneal 25(OH)D was administered following severe UV-induced skin injury. On immunofluorescence microscopy, mice treated with VD showed enhanced autophagy within the macrophages infiltrating UV-irradiated skin.³⁶ The use of high-dose VD to treat UV-irradiated skin in these studies established a precedent for using VD to heal cutaneous injury caused by ionizing radiation therapy.

Some studies have focused on the role of VD for treating acute radiation dermatitis. A study of 23 patients with ductal carcinoma in situ or localized invasive ductal carcinoma breast cancer compared the effectiveness of topical calcipotriol to that of a standard hydrating ointment.³⁷ Participants were randomized to 1 of 2 treatments before starting adjuvant radiotherapy to evaluate their potential in preventing radiation dermatitis. In 87% (20/23) of these patients, no difference in skin reaction was observed between the 2 treatments, suggesting that topical VD application may not offer any advantage over the standard hydrating ointment for the prevention of radiation dermatitis.³⁷

Benefits of high-dose oral VD for treating radiation dermatitis also have been reported. Nguyen et al³⁸ documented 3 cases in which patients with neuroendocrine carcinoma of the pancreas, tonsillar carcinoma, and breast cancer received 200,000 IU of oral ergocalciferol distributed over 2 doses given 7 days apart for radiation dermatitis. These patients experienced substantial improvements in pain, swelling, and redness within a week of the initial dose. Additionally, a case of radiation recall dermatitis, which occurred a week after vinorelbine chemotherapy, was treated with 2 doses totaling 100,000 IU of oral ergocalciferol. This patient also had improvement in pain and swelling but continued to have tumor-related induration and ulceration.³⁹

Although topical VD did not show significant benefits over standard treatments for radiation dermatitis, high-dose oral VD appears promising in improving patient outcomes of pain and swelling more rapidly than current practices. Further research is needed to confirm these findings and establish standardized treatment protocols.

Final Thoughts

Suboptimal VD levels are prevalent in numerous cancer types. Chemotherapy often is associated with acute, potentially transient worsening of VD status in patients with breast and colorectal cancer. Although 25(OH)D levels have not corresponded with increased frequency of ­chemotherapy-related dermatologic AEs, suboptimal 25(OH)D levels appear to be associated with increased severity of radiation-induced mucositis and dermatitis.^20,25,26 The use of high-dose VD as a therapeutic agent shows promise in mitigating chemotherapy-induced and radiation therapy–induced rashes in multiple cancer types with reduction of inflammatory markers and a durable anti-inflammatory impact. Although the mechanisms of cellular injury vary among chemotherapeutic agents, the anti-inflammatory and tissue repair properties of VD may make it an effective treatment for chemotherapy-induced cutaneous damage regardless of injury mechanism.^2-4,35 However, reports of clinical improvement vary, and further objective studies to classify optimal dosing, administration, and outcome measures are needed. The absence of reported AEs associated with high-dose VD supplementation is encouraging, but selection of a safe and optimal dosing regimen can only occur with dedicated clinical trials.

Vitamin D (VD) regulates keratinocyte proliferation and differentiation, modulates inflammatory pathways, and protects against cellular damage in the skin. ¹ In the setting of tissue injury and acute skin inflammation, active vitamin D—1,25(OH) ₂ D—suppresses signaling from pro-inflammatory chemokines and cytokines such as IFN- γ and IL-17. ^2,3 This suppression reduces proliferation of helper T cells (T _H 1, T _H 17) and B cells, decreasing tissue damage from reactive oxygen species release while enhancing secretion of the anti-inflammatory cytokine IL-10 by antigen-presenting cells. ^2-4

Suboptimal VD levels have been associated with numerous health consequences including malignancy, prompting interest in VD supplementation for improving cancer-related outcomes.⁵ Beyond disease prognosis, high-dose VD supplementation has been suggested as a potential therapy for adverse events (AEs) related to cancer treatments. In one study, mice that received oral vitamin D₃ supplementation of 11,500 IU/kg daily had fewer doxorubicin-induced cardiotoxic effects on ejection fraction (P<.0001) and stroke volume (P<.01) than mice that received VD supplementation of 1500 IU/kg daily.⁶

In this review, we examine the impact of chemoradiation on 25(OH)D levels—which more accurately reflects VD stores than 1,25(OH)₂D levels—and the impact of suboptimal VD on cutaneous toxicities related to chemoradiation. To define the suboptimal VD threshold, we used the Endocrine Society’s clinical practice guidelines, which characterize suboptimal 25(OH)D levels as insufficiency (21–29 ng/mL [52.5–72.5 nmol/L]) or deficiency (<20 ng/mL [50 nmol/L])⁷; deficiency can be further categorized as severe deficiency (<12 ng/mL [30 nmol/L]).⁸ This review also evaluates the evidence for vitamin D₃ supplementation to alleviate the cutaneous AEs of chemotherapy and radiation treatments.

Effects of Chemotherapy on Vitamin D Levels

A high prevalence of VD deficiency is seen in various cancers. In a retrospective review of 25(OH)D levels in 2098 adults with solid tumors of any stage (6% had metastatic disease [n=124]), suboptimal levels were found in 69% of patients with breast cancer (n=617), 75% with colorectal cancer (n=84), 72% with gynecologic cancer (n=65), 79% with kidney and bladder cancer (n=145), 83% with pancreatic and upper gastrointestinal tract cancer (n=178), 73% with lung cancer (n=73), 69% with prostate cancer (n=225), 61% with skin cancer (n=399), and 63% with thyroid cancer (n=172).⁵ Suboptimal VD also has been found in hematologic malignancies. In a prospective cohort study, mean serum 25(OH)D levels in 23 patients with recently diagnosed acute myeloid leukemia demonstrated VD deficiency (mean [SD], 18.6 [6.6] nmol/L).⁹ Given that many patients already exhibit a baseline VD deficiency at cancer diagnosis, it is important to understand the relationship between VD and cancer treatment modalities.⁵

In the United States, breast and colorectal cancers were estimated to be the first and fourth most common cancers, with 313,510 and 152,810 predicted new cases in 2024, respectively.¹⁰ This review will focus on breast and colorectal cancer when describing VD variation associated with chemotherapy exposure due to their high prevalence.

Effects of Chemotherapy on Vitamin D Levels in Breast Cancer—Breast cancer studies have shown suboptimal VD levels in 76% of females 75 years or younger with any T1, T2, or T3; N0 or N1; and M0 breast cancer, in which 38.5% (n=197) had insufficient and 37.5% (n=192) had deficient 25(OH)D levels.¹¹ In a study of female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), VD deficiency was seen in 60% of patients not receiving VD supplementation.^12,13 A systematic review that included 7 studies of different types of breast cancer suggested that circulating 25(OH)D may be associated with improved prognosis.¹⁴ Thus, studies have investigated risk factors associated with poor or worsening VD status in individuals with breast cancer, including exposure to chemotherapy and/or radiation treatment.^12,15-18

A prospective cohort study assessed 25(OH)D levels in 95 patients with any breast cancer (stages I, II, IIIA, IIIB) before and after initiating chemotherapy with docetaxel, doxorubicin, epirubicin, 5-fluorouracil, or cyclophosphamide, compared with a group of 52 females without cancer.¹⁷ In the breast cancer group, approximately 80% (76/95) had suboptimal and 50% (47/95) had deficient VD levels before chemotherapy initiation (mean [SD], 54.1 [22.8] nmol/L). In the comparison group, 60% (31/52) had suboptimal and 30% (15/52) had deficient VD at baseline (mean [SD], 66.1 [23.5] nmol/L), which was higher than the breast cancer group (P=.03). A subgroup analysis excluded participants who started, stopped, or lacked data on dietary supplements containing VD (n=39); in the remaining 56 participants, a significant decrease in 25(OH)D levels was observed shortly after finishing chemotherapy compared with the prechemotherapy baseline value (mean, −7.9 nmol/L; P=.004). Notably, 6 months after chemotherapy completion, 25(OH)D levels increased (mean, +12.8 nmol/L; P<.001). Vitamin D levels remained stable in the comparison group (P=.987).¹⁷

Consistent with these findings, a cross-sectional study assessing VD status in 394 female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), found that a history of chemotherapy was associated with increased odds of 25(OH)D levels less than 20 ng/mL compared with breast cancer patients with no prior chemotherapy (odds ratio, 1.86; 95% CI, 1.03-3.38).¹² Although the study data included chemotherapy history, no information was provided on specific chemotherapy agents or regimens used in this cohort, limiting the ability to detect the drugs most often implicated.

Both studies indicated a complex interplay between chemotherapy and VD levels in breast cancer patients. Although Kok et al¹⁷ suggested a transient decrease in VD levels during chemotherapy with a subsequent recovery after cessation, Fassio et al¹² highlighted the increased odds of VD deficiency associated with chemotherapy. Ultimately, larger randomized controlled trials are needed to better understand the relationship between chemotherapy and VD status in breast cancer patients.

Effects of Chemotherapy on Vitamin D Levels in Colorectal Cancer—Similar to patterns seen in breast cancer, a systematic review with 6 studies of different types of colorectal cancer suggested that circulating 25(OH)D levels may be associated with prognosis.¹⁴ Studies also have investigated the relationship between colorectal chemotherapy regimens and VD status.^15,16,18,19

A retrospective study assessed 25(OH)D levels in 315 patients with any colorectal cancer (stage I–IV).¹⁵ Patients were included in the analysis if they received less than 400 IU daily of VD supplementation at baseline. For the whole study sample, the mean (SD) VD level was 23.7 (13.71) ng/mL. Patients who had not received chemotherapy within 3 months of the VD level assessment were categorized as the no chemotherapy group, and the others were designated as the chemotherapy group; the latter group was exposed to various chemotherapy regimens, including combinations of irinotecan, oxaliplatin, 5-fluorouracil, leucovorin, bevacizumab, or cetuximab. Multivariate analysis showed that the chemotherapy group was 3.7 times more likely to have very low VD levels (≤15 ng/mL) compared with those in the no chemotherapy group (P<.0001).¹⁵

A separate cross-sectional study examined serum 25(OH)D concentrations in 1201 patients with any newly diagnosed colorectal carcinoma (stage I–III); 91% of cases were adenocarcinoma.¹⁸ In a multivariate analysis, chemotherapy plus surgery was associated with lower VD levels than surgery alone 6 months after diagnosis (mean, −8.74 nmol/L; 95% CI, −11.30 to −6.18 nmol/L), specifically decreasing by a mean of 6.7 nmol/L (95% CI, −9.8 to −3.8 nmol/L) after adjusting for demographic and lifestyle factors.¹⁸ However, a prospective cohort study demonstrated different findings.¹⁹ Comparing 58 patients with newly diagnosed colorectal adenocarcinoma (stages I–IV) who underwent chemotherapy and 36 patients who did not receive chemotherapy, there was no significant change in 25(OH)D levels from the time of diagnosis to 6 months later. Median VD levels decreased by 0.7 ng/mL in those who received chemotherapy, while a minimal (and not significant) increase of 1.6 ng/mL was observed in those without chemotherapy intervention (P=.26). Notably, supplementation was not restricted in this cohort, which may have resulted in higher VD levels in those taking supplements.¹⁹

Since time of year and geographic location can influence VD levels, one prospective cohort study controlled for differential sun exposure due to these factors in their analysis.¹⁶ Assessment of 25(OH)D levels was completed in 81 chemotherapy-naïve cancer patients immediately before beginning chemotherapy as well as 6 and 12 weeks into treatment. More than 8 primary cancer types were represented in this study, with breast (34% [29/81]) and colorectal (14% [12/81]) cancer being the most common, but the cancer stages of the participants were not detailed. Vitamin D levels decreased after commencing chemotherapy, with the largest drop occurring 6 weeks into treatment. From the 6- to 12-week end points, VD increased but remained below the original baseline level (baseline: mean [SD], 49.2 [22.3] nmol/L; 6 weeks: mean [SD], 40.9 [19.0] nmol/L; 12 weeks: mean [SD], 45.9 [19.7] nmol/L; P=.05).¹⁶

Although focused on breast and colorectal cancers, these studies suggest that various chemotherapy regimens may confer a higher risk for VD deficiency compared with VD status at diagnosis and/or prior to chemotherapy treatment. However, most of these studies only discussed stage-based differences, excluding analysis of the variety of cancer subtypes that comprise breast and colorectal malignancies, which may limit our ability to extrapolate from these data. Ultimately, larger randomized controlled trials are needed to better understand the relationship between chemotherapy and VD status across various primary cancer types.

Effects of Radiation Therapy on Vitamin D Levels

Unlike chemotherapy, studies on the association between radiation therapy and VD levels are minimal, with most reports in the literature discussing the use of VD to potentiate the effects of radiation therapy. In one cross-sectional analysis of 1201 patients with newly diagnosed stage I, II, or III colorectal cancer of any type (94% were adenocarcinoma), radiation plus surgery was associated with slightly lower 25(OH)D levels than surgery alone for tumor treatment 6 months after diagnosis (mean, −3.17; 95% CI, −6.07 to −0.28 nmol/L). However, after adjustment for demographic and lifestyle factors, this decrease in VD levels attributable to radiotherapy was not statistically significant compared with the surgery-only cohort (mean, −1.78; 95% CI, −5.07 to 1.52 nmol/L).¹⁸

Similarly, a cross-sectional study assessing VD status in 394 female patients with primary breast cancer (stage I, II, or III and T1 with high Ki67 expression [≥30%], T2, or T3), found that a history of radiotherapy was not associated with a difference in serum 25(OH)D levels compared with those with breast cancer without prior radiotherapy (odds ratio, 0.90; 95% CI, 0.52-1.54).¹² From the limited existing literature specifically addressing variations of VD levels with radiation, radiation therapy does not appear to significantly impact VD levels.

Vitamin D Levels and the Severity of Chemotherapy- or Radiation Therapy–Induced AEs

A prospective cohort of 241 patients did not find an increase in the incidence or severity of chemotherapy-induced cutaneous toxicities in those with suboptimal 1,25(OH)₂D₃ levels (≤75 nmol/L).²⁰ Eight different primary cancer types were represented, including breast and colorectal cancer; the tumor stages of the participants were not detailed. Forty-one patients had normal 1,25(OH)₂D₃ levels, while the remaining 200 had suboptimal levels. There was no significant association between serum VD levels and the following dermatologic toxicities: desquamation (P=.26), xerosis (P=.15), mucositis (P=.30), or painful rash (P=.87). Surprisingly, nail changes and hand-foot reactions occurred with greater frequency in patients with normal VD levels (P=.01 and P=.03, respectively).²⁰ Hand-foot reaction is part of the toxic erythema of chemotherapy (TEC) spectrum, which is comprised of a range of cytotoxic skin injuries that typically manifest within 2 to 3 weeks of exposure to the offending chemotherapeutic agents, often characterized by erythema, pain, swelling, and blistering, particularly in intertriginous and acral areas.^21-23 Recovery from TEC generally takes at least 2 to 4 weeks and may necessitate cessation of the offending chemotherapeutic agent.^21,24 Notably, this study measured 1,25(OH)₂D₃ levels instead of 25(OH)D levels, which may not reliably indicate body stores of VD.^7,20 These results underscore the complex nature between chemotherapy and VD; however, VD levels alone do not appear to be a sufficient biomarker for predicting chemotherapy-associated cutaneous AEs.

Interestingly, radiation therapy–induced AEs may be associated with VD levels. A prospective cohort study of 98 patients with prostate, bladder, or gynecologic cancers (tumor stages were not detailed) undergoing pelvic radiotherapy found that females and males with 25(OH)D levels below a threshold of 35 and 40 nmol/L, respectively, were more likely to experience higher Radiation Therapy Oncology Group (RTOG) grade acute proctitis compared with those with VD above these thresholds.²⁵ Specifically, VD below these thresholds was associated with increased odds of RTOG grade 2 or higher radiation-induced proctitis (OR, 3.07; 95% CI, 1.27-7.50 [P=.013]). Additionally, a weak correlation was noted between VD below these thresholds and the RTOG grade, with a Spearman correlation value of −0.189 (P=.031).²⁵

One prospective cohort study included 28 patients with any cancer of the oral cavity, oropharynx, hypopharynx, or larynx stages II, III, or IVA; 93% (26/28) were stage III or IVA.²⁶ The 20 (71%) patients with suboptimal 25(OH)D levels (≤75 nmol/L) experienced a higher prevalence of grade II radiation dermatitis compared with the 8 (29%) patients with optimal VD levels (χ²₂=5.973; P=.0505). This pattern persisted with the severity of mucositis; patients from the suboptimal VD group presented with higher rates of grades II and III mucositis compared with the VD optimal group (χ²₂=13.627; P=.0011).²⁶ Recognizing the small cohort evaluated in the study, we highlight the importance of further studies to clarify these associations.

Chemotherapy-Induced Cutaneous Events Treated with High-Dose Vitamin D

Chemotherapeutic agents are known to induce cellular damage, resulting in a range of cutaneous AEs that can invoke discontinuation of otherwise effective chemotherapeutic interventions.^27,28 Recent research has explored the potential of high-dose vitamin D₃ as a therapeutic agent to mitigate cutaneous reactions.^29,30

A randomized, double-blind, placebo-controlled trial investigated the use of a single high dose of oral ­25(OH)D to treat topical nitrogen mustard (NM)–induced rash.²⁹ To characterize baseline inflammatory responses from NM injury without intervention, clinical measures, serum studies, and tissue analyses from skin biopsies were performed on 28 healthy adults after exposure to topical NM—a chemotherapeutic agent classified as a DNA alkylator. Two weeks later, participants were exposed to topical NM a second time and were split into 2 groups: 14 patients received a single 200,000-IU dose of oral 25(OH)D while the other 14 participants were given a placebo. Using the inflammatory markers induced from baseline exposure to NM alone, posttreatment analysis revealed that the punch biopsies from the 25(OH)D group expressed fewer NM-induced inflammatory markers compared with the placebo group at both 72 hours and 6 weeks following NM injury (72 hours: 12 vs 17 inflammatory markers; 6 weeks: 4 vs 11 inflammatory markers). Notably, NM inflammatory markers were enriched for IL-17 signaling pathways in the placebo biopsies but not in the 25(OH)D intervention group. This study also identified mild and severe patterns of inflammatory responses to NM that were independent of the 25(OH)D intervention. Biomarkers specific to skin biopsies from participants with the severe response included CCL20, CCL2, and CXCL8 (adjusted P<.05). At 6 weeks posttreatment, the 25(OH)D group showed a 67% reduction in NM injury markers compared with a 35% reduction in the placebo group. Despite a reduction in tissue inflammatory markers, there were no clinically significant changes observed in skin redness, swelling, or histologic structure when comparing the 25(OH)D- supplemented group to the placebo group at any time during the study, necessitating further research into the mechanistic roles of high doses VD supplementation.²⁹

Although Ernst et al²⁹ did not observe any clinically significant improvements with VD treatment, a case series of 6 patients with either glioblastoma multiforme, acute myeloid leukemia, or aplastic anemia did demonstrate clinical improvement of TEC after receiving high-dose vitamin D₃.³⁰ The mean time to onset of TEC was noted at 8.5 days following administration of the inciting chemotherapeutic agent, which included combinations of anthracycline, antimetabolite, kinase inhibitor, B-cell lymphoma 2 inhibitor, purine analogue, and alkylating agents. A combination of clinical and histologic findings was used to diagnose TEC. Baseline 25(OH)D levels were not established prior to treatment. The treatment regimen for 1 patient included 2 doses of 50,000 IU of VD spaced 1 week apart, totaling 100,000 IU, while the remaining 5 patients received a total of 200,000 IU, also split into 2 doses given 1 week apart. All patients received their first dose of VD within a week of the cutaneous eruption. Following the initial VD dose, there was a notable improvement in pain, pruritus, or swelling by the next day. Reduction in erythema also was observed within 1 to 4 days.³⁰

No AEs associated with VD supplementation were reported, suggesting a potential beneficial role of high-dose VD in accelerating recovery from chemotherapy-induced rashes without evident safety concerns.

Radiation Therapy–Induced Cutaneous Events Treated with High-Dose Vitamin D

Radiation dermatitis is a common and often severe complication of radiation therapy that affects more than 90% of patients undergoing treatment, with half of these individuals experiencing grade 2 toxicity, according to the National Cancer Institute’s Common Terminology Criteria for Adverse Events.^31,32 Radiation damage to basal keratinocytes and hair follicle stem cells disrupts the renewal of the skin’s outer layer, while a surge of free radicals causes irreversible DNA damage.³³ Symptoms of radiation dermatitis can vary from mild pink erythema to tissue ulceration and necrosis, typically within 1 to 4 weeks of radiation exposure.³⁴ The resulting dermatitis can take 2 to 4 weeks to heal, notably impacting patient quality of life and often necessitating modifications or interruptions in cancer therapy.³³

Prior studies have demonstrated the use of high-dose VD to improve the healing of UV-irradiated skin. A randomized controlled trial investigated high-dose vitamin D₃ to treat experimentally induced sunburn in 20 healthy adults. Compared with those who received a placebo, participants receiving the oral dose of 200,000 IU of vitamin D₃ demonstrated suppression of the pro-inflammatory mediators tumor necrosis factor α (P=.04) and inducible nitric oxide synthase (P=.02), while expression of tissue repair enhancer arginase 1 was increased (P<.005).³⁵ The mechanism of this enhanced tissue repair was investigated using a mouse model, in which intraperitoneal 25(OH)D was administered following severe UV-induced skin injury. On immunofluorescence microscopy, mice treated with VD showed enhanced autophagy within the macrophages infiltrating UV-irradiated skin.³⁶ The use of high-dose VD to treat UV-irradiated skin in these studies established a precedent for using VD to heal cutaneous injury caused by ionizing radiation therapy.

Some studies have focused on the role of VD for treating acute radiation dermatitis. A study of 23 patients with ductal carcinoma in situ or localized invasive ductal carcinoma breast cancer compared the effectiveness of topical calcipotriol to that of a standard hydrating ointment.³⁷ Participants were randomized to 1 of 2 treatments before starting adjuvant radiotherapy to evaluate their potential in preventing radiation dermatitis. In 87% (20/23) of these patients, no difference in skin reaction was observed between the 2 treatments, suggesting that topical VD application may not offer any advantage over the standard hydrating ointment for the prevention of radiation dermatitis.³⁷

Benefits of high-dose oral VD for treating radiation dermatitis also have been reported. Nguyen et al³⁸ documented 3 cases in which patients with neuroendocrine carcinoma of the pancreas, tonsillar carcinoma, and breast cancer received 200,000 IU of oral ergocalciferol distributed over 2 doses given 7 days apart for radiation dermatitis. These patients experienced substantial improvements in pain, swelling, and redness within a week of the initial dose. Additionally, a case of radiation recall dermatitis, which occurred a week after vinorelbine chemotherapy, was treated with 2 doses totaling 100,000 IU of oral ergocalciferol. This patient also had improvement in pain and swelling but continued to have tumor-related induration and ulceration.³⁹

Although topical VD did not show significant benefits over standard treatments for radiation dermatitis, high-dose oral VD appears promising in improving patient outcomes of pain and swelling more rapidly than current practices. Further research is needed to confirm these findings and establish standardized treatment protocols.

Final Thoughts

Suboptimal VD levels are prevalent in numerous cancer types. Chemotherapy often is associated with acute, potentially transient worsening of VD status in patients with breast and colorectal cancer. Although 25(OH)D levels have not corresponded with increased frequency of ­chemotherapy-related dermatologic AEs, suboptimal 25(OH)D levels appear to be associated with increased severity of radiation-induced mucositis and dermatitis.^20,25,26 The use of high-dose VD as a therapeutic agent shows promise in mitigating chemotherapy-induced and radiation therapy–induced rashes in multiple cancer types with reduction of inflammatory markers and a durable anti-inflammatory impact. Although the mechanisms of cellular injury vary among chemotherapeutic agents, the anti-inflammatory and tissue repair properties of VD may make it an effective treatment for chemotherapy-induced cutaneous damage regardless of injury mechanism.^2-4,35 However, reports of clinical improvement vary, and further objective studies to classify optimal dosing, administration, and outcome measures are needed. The absence of reported AEs associated with high-dose VD supplementation is encouraging, but selection of a safe and optimal dosing regimen can only occur with dedicated clinical trials.

Frontal fibrosing alopecia (FFA) has become increasingly common since it was first described in 1994.¹ A positive correlation between FFA and the use of sunscreens was reported in an observational study.² The geographic distribution of this association has spanned the United Kingdom (UK), Europe, and Asia, though data from the United States are lacking. Various international studies have demonstrated an association between FFA and sunscreen use, further exemplifying this stark contrast.

In the United Kingdom (UK), Aldoori et al² found that women who used sunscreen at least twice weekly had 2 times the likelihood of developing FFA compared with women who did not use sunscreen regularly. Kidambi et al³ found similar results in UK men with FFA who had higher rates of primary sunscreen use and higher rates of at least twice-weekly use of facial moisturizer with unspecified sunscreen content.

These associations between FFA and sunscreen use are not unique to the UK. A study conducted in Spain identified a statistical association between FFA and use of facial sunscreen in women (odds ratio, 1.6 [95% CI, 1.06-2.41]) and men (odds ratio, 1.84 [95% CI, 1.04-3.23]).⁴ In Thailand, FFA was nearly twice as likely to be present in patients with regular sunscreen use compared to controls who did not apply sunscreen regularly.⁵ Interestingly, a Brazilian study showed no connection between sunscreen use and FFA. Instead, FFA was associated with hair straightening with formalin or use of facial soap orfacial moisturizer.⁶ An international systematic review of 1248 patients with FFA and 1459 controls determined that sunscreen users were 2.21 times more likely to develop FFA than their counterparts who did not use sunscreen regularly.⁷

Quite glaring is the lack of data from the United States, which could be used to compare FFA and sunscreen associations to other nations. It is possible that certain regions of the world such as the United States may not have an increased risk for FFA in sunscreen users due to other environmental factors, differing sunscreen application practices, or differing chemical ingredients. At the same time, many other countries cannot afford or lack access to sunscreens or facial moisturizers, which is an additional variable that may complicate this association. These populations need to be studied to determine whether they are as susceptible to FFA as those who use sunscreen regularly around the world.

Another underlying factor supporting this association is the inherent need for sunscreen use. For instance, research has shown that patients with FFA had higher rates of actinic skin damage, which could explain increased sunscreen use.⁸

To make more clear and distinct claims, further studies are needed in regions that are known to use sunscreen extensively (eg, United States) to compare with their European, Asian, and South American counterparts. Moreover, it also is important to study regions where sunscreen access is limited and whether there is FFA development in these populations.

Given the potential association between sunscreen use and FFA, dermatologists can take a cautious approach tailored to the patient by recommending noncomedogenic mineral sunscreens with zinc or titanium oxide, which are less irritating than chemical sunscreens. Avoidance of sunscreen application to the hairline and use of additional sun-protection methods such as broad-brimmed hats also should be emphasized.

Frontal fibrosing alopecia (FFA) has become increasingly common since it was first described in 1994.¹ A positive correlation between FFA and the use of sunscreens was reported in an observational study.² The geographic distribution of this association has spanned the United Kingdom (UK), Europe, and Asia, though data from the United States are lacking. Various international studies have demonstrated an association between FFA and sunscreen use, further exemplifying this stark contrast.

In the United Kingdom (UK), Aldoori et al² found that women who used sunscreen at least twice weekly had 2 times the likelihood of developing FFA compared with women who did not use sunscreen regularly. Kidambi et al³ found similar results in UK men with FFA who had higher rates of primary sunscreen use and higher rates of at least twice-weekly use of facial moisturizer with unspecified sunscreen content.

These associations between FFA and sunscreen use are not unique to the UK. A study conducted in Spain identified a statistical association between FFA and use of facial sunscreen in women (odds ratio, 1.6 [95% CI, 1.06-2.41]) and men (odds ratio, 1.84 [95% CI, 1.04-3.23]).⁴ In Thailand, FFA was nearly twice as likely to be present in patients with regular sunscreen use compared to controls who did not apply sunscreen regularly.⁵ Interestingly, a Brazilian study showed no connection between sunscreen use and FFA. Instead, FFA was associated with hair straightening with formalin or use of facial soap orfacial moisturizer.⁶ An international systematic review of 1248 patients with FFA and 1459 controls determined that sunscreen users were 2.21 times more likely to develop FFA than their counterparts who did not use sunscreen regularly.⁷

Quite glaring is the lack of data from the United States, which could be used to compare FFA and sunscreen associations to other nations. It is possible that certain regions of the world such as the United States may not have an increased risk for FFA in sunscreen users due to other environmental factors, differing sunscreen application practices, or differing chemical ingredients. At the same time, many other countries cannot afford or lack access to sunscreens or facial moisturizers, which is an additional variable that may complicate this association. These populations need to be studied to determine whether they are as susceptible to FFA as those who use sunscreen regularly around the world.

Another underlying factor supporting this association is the inherent need for sunscreen use. For instance, research has shown that patients with FFA had higher rates of actinic skin damage, which could explain increased sunscreen use.⁸

To make more clear and distinct claims, further studies are needed in regions that are known to use sunscreen extensively (eg, United States) to compare with their European, Asian, and South American counterparts. Moreover, it also is important to study regions where sunscreen access is limited and whether there is FFA development in these populations.

Given the potential association between sunscreen use and FFA, dermatologists can take a cautious approach tailored to the patient by recommending noncomedogenic mineral sunscreens with zinc or titanium oxide, which are less irritating than chemical sunscreens. Avoidance of sunscreen application to the hairline and use of additional sun-protection methods such as broad-brimmed hats also should be emphasized.

Frontal fibrosing alopecia (FFA) has become increasingly common since it was first described in 1994.¹ A positive correlation between FFA and the use of sunscreens was reported in an observational study.² The geographic distribution of this association has spanned the United Kingdom (UK), Europe, and Asia, though data from the United States are lacking. Various international studies have demonstrated an association between FFA and sunscreen use, further exemplifying this stark contrast.

In the United Kingdom (UK), Aldoori et al² found that women who used sunscreen at least twice weekly had 2 times the likelihood of developing FFA compared with women who did not use sunscreen regularly. Kidambi et al³ found similar results in UK men with FFA who had higher rates of primary sunscreen use and higher rates of at least twice-weekly use of facial moisturizer with unspecified sunscreen content.

These associations between FFA and sunscreen use are not unique to the UK. A study conducted in Spain identified a statistical association between FFA and use of facial sunscreen in women (odds ratio, 1.6 [95% CI, 1.06-2.41]) and men (odds ratio, 1.84 [95% CI, 1.04-3.23]).⁴ In Thailand, FFA was nearly twice as likely to be present in patients with regular sunscreen use compared to controls who did not apply sunscreen regularly.⁵ Interestingly, a Brazilian study showed no connection between sunscreen use and FFA. Instead, FFA was associated with hair straightening with formalin or use of facial soap orfacial moisturizer.⁶ An international systematic review of 1248 patients with FFA and 1459 controls determined that sunscreen users were 2.21 times more likely to develop FFA than their counterparts who did not use sunscreen regularly.⁷

Quite glaring is the lack of data from the United States, which could be used to compare FFA and sunscreen associations to other nations. It is possible that certain regions of the world such as the United States may not have an increased risk for FFA in sunscreen users due to other environmental factors, differing sunscreen application practices, or differing chemical ingredients. At the same time, many other countries cannot afford or lack access to sunscreens or facial moisturizers, which is an additional variable that may complicate this association. These populations need to be studied to determine whether they are as susceptible to FFA as those who use sunscreen regularly around the world.

Another underlying factor supporting this association is the inherent need for sunscreen use. For instance, research has shown that patients with FFA had higher rates of actinic skin damage, which could explain increased sunscreen use.⁸

To make more clear and distinct claims, further studies are needed in regions that are known to use sunscreen extensively (eg, United States) to compare with their European, Asian, and South American counterparts. Moreover, it also is important to study regions where sunscreen access is limited and whether there is FFA development in these populations.

Given the potential association between sunscreen use and FFA, dermatologists can take a cautious approach tailored to the patient by recommending noncomedogenic mineral sunscreens with zinc or titanium oxide, which are less irritating than chemical sunscreens. Avoidance of sunscreen application to the hairline and use of additional sun-protection methods such as broad-brimmed hats also should be emphasized.

To the Editor:

We read with interest the case reported by Yanovsky et al¹ (Cutis. 2023;112:E23-E25). We thank the authors for updating our knowledge about atopic dermatitis (AD) and omalizumab and improving our understanding of the various wanted and unwanted effects that may manifest with omalizumab. We wish to clarify a few points on omalizumab use.

First, Yanovsky et al¹ reported that their patient’s AD flares occurred within a few days after omalizumab injections to control asthma, possibly because omalizumab may have caused a paradoxical increase in sensitivity to other cytokines such as IL-33 in basophils and increased IL-4/IL-13 production in the skin. The authors cited Imai² to explain that IL-33 plays a role in the pathogenesis of AD, increases itching, and disrupts the skin barrier. However, Imai² did not discuss a relationship with omalizumab. As a recombinant humanized IgG1 monoclonal anti-IgE antibody, omalizumab works by interacting with the high-affinity receptor Fc epsilon RI that typically is found on eosinophils, mast cells, and basophils and plays a critical role in preventing the allergic cascade.³ We could not find any studies in the literature regarding omalizumab having a specific effect on the skin, causing cytokine imbalance, or increasing IL-4/IL-13 levels.

Second, the case report indicated that AD lesions improved with the biologic dupilumab,¹ which seems amazing. Dupilumab is a monoclonal antibody used in patients with moderate to severe AD that blocks IL-4/IL-13 signaling and thus inhibits receptor signaling downstream of the Janus kinase signal transducer and activator of transcription protein pathway.⁴ It also has been shown to be beneficial in children with moderate to severe uncontrolled asthma.⁵ In vivo studies are needed to learn about the effects of these biologics on asthma and AD, whose complex immunologic effects are increasingly well understood by real patient experience.

Third, omalizumab has been found to relieve AD, not exacerbate it, in our own experience with 7 patients (unpublished data, 2024) and randomized controlled trials.⁶

Fourth, Yanovsky et al¹ reported that the patient’s lesions flared up within a few days after taking omalizumab, which suggests a non-IgE delayed reaction. Could this reaction be related to polysorbate 20 used as an excipient in the commercial preparation? When we examined both preparations, the presence of polysorbate 80 in dupilumab was noteworthy,⁷ unlike omalizumab. We suggest the authors perform a patch test including polysorbate 20 and polysorbate 80.

Finally, the authors mentioned that omalizumab may cause a paradoxical exacerbation of AD in certain patients, as in tumor necrosis factor α inhibitor–induced psoriasis.⁸ This has been reported,⁸ but tumor necrosis factor α inhibitors are cytokine inhibitors and can lead to cytokine imbalance, while omalizumab is an IgE inhibitor.

Yanovsky et al¹ described AD flares as “triggered by omalizumab,” which we believe was not the case. Because this patient had chronic AD, other causes of AD exacerbation in this patient could include stress or infection. Also, when they say that AD is triggered or induced, it implies that they are attributing the occurrence/development of AD in this patient to omalizumab. Of course, this also is not true.

Author’s Response

Thank you for your thoughtful comments. Although we agree that we cannot prove omalizumab was the cause of our patient’s AD flares, the new onset of severely worsening disease that was exacerbated by each dose of omalizumab as well as subsequent resolution upon switching to dupilumab was highly suggestive for a causal relationship. Our goal was to alert physicians to the possibility of this phenomenon and to encourage further study.

Karen A. Chernoff, MD
From the Department of Dermatology, Weill Cornell Medical College, New York, New York.
The author has no relevant financial disclosures to report.

To the Editor:

We read with interest the case reported by Yanovsky et al¹ (Cutis. 2023;112:E23-E25). We thank the authors for updating our knowledge about atopic dermatitis (AD) and omalizumab and improving our understanding of the various wanted and unwanted effects that may manifest with omalizumab. We wish to clarify a few points on omalizumab use.

First, Yanovsky et al¹ reported that their patient’s AD flares occurred within a few days after omalizumab injections to control asthma, possibly because omalizumab may have caused a paradoxical increase in sensitivity to other cytokines such as IL-33 in basophils and increased IL-4/IL-13 production in the skin. The authors cited Imai² to explain that IL-33 plays a role in the pathogenesis of AD, increases itching, and disrupts the skin barrier. However, Imai² did not discuss a relationship with omalizumab. As a recombinant humanized IgG1 monoclonal anti-IgE antibody, omalizumab works by interacting with the high-affinity receptor Fc epsilon RI that typically is found on eosinophils, mast cells, and basophils and plays a critical role in preventing the allergic cascade.³ We could not find any studies in the literature regarding omalizumab having a specific effect on the skin, causing cytokine imbalance, or increasing IL-4/IL-13 levels.

Second, the case report indicated that AD lesions improved with the biologic dupilumab,¹ which seems amazing. Dupilumab is a monoclonal antibody used in patients with moderate to severe AD that blocks IL-4/IL-13 signaling and thus inhibits receptor signaling downstream of the Janus kinase signal transducer and activator of transcription protein pathway.⁴ It also has been shown to be beneficial in children with moderate to severe uncontrolled asthma.⁵ In vivo studies are needed to learn about the effects of these biologics on asthma and AD, whose complex immunologic effects are increasingly well understood by real patient experience.

Third, omalizumab has been found to relieve AD, not exacerbate it, in our own experience with 7 patients (unpublished data, 2024) and randomized controlled trials.⁶

Fourth, Yanovsky et al¹ reported that the patient’s lesions flared up within a few days after taking omalizumab, which suggests a non-IgE delayed reaction. Could this reaction be related to polysorbate 20 used as an excipient in the commercial preparation? When we examined both preparations, the presence of polysorbate 80 in dupilumab was noteworthy,⁷ unlike omalizumab. We suggest the authors perform a patch test including polysorbate 20 and polysorbate 80.

Finally, the authors mentioned that omalizumab may cause a paradoxical exacerbation of AD in certain patients, as in tumor necrosis factor α inhibitor–induced psoriasis.⁸ This has been reported,⁸ but tumor necrosis factor α inhibitors are cytokine inhibitors and can lead to cytokine imbalance, while omalizumab is an IgE inhibitor.

Yanovsky et al¹ described AD flares as “triggered by omalizumab,” which we believe was not the case. Because this patient had chronic AD, other causes of AD exacerbation in this patient could include stress or infection. Also, when they say that AD is triggered or induced, it implies that they are attributing the occurrence/development of AD in this patient to omalizumab. Of course, this also is not true.

Author’s Response

Thank you for your thoughtful comments. Although we agree that we cannot prove omalizumab was the cause of our patient’s AD flares, the new onset of severely worsening disease that was exacerbated by each dose of omalizumab as well as subsequent resolution upon switching to dupilumab was highly suggestive for a causal relationship. Our goal was to alert physicians to the possibility of this phenomenon and to encourage further study.

Karen A. Chernoff, MD
From the Department of Dermatology, Weill Cornell Medical College, New York, New York.
The author has no relevant financial disclosures to report.

To the Editor:

We read with interest the case reported by Yanovsky et al¹ (Cutis. 2023;112:E23-E25). We thank the authors for updating our knowledge about atopic dermatitis (AD) and omalizumab and improving our understanding of the various wanted and unwanted effects that may manifest with omalizumab. We wish to clarify a few points on omalizumab use.

First, Yanovsky et al¹ reported that their patient’s AD flares occurred within a few days after omalizumab injections to control asthma, possibly because omalizumab may have caused a paradoxical increase in sensitivity to other cytokines such as IL-33 in basophils and increased IL-4/IL-13 production in the skin. The authors cited Imai² to explain that IL-33 plays a role in the pathogenesis of AD, increases itching, and disrupts the skin barrier. However, Imai² did not discuss a relationship with omalizumab. As a recombinant humanized IgG1 monoclonal anti-IgE antibody, omalizumab works by interacting with the high-affinity receptor Fc epsilon RI that typically is found on eosinophils, mast cells, and basophils and plays a critical role in preventing the allergic cascade.³ We could not find any studies in the literature regarding omalizumab having a specific effect on the skin, causing cytokine imbalance, or increasing IL-4/IL-13 levels.

Second, the case report indicated that AD lesions improved with the biologic dupilumab,¹ which seems amazing. Dupilumab is a monoclonal antibody used in patients with moderate to severe AD that blocks IL-4/IL-13 signaling and thus inhibits receptor signaling downstream of the Janus kinase signal transducer and activator of transcription protein pathway.⁴ It also has been shown to be beneficial in children with moderate to severe uncontrolled asthma.⁵ In vivo studies are needed to learn about the effects of these biologics on asthma and AD, whose complex immunologic effects are increasingly well understood by real patient experience.

Third, omalizumab has been found to relieve AD, not exacerbate it, in our own experience with 7 patients (unpublished data, 2024) and randomized controlled trials.⁶

Fourth, Yanovsky et al¹ reported that the patient’s lesions flared up within a few days after taking omalizumab, which suggests a non-IgE delayed reaction. Could this reaction be related to polysorbate 20 used as an excipient in the commercial preparation? When we examined both preparations, the presence of polysorbate 80 in dupilumab was noteworthy,⁷ unlike omalizumab. We suggest the authors perform a patch test including polysorbate 20 and polysorbate 80.

Finally, the authors mentioned that omalizumab may cause a paradoxical exacerbation of AD in certain patients, as in tumor necrosis factor α inhibitor–induced psoriasis.⁸ This has been reported,⁸ but tumor necrosis factor α inhibitors are cytokine inhibitors and can lead to cytokine imbalance, while omalizumab is an IgE inhibitor.

Yanovsky et al¹ described AD flares as “triggered by omalizumab,” which we believe was not the case. Because this patient had chronic AD, other causes of AD exacerbation in this patient could include stress or infection. Also, when they say that AD is triggered or induced, it implies that they are attributing the occurrence/development of AD in this patient to omalizumab. Of course, this also is not true.

Author’s Response

Thank you for your thoughtful comments. Although we agree that we cannot prove omalizumab was the cause of our patient’s AD flares, the new onset of severely worsening disease that was exacerbated by each dose of omalizumab as well as subsequent resolution upon switching to dupilumab was highly suggestive for a causal relationship. Our goal was to alert physicians to the possibility of this phenomenon and to encourage further study.

Karen A. Chernoff, MD
From the Department of Dermatology, Weill Cornell Medical College, New York, New York.
The author has no relevant financial disclosures to report.

There is a well-established connection between the mind and the skin, and it is clear that this relationship is bidirectional—not only does skin disease increase the risk for depression, anxiety, sleep disturbance, and suicidality, but psychologic stress actually can worsen skin disease through multiple mechanisms, including direct damage to the skin barrier.^1,2 Psychologic stress also impacts the microbiome, another critical driver of skin disease.^3,4 The concept of the itch-scratch cycle vividly illustrates the vicious interplay between the mind and body in atopic dermatitis (AD).

However, patients with AD are not the only ones impacted—caregivers also experience psychologic stress. Remarkably, one study of patients with AD and their caregivers found that the caregivers actually reported significantly worse mental health and anxiety (P=.01 and P=.03, respectively) than patients themselves, even when controlling for the severity of disease.⁵

Thus, it would seem obvious for mental health to be a central component of AD care—to improve patient and caregiver quality of life while also improving symptoms. Research has actually borne this out, with one systematic review and meta-analysis concluding that psychological intervention has a beneficial effect on AD,⁶ and another that the addition of psychological and educational interventions to conventional treatment provided better therapeutic results in alleviating eczema severity and psychological symptoms.⁷ One study demonstrated that patients with AD who received cognitive behavioral therapy via the internet displayed a statistically significant improvement in their disease (P<.001) as measured by the Patient-Oriented Eczema Measure compared with those in the control group who received standard care alone. They also reported improvements in perceived stress, sleep problems, and depression in the intervention group that were sustained at 1-year follow-up.⁸ These findings are particularly impactful because clinical results were achieved while leveraging an internet-based approach to therapy.

Regrettably, despite the preponderance of evidence supporting the connection between mental health and AD, there remain considerable unmet needs. A recent cross-sectional survey of 954 adults with AD and caregivers of children with AD (N=954) conducted by the National Eczema Association found that half of patients were never asked about mental health during any of their visits, and of those referred for mental health resources, only 57% utilized the recommended services.⁹ Importantly, patients aged 18 to 34 years reported wanting to be asked about mental health. Of those who did receive referrals, most were for counseling services (23%), followed by alternative mental health therapy such as music or art therapy (15%), cognitive behavioral therapy (13%), or peer/social support groups (12%). Approximately 10% reported receiving a pamphlet or a brochure only.⁹

Physicians who treat patients with AD can and must do better, but first we must explore why these referral rates are so low. As with many complex problems, there is unlikely to be one simple unifying reason. As expected, the answer is nuanced and multifaceted, and—most importantly—staggeringly incomplete.

For starters, mental health interventions rarely are as easy as applying a cream or taking a pill. Hedman-Lagerlöf et al⁸ specifically pointed out that although their approach—using internet-based cognitive behavioral therapy—was explicitly designed to be more accessible with fewer resources, it required approximately 35 hours of treatment over 12 weeks, requiring both substantial time and commitment from patients who often are already burned out and exhausted due to AD. They even underscored that the most commonly reported adverse effect of therapy was increased stress or worry, making it a difficult sell.⁸

Even before most patients have a chance to consider the time required and the potential adverse effects of mental health interventions for AD, greater hurdles exist. Finances, medical insurance, and wait times were highlighted as barriers to care in a systematic review.¹⁰ These are deep-seated problems in the United States; while they may be surmountable in certain geo­graphic areas, the frequency with which these concerns arise means that it does not take too many failed attempts at referring patients for mental health services before clinicians just give up—similar to any form of operant conditioning.

A more elusive concept is stigmatization. Although it may not be quantifiable, the idea is that patients may encounter additional challenges when seeking mental health care, either because the interactions themselves may worsen their symptoms (eg, increased anxiety) or they may be more likely to have a negative perception of the experience.¹¹ A 2020 systematic review of barriers to addressing common mental health problems found that stigma was the most prominent barrier in adolescents, with the second most prominent being negative attitudes and beliefs about mental health services and professionals.¹² As a clinician, I can attest that I have sometimes detected skepticism when I have suggested mental health services to patients and have even been asked outright if I thought the problem was all in their head. My patients with AD generally have been much more open to the idea of mental health support, especially after I explain the powerful mind-body connection, than patients with other conditions—most notably delusions of parasitosis—who have been much more dismissive of such overtures. An oft-cited paper from 1976 frames the problem perfectly, describing what can happen after a referral for mental health services.¹³ The authors stated that the suggestion of mental health makes patients feel that the dermatologist does not believe them in the first place. Beyond this, the authors pointed out that referring the patient elsewhere reduces their hopes for dermatologic treatment.¹³

Knowing now—perhaps more than ever before—that the mind and skin are intimately connected compels us to solve these problems and find ways around these obstacles. Selecting the optimal forms of mental health services for each patient, having the structural support of the health care system, and winning the trust of patients and caregivers while combating stigma are undoubtedly tall orders; however, understanding the stakes for patients with AD, their caregivers, and society as a whole should inspire us to keep pushing forward.

There is a well-established connection between the mind and the skin, and it is clear that this relationship is bidirectional—not only does skin disease increase the risk for depression, anxiety, sleep disturbance, and suicidality, but psychologic stress actually can worsen skin disease through multiple mechanisms, including direct damage to the skin barrier.^1,2 Psychologic stress also impacts the microbiome, another critical driver of skin disease.^3,4 The concept of the itch-scratch cycle vividly illustrates the vicious interplay between the mind and body in atopic dermatitis (AD).

However, patients with AD are not the only ones impacted—caregivers also experience psychologic stress. Remarkably, one study of patients with AD and their caregivers found that the caregivers actually reported significantly worse mental health and anxiety (P=.01 and P=.03, respectively) than patients themselves, even when controlling for the severity of disease.⁵

Thus, it would seem obvious for mental health to be a central component of AD care—to improve patient and caregiver quality of life while also improving symptoms. Research has actually borne this out, with one systematic review and meta-analysis concluding that psychological intervention has a beneficial effect on AD,⁶ and another that the addition of psychological and educational interventions to conventional treatment provided better therapeutic results in alleviating eczema severity and psychological symptoms.⁷ One study demonstrated that patients with AD who received cognitive behavioral therapy via the internet displayed a statistically significant improvement in their disease (P<.001) as measured by the Patient-Oriented Eczema Measure compared with those in the control group who received standard care alone. They also reported improvements in perceived stress, sleep problems, and depression in the intervention group that were sustained at 1-year follow-up.⁸ These findings are particularly impactful because clinical results were achieved while leveraging an internet-based approach to therapy.

Regrettably, despite the preponderance of evidence supporting the connection between mental health and AD, there remain considerable unmet needs. A recent cross-sectional survey of 954 adults with AD and caregivers of children with AD (N=954) conducted by the National Eczema Association found that half of patients were never asked about mental health during any of their visits, and of those referred for mental health resources, only 57% utilized the recommended services.⁹ Importantly, patients aged 18 to 34 years reported wanting to be asked about mental health. Of those who did receive referrals, most were for counseling services (23%), followed by alternative mental health therapy such as music or art therapy (15%), cognitive behavioral therapy (13%), or peer/social support groups (12%). Approximately 10% reported receiving a pamphlet or a brochure only.⁹

Physicians who treat patients with AD can and must do better, but first we must explore why these referral rates are so low. As with many complex problems, there is unlikely to be one simple unifying reason. As expected, the answer is nuanced and multifaceted, and—most importantly—staggeringly incomplete.

For starters, mental health interventions rarely are as easy as applying a cream or taking a pill. Hedman-Lagerlöf et al⁸ specifically pointed out that although their approach—using internet-based cognitive behavioral therapy—was explicitly designed to be more accessible with fewer resources, it required approximately 35 hours of treatment over 12 weeks, requiring both substantial time and commitment from patients who often are already burned out and exhausted due to AD. They even underscored that the most commonly reported adverse effect of therapy was increased stress or worry, making it a difficult sell.⁸

Even before most patients have a chance to consider the time required and the potential adverse effects of mental health interventions for AD, greater hurdles exist. Finances, medical insurance, and wait times were highlighted as barriers to care in a systematic review.¹⁰ These are deep-seated problems in the United States; while they may be surmountable in certain geo­graphic areas, the frequency with which these concerns arise means that it does not take too many failed attempts at referring patients for mental health services before clinicians just give up—similar to any form of operant conditioning.

A more elusive concept is stigmatization. Although it may not be quantifiable, the idea is that patients may encounter additional challenges when seeking mental health care, either because the interactions themselves may worsen their symptoms (eg, increased anxiety) or they may be more likely to have a negative perception of the experience.¹¹ A 2020 systematic review of barriers to addressing common mental health problems found that stigma was the most prominent barrier in adolescents, with the second most prominent being negative attitudes and beliefs about mental health services and professionals.¹² As a clinician, I can attest that I have sometimes detected skepticism when I have suggested mental health services to patients and have even been asked outright if I thought the problem was all in their head. My patients with AD generally have been much more open to the idea of mental health support, especially after I explain the powerful mind-body connection, than patients with other conditions—most notably delusions of parasitosis—who have been much more dismissive of such overtures. An oft-cited paper from 1976 frames the problem perfectly, describing what can happen after a referral for mental health services.¹³ The authors stated that the suggestion of mental health makes patients feel that the dermatologist does not believe them in the first place. Beyond this, the authors pointed out that referring the patient elsewhere reduces their hopes for dermatologic treatment.¹³

Knowing now—perhaps more than ever before—that the mind and skin are intimately connected compels us to solve these problems and find ways around these obstacles. Selecting the optimal forms of mental health services for each patient, having the structural support of the health care system, and winning the trust of patients and caregivers while combating stigma are undoubtedly tall orders; however, understanding the stakes for patients with AD, their caregivers, and society as a whole should inspire us to keep pushing forward.

There is a well-established connection between the mind and the skin, and it is clear that this relationship is bidirectional—not only does skin disease increase the risk for depression, anxiety, sleep disturbance, and suicidality, but psychologic stress actually can worsen skin disease through multiple mechanisms, including direct damage to the skin barrier.^1,2 Psychologic stress also impacts the microbiome, another critical driver of skin disease.^3,4 The concept of the itch-scratch cycle vividly illustrates the vicious interplay between the mind and body in atopic dermatitis (AD).

However, patients with AD are not the only ones impacted—caregivers also experience psychologic stress. Remarkably, one study of patients with AD and their caregivers found that the caregivers actually reported significantly worse mental health and anxiety (P=.01 and P=.03, respectively) than patients themselves, even when controlling for the severity of disease.⁵

Thus, it would seem obvious for mental health to be a central component of AD care—to improve patient and caregiver quality of life while also improving symptoms. Research has actually borne this out, with one systematic review and meta-analysis concluding that psychological intervention has a beneficial effect on AD,⁶ and another that the addition of psychological and educational interventions to conventional treatment provided better therapeutic results in alleviating eczema severity and psychological symptoms.⁷ One study demonstrated that patients with AD who received cognitive behavioral therapy via the internet displayed a statistically significant improvement in their disease (P<.001) as measured by the Patient-Oriented Eczema Measure compared with those in the control group who received standard care alone. They also reported improvements in perceived stress, sleep problems, and depression in the intervention group that were sustained at 1-year follow-up.⁸ These findings are particularly impactful because clinical results were achieved while leveraging an internet-based approach to therapy.

Regrettably, despite the preponderance of evidence supporting the connection between mental health and AD, there remain considerable unmet needs. A recent cross-sectional survey of 954 adults with AD and caregivers of children with AD (N=954) conducted by the National Eczema Association found that half of patients were never asked about mental health during any of their visits, and of those referred for mental health resources, only 57% utilized the recommended services.⁹ Importantly, patients aged 18 to 34 years reported wanting to be asked about mental health. Of those who did receive referrals, most were for counseling services (23%), followed by alternative mental health therapy such as music or art therapy (15%), cognitive behavioral therapy (13%), or peer/social support groups (12%). Approximately 10% reported receiving a pamphlet or a brochure only.⁹

Physicians who treat patients with AD can and must do better, but first we must explore why these referral rates are so low. As with many complex problems, there is unlikely to be one simple unifying reason. As expected, the answer is nuanced and multifaceted, and—most importantly—staggeringly incomplete.

For starters, mental health interventions rarely are as easy as applying a cream or taking a pill. Hedman-Lagerlöf et al⁸ specifically pointed out that although their approach—using internet-based cognitive behavioral therapy—was explicitly designed to be more accessible with fewer resources, it required approximately 35 hours of treatment over 12 weeks, requiring both substantial time and commitment from patients who often are already burned out and exhausted due to AD. They even underscored that the most commonly reported adverse effect of therapy was increased stress or worry, making it a difficult sell.⁸

Even before most patients have a chance to consider the time required and the potential adverse effects of mental health interventions for AD, greater hurdles exist. Finances, medical insurance, and wait times were highlighted as barriers to care in a systematic review.¹⁰ These are deep-seated problems in the United States; while they may be surmountable in certain geo­graphic areas, the frequency with which these concerns arise means that it does not take too many failed attempts at referring patients for mental health services before clinicians just give up—similar to any form of operant conditioning.

A more elusive concept is stigmatization. Although it may not be quantifiable, the idea is that patients may encounter additional challenges when seeking mental health care, either because the interactions themselves may worsen their symptoms (eg, increased anxiety) or they may be more likely to have a negative perception of the experience.¹¹ A 2020 systematic review of barriers to addressing common mental health problems found that stigma was the most prominent barrier in adolescents, with the second most prominent being negative attitudes and beliefs about mental health services and professionals.¹² As a clinician, I can attest that I have sometimes detected skepticism when I have suggested mental health services to patients and have even been asked outright if I thought the problem was all in their head. My patients with AD generally have been much more open to the idea of mental health support, especially after I explain the powerful mind-body connection, than patients with other conditions—most notably delusions of parasitosis—who have been much more dismissive of such overtures. An oft-cited paper from 1976 frames the problem perfectly, describing what can happen after a referral for mental health services.¹³ The authors stated that the suggestion of mental health makes patients feel that the dermatologist does not believe them in the first place. Beyond this, the authors pointed out that referring the patient elsewhere reduces their hopes for dermatologic treatment.¹³

Knowing now—perhaps more than ever before—that the mind and skin are intimately connected compels us to solve these problems and find ways around these obstacles. Selecting the optimal forms of mental health services for each patient, having the structural support of the health care system, and winning the trust of patients and caregivers while combating stigma are undoubtedly tall orders; however, understanding the stakes for patients with AD, their caregivers, and society as a whole should inspire us to keep pushing forward.

The Diagnosis: Mycobacterial Infection

An injury sustained in a wet environment that results in chronic indolent abscesses, nodules, or draining sinus tracts suggests a mycobacterial infection. In our patient, a culture revealed MycobacteriuM fortuitum, which is classified in the rapid grower nontuberculous mycobacteria (NTM) group, along with Mycobacterium chelonae and Mycobacterium abscessus.¹ The patient’s history of skin injury while cutting wet grass and the common presence of M fortuitum in the environment suggested that the organism entered the wound. The patient healed completely following surgical excision and a 2-month course of clarithromycin 1 g daily and rifampin 600 mg daily.

MycobacteriuM fortuitum was first isolated from an amphibian source in 1905 and later identified in a human with cutaneous infection in 1938. It commonly is found in soil and water.2 Skin and soft-tissue infections with M fortuitum usually are acquired from direct entry of the organism through a damaged skin barrier from trauma, medical injection, surgery, or tattoo placement.^2,3

Skin lesions caused by NTM often are nonspecific and can mimic a variety of other dermatologic conditions, making clinical diagnosis challenging. As such, cutaneous manifestations of M fortuitum infection can include recurrent cutaneous abscesses, nodular lesions, chronic discharging sinuses, cellulitis, and surgical site infections.4 Although cutaneous infection with M fortuitum classically manifests with a single subcutaneous nodule at the site of trauma or surgery,⁵ it also can manifest as multiple draining sinus tracts, as seen in our patient. Hence, the diagnosis and treatment of cutaneous NTM infection is challenging, especially when M fortuitum skin manifestations can take up to 4 to 6 weeks to develop after inoculation. Diagnosis often requires a detailed patient history, tissue cultures, and histopathology.⁵

In recent years, rapid detection with polymerase chain reaction (PCR) techniques has been employed more widely. Notably, a molecular system based on multiplex real-time PCR with high-resolution melting was shown to have a sensitivity of up to 54% for distinguishing M fortuitum from other NTM.⁶ More recently, a 2-step real-time PCR method has demonstrated diagnostic sensitivity and specificity for differentiating NTM from Mycobacterium tuberculosis infections and identifying the causative NTM agent.⁷

Compared to immunocompetent individuals, those who are immunocompromised are more susceptible to less pathogenic strains of NTM, which can cause dissemination and lead to tenosynovitis, myositis, osteomyelitis, and septic arthritis.^8-12 Nonetheless, cases of infections with NTM—including M fortuitum—are becoming harder to treat. Several single nucleotide polymorphisms and point mutations have been demonstrated in the ribosomal RNA methylase gene erm(39) related to clarithromycin resistance and in the rrl gene related to linezolid resistance.¹³ Due to increasing inducible resistance to common classes of antibiotics, such as macrolides and linezolid, treatment of M fortuitum requires multidrug regimens.^13,14 Drug susceptibility testing also may be required, as M fortuitum has shown low resistance to tigecycline, tetracycline, cefmetazole, imipenem, and aminoglycosides (eg, amikacin, tobramycin, neomycin, gentamycin). Surgery is an important adjunctive tool in treating M fortuitum infections; patients with a single lesion are more likely to undergo surgical treatment alone or in combination with antibiotic therapy.¹⁵ More recently, antimicrobial photodynamic therapy has been explored as an alternative to eliminate NTM, including M fortuitum.¹⁶

The differential diagnosis for skin lesions manifesting with draining fistulae and sinus tracts includes conditions with infectious (cellulitis and chromomycosis) and inflammatory (pyoderma gangrenosum [PG] and hidradenitis suppurativa [HS]) causes.

Cellulitis is a common infection of the skin and subcutaneous tissue that predominantly is caused by gram-positive organisms such as β-hemolytic streptococci.¹⁷ Clinical manifestations include acute skin erythema, swelling, tenderness, and warmth. The legs are the most common sites of infection, but any area of the skin can be involved.17 Cellulitis comprises 10% of all infectious disease hospitalizations and up to 11% of all dermatologic admissions.^18,19 It frequently is misdiagnosed, perhaps due to the lack of a reliable confirmatory laboratory test or imaging study, in addition to the plethora of diseases that mimic cellulitis, such as stasis dermatitis, lipodermatosclerosis, contact dermatitis, lymphedema, eosinophilic cellulitis, and papular urticaria.^20,21 The consequences of misdiagnosis include but are not limited to unnecessary hospitalizations, inappropriate antibiotic use, and delayed management of the disease; thus, there is an urgent need for a reliable standard test to confirm the diagnosis, especially among nonspecialist physicians. ²⁰ Most patients with uncomplicated cellulitis can be treated with empiric oral antibiotics that target β-hemolytic streptococci (ie, penicillin V potassium, amoxicillin).¹⁷ Methicillin-resistant Staphylococcus aureus coverage generally is unnecessary for nonpurulent cellulitis, but clinicians can consider adding amoxicillin-clavulanate, dicloxacillin, and cephalexin to the regimen. For purulent cellulitis, incision and drainage should be performed. In severe cases that manifest with sepsis, altered mental status, or hemodynamic instability, inpatient management is required.¹⁷

Chromomycosis (also known as chromoblastomycosis) is a chronic, indolent, granulomatous, suppurative mycosis of the skin and subcutaneous tissue²² that is caused by traumatic inoculation of various fungi of the order Chaetothyriales and family Herpotrichiellaceae, which are present in soil, plants, and decomposing wood. Chromomycosis is prevalent in tropical and subtropical regions.^23,24 Clinically, it manifests as oligosymptomatic or asymptomatic lesions around an infection site that can manifest as papules with centrifugal growth evolving into nodular, verrucous, plaque, tumoral, or atrophic forms.²² Diagnosis is made with direct microscopy using potassium hydroxide, which reveals muriform bodies. Fungal culture in Sabouraud agar also can be used to isolate the causative pathogen.²² Unfortunately, chromomycosis is difficult to treat, with low cure rates and high relapse rates. Antifungal agents combined with surgery, cryotherapy, or thermotherapy often are used, with cure rates ranging from 15% to 80%.^22,25

Pyoderma gangrenosum is a reactive noninfectious inflammatory dermatosis associated with inflammatory bowel disease and rheumatoid arthritis. The exact etiology is not clearly understood, but it generally is considered an autoinflammatory disorder.²⁶ The most common form—classical PG—occurs in approximately 85% of cases and manifests as a painful erythematous lesion that progresses to a blistered or necrotic ulcer. It primarily affects the lower legs but can occur in other body sites.²⁷ The diagnosis is based on clinical symptoms after excluding other similar conditions; histopathology of biopsied wound tissues often are required for confirmation. Treatment of PG starts with fast-acting immunosuppressive drugs (corticosteroids and/or cyclosporine) followed by slowacting immunosuppressive drugs (biologics).²⁶

Hidradenitis suppurativa is a chronic recurrent disease of the hair follicle unit that develops after puberty.²⁸ Clinically, HS manifests with painful nodules, abscesses, chronically draining fistulas, and scarring in areas of the body rich in apocrine glands.^29,30 Treatment of HS is challenging due to its diverse clinical manifestations and unclear etiology. Topical therapy, systemic treatments, biologic agents, surgery, and light therapy have shown variable results.^28,31

The Diagnosis: Mycobacterial Infection

An injury sustained in a wet environment that results in chronic indolent abscesses, nodules, or draining sinus tracts suggests a mycobacterial infection. In our patient, a culture revealed MycobacteriuM fortuitum, which is classified in the rapid grower nontuberculous mycobacteria (NTM) group, along with Mycobacterium chelonae and Mycobacterium abscessus.¹ The patient’s history of skin injury while cutting wet grass and the common presence of M fortuitum in the environment suggested that the organism entered the wound. The patient healed completely following surgical excision and a 2-month course of clarithromycin 1 g daily and rifampin 600 mg daily.

MycobacteriuM fortuitum was first isolated from an amphibian source in 1905 and later identified in a human with cutaneous infection in 1938. It commonly is found in soil and water.2 Skin and soft-tissue infections with M fortuitum usually are acquired from direct entry of the organism through a damaged skin barrier from trauma, medical injection, surgery, or tattoo placement.^2,3

Skin lesions caused by NTM often are nonspecific and can mimic a variety of other dermatologic conditions, making clinical diagnosis challenging. As such, cutaneous manifestations of M fortuitum infection can include recurrent cutaneous abscesses, nodular lesions, chronic discharging sinuses, cellulitis, and surgical site infections.4 Although cutaneous infection with M fortuitum classically manifests with a single subcutaneous nodule at the site of trauma or surgery,⁵ it also can manifest as multiple draining sinus tracts, as seen in our patient. Hence, the diagnosis and treatment of cutaneous NTM infection is challenging, especially when M fortuitum skin manifestations can take up to 4 to 6 weeks to develop after inoculation. Diagnosis often requires a detailed patient history, tissue cultures, and histopathology.⁵

In recent years, rapid detection with polymerase chain reaction (PCR) techniques has been employed more widely. Notably, a molecular system based on multiplex real-time PCR with high-resolution melting was shown to have a sensitivity of up to 54% for distinguishing M fortuitum from other NTM.⁶ More recently, a 2-step real-time PCR method has demonstrated diagnostic sensitivity and specificity for differentiating NTM from Mycobacterium tuberculosis infections and identifying the causative NTM agent.⁷

Compared to immunocompetent individuals, those who are immunocompromised are more susceptible to less pathogenic strains of NTM, which can cause dissemination and lead to tenosynovitis, myositis, osteomyelitis, and septic arthritis.^8-12 Nonetheless, cases of infections with NTM—including M fortuitum—are becoming harder to treat. Several single nucleotide polymorphisms and point mutations have been demonstrated in the ribosomal RNA methylase gene erm(39) related to clarithromycin resistance and in the rrl gene related to linezolid resistance.¹³ Due to increasing inducible resistance to common classes of antibiotics, such as macrolides and linezolid, treatment of M fortuitum requires multidrug regimens.^13,14 Drug susceptibility testing also may be required, as M fortuitum has shown low resistance to tigecycline, tetracycline, cefmetazole, imipenem, and aminoglycosides (eg, amikacin, tobramycin, neomycin, gentamycin). Surgery is an important adjunctive tool in treating M fortuitum infections; patients with a single lesion are more likely to undergo surgical treatment alone or in combination with antibiotic therapy.¹⁵ More recently, antimicrobial photodynamic therapy has been explored as an alternative to eliminate NTM, including M fortuitum.¹⁶

The differential diagnosis for skin lesions manifesting with draining fistulae and sinus tracts includes conditions with infectious (cellulitis and chromomycosis) and inflammatory (pyoderma gangrenosum [PG] and hidradenitis suppurativa [HS]) causes.

Cellulitis is a common infection of the skin and subcutaneous tissue that predominantly is caused by gram-positive organisms such as β-hemolytic streptococci.¹⁷ Clinical manifestations include acute skin erythema, swelling, tenderness, and warmth. The legs are the most common sites of infection, but any area of the skin can be involved.17 Cellulitis comprises 10% of all infectious disease hospitalizations and up to 11% of all dermatologic admissions.^18,19 It frequently is misdiagnosed, perhaps due to the lack of a reliable confirmatory laboratory test or imaging study, in addition to the plethora of diseases that mimic cellulitis, such as stasis dermatitis, lipodermatosclerosis, contact dermatitis, lymphedema, eosinophilic cellulitis, and papular urticaria.^20,21 The consequences of misdiagnosis include but are not limited to unnecessary hospitalizations, inappropriate antibiotic use, and delayed management of the disease; thus, there is an urgent need for a reliable standard test to confirm the diagnosis, especially among nonspecialist physicians. ²⁰ Most patients with uncomplicated cellulitis can be treated with empiric oral antibiotics that target β-hemolytic streptococci (ie, penicillin V potassium, amoxicillin).¹⁷ Methicillin-resistant Staphylococcus aureus coverage generally is unnecessary for nonpurulent cellulitis, but clinicians can consider adding amoxicillin-clavulanate, dicloxacillin, and cephalexin to the regimen. For purulent cellulitis, incision and drainage should be performed. In severe cases that manifest with sepsis, altered mental status, or hemodynamic instability, inpatient management is required.¹⁷

Chromomycosis (also known as chromoblastomycosis) is a chronic, indolent, granulomatous, suppurative mycosis of the skin and subcutaneous tissue²² that is caused by traumatic inoculation of various fungi of the order Chaetothyriales and family Herpotrichiellaceae, which are present in soil, plants, and decomposing wood. Chromomycosis is prevalent in tropical and subtropical regions.^23,24 Clinically, it manifests as oligosymptomatic or asymptomatic lesions around an infection site that can manifest as papules with centrifugal growth evolving into nodular, verrucous, plaque, tumoral, or atrophic forms.²² Diagnosis is made with direct microscopy using potassium hydroxide, which reveals muriform bodies. Fungal culture in Sabouraud agar also can be used to isolate the causative pathogen.²² Unfortunately, chromomycosis is difficult to treat, with low cure rates and high relapse rates. Antifungal agents combined with surgery, cryotherapy, or thermotherapy often are used, with cure rates ranging from 15% to 80%.^22,25

Pyoderma gangrenosum is a reactive noninfectious inflammatory dermatosis associated with inflammatory bowel disease and rheumatoid arthritis. The exact etiology is not clearly understood, but it generally is considered an autoinflammatory disorder.²⁶ The most common form—classical PG—occurs in approximately 85% of cases and manifests as a painful erythematous lesion that progresses to a blistered or necrotic ulcer. It primarily affects the lower legs but can occur in other body sites.²⁷ The diagnosis is based on clinical symptoms after excluding other similar conditions; histopathology of biopsied wound tissues often are required for confirmation. Treatment of PG starts with fast-acting immunosuppressive drugs (corticosteroids and/or cyclosporine) followed by slowacting immunosuppressive drugs (biologics).²⁶

Hidradenitis suppurativa is a chronic recurrent disease of the hair follicle unit that develops after puberty.²⁸ Clinically, HS manifests with painful nodules, abscesses, chronically draining fistulas, and scarring in areas of the body rich in apocrine glands.^29,30 Treatment of HS is challenging due to its diverse clinical manifestations and unclear etiology. Topical therapy, systemic treatments, biologic agents, surgery, and light therapy have shown variable results.^28,31

The Diagnosis: Mycobacterial Infection

An injury sustained in a wet environment that results in chronic indolent abscesses, nodules, or draining sinus tracts suggests a mycobacterial infection. In our patient, a culture revealed MycobacteriuM fortuitum, which is classified in the rapid grower nontuberculous mycobacteria (NTM) group, along with Mycobacterium chelonae and Mycobacterium abscessus.¹ The patient’s history of skin injury while cutting wet grass and the common presence of M fortuitum in the environment suggested that the organism entered the wound. The patient healed completely following surgical excision and a 2-month course of clarithromycin 1 g daily and rifampin 600 mg daily.

MycobacteriuM fortuitum was first isolated from an amphibian source in 1905 and later identified in a human with cutaneous infection in 1938. It commonly is found in soil and water.2 Skin and soft-tissue infections with M fortuitum usually are acquired from direct entry of the organism through a damaged skin barrier from trauma, medical injection, surgery, or tattoo placement.^2,3

Skin lesions caused by NTM often are nonspecific and can mimic a variety of other dermatologic conditions, making clinical diagnosis challenging. As such, cutaneous manifestations of M fortuitum infection can include recurrent cutaneous abscesses, nodular lesions, chronic discharging sinuses, cellulitis, and surgical site infections.4 Although cutaneous infection with M fortuitum classically manifests with a single subcutaneous nodule at the site of trauma or surgery,⁵ it also can manifest as multiple draining sinus tracts, as seen in our patient. Hence, the diagnosis and treatment of cutaneous NTM infection is challenging, especially when M fortuitum skin manifestations can take up to 4 to 6 weeks to develop after inoculation. Diagnosis often requires a detailed patient history, tissue cultures, and histopathology.⁵

In recent years, rapid detection with polymerase chain reaction (PCR) techniques has been employed more widely. Notably, a molecular system based on multiplex real-time PCR with high-resolution melting was shown to have a sensitivity of up to 54% for distinguishing M fortuitum from other NTM.⁶ More recently, a 2-step real-time PCR method has demonstrated diagnostic sensitivity and specificity for differentiating NTM from Mycobacterium tuberculosis infections and identifying the causative NTM agent.⁷

Compared to immunocompetent individuals, those who are immunocompromised are more susceptible to less pathogenic strains of NTM, which can cause dissemination and lead to tenosynovitis, myositis, osteomyelitis, and septic arthritis.^8-12 Nonetheless, cases of infections with NTM—including M fortuitum—are becoming harder to treat. Several single nucleotide polymorphisms and point mutations have been demonstrated in the ribosomal RNA methylase gene erm(39) related to clarithromycin resistance and in the rrl gene related to linezolid resistance.¹³ Due to increasing inducible resistance to common classes of antibiotics, such as macrolides and linezolid, treatment of M fortuitum requires multidrug regimens.^13,14 Drug susceptibility testing also may be required, as M fortuitum has shown low resistance to tigecycline, tetracycline, cefmetazole, imipenem, and aminoglycosides (eg, amikacin, tobramycin, neomycin, gentamycin). Surgery is an important adjunctive tool in treating M fortuitum infections; patients with a single lesion are more likely to undergo surgical treatment alone or in combination with antibiotic therapy.¹⁵ More recently, antimicrobial photodynamic therapy has been explored as an alternative to eliminate NTM, including M fortuitum.¹⁶

The differential diagnosis for skin lesions manifesting with draining fistulae and sinus tracts includes conditions with infectious (cellulitis and chromomycosis) and inflammatory (pyoderma gangrenosum [PG] and hidradenitis suppurativa [HS]) causes.

Cellulitis is a common infection of the skin and subcutaneous tissue that predominantly is caused by gram-positive organisms such as β-hemolytic streptococci.¹⁷ Clinical manifestations include acute skin erythema, swelling, tenderness, and warmth. The legs are the most common sites of infection, but any area of the skin can be involved.17 Cellulitis comprises 10% of all infectious disease hospitalizations and up to 11% of all dermatologic admissions.^18,19 It frequently is misdiagnosed, perhaps due to the lack of a reliable confirmatory laboratory test or imaging study, in addition to the plethora of diseases that mimic cellulitis, such as stasis dermatitis, lipodermatosclerosis, contact dermatitis, lymphedema, eosinophilic cellulitis, and papular urticaria.^20,21 The consequences of misdiagnosis include but are not limited to unnecessary hospitalizations, inappropriate antibiotic use, and delayed management of the disease; thus, there is an urgent need for a reliable standard test to confirm the diagnosis, especially among nonspecialist physicians. ²⁰ Most patients with uncomplicated cellulitis can be treated with empiric oral antibiotics that target β-hemolytic streptococci (ie, penicillin V potassium, amoxicillin).¹⁷ Methicillin-resistant Staphylococcus aureus coverage generally is unnecessary for nonpurulent cellulitis, but clinicians can consider adding amoxicillin-clavulanate, dicloxacillin, and cephalexin to the regimen. For purulent cellulitis, incision and drainage should be performed. In severe cases that manifest with sepsis, altered mental status, or hemodynamic instability, inpatient management is required.¹⁷

Chromomycosis (also known as chromoblastomycosis) is a chronic, indolent, granulomatous, suppurative mycosis of the skin and subcutaneous tissue²² that is caused by traumatic inoculation of various fungi of the order Chaetothyriales and family Herpotrichiellaceae, which are present in soil, plants, and decomposing wood. Chromomycosis is prevalent in tropical and subtropical regions.^23,24 Clinically, it manifests as oligosymptomatic or asymptomatic lesions around an infection site that can manifest as papules with centrifugal growth evolving into nodular, verrucous, plaque, tumoral, or atrophic forms.²² Diagnosis is made with direct microscopy using potassium hydroxide, which reveals muriform bodies. Fungal culture in Sabouraud agar also can be used to isolate the causative pathogen.²² Unfortunately, chromomycosis is difficult to treat, with low cure rates and high relapse rates. Antifungal agents combined with surgery, cryotherapy, or thermotherapy often are used, with cure rates ranging from 15% to 80%.^22,25

Pyoderma gangrenosum is a reactive noninfectious inflammatory dermatosis associated with inflammatory bowel disease and rheumatoid arthritis. The exact etiology is not clearly understood, but it generally is considered an autoinflammatory disorder.²⁶ The most common form—classical PG—occurs in approximately 85% of cases and manifests as a painful erythematous lesion that progresses to a blistered or necrotic ulcer. It primarily affects the lower legs but can occur in other body sites.²⁷ The diagnosis is based on clinical symptoms after excluding other similar conditions; histopathology of biopsied wound tissues often are required for confirmation. Treatment of PG starts with fast-acting immunosuppressive drugs (corticosteroids and/or cyclosporine) followed by slowacting immunosuppressive drugs (biologics).²⁶

Hidradenitis suppurativa is a chronic recurrent disease of the hair follicle unit that develops after puberty.²⁸ Clinically, HS manifests with painful nodules, abscesses, chronically draining fistulas, and scarring in areas of the body rich in apocrine glands.^29,30 Treatment of HS is challenging due to its diverse clinical manifestations and unclear etiology. Topical therapy, systemic treatments, biologic agents, surgery, and light therapy have shown variable results.^28,31

The Diagnosis: Erythema Nodosum Leprosum

Erythema nodosum leprosum (ENL) is a type 2 reaction sometimes seen in patients infected with Mycobacterium leprae—primarily those with lepromatous or borderline lepromatous subtypes. Clinically, ENL manifests with abrupt onset of tender erythematous papules with associated fevers and general malaise. Studies have demonstrated a complex immune system reaction in ENL, but the detailed pathophysiology is not fully understood.¹ Biopsies conducted within 24 hours of lesion formation are most elucidating. Foamy histiocytes admixed with neutrophils are seen in the subcutis, often causing a lobular panniculitis (quiz image).² Neutrophils rarely are seen in other types of leprosy and thus are a useful diagnostic clue for ENL. Vasculitis of small- to medium-sized vessels can be seen but is not a necessary diagnostic criterion. Fite staining will highlight many acid-fast bacilli within the histiocytes (Figure 1).

Erythema nodosum leprosum is treated with a combination of immunosuppressants such as prednisone and thalidomide. Our patient was taking triple-antibiotic therapy—dapsone, rifampin, and clofazimine—for lepromatous leprosy when the erythematous papules developed on the arms and legs. After a skin biopsy confirmed the diagnosis of ENL, he was started on prednisone 20 mg daily with plans for close follow-up. Unfortunately, the patient was subsequently lost to follow-up.

Acute febrile neutrophilic dermatosis (also known as Sweet syndrome) is an acute inflammatory disease characterized by abrupt onset of painful erythematous papules, plaques, or nodules on the skin. It often is seen in association with preceding infections (especially those in the upper respiratory or gastrointestinal tracts), hematologic malignancies, inflammatory bowel disease, or exposure to certain classes of medications (eg, granulocyte colony-stimulating factor, tyrosine kinase inhibitors, various antibiotics).³ Histologically, acute febrile neutrophilic dermatosis is characterized by dense neutrophilic infiltrates, often with notable dermal edema (Figure 2).⁴ Many cases also show leukocytoclastic vasculitis; however, foamy histiocytes are not a notable component of the inflammatory infiltrate, though a histiocytoid form of acute febrile neutrophilic dermatosis has been described.⁵ Infections must be rigorously ruled out prior to diagnosing a patient with acute febrile neutrophilic dermatosis, making it a diagnosis of exclusion.

Cutaneous coccidioidomycosis is an infection caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. Cutaneous disease is rare but can occur from direct inoculation or dissemination from pulmonary disease in immunocompetent or immunocompromised patients. Papules, pustules, or plaques are seen clinically. Histologically, cutaneous coccidioidomycosis shows spherules that vary from 10 to 100 μm and are filled with multiple smaller endospores (Figure 3).⁶ Pseudoepitheliomatous hyperplasia with dense suppurative and granulomatous infiltrates also is seen.

Erythema induratum is characterized by tender nodules on the lower extremities and has a substantial female predominance. Many cases are associated with Mycobacterium tuberculosis infection. The bacteria are not seen directly in the skin but are instead detectable through DNA polymerase chain reaction testing or investigation of other organ systems.^7,8 Histologically, lesions show a lobular panniculitis with a mixed infiltrate. Vasculitis is seen in approximately 90% of erythema induratum cases vs approximately 25% of classic ENL cases (Figure 4),^2,9 which has led some to use the term nodular vasculitis to describe this disease entity. Nodular vasculitis is considered by others to be a distinct disease entity in which there are clinical and histologic features similar to erythema induratum but no evidence of M tuberculosis infection.⁹

Polyarteritis nodosa is a vasculitis that affects medium- sized vessels of various organ systems. The presenting signs and symptoms vary based on the affected organ systems. Palpable to retiform purpura, livedo racemosa, subcutaneous nodules, or ulcers are seen when the skin is involved. The histologic hallmark is necrotizing vasculitis of medium-sized arterioles (Figure 5), although leukocytoclastic vasculitis of small-caliber vessels also can be seen in biopsies of affected skin.¹⁰ The vascular changes are said to be segmental, with uninvolved segments interspersed with involved segments. Antineutrophil cytoplasmic antibody (ANCA)– associated vasculitis also must be considered when one sees leukocytoclastic vasculitis of small-caliber vessels in the skin, as it can be distinguished most readily by detecting circulating antibodies specific for myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA).

The Diagnosis: Erythema Nodosum Leprosum

Erythema nodosum leprosum (ENL) is a type 2 reaction sometimes seen in patients infected with Mycobacterium leprae—primarily those with lepromatous or borderline lepromatous subtypes. Clinically, ENL manifests with abrupt onset of tender erythematous papules with associated fevers and general malaise. Studies have demonstrated a complex immune system reaction in ENL, but the detailed pathophysiology is not fully understood.¹ Biopsies conducted within 24 hours of lesion formation are most elucidating. Foamy histiocytes admixed with neutrophils are seen in the subcutis, often causing a lobular panniculitis (quiz image).² Neutrophils rarely are seen in other types of leprosy and thus are a useful diagnostic clue for ENL. Vasculitis of small- to medium-sized vessels can be seen but is not a necessary diagnostic criterion. Fite staining will highlight many acid-fast bacilli within the histiocytes (Figure 1).

Erythema nodosum leprosum is treated with a combination of immunosuppressants such as prednisone and thalidomide. Our patient was taking triple-antibiotic therapy—dapsone, rifampin, and clofazimine—for lepromatous leprosy when the erythematous papules developed on the arms and legs. After a skin biopsy confirmed the diagnosis of ENL, he was started on prednisone 20 mg daily with plans for close follow-up. Unfortunately, the patient was subsequently lost to follow-up.

Acute febrile neutrophilic dermatosis (also known as Sweet syndrome) is an acute inflammatory disease characterized by abrupt onset of painful erythematous papules, plaques, or nodules on the skin. It often is seen in association with preceding infections (especially those in the upper respiratory or gastrointestinal tracts), hematologic malignancies, inflammatory bowel disease, or exposure to certain classes of medications (eg, granulocyte colony-stimulating factor, tyrosine kinase inhibitors, various antibiotics).³ Histologically, acute febrile neutrophilic dermatosis is characterized by dense neutrophilic infiltrates, often with notable dermal edema (Figure 2).⁴ Many cases also show leukocytoclastic vasculitis; however, foamy histiocytes are not a notable component of the inflammatory infiltrate, though a histiocytoid form of acute febrile neutrophilic dermatosis has been described.⁵ Infections must be rigorously ruled out prior to diagnosing a patient with acute febrile neutrophilic dermatosis, making it a diagnosis of exclusion.

Cutaneous coccidioidomycosis is an infection caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. Cutaneous disease is rare but can occur from direct inoculation or dissemination from pulmonary disease in immunocompetent or immunocompromised patients. Papules, pustules, or plaques are seen clinically. Histologically, cutaneous coccidioidomycosis shows spherules that vary from 10 to 100 μm and are filled with multiple smaller endospores (Figure 3).⁶ Pseudoepitheliomatous hyperplasia with dense suppurative and granulomatous infiltrates also is seen.

Erythema induratum is characterized by tender nodules on the lower extremities and has a substantial female predominance. Many cases are associated with Mycobacterium tuberculosis infection. The bacteria are not seen directly in the skin but are instead detectable through DNA polymerase chain reaction testing or investigation of other organ systems.^7,8 Histologically, lesions show a lobular panniculitis with a mixed infiltrate. Vasculitis is seen in approximately 90% of erythema induratum cases vs approximately 25% of classic ENL cases (Figure 4),^2,9 which has led some to use the term nodular vasculitis to describe this disease entity. Nodular vasculitis is considered by others to be a distinct disease entity in which there are clinical and histologic features similar to erythema induratum but no evidence of M tuberculosis infection.⁹

Polyarteritis nodosa is a vasculitis that affects medium- sized vessels of various organ systems. The presenting signs and symptoms vary based on the affected organ systems. Palpable to retiform purpura, livedo racemosa, subcutaneous nodules, or ulcers are seen when the skin is involved. The histologic hallmark is necrotizing vasculitis of medium-sized arterioles (Figure 5), although leukocytoclastic vasculitis of small-caliber vessels also can be seen in biopsies of affected skin.¹⁰ The vascular changes are said to be segmental, with uninvolved segments interspersed with involved segments. Antineutrophil cytoplasmic antibody (ANCA)– associated vasculitis also must be considered when one sees leukocytoclastic vasculitis of small-caliber vessels in the skin, as it can be distinguished most readily by detecting circulating antibodies specific for myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA).

The Diagnosis: Erythema Nodosum Leprosum

Erythema nodosum leprosum (ENL) is a type 2 reaction sometimes seen in patients infected with Mycobacterium leprae—primarily those with lepromatous or borderline lepromatous subtypes. Clinically, ENL manifests with abrupt onset of tender erythematous papules with associated fevers and general malaise. Studies have demonstrated a complex immune system reaction in ENL, but the detailed pathophysiology is not fully understood.¹ Biopsies conducted within 24 hours of lesion formation are most elucidating. Foamy histiocytes admixed with neutrophils are seen in the subcutis, often causing a lobular panniculitis (quiz image).² Neutrophils rarely are seen in other types of leprosy and thus are a useful diagnostic clue for ENL. Vasculitis of small- to medium-sized vessels can be seen but is not a necessary diagnostic criterion. Fite staining will highlight many acid-fast bacilli within the histiocytes (Figure 1).

Erythema nodosum leprosum is treated with a combination of immunosuppressants such as prednisone and thalidomide. Our patient was taking triple-antibiotic therapy—dapsone, rifampin, and clofazimine—for lepromatous leprosy when the erythematous papules developed on the arms and legs. After a skin biopsy confirmed the diagnosis of ENL, he was started on prednisone 20 mg daily with plans for close follow-up. Unfortunately, the patient was subsequently lost to follow-up.

Acute febrile neutrophilic dermatosis (also known as Sweet syndrome) is an acute inflammatory disease characterized by abrupt onset of painful erythematous papules, plaques, or nodules on the skin. It often is seen in association with preceding infections (especially those in the upper respiratory or gastrointestinal tracts), hematologic malignancies, inflammatory bowel disease, or exposure to certain classes of medications (eg, granulocyte colony-stimulating factor, tyrosine kinase inhibitors, various antibiotics).³ Histologically, acute febrile neutrophilic dermatosis is characterized by dense neutrophilic infiltrates, often with notable dermal edema (Figure 2).⁴ Many cases also show leukocytoclastic vasculitis; however, foamy histiocytes are not a notable component of the inflammatory infiltrate, though a histiocytoid form of acute febrile neutrophilic dermatosis has been described.⁵ Infections must be rigorously ruled out prior to diagnosing a patient with acute febrile neutrophilic dermatosis, making it a diagnosis of exclusion.

Cutaneous coccidioidomycosis is an infection caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. Cutaneous disease is rare but can occur from direct inoculation or dissemination from pulmonary disease in immunocompetent or immunocompromised patients. Papules, pustules, or plaques are seen clinically. Histologically, cutaneous coccidioidomycosis shows spherules that vary from 10 to 100 μm and are filled with multiple smaller endospores (Figure 3).⁶ Pseudoepitheliomatous hyperplasia with dense suppurative and granulomatous infiltrates also is seen.

Erythema induratum is characterized by tender nodules on the lower extremities and has a substantial female predominance. Many cases are associated with Mycobacterium tuberculosis infection. The bacteria are not seen directly in the skin but are instead detectable through DNA polymerase chain reaction testing or investigation of other organ systems.^7,8 Histologically, lesions show a lobular panniculitis with a mixed infiltrate. Vasculitis is seen in approximately 90% of erythema induratum cases vs approximately 25% of classic ENL cases (Figure 4),^2,9 which has led some to use the term nodular vasculitis to describe this disease entity. Nodular vasculitis is considered by others to be a distinct disease entity in which there are clinical and histologic features similar to erythema induratum but no evidence of M tuberculosis infection.⁹

Polyarteritis nodosa is a vasculitis that affects medium- sized vessels of various organ systems. The presenting signs and symptoms vary based on the affected organ systems. Palpable to retiform purpura, livedo racemosa, subcutaneous nodules, or ulcers are seen when the skin is involved. The histologic hallmark is necrotizing vasculitis of medium-sized arterioles (Figure 5), although leukocytoclastic vasculitis of small-caliber vessels also can be seen in biopsies of affected skin.¹⁰ The vascular changes are said to be segmental, with uninvolved segments interspersed with involved segments. Antineutrophil cytoplasmic antibody (ANCA)– associated vasculitis also must be considered when one sees leukocytoclastic vasculitis of small-caliber vessels in the skin, as it can be distinguished most readily by detecting circulating antibodies specific for myeloperoxidase (MPO-ANCA) or proteinase 3 (PR3-ANCA).

Prurigo nodularis (PN)(also called chronic nodular prurigo, prurigo nodularis of Hyde, or picker’s nodules) was first characterized by James Hyde in 1909.^1-3 Prurigo nodularis manifests with symmetrical, intensely pruritic, eroded, or hyperkeratotic nodules or papules on the extremities and trunk.^1,2,4,5 Studies have shown that individuals with PN experience pruritus, sleep loss, decreased social functioning from the appearance of the nodules, and a higher incidence of anxiety and depression, causing a negative impact on their quality of life.^2,6 In addition, the manifestation of PN has been linked to neurologic and psychiatric disorders; however, PN also can be idiopathic and manifest without underlying illnesses.^2,6,7

Prurigo nodularis has been associated with other dermatologic conditions such as atopic dermatitis (up to 50%), lichen planus, keratoacanthomas (KAs), and bullous pemphigoid.^7-9 It also has been linked to systemic diseases in 38% to 50% of cases, including chronic kidney disease, liver disease, type 2 diabetes mellitus, malignancies (hematopoietic, liver, and skin), and HIV infection.^6,8,10

The pathophysiology of PN is highly complex and has yet to be fully elucidated. It is thought to be due to dysregulation and interaction of the increase in neural and immunologic responses of proinflammatory and pruritogenic cytokines.^2,11 Treatments aim to break the itch-scratch cycle that perpetuates this disorder; however, this proves difficult, as PN is associated with a higher itch intensity than atopic dermatitis and psoriasis.¹⁰ Therefore, most patients attempt multiple forms of treatment for PN, ranging from topical therapies, oral immunosuppressants, and phototherapy to the newest and only medication approved by the US Food and Drug Administration for the treatment of PN—dupilumab.^1,7,11 Herein, we provide an updated review of PN with a focus on its epidemiology, histopathology and pathophysiology, comorbidities, clinical presentation, differential diagnosis, and current treatment options.

Epidemiology

There are few studies on the epidemiology of PN; however, middle-aged populations with underlying dermatologic or psychiatric disorders tend to be impacted most frequently.^2,12,13 In 2016, it was estimated that almost 88,000 individuals had PN in the United States, with the majority being female; however, this estimate only took into account those aged 18 to 64 years and utilized data from IBM MarketScan Commercial Claims and Encounters Database (IBM Watson Health) from October 2015 to December 2016.¹⁴ More recently, a retrospective database analysis estimated the prevalence of PN in the United States to be anywhere from 36.7 to 43.9 cases per 100,000 individuals. However, this retrospective review utilized the International Classification of Diseases, Tenth Revision code; PN has 2 codes associated with the diagnosis, and the coding accuracy is unknown.¹⁵ Sutaria et al¹⁶ looked at racial disparities in patients with PN utilizing data from TriNetX and found that patients who received a diagnosis of PN were more likely to be women, non-Hispanic, and Black compared with control patients. However, these estimates are restricted to the health care organizations within this database.

In 2018, Poland reported an annual prevalence of 6.52 cases per 100,000 individuals,¹⁷ while England reported a yearly prevalence of 3.27 cases per 100,000 individuals.¹⁸ Both countries reported most cases were female. However, these studies are not without limitations. Poland only uses the primary diagnosis code for medical billing to simplify clinical coding, thus underestimating the actual prevalence; furthermore, clinical codes more often than not are assigned by someone other than the diagnosing physician, leaving room for error.¹⁷ In addition, England’s PN estimate utilized diagnosis data from primary care and inpatient datasets, leaving out outpatient datasets in which patients with PN may have been referred and obtained the diagnosis, potentially underestimating the prevalence in this population.¹⁸

In contrast, Korea estimated the annual prevalence of PN to be 4.82 cases per 1000 dermatology outpatients, with the majority being men, based on results from a cross-sectional study among outpatients from the Catholic Medical Center. Although this is the largest health organization in Korea, the scope of this study is limited and lacks data from other medical centers in Korea.¹⁹

Histopathology and Pathophysiology

Almost all cells in the skin are involved in PN: keratinocytes, mast cells, dendritic cells, endothelial cells, lymphocytes, eosinophils, collagen fibers, and nerve fibers.^11,20 Classically, PN manifests as a dome-shaped lesion with hyperkeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia with increased thickness of the papillary dermis consisting of coarse collagen with compact interstitial and circumvascular infiltration as well as increased lymphocytes and histocytes in the superficial dermis (Figure 1).²⁰ Hyperkeratosis is thought to be due to either the alteration of keratinocyte structures from scratching or keratinocyte abnormalities triggering PN.²¹ However, the increase in keratinocytes, which secrete nerve growth factor, allows for neuronal hyperplasia within the dermis.²² Nerve growth factor can stimulate keratinocyte proliferation²³ in addition to the upregulation of substance P (SP), a tachykinin that triggers vascular dilation and pruritus in the skin.²⁴ The density of SP nerve fibers in the dermis increases in PN, causing proinflammatory effects, upregulating the immune response to promote endothelial hyperplasia and increased vascularization.²⁵ The increase in these fibers may lead to pruritus associated with PN.^2,26

Many inflammatory cytokines and mediators also have been implicated in PN. Increased messenger RNA expression of IL-4, IL-17, IL-22, and IL-31 has been described in PN lesions.^3,27 Furthermore, studies also have reported increased helper T cell (T_H2) cytokines, including IL-4, IL-5, IL-10, and IL-13, in the dermis of PN lesions in patients without a history of atopy.^3,28 These pruritogenic cytokines in conjunction with the SP fibers may create an intractable itch for those with PN. The interaction and culmination of the neural and immune responses make PN a complex condition to treat with the multifactorial interaction of systems. 

Comorbidities

Prurigo nodularis has been associated with a wide array of comorbidities; however, the direction of the relationship between PN and these conditions makes it difficult to discern if PN is a primary or secondary condition.²⁹ Prurigo nodularis commonly has been connected to other inflammatory dermatoses, with a link to atopic dermatitis being the strongest.^5,29 However, PN also has been linked to other pruritic inflammatory cutaneous disorders, including psoriasis, cutaneous T-cell lymphoma, lichen planus, and dermatitis herpetiformis.^14,29

Huang et al¹⁴ found an increased likelihood of psychiatric illnesses in patients with PN, including eating disorders, nonsuicidal self-injury disorder, attention-deficit/hyperactivity disorder, schizophrenia, mood disorders, anxiety, and substance abuse disorders. Treatments directed at the neural aspect of PN have included selective serotonin reuptake inhibitors (SSRIs), which also are utilized to treat these mental health disorders.

Furthermore, systemic diseases also have been found to be associated with PN, including hypertension, type 2 diabetes mellitus, chronic kidney disease, heart failure, cerebrovascular disease, coronary heart disease, and chronic obstructive pulmonary disease.¹⁴ The relationship between PN and systemic conditions may be due to increased systemic inflammation and dysregulation of neural and metabolic functions implicated in these conditions from increased pruritic manifestations.^29,30 However, studies also have connected PN to infectious conditions such as HIV. One study found that patients with PN had 2.68 higher odds of infection with HIV compared to age- and sex-matched controls.¹⁴ It is unknown if these conditions contributed to the development of PN or PN contributed to the development of these disorders.

Clinical Presentations

Prurigo nodularis is a chronic inflammatory skin disease that typically manifests with multiple severely pruritic, dome-shaped, firm, hyperpigmented papulonodules with central scale or crust, often with erosion, due to chronic repetitive scratching and picking secondary to pruritic systemic or dermatologic diseases or psychological disorders (Figure 2).^1,2,4,5,8,31 Most often, diagnosis of PN is based on history and physical examination of the lesion; however, biopsies may be performed. These nodules commonly manifest with ulceration distributed symmetrically on extensor extremities in easy-to-reach places, sparing the mid back (called the butterfly sign).⁸ Lesions—either a few or hundreds—can range from a few millimeters to 2 to 3 cm.^8,32 The lesions differ in appearance depending on the pigment in the patient’s skin. In patients with darker skin tones, hyperpigmented or hypopigmented papulonodules are not uncommon, while those with fairer skin tones tend to present with erythema.³¹

Differential Diagnosis

Because of the variation in manifestation of PN, these lesions may resemble other cutaneous conditions. If the lesions are hyperkeratotic, they can mimic hypertrophic lichen planus, which mainfests with hyperkeratotic plaques or nodules on the lower extremities.^8,29 In addition, the histopathology of lichen planus resembles the appearance of PN, with epidermal hyperplasia, hypergranulosis, hyperkeratosis, and increased fibroblasts and capillaries.^8,29

Pemphigoid nodularis is a rare subtype of bullous pemphigoid that exhibits characteristics of PN with pruritic plaques and erosions.^8,29,33 The patient population for pemphigoid nodularis tends to be aged 50 to 60 years, and females are affected more frequently than males. However, pemphigoid nodularis may manifest with blistering and large plaques, which are not seen commonly with PN.²⁹ On histopathology, pemphigoid nodularis deposits IgG and C3 on the basement membrane and has subepidermal clefting, unlike PN.^7,29

Actinic prurigo manifests with pruritic papules or nodules post–UV exposure to unprotected skin.^8,29,33 This rare condition usually manifests with cheilitis and conjunctivitis. Unlike PN, which commonly affects elderly populations, actinic prurigo typically is found in young females.^8,29 Cytologic examination shows hyperkeratosis, spongiosis, and acanthosis of the epidermis with lymphocytic perivascular infiltration of the dermis.³⁴

Neurotic excoriations also tend to mimic PN with raised excoriated lesions; however, this disorder is due to neurotic picking of the skin without associated pruritus or true hyperkeratosis.^8,29,33 Histopathology shows epidermal crusting with inflammation of the upper dermis.³⁵

Infiltrative cutaneous squamous cell carcinoma (SCC) may imitate PN in appearance. It manifests as tender, ulcerated, scaly plaques or nodules. Histopathology shows cytologic atypia with an infiltrative architectural pattern and presence of collections of compact keratin and parakeratin (called keratin pearls).

Keratoacanthomas can resemble PN lesions. They usually manifest as nodules measuring 1 to 2 cm in diameter and 0.5 cm thick, resembling crateriform tumors.³⁶ On histopathology, KAs can resemble SCCs; however, KAs tend to manifest more frequently with a keratin-filled crater with a ground-glass appearance.³⁶

Inverted follicular keratosis commonly manifests on the face in elderly men as a single, flesh-colored, verrucous papule that may resemble PN. However, cytology of inverted follicular keratosis is characterized by proliferation and squamous eddies.³⁷ Consideration of the histologic findings and clinical appearance are important to differentiate between PN and cutaneous SCC.

Pseudoepitheliomatous hyperplasia is a benign condition that manifests as a plaque or nodule with crust, scale, or ulceration. Histologically, this condition presents with hyperplastic proliferation of the epidermis and adnexal epithelium.³⁸ The clinical and histologic appearance can mimic PN and other cutaneous eruptions with epidermal hyperplasia. 

In clinical cases that are resistant to treatment, biopsy is the best approach to diagnose the lesion. Due to similarities in physical appearance and superficial histologic presentation of PN, KAs from SCC, hypertrophic lichen planus, and other hyperkeratotic lesions, the biopsy should be taken at the base of the lesion to sample deeper layers of skin to differentiate these dermatologic disorders.

Management

Current treatments for PN yield varied results. Many patients with moderate to severe PN attempt multiple therapies before seeing improvement.³¹ Treatments include topical, oral, and injectable medications and are either directed at the neural or immune components of PN due to the interplay between increased nerve fibers in the lesions (neural axis) as well as increases in cytokines and other immunologic mediators (immune axis) of this condition. However, the FDA recently approved the first treatment for PN—dupilumab—which is an injectable IL-4 receptor antagonist directed at the immunologic interactions affiliated with PN.

Immune-Mediated Topical Therapies—Immunologic topical therapies include corticosteroids, calcipotriol, and calcineurin inhibitors. Studies that have analyzed these treatments are limited to case reports and small intraindividual and randomized controlled trials (Table 1). Topical therapies usually are first-line agents for most patients. Adverse effects include transient irritation of the skin.^40,42,43

Supplements—N-acetyl cysteine is an over-the-counter supplement that has been reported to improve symptoms in patients with skin-picking disorders.⁴⁸ The mechanism of action includes antioxidant effects such as decreasing reactive oxygen species, decreasing inflammatory markers, regulating neurotransmitters, and inhibiting hyperkeratosis.⁴⁹ N-acetyl cysteine has been poorly studied for its application in PN. A small study of 3 patients with subacute PN receiving 1200 mg of oral N-acetyl cysteine reported varying levels of improvement in skin appearance and reduction in skin picking.⁵⁰

Phototherapy—Phototherapy, a typical first- or second-line treatment modality for PN, targets both the neural- and immune-mediated aspects associated with pruritus in PN (Table 1).⁵¹ UV light can penetrate through the epidermal layer of the skin and reach the keratinocytes, which play a role in the immune-related response of PN. In addition, the cutaneous sensory nerves are located in the upper dermal layer, from which nerve fibers grow and penetrate into the epidermis, thereby interacting with the keratinocytes where pruritic signals are transmitted from the periphery up to the brain.⁵¹

Studies analyzing the effects of phototherapy on PN are limited to case series and a small randomized controlled trial. However, this trial has shown improvements in pruritus in the participants. Adverse effects include transient burning and erythema at the treated sites.^44,45

Immune-Mediated Oral Therapies—Immunologic-targeted oral therapies include bilastine, methotrexate, and cyclosporine (Table 2).^52,53 Bilastine efficacy was analyzed in a small phase 3, open-label, multicenter study in Japan; however, patients were allowed to use topical steroids in conjunction with the oral antihistamine.⁵⁴ Methotrexate and cyclosporine are immunosuppressive medications and were analyzed in small retrospective studies. Both treatments yielded notable relief for patients; however, 38.5% (15/39) of patients receiving methotrexate experienced adverse events, and 50.0% (4/8) experienced adverse events with cyclosporine.^52,53

Thalidomide was studied in a small retrospective case review that showed notable improvement in PN. Dosages of thalidomide varied, but on average the dose was 100 mg/d. However, greater than 50% of patients experienced at least 1 adverse effect with this treatment.⁶³

A study performed in Italy showed promising results for patients treated with pregabalin, with 70.0% (21/30) continuing to take pregabalin for almost 2 years following completion of the initial 3-month trial.⁵⁵ Naltrexone decreased pruritus in more than half of patients (9/17).⁵⁹ Amitriptyline yielded improvements in patients with PN; however, disease recurred in 5 patients (29%) after 7 months.⁶² A study performed in Germany reported promising results for paroxetine and fluvoxamine; however, some patients enrolled in the study had some form of psychiatric disorder.⁶¹

Serlopitant, aprepitant, and nalbuphine were studied in randomized controlled trials. The serlopitant trials were the largest of the neurally mediated oral medication studies; one showed substantial improvement in patients with PN,⁵⁶ while the most recent trial did not show significant improvement (ClinicalTrials.gov identifier NCT03546816).⁵⁷ On the other hand, aprepitant showed no major difference between the experimental and placebo groups.⁵⁸ Nalbuphine 162 mg twice daily showed greater improvement in PN than nalbuphine 81 mg twice daily.⁶⁰

Immune-Mediated Injectable Therapies—Immune-targeted injectables include nemolizumab and dupilumab (Table 2). Nemolizumab is an IL-31 antagonist that has been studied in a small randomized controlled trial that showed great success in decreasing pruritus associated with PN.⁶⁴ IL-31 has been implicated in PN, and inhibition of the IL-31 receptor has been shown to disrupt the itch-scratch cycle of PN. Dupilumab is a monoclonal antibody against the IL-4 and IL-13 receptors, and it is the only FDA-approved treatment for PN.⁶⁵ Blockage of these protein receptors decreases type 2 inflammation and chronic pruritus.^66,67 Dupilumab is FDA approved for the treatment of atopic dermatitis and recently was approved for adults with PN. Dupilumab acts to block the shared α-subunit of the pruritogenic cytokines IL-4 and IL-13 pathways,²⁹ thereby breaking the itch-scratch cycle associated with PN and allowing for the healing of these lesions. Results from 2 clinical trials showed substantially reduced itch in patients with PN.⁶⁵ Dupilumab also was approved by the European Medicines Agency for moderate to severe PN.⁶⁸

Conclusion

Prurigo nodularis is a chronic condition that affects patient quality of life and can mimic various dermatologic conditions. The epidemiology and pathophysiology of PN have not been fully expounded. More research should be conducted to determine the underpinnings of PN to help identify more consistently effective therapies for this complex condition.

Prurigo nodularis (PN)(also called chronic nodular prurigo, prurigo nodularis of Hyde, or picker’s nodules) was first characterized by James Hyde in 1909.^1-3 Prurigo nodularis manifests with symmetrical, intensely pruritic, eroded, or hyperkeratotic nodules or papules on the extremities and trunk.^1,2,4,5 Studies have shown that individuals with PN experience pruritus, sleep loss, decreased social functioning from the appearance of the nodules, and a higher incidence of anxiety and depression, causing a negative impact on their quality of life.^2,6 In addition, the manifestation of PN has been linked to neurologic and psychiatric disorders; however, PN also can be idiopathic and manifest without underlying illnesses.^2,6,7

Prurigo nodularis has been associated with other dermatologic conditions such as atopic dermatitis (up to 50%), lichen planus, keratoacanthomas (KAs), and bullous pemphigoid.^7-9 It also has been linked to systemic diseases in 38% to 50% of cases, including chronic kidney disease, liver disease, type 2 diabetes mellitus, malignancies (hematopoietic, liver, and skin), and HIV infection.^6,8,10

The pathophysiology of PN is highly complex and has yet to be fully elucidated. It is thought to be due to dysregulation and interaction of the increase in neural and immunologic responses of proinflammatory and pruritogenic cytokines.^2,11 Treatments aim to break the itch-scratch cycle that perpetuates this disorder; however, this proves difficult, as PN is associated with a higher itch intensity than atopic dermatitis and psoriasis.¹⁰ Therefore, most patients attempt multiple forms of treatment for PN, ranging from topical therapies, oral immunosuppressants, and phototherapy to the newest and only medication approved by the US Food and Drug Administration for the treatment of PN—dupilumab.^1,7,11 Herein, we provide an updated review of PN with a focus on its epidemiology, histopathology and pathophysiology, comorbidities, clinical presentation, differential diagnosis, and current treatment options.

Epidemiology

There are few studies on the epidemiology of PN; however, middle-aged populations with underlying dermatologic or psychiatric disorders tend to be impacted most frequently.^2,12,13 In 2016, it was estimated that almost 88,000 individuals had PN in the United States, with the majority being female; however, this estimate only took into account those aged 18 to 64 years and utilized data from IBM MarketScan Commercial Claims and Encounters Database (IBM Watson Health) from October 2015 to December 2016.¹⁴ More recently, a retrospective database analysis estimated the prevalence of PN in the United States to be anywhere from 36.7 to 43.9 cases per 100,000 individuals. However, this retrospective review utilized the International Classification of Diseases, Tenth Revision code; PN has 2 codes associated with the diagnosis, and the coding accuracy is unknown.¹⁵ Sutaria et al¹⁶ looked at racial disparities in patients with PN utilizing data from TriNetX and found that patients who received a diagnosis of PN were more likely to be women, non-Hispanic, and Black compared with control patients. However, these estimates are restricted to the health care organizations within this database.

In 2018, Poland reported an annual prevalence of 6.52 cases per 100,000 individuals,¹⁷ while England reported a yearly prevalence of 3.27 cases per 100,000 individuals.¹⁸ Both countries reported most cases were female. However, these studies are not without limitations. Poland only uses the primary diagnosis code for medical billing to simplify clinical coding, thus underestimating the actual prevalence; furthermore, clinical codes more often than not are assigned by someone other than the diagnosing physician, leaving room for error.¹⁷ In addition, England’s PN estimate utilized diagnosis data from primary care and inpatient datasets, leaving out outpatient datasets in which patients with PN may have been referred and obtained the diagnosis, potentially underestimating the prevalence in this population.¹⁸

In contrast, Korea estimated the annual prevalence of PN to be 4.82 cases per 1000 dermatology outpatients, with the majority being men, based on results from a cross-sectional study among outpatients from the Catholic Medical Center. Although this is the largest health organization in Korea, the scope of this study is limited and lacks data from other medical centers in Korea.¹⁹

Histopathology and Pathophysiology

Almost all cells in the skin are involved in PN: keratinocytes, mast cells, dendritic cells, endothelial cells, lymphocytes, eosinophils, collagen fibers, and nerve fibers.^11,20 Classically, PN manifests as a dome-shaped lesion with hyperkeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia with increased thickness of the papillary dermis consisting of coarse collagen with compact interstitial and circumvascular infiltration as well as increased lymphocytes and histocytes in the superficial dermis (Figure 1).²⁰ Hyperkeratosis is thought to be due to either the alteration of keratinocyte structures from scratching or keratinocyte abnormalities triggering PN.²¹ However, the increase in keratinocytes, which secrete nerve growth factor, allows for neuronal hyperplasia within the dermis.²² Nerve growth factor can stimulate keratinocyte proliferation²³ in addition to the upregulation of substance P (SP), a tachykinin that triggers vascular dilation and pruritus in the skin.²⁴ The density of SP nerve fibers in the dermis increases in PN, causing proinflammatory effects, upregulating the immune response to promote endothelial hyperplasia and increased vascularization.²⁵ The increase in these fibers may lead to pruritus associated with PN.^2,26

Many inflammatory cytokines and mediators also have been implicated in PN. Increased messenger RNA expression of IL-4, IL-17, IL-22, and IL-31 has been described in PN lesions.^3,27 Furthermore, studies also have reported increased helper T cell (T_H2) cytokines, including IL-4, IL-5, IL-10, and IL-13, in the dermis of PN lesions in patients without a history of atopy.^3,28 These pruritogenic cytokines in conjunction with the SP fibers may create an intractable itch for those with PN. The interaction and culmination of the neural and immune responses make PN a complex condition to treat with the multifactorial interaction of systems. 

Comorbidities

Prurigo nodularis has been associated with a wide array of comorbidities; however, the direction of the relationship between PN and these conditions makes it difficult to discern if PN is a primary or secondary condition.²⁹ Prurigo nodularis commonly has been connected to other inflammatory dermatoses, with a link to atopic dermatitis being the strongest.^5,29 However, PN also has been linked to other pruritic inflammatory cutaneous disorders, including psoriasis, cutaneous T-cell lymphoma, lichen planus, and dermatitis herpetiformis.^14,29

Huang et al¹⁴ found an increased likelihood of psychiatric illnesses in patients with PN, including eating disorders, nonsuicidal self-injury disorder, attention-deficit/hyperactivity disorder, schizophrenia, mood disorders, anxiety, and substance abuse disorders. Treatments directed at the neural aspect of PN have included selective serotonin reuptake inhibitors (SSRIs), which also are utilized to treat these mental health disorders.

Furthermore, systemic diseases also have been found to be associated with PN, including hypertension, type 2 diabetes mellitus, chronic kidney disease, heart failure, cerebrovascular disease, coronary heart disease, and chronic obstructive pulmonary disease.¹⁴ The relationship between PN and systemic conditions may be due to increased systemic inflammation and dysregulation of neural and metabolic functions implicated in these conditions from increased pruritic manifestations.^29,30 However, studies also have connected PN to infectious conditions such as HIV. One study found that patients with PN had 2.68 higher odds of infection with HIV compared to age- and sex-matched controls.¹⁴ It is unknown if these conditions contributed to the development of PN or PN contributed to the development of these disorders.

Clinical Presentations

Prurigo nodularis is a chronic inflammatory skin disease that typically manifests with multiple severely pruritic, dome-shaped, firm, hyperpigmented papulonodules with central scale or crust, often with erosion, due to chronic repetitive scratching and picking secondary to pruritic systemic or dermatologic diseases or psychological disorders (Figure 2).^1,2,4,5,8,31 Most often, diagnosis of PN is based on history and physical examination of the lesion; however, biopsies may be performed. These nodules commonly manifest with ulceration distributed symmetrically on extensor extremities in easy-to-reach places, sparing the mid back (called the butterfly sign).⁸ Lesions—either a few or hundreds—can range from a few millimeters to 2 to 3 cm.^8,32 The lesions differ in appearance depending on the pigment in the patient’s skin. In patients with darker skin tones, hyperpigmented or hypopigmented papulonodules are not uncommon, while those with fairer skin tones tend to present with erythema.³¹

Differential Diagnosis

Because of the variation in manifestation of PN, these lesions may resemble other cutaneous conditions. If the lesions are hyperkeratotic, they can mimic hypertrophic lichen planus, which mainfests with hyperkeratotic plaques or nodules on the lower extremities.^8,29 In addition, the histopathology of lichen planus resembles the appearance of PN, with epidermal hyperplasia, hypergranulosis, hyperkeratosis, and increased fibroblasts and capillaries.^8,29

Pemphigoid nodularis is a rare subtype of bullous pemphigoid that exhibits characteristics of PN with pruritic plaques and erosions.^8,29,33 The patient population for pemphigoid nodularis tends to be aged 50 to 60 years, and females are affected more frequently than males. However, pemphigoid nodularis may manifest with blistering and large plaques, which are not seen commonly with PN.²⁹ On histopathology, pemphigoid nodularis deposits IgG and C3 on the basement membrane and has subepidermal clefting, unlike PN.^7,29

Actinic prurigo manifests with pruritic papules or nodules post–UV exposure to unprotected skin.^8,29,33 This rare condition usually manifests with cheilitis and conjunctivitis. Unlike PN, which commonly affects elderly populations, actinic prurigo typically is found in young females.^8,29 Cytologic examination shows hyperkeratosis, spongiosis, and acanthosis of the epidermis with lymphocytic perivascular infiltration of the dermis.³⁴

Neurotic excoriations also tend to mimic PN with raised excoriated lesions; however, this disorder is due to neurotic picking of the skin without associated pruritus or true hyperkeratosis.^8,29,33 Histopathology shows epidermal crusting with inflammation of the upper dermis.³⁵

Infiltrative cutaneous squamous cell carcinoma (SCC) may imitate PN in appearance. It manifests as tender, ulcerated, scaly plaques or nodules. Histopathology shows cytologic atypia with an infiltrative architectural pattern and presence of collections of compact keratin and parakeratin (called keratin pearls).

Keratoacanthomas can resemble PN lesions. They usually manifest as nodules measuring 1 to 2 cm in diameter and 0.5 cm thick, resembling crateriform tumors.³⁶ On histopathology, KAs can resemble SCCs; however, KAs tend to manifest more frequently with a keratin-filled crater with a ground-glass appearance.³⁶

Inverted follicular keratosis commonly manifests on the face in elderly men as a single, flesh-colored, verrucous papule that may resemble PN. However, cytology of inverted follicular keratosis is characterized by proliferation and squamous eddies.³⁷ Consideration of the histologic findings and clinical appearance are important to differentiate between PN and cutaneous SCC.

Pseudoepitheliomatous hyperplasia is a benign condition that manifests as a plaque or nodule with crust, scale, or ulceration. Histologically, this condition presents with hyperplastic proliferation of the epidermis and adnexal epithelium.³⁸ The clinical and histologic appearance can mimic PN and other cutaneous eruptions with epidermal hyperplasia. 

In clinical cases that are resistant to treatment, biopsy is the best approach to diagnose the lesion. Due to similarities in physical appearance and superficial histologic presentation of PN, KAs from SCC, hypertrophic lichen planus, and other hyperkeratotic lesions, the biopsy should be taken at the base of the lesion to sample deeper layers of skin to differentiate these dermatologic disorders.

Management

Current treatments for PN yield varied results. Many patients with moderate to severe PN attempt multiple therapies before seeing improvement.³¹ Treatments include topical, oral, and injectable medications and are either directed at the neural or immune components of PN due to the interplay between increased nerve fibers in the lesions (neural axis) as well as increases in cytokines and other immunologic mediators (immune axis) of this condition. However, the FDA recently approved the first treatment for PN—dupilumab—which is an injectable IL-4 receptor antagonist directed at the immunologic interactions affiliated with PN.

Immune-Mediated Topical Therapies—Immunologic topical therapies include corticosteroids, calcipotriol, and calcineurin inhibitors. Studies that have analyzed these treatments are limited to case reports and small intraindividual and randomized controlled trials (Table 1). Topical therapies usually are first-line agents for most patients. Adverse effects include transient irritation of the skin.^40,42,43

Supplements—N-acetyl cysteine is an over-the-counter supplement that has been reported to improve symptoms in patients with skin-picking disorders.⁴⁸ The mechanism of action includes antioxidant effects such as decreasing reactive oxygen species, decreasing inflammatory markers, regulating neurotransmitters, and inhibiting hyperkeratosis.⁴⁹ N-acetyl cysteine has been poorly studied for its application in PN. A small study of 3 patients with subacute PN receiving 1200 mg of oral N-acetyl cysteine reported varying levels of improvement in skin appearance and reduction in skin picking.⁵⁰

Phototherapy—Phototherapy, a typical first- or second-line treatment modality for PN, targets both the neural- and immune-mediated aspects associated with pruritus in PN (Table 1).⁵¹ UV light can penetrate through the epidermal layer of the skin and reach the keratinocytes, which play a role in the immune-related response of PN. In addition, the cutaneous sensory nerves are located in the upper dermal layer, from which nerve fibers grow and penetrate into the epidermis, thereby interacting with the keratinocytes where pruritic signals are transmitted from the periphery up to the brain.⁵¹

Studies analyzing the effects of phototherapy on PN are limited to case series and a small randomized controlled trial. However, this trial has shown improvements in pruritus in the participants. Adverse effects include transient burning and erythema at the treated sites.^44,45

Immune-Mediated Oral Therapies—Immunologic-targeted oral therapies include bilastine, methotrexate, and cyclosporine (Table 2).^52,53 Bilastine efficacy was analyzed in a small phase 3, open-label, multicenter study in Japan; however, patients were allowed to use topical steroids in conjunction with the oral antihistamine.⁵⁴ Methotrexate and cyclosporine are immunosuppressive medications and were analyzed in small retrospective studies. Both treatments yielded notable relief for patients; however, 38.5% (15/39) of patients receiving methotrexate experienced adverse events, and 50.0% (4/8) experienced adverse events with cyclosporine.^52,53

Thalidomide was studied in a small retrospective case review that showed notable improvement in PN. Dosages of thalidomide varied, but on average the dose was 100 mg/d. However, greater than 50% of patients experienced at least 1 adverse effect with this treatment.⁶³

A study performed in Italy showed promising results for patients treated with pregabalin, with 70.0% (21/30) continuing to take pregabalin for almost 2 years following completion of the initial 3-month trial.⁵⁵ Naltrexone decreased pruritus in more than half of patients (9/17).⁵⁹ Amitriptyline yielded improvements in patients with PN; however, disease recurred in 5 patients (29%) after 7 months.⁶² A study performed in Germany reported promising results for paroxetine and fluvoxamine; however, some patients enrolled in the study had some form of psychiatric disorder.⁶¹

Serlopitant, aprepitant, and nalbuphine were studied in randomized controlled trials. The serlopitant trials were the largest of the neurally mediated oral medication studies; one showed substantial improvement in patients with PN,⁵⁶ while the most recent trial did not show significant improvement (ClinicalTrials.gov identifier NCT03546816).⁵⁷ On the other hand, aprepitant showed no major difference between the experimental and placebo groups.⁵⁸ Nalbuphine 162 mg twice daily showed greater improvement in PN than nalbuphine 81 mg twice daily.⁶⁰

Immune-Mediated Injectable Therapies—Immune-targeted injectables include nemolizumab and dupilumab (Table 2). Nemolizumab is an IL-31 antagonist that has been studied in a small randomized controlled trial that showed great success in decreasing pruritus associated with PN.⁶⁴ IL-31 has been implicated in PN, and inhibition of the IL-31 receptor has been shown to disrupt the itch-scratch cycle of PN. Dupilumab is a monoclonal antibody against the IL-4 and IL-13 receptors, and it is the only FDA-approved treatment for PN.⁶⁵ Blockage of these protein receptors decreases type 2 inflammation and chronic pruritus.^66,67 Dupilumab is FDA approved for the treatment of atopic dermatitis and recently was approved for adults with PN. Dupilumab acts to block the shared α-subunit of the pruritogenic cytokines IL-4 and IL-13 pathways,²⁹ thereby breaking the itch-scratch cycle associated with PN and allowing for the healing of these lesions. Results from 2 clinical trials showed substantially reduced itch in patients with PN.⁶⁵ Dupilumab also was approved by the European Medicines Agency for moderate to severe PN.⁶⁸

Conclusion

Prurigo nodularis is a chronic condition that affects patient quality of life and can mimic various dermatologic conditions. The epidemiology and pathophysiology of PN have not been fully expounded. More research should be conducted to determine the underpinnings of PN to help identify more consistently effective therapies for this complex condition.

Prurigo nodularis (PN)(also called chronic nodular prurigo, prurigo nodularis of Hyde, or picker’s nodules) was first characterized by James Hyde in 1909.^1-3 Prurigo nodularis manifests with symmetrical, intensely pruritic, eroded, or hyperkeratotic nodules or papules on the extremities and trunk.^1,2,4,5 Studies have shown that individuals with PN experience pruritus, sleep loss, decreased social functioning from the appearance of the nodules, and a higher incidence of anxiety and depression, causing a negative impact on their quality of life.^2,6 In addition, the manifestation of PN has been linked to neurologic and psychiatric disorders; however, PN also can be idiopathic and manifest without underlying illnesses.^2,6,7

Prurigo nodularis has been associated with other dermatologic conditions such as atopic dermatitis (up to 50%), lichen planus, keratoacanthomas (KAs), and bullous pemphigoid.^7-9 It also has been linked to systemic diseases in 38% to 50% of cases, including chronic kidney disease, liver disease, type 2 diabetes mellitus, malignancies (hematopoietic, liver, and skin), and HIV infection.^6,8,10

The pathophysiology of PN is highly complex and has yet to be fully elucidated. It is thought to be due to dysregulation and interaction of the increase in neural and immunologic responses of proinflammatory and pruritogenic cytokines.^2,11 Treatments aim to break the itch-scratch cycle that perpetuates this disorder; however, this proves difficult, as PN is associated with a higher itch intensity than atopic dermatitis and psoriasis.¹⁰ Therefore, most patients attempt multiple forms of treatment for PN, ranging from topical therapies, oral immunosuppressants, and phototherapy to the newest and only medication approved by the US Food and Drug Administration for the treatment of PN—dupilumab.^1,7,11 Herein, we provide an updated review of PN with a focus on its epidemiology, histopathology and pathophysiology, comorbidities, clinical presentation, differential diagnosis, and current treatment options.

Epidemiology

There are few studies on the epidemiology of PN; however, middle-aged populations with underlying dermatologic or psychiatric disorders tend to be impacted most frequently.^2,12,13 In 2016, it was estimated that almost 88,000 individuals had PN in the United States, with the majority being female; however, this estimate only took into account those aged 18 to 64 years and utilized data from IBM MarketScan Commercial Claims and Encounters Database (IBM Watson Health) from October 2015 to December 2016.¹⁴ More recently, a retrospective database analysis estimated the prevalence of PN in the United States to be anywhere from 36.7 to 43.9 cases per 100,000 individuals. However, this retrospective review utilized the International Classification of Diseases, Tenth Revision code; PN has 2 codes associated with the diagnosis, and the coding accuracy is unknown.¹⁵ Sutaria et al¹⁶ looked at racial disparities in patients with PN utilizing data from TriNetX and found that patients who received a diagnosis of PN were more likely to be women, non-Hispanic, and Black compared with control patients. However, these estimates are restricted to the health care organizations within this database.

In 2018, Poland reported an annual prevalence of 6.52 cases per 100,000 individuals,¹⁷ while England reported a yearly prevalence of 3.27 cases per 100,000 individuals.¹⁸ Both countries reported most cases were female. However, these studies are not without limitations. Poland only uses the primary diagnosis code for medical billing to simplify clinical coding, thus underestimating the actual prevalence; furthermore, clinical codes more often than not are assigned by someone other than the diagnosing physician, leaving room for error.¹⁷ In addition, England’s PN estimate utilized diagnosis data from primary care and inpatient datasets, leaving out outpatient datasets in which patients with PN may have been referred and obtained the diagnosis, potentially underestimating the prevalence in this population.¹⁸

In contrast, Korea estimated the annual prevalence of PN to be 4.82 cases per 1000 dermatology outpatients, with the majority being men, based on results from a cross-sectional study among outpatients from the Catholic Medical Center. Although this is the largest health organization in Korea, the scope of this study is limited and lacks data from other medical centers in Korea.¹⁹

Histopathology and Pathophysiology

Almost all cells in the skin are involved in PN: keratinocytes, mast cells, dendritic cells, endothelial cells, lymphocytes, eosinophils, collagen fibers, and nerve fibers.^11,20 Classically, PN manifests as a dome-shaped lesion with hyperkeratosis, hypergranulosis, and psoriasiform epidermal hyperplasia with increased thickness of the papillary dermis consisting of coarse collagen with compact interstitial and circumvascular infiltration as well as increased lymphocytes and histocytes in the superficial dermis (Figure 1).²⁰ Hyperkeratosis is thought to be due to either the alteration of keratinocyte structures from scratching or keratinocyte abnormalities triggering PN.²¹ However, the increase in keratinocytes, which secrete nerve growth factor, allows for neuronal hyperplasia within the dermis.²² Nerve growth factor can stimulate keratinocyte proliferation²³ in addition to the upregulation of substance P (SP), a tachykinin that triggers vascular dilation and pruritus in the skin.²⁴ The density of SP nerve fibers in the dermis increases in PN, causing proinflammatory effects, upregulating the immune response to promote endothelial hyperplasia and increased vascularization.²⁵ The increase in these fibers may lead to pruritus associated with PN.^2,26

Many inflammatory cytokines and mediators also have been implicated in PN. Increased messenger RNA expression of IL-4, IL-17, IL-22, and IL-31 has been described in PN lesions.^3,27 Furthermore, studies also have reported increased helper T cell (T_H2) cytokines, including IL-4, IL-5, IL-10, and IL-13, in the dermis of PN lesions in patients without a history of atopy.^3,28 These pruritogenic cytokines in conjunction with the SP fibers may create an intractable itch for those with PN. The interaction and culmination of the neural and immune responses make PN a complex condition to treat with the multifactorial interaction of systems. 

Comorbidities

Prurigo nodularis has been associated with a wide array of comorbidities; however, the direction of the relationship between PN and these conditions makes it difficult to discern if PN is a primary or secondary condition.²⁹ Prurigo nodularis commonly has been connected to other inflammatory dermatoses, with a link to atopic dermatitis being the strongest.^5,29 However, PN also has been linked to other pruritic inflammatory cutaneous disorders, including psoriasis, cutaneous T-cell lymphoma, lichen planus, and dermatitis herpetiformis.^14,29

Huang et al¹⁴ found an increased likelihood of psychiatric illnesses in patients with PN, including eating disorders, nonsuicidal self-injury disorder, attention-deficit/hyperactivity disorder, schizophrenia, mood disorders, anxiety, and substance abuse disorders. Treatments directed at the neural aspect of PN have included selective serotonin reuptake inhibitors (SSRIs), which also are utilized to treat these mental health disorders.

Furthermore, systemic diseases also have been found to be associated with PN, including hypertension, type 2 diabetes mellitus, chronic kidney disease, heart failure, cerebrovascular disease, coronary heart disease, and chronic obstructive pulmonary disease.¹⁴ The relationship between PN and systemic conditions may be due to increased systemic inflammation and dysregulation of neural and metabolic functions implicated in these conditions from increased pruritic manifestations.^29,30 However, studies also have connected PN to infectious conditions such as HIV. One study found that patients with PN had 2.68 higher odds of infection with HIV compared to age- and sex-matched controls.¹⁴ It is unknown if these conditions contributed to the development of PN or PN contributed to the development of these disorders.

Clinical Presentations

Prurigo nodularis is a chronic inflammatory skin disease that typically manifests with multiple severely pruritic, dome-shaped, firm, hyperpigmented papulonodules with central scale or crust, often with erosion, due to chronic repetitive scratching and picking secondary to pruritic systemic or dermatologic diseases or psychological disorders (Figure 2).^1,2,4,5,8,31 Most often, diagnosis of PN is based on history and physical examination of the lesion; however, biopsies may be performed. These nodules commonly manifest with ulceration distributed symmetrically on extensor extremities in easy-to-reach places, sparing the mid back (called the butterfly sign).⁸ Lesions—either a few or hundreds—can range from a few millimeters to 2 to 3 cm.^8,32 The lesions differ in appearance depending on the pigment in the patient’s skin. In patients with darker skin tones, hyperpigmented or hypopigmented papulonodules are not uncommon, while those with fairer skin tones tend to present with erythema.³¹

Differential Diagnosis

Because of the variation in manifestation of PN, these lesions may resemble other cutaneous conditions. If the lesions are hyperkeratotic, they can mimic hypertrophic lichen planus, which mainfests with hyperkeratotic plaques or nodules on the lower extremities.^8,29 In addition, the histopathology of lichen planus resembles the appearance of PN, with epidermal hyperplasia, hypergranulosis, hyperkeratosis, and increased fibroblasts and capillaries.^8,29

Pemphigoid nodularis is a rare subtype of bullous pemphigoid that exhibits characteristics of PN with pruritic plaques and erosions.^8,29,33 The patient population for pemphigoid nodularis tends to be aged 50 to 60 years, and females are affected more frequently than males. However, pemphigoid nodularis may manifest with blistering and large plaques, which are not seen commonly with PN.²⁹ On histopathology, pemphigoid nodularis deposits IgG and C3 on the basement membrane and has subepidermal clefting, unlike PN.^7,29

Actinic prurigo manifests with pruritic papules or nodules post–UV exposure to unprotected skin.^8,29,33 This rare condition usually manifests with cheilitis and conjunctivitis. Unlike PN, which commonly affects elderly populations, actinic prurigo typically is found in young females.^8,29 Cytologic examination shows hyperkeratosis, spongiosis, and acanthosis of the epidermis with lymphocytic perivascular infiltration of the dermis.³⁴

Neurotic excoriations also tend to mimic PN with raised excoriated lesions; however, this disorder is due to neurotic picking of the skin without associated pruritus or true hyperkeratosis.^8,29,33 Histopathology shows epidermal crusting with inflammation of the upper dermis.³⁵

Infiltrative cutaneous squamous cell carcinoma (SCC) may imitate PN in appearance. It manifests as tender, ulcerated, scaly plaques or nodules. Histopathology shows cytologic atypia with an infiltrative architectural pattern and presence of collections of compact keratin and parakeratin (called keratin pearls).

Keratoacanthomas can resemble PN lesions. They usually manifest as nodules measuring 1 to 2 cm in diameter and 0.5 cm thick, resembling crateriform tumors.³⁶ On histopathology, KAs can resemble SCCs; however, KAs tend to manifest more frequently with a keratin-filled crater with a ground-glass appearance.³⁶

Inverted follicular keratosis commonly manifests on the face in elderly men as a single, flesh-colored, verrucous papule that may resemble PN. However, cytology of inverted follicular keratosis is characterized by proliferation and squamous eddies.³⁷ Consideration of the histologic findings and clinical appearance are important to differentiate between PN and cutaneous SCC.

Pseudoepitheliomatous hyperplasia is a benign condition that manifests as a plaque or nodule with crust, scale, or ulceration. Histologically, this condition presents with hyperplastic proliferation of the epidermis and adnexal epithelium.³⁸ The clinical and histologic appearance can mimic PN and other cutaneous eruptions with epidermal hyperplasia. 

In clinical cases that are resistant to treatment, biopsy is the best approach to diagnose the lesion. Due to similarities in physical appearance and superficial histologic presentation of PN, KAs from SCC, hypertrophic lichen planus, and other hyperkeratotic lesions, the biopsy should be taken at the base of the lesion to sample deeper layers of skin to differentiate these dermatologic disorders.

Management

Current treatments for PN yield varied results. Many patients with moderate to severe PN attempt multiple therapies before seeing improvement.³¹ Treatments include topical, oral, and injectable medications and are either directed at the neural or immune components of PN due to the interplay between increased nerve fibers in the lesions (neural axis) as well as increases in cytokines and other immunologic mediators (immune axis) of this condition. However, the FDA recently approved the first treatment for PN—dupilumab—which is an injectable IL-4 receptor antagonist directed at the immunologic interactions affiliated with PN.

Immune-Mediated Topical Therapies—Immunologic topical therapies include corticosteroids, calcipotriol, and calcineurin inhibitors. Studies that have analyzed these treatments are limited to case reports and small intraindividual and randomized controlled trials (Table 1). Topical therapies usually are first-line agents for most patients. Adverse effects include transient irritation of the skin.^40,42,43

Supplements—N-acetyl cysteine is an over-the-counter supplement that has been reported to improve symptoms in patients with skin-picking disorders.⁴⁸ The mechanism of action includes antioxidant effects such as decreasing reactive oxygen species, decreasing inflammatory markers, regulating neurotransmitters, and inhibiting hyperkeratosis.⁴⁹ N-acetyl cysteine has been poorly studied for its application in PN. A small study of 3 patients with subacute PN receiving 1200 mg of oral N-acetyl cysteine reported varying levels of improvement in skin appearance and reduction in skin picking.⁵⁰

Phototherapy—Phototherapy, a typical first- or second-line treatment modality for PN, targets both the neural- and immune-mediated aspects associated with pruritus in PN (Table 1).⁵¹ UV light can penetrate through the epidermal layer of the skin and reach the keratinocytes, which play a role in the immune-related response of PN. In addition, the cutaneous sensory nerves are located in the upper dermal layer, from which nerve fibers grow and penetrate into the epidermis, thereby interacting with the keratinocytes where pruritic signals are transmitted from the periphery up to the brain.⁵¹

Studies analyzing the effects of phototherapy on PN are limited to case series and a small randomized controlled trial. However, this trial has shown improvements in pruritus in the participants. Adverse effects include transient burning and erythema at the treated sites.^44,45

Immune-Mediated Oral Therapies—Immunologic-targeted oral therapies include bilastine, methotrexate, and cyclosporine (Table 2).^52,53 Bilastine efficacy was analyzed in a small phase 3, open-label, multicenter study in Japan; however, patients were allowed to use topical steroids in conjunction with the oral antihistamine.⁵⁴ Methotrexate and cyclosporine are immunosuppressive medications and were analyzed in small retrospective studies. Both treatments yielded notable relief for patients; however, 38.5% (15/39) of patients receiving methotrexate experienced adverse events, and 50.0% (4/8) experienced adverse events with cyclosporine.^52,53

Thalidomide was studied in a small retrospective case review that showed notable improvement in PN. Dosages of thalidomide varied, but on average the dose was 100 mg/d. However, greater than 50% of patients experienced at least 1 adverse effect with this treatment.⁶³

A study performed in Italy showed promising results for patients treated with pregabalin, with 70.0% (21/30) continuing to take pregabalin for almost 2 years following completion of the initial 3-month trial.⁵⁵ Naltrexone decreased pruritus in more than half of patients (9/17).⁵⁹ Amitriptyline yielded improvements in patients with PN; however, disease recurred in 5 patients (29%) after 7 months.⁶² A study performed in Germany reported promising results for paroxetine and fluvoxamine; however, some patients enrolled in the study had some form of psychiatric disorder.⁶¹

Serlopitant, aprepitant, and nalbuphine were studied in randomized controlled trials. The serlopitant trials were the largest of the neurally mediated oral medication studies; one showed substantial improvement in patients with PN,⁵⁶ while the most recent trial did not show significant improvement (ClinicalTrials.gov identifier NCT03546816).⁵⁷ On the other hand, aprepitant showed no major difference between the experimental and placebo groups.⁵⁸ Nalbuphine 162 mg twice daily showed greater improvement in PN than nalbuphine 81 mg twice daily.⁶⁰

Immune-Mediated Injectable Therapies—Immune-targeted injectables include nemolizumab and dupilumab (Table 2). Nemolizumab is an IL-31 antagonist that has been studied in a small randomized controlled trial that showed great success in decreasing pruritus associated with PN.⁶⁴ IL-31 has been implicated in PN, and inhibition of the IL-31 receptor has been shown to disrupt the itch-scratch cycle of PN. Dupilumab is a monoclonal antibody against the IL-4 and IL-13 receptors, and it is the only FDA-approved treatment for PN.⁶⁵ Blockage of these protein receptors decreases type 2 inflammation and chronic pruritus.^66,67 Dupilumab is FDA approved for the treatment of atopic dermatitis and recently was approved for adults with PN. Dupilumab acts to block the shared α-subunit of the pruritogenic cytokines IL-4 and IL-13 pathways,²⁹ thereby breaking the itch-scratch cycle associated with PN and allowing for the healing of these lesions. Results from 2 clinical trials showed substantially reduced itch in patients with PN.⁶⁵ Dupilumab also was approved by the European Medicines Agency for moderate to severe PN.⁶⁸

Conclusion

Prurigo nodularis is a chronic condition that affects patient quality of life and can mimic various dermatologic conditions. The epidemiology and pathophysiology of PN have not been fully expounded. More research should be conducted to determine the underpinnings of PN to help identify more consistently effective therapies for this complex condition.

To the Editor:

Pityriasis rubra pilaris (PRP) is a rare papulosquamous condition with an unknown pathogenesis and limited efficacy data, which can make treatment challenging. Some cases of PRP spontaneously resolve in a few months, which is most common in the pediatric population.¹ Pityriasis rubra pilaris in adults is likely to persist for years, and spontaneous resolution is unpredictable. Randomized clinical trials are difficult to perform due to the rarity of PRP.

Although there is no cure and no standard protocol for treating PRP, systemic retinoids historically are considered first-line therapy for moderate to severe cases.² Additional management approaches include symptomatic control with moisturizers and psychological support. Alternative systemic treatments for moderate to severe cases include methotrexate, phototherapy, and cyclosporine.²

Pityriasis rubra pilaris demonstrates a favorable response to methotrexate treatment, especially in type I cases; however, patients on this alternative therapy should be monitored for severe adverse effects (eg, hepatotoxicity, pancytopenia, pneumonitis).² Phototherapy should be approached with caution. Narrowband UVB, UVA1, and psoralen plus UVA therapy have successfully treated PRP; however, the response is variable. In some cases, the opposite effect can occur, in which the condition is photoaggravated. Phototherapy is a valid alternative form of treatment when used in combination with acitretin, and a phototest should be performed prior to starting this regimen. Cyclosporine is another immunosuppressant that can be considered for PRP treatment, though there are limited data demonstrating its efficacy.²

The introduction of biologic agents has changed the treatment approach for many dermatologic diseases, including PRP. Given the similar features between psoriasis and PRP, the biologics prescribed for psoriasis therapy also are used for patients with PRP that is challenging to treat, such as anti–tumor necrosis factor α inhibitors and IL inhibitors—specifically IL-17 and IL-23. Remission has been achieved with the use of biologics in combination with retinoid therapy.²

Biologic therapies used for PRP effectively inhibit cytokines and reduce the overall inflammatory processes involved in the development of the scaly patches and plaques seen in this condition. However, most reported clinical experiences are case studies, and more research in the form of randomized clinical trials is needed to understand the efficacy and long-term effects of this form of treatment in PRP. We present a case of a patient with refractory adult subtype I PRP that was successfully treated with the IL-23 inhibitor risankizumab.

A 65-year-old man was referred to Florida Academic Dermatology Center (Coral Gables, Florida) with biopsy-proven PRP diagnosed 1 year prior. The patient reported experiencing a debilitating quality of life in the year since diagnosis (Figure 1). Treatment attempts with dupilumab, tralokinumab, intramuscular steroid injections, and topical corticosteroids had failed (Figure 2). Following evaluation at Florida Academic Dermatology Center, the patient was started on acitretin 25 mg every other day and received an initial subcutaneous injection of ixekizumab 160 mg (an IL-17 inhibitor) followed 2 weeks later by a second injection of 80 mg. After the 2 doses of ixekizumab, the patient’s condition worsened with the development of pinpoint hemorrhagic lesions. The medication was discontinued, and he was started on risankizumab 150 mg at the approved dosing regimen for plaque psoriasis in combination with the acitretin therapy. Prior to starting risankizumab, the affected body surface area (BSA) was 80%. At 1-month follow-up, he showed improvement with reduction in scaling and erythema and an affected BSA of 30% (Figure 3). At 4-month follow-up, he continued showing improvement with an affected BSA of 10% (Figure 4). Acitretin was discontinued, and the patient has been successfully maintained on risankizumab 150 mg/mL subcutaneous injections every 12 weeks since.

To the Editor:

Pityriasis rubra pilaris (PRP) is a rare papulosquamous condition with an unknown pathogenesis and limited efficacy data, which can make treatment challenging. Some cases of PRP spontaneously resolve in a few months, which is most common in the pediatric population.¹ Pityriasis rubra pilaris in adults is likely to persist for years, and spontaneous resolution is unpredictable. Randomized clinical trials are difficult to perform due to the rarity of PRP.

Although there is no cure and no standard protocol for treating PRP, systemic retinoids historically are considered first-line therapy for moderate to severe cases.² Additional management approaches include symptomatic control with moisturizers and psychological support. Alternative systemic treatments for moderate to severe cases include methotrexate, phototherapy, and cyclosporine.²

Pityriasis rubra pilaris demonstrates a favorable response to methotrexate treatment, especially in type I cases; however, patients on this alternative therapy should be monitored for severe adverse effects (eg, hepatotoxicity, pancytopenia, pneumonitis).² Phototherapy should be approached with caution. Narrowband UVB, UVA1, and psoralen plus UVA therapy have successfully treated PRP; however, the response is variable. In some cases, the opposite effect can occur, in which the condition is photoaggravated. Phototherapy is a valid alternative form of treatment when used in combination with acitretin, and a phototest should be performed prior to starting this regimen. Cyclosporine is another immunosuppressant that can be considered for PRP treatment, though there are limited data demonstrating its efficacy.²

The introduction of biologic agents has changed the treatment approach for many dermatologic diseases, including PRP. Given the similar features between psoriasis and PRP, the biologics prescribed for psoriasis therapy also are used for patients with PRP that is challenging to treat, such as anti–tumor necrosis factor α inhibitors and IL inhibitors—specifically IL-17 and IL-23. Remission has been achieved with the use of biologics in combination with retinoid therapy.²

Biologic therapies used for PRP effectively inhibit cytokines and reduce the overall inflammatory processes involved in the development of the scaly patches and plaques seen in this condition. However, most reported clinical experiences are case studies, and more research in the form of randomized clinical trials is needed to understand the efficacy and long-term effects of this form of treatment in PRP. We present a case of a patient with refractory adult subtype I PRP that was successfully treated with the IL-23 inhibitor risankizumab.

A 65-year-old man was referred to Florida Academic Dermatology Center (Coral Gables, Florida) with biopsy-proven PRP diagnosed 1 year prior. The patient reported experiencing a debilitating quality of life in the year since diagnosis (Figure 1). Treatment attempts with dupilumab, tralokinumab, intramuscular steroid injections, and topical corticosteroids had failed (Figure 2). Following evaluation at Florida Academic Dermatology Center, the patient was started on acitretin 25 mg every other day and received an initial subcutaneous injection of ixekizumab 160 mg (an IL-17 inhibitor) followed 2 weeks later by a second injection of 80 mg. After the 2 doses of ixekizumab, the patient’s condition worsened with the development of pinpoint hemorrhagic lesions. The medication was discontinued, and he was started on risankizumab 150 mg at the approved dosing regimen for plaque psoriasis in combination with the acitretin therapy. Prior to starting risankizumab, the affected body surface area (BSA) was 80%. At 1-month follow-up, he showed improvement with reduction in scaling and erythema and an affected BSA of 30% (Figure 3). At 4-month follow-up, he continued showing improvement with an affected BSA of 10% (Figure 4). Acitretin was discontinued, and the patient has been successfully maintained on risankizumab 150 mg/mL subcutaneous injections every 12 weeks since.

To the Editor:

Pityriasis rubra pilaris (PRP) is a rare papulosquamous condition with an unknown pathogenesis and limited efficacy data, which can make treatment challenging. Some cases of PRP spontaneously resolve in a few months, which is most common in the pediatric population.¹ Pityriasis rubra pilaris in adults is likely to persist for years, and spontaneous resolution is unpredictable. Randomized clinical trials are difficult to perform due to the rarity of PRP.

Although there is no cure and no standard protocol for treating PRP, systemic retinoids historically are considered first-line therapy for moderate to severe cases.² Additional management approaches include symptomatic control with moisturizers and psychological support. Alternative systemic treatments for moderate to severe cases include methotrexate, phototherapy, and cyclosporine.²

Pityriasis rubra pilaris demonstrates a favorable response to methotrexate treatment, especially in type I cases; however, patients on this alternative therapy should be monitored for severe adverse effects (eg, hepatotoxicity, pancytopenia, pneumonitis).² Phototherapy should be approached with caution. Narrowband UVB, UVA1, and psoralen plus UVA therapy have successfully treated PRP; however, the response is variable. In some cases, the opposite effect can occur, in which the condition is photoaggravated. Phototherapy is a valid alternative form of treatment when used in combination with acitretin, and a phototest should be performed prior to starting this regimen. Cyclosporine is another immunosuppressant that can be considered for PRP treatment, though there are limited data demonstrating its efficacy.²

The introduction of biologic agents has changed the treatment approach for many dermatologic diseases, including PRP. Given the similar features between psoriasis and PRP, the biologics prescribed for psoriasis therapy also are used for patients with PRP that is challenging to treat, such as anti–tumor necrosis factor α inhibitors and IL inhibitors—specifically IL-17 and IL-23. Remission has been achieved with the use of biologics in combination with retinoid therapy.²

Biologic therapies used for PRP effectively inhibit cytokines and reduce the overall inflammatory processes involved in the development of the scaly patches and plaques seen in this condition. However, most reported clinical experiences are case studies, and more research in the form of randomized clinical trials is needed to understand the efficacy and long-term effects of this form of treatment in PRP. We present a case of a patient with refractory adult subtype I PRP that was successfully treated with the IL-23 inhibitor risankizumab.

A 65-year-old man was referred to Florida Academic Dermatology Center (Coral Gables, Florida) with biopsy-proven PRP diagnosed 1 year prior. The patient reported experiencing a debilitating quality of life in the year since diagnosis (Figure 1). Treatment attempts with dupilumab, tralokinumab, intramuscular steroid injections, and topical corticosteroids had failed (Figure 2). Following evaluation at Florida Academic Dermatology Center, the patient was started on acitretin 25 mg every other day and received an initial subcutaneous injection of ixekizumab 160 mg (an IL-17 inhibitor) followed 2 weeks later by a second injection of 80 mg. After the 2 doses of ixekizumab, the patient’s condition worsened with the development of pinpoint hemorrhagic lesions. The medication was discontinued, and he was started on risankizumab 150 mg at the approved dosing regimen for plaque psoriasis in combination with the acitretin therapy. Prior to starting risankizumab, the affected body surface area (BSA) was 80%. At 1-month follow-up, he showed improvement with reduction in scaling and erythema and an affected BSA of 30% (Figure 3). At 4-month follow-up, he continued showing improvement with an affected BSA of 10% (Figure 4). Acitretin was discontinued, and the patient has been successfully maintained on risankizumab 150 mg/mL subcutaneous injections every 12 weeks since.