UV Exposure Tied to Dermatomyositis in Women

The intensity of exposure to ambient ultraviolet radiation appears to determine the prevalence of dermatomyositis and an autoantibody specific to the disease in women, based on a study published in Arthritis & Rheumatism.

The UV Index across geographical regions of the United States also significantly correlated with the presence of an autoantibody unique to dermatomyositis (DM)—known as anti-Mi-2—and not to autoantibodies more commonly found in polymyositis (PM).

The association between UV radiation and DM was strongest in a collective group of white, Hispanic, and Asian American women, but it also was significant among black women.

This is the first study to show evidence of the influence of sex on the association between UV radiation and autoimmune disorders, commented Dr. Victoria P. Werth, professor of dermatology at the University of Pennsylvania, Philadelphia, and chief of dermatology at the Philadelphia Veterans Affairs Medical Center.

“This is the best study that I've seen so far in reference to dermatomyositis” and exposure to UV radiation, she said.

The study brings up many “intriguing kinds of things that we don't totally understand,” such as differences in risk factors and responses to UV radiation between men and women and between polymyositis and dermatomyositis.

These types of “interesting epidemiologic observations” may help in the future to understand more about the differences in pathogenesis, Dr. Werth said in an interview.

In the cross-sectional, retrospective study, Dr. Lori A. Love of the National Institute of Environmental Health Sciences and her coinvestigators gathered clinical data and serum samples from 202 PM and 178 DM patients at referral centers across the United States.

The investigators detected myositis-specific autoantibodies in 172 patients (45%), some of which were found in both polymyositis and dermatomyositis patients, whereas others were found only in each particular phenotypic type of myositis, such as anti-SRP in 21 PM patients and anti-Mi-2 in 23 DM patients.

Polymyositis occurred in a significantly greater proportion of black patients (66%) than among nonblack patients (48%), the study showed.

Most (86%) of the patients with anti-SRP antibodies were black, Dr. Love and her associates reported (Arthritis Rheum. 2009;60:2499-504).

The proportion of patients in the study who had anti-Mi-2 autoantibodies was significantly associated with the UV Index for the seven regions (comprising 37 states) that the investigators categorized according to shared geoclimatic factors. However, the UV Index was not associated with the proportion of patients with DM. Both of these comparisons proved to be significant for women but not for men.

Evidence from a previous study has shown that the dose of UV radiation required to induce immunosuppression is three times higher in women than in men, which may mean “other mechanisms would need to be operative to potentially explain how UV radiation preferentially results in the development of dermatomyositis and anti-Mi-2 autoantibodies in women,” the investigators wrote.

They noted that “it is tempting to speculate that the development of DM and DM-specific anti-Mi-2 autoantibodies, which are associated with certain major histocompatibility loci, is related to UV-induced increased expression of target autoantigens combined with altered immune responses in genetically susceptible individuals.”

The fact that not all dermatomyositis patients have anti-Mi-2 autoantibodies but still develop dermatomyositis means that other environmental risk factors outside of UV radiation must be operating to contribute to the development of the disease, said Dr. Steven Ytterberg of the division of rheumatology at the Mayo Clinic, Rochester, Minn.

It would be worthwhile to determine if DM patients with anti-Mi-2 autoantibodies are more likely to get clinical disease flares from UV radiation exposure than are those who do not have the autoantibodies. Dermatomyositis patients who are negative for anti-Mi-2 may have a different environmental risk factor, Dr. Ytterberg said in an interview.

The investigators noted that the study may be limited by the following: referral bias, because patients with myositis who are seen at referral centers may not be representative of the larger population of patients with myositis; the use of state-level UV radiation intensities, which can vary considerably from one part of a state to another; the lack of accounting for individual-level exposure; differences in UV radiation exposure at different locations over time; and the use of personal photoprotective measures.

The study was funded in part by the intramural research programs of the National Institute of Environmental Health Sciences.

Dr. Werth and Dr. Ytterberg said they had no relevant disclosures.

The intensity of UV radiation exposure may be tied to the preva-lence of dermatomyositis in women, such as this hand involvement.

Source Courtesy Dr. Victoria P. Werth

The intensity of exposure to ambient ultraviolet radiation appears to determine the prevalence of dermatomyositis and an autoantibody specific to the disease in women, based on a study published in Arthritis & Rheumatism.

The UV Index across geographical regions of the United States also significantly correlated with the presence of an autoantibody unique to dermatomyositis (DM)—known as anti-Mi-2—and not to autoantibodies more commonly found in polymyositis (PM).

The association between UV radiation and DM was strongest in a collective group of white, Hispanic, and Asian American women, but it also was significant among black women.

This is the first study to show evidence of the influence of sex on the association between UV radiation and autoimmune disorders, commented Dr. Victoria P. Werth, professor of dermatology at the University of Pennsylvania, Philadelphia, and chief of dermatology at the Philadelphia Veterans Affairs Medical Center.

“This is the best study that I've seen so far in reference to dermatomyositis” and exposure to UV radiation, she said.

The study brings up many “intriguing kinds of things that we don't totally understand,” such as differences in risk factors and responses to UV radiation between men and women and between polymyositis and dermatomyositis.

These types of “interesting epidemiologic observations” may help in the future to understand more about the differences in pathogenesis, Dr. Werth said in an interview.

In the cross-sectional, retrospective study, Dr. Lori A. Love of the National Institute of Environmental Health Sciences and her coinvestigators gathered clinical data and serum samples from 202 PM and 178 DM patients at referral centers across the United States.

The investigators detected myositis-specific autoantibodies in 172 patients (45%), some of which were found in both polymyositis and dermatomyositis patients, whereas others were found only in each particular phenotypic type of myositis, such as anti-SRP in 21 PM patients and anti-Mi-2 in 23 DM patients.

Polymyositis occurred in a significantly greater proportion of black patients (66%) than among nonblack patients (48%), the study showed.

Most (86%) of the patients with anti-SRP antibodies were black, Dr. Love and her associates reported (Arthritis Rheum. 2009;60:2499-504).

The proportion of patients in the study who had anti-Mi-2 autoantibodies was significantly associated with the UV Index for the seven regions (comprising 37 states) that the investigators categorized according to shared geoclimatic factors. However, the UV Index was not associated with the proportion of patients with DM. Both of these comparisons proved to be significant for women but not for men.

Evidence from a previous study has shown that the dose of UV radiation required to induce immunosuppression is three times higher in women than in men, which may mean “other mechanisms would need to be operative to potentially explain how UV radiation preferentially results in the development of dermatomyositis and anti-Mi-2 autoantibodies in women,” the investigators wrote.

They noted that “it is tempting to speculate that the development of DM and DM-specific anti-Mi-2 autoantibodies, which are associated with certain major histocompatibility loci, is related to UV-induced increased expression of target autoantigens combined with altered immune responses in genetically susceptible individuals.”

The fact that not all dermatomyositis patients have anti-Mi-2 autoantibodies but still develop dermatomyositis means that other environmental risk factors outside of UV radiation must be operating to contribute to the development of the disease, said Dr. Steven Ytterberg of the division of rheumatology at the Mayo Clinic, Rochester, Minn.

It would be worthwhile to determine if DM patients with anti-Mi-2 autoantibodies are more likely to get clinical disease flares from UV radiation exposure than are those who do not have the autoantibodies. Dermatomyositis patients who are negative for anti-Mi-2 may have a different environmental risk factor, Dr. Ytterberg said in an interview.

The investigators noted that the study may be limited by the following: referral bias, because patients with myositis who are seen at referral centers may not be representative of the larger population of patients with myositis; the use of state-level UV radiation intensities, which can vary considerably from one part of a state to another; the lack of accounting for individual-level exposure; differences in UV radiation exposure at different locations over time; and the use of personal photoprotective measures.

The study was funded in part by the intramural research programs of the National Institute of Environmental Health Sciences.

Dr. Werth and Dr. Ytterberg said they had no relevant disclosures.

The intensity of UV radiation exposure may be tied to the preva-lence of dermatomyositis in women, such as this hand involvement.

Source Courtesy Dr. Victoria P. Werth

The intensity of exposure to ambient ultraviolet radiation appears to determine the prevalence of dermatomyositis and an autoantibody specific to the disease in women, based on a study published in Arthritis & Rheumatism.

The UV Index across geographical regions of the United States also significantly correlated with the presence of an autoantibody unique to dermatomyositis (DM)—known as anti-Mi-2—and not to autoantibodies more commonly found in polymyositis (PM).

The association between UV radiation and DM was strongest in a collective group of white, Hispanic, and Asian American women, but it also was significant among black women.

This is the first study to show evidence of the influence of sex on the association between UV radiation and autoimmune disorders, commented Dr. Victoria P. Werth, professor of dermatology at the University of Pennsylvania, Philadelphia, and chief of dermatology at the Philadelphia Veterans Affairs Medical Center.

“This is the best study that I've seen so far in reference to dermatomyositis” and exposure to UV radiation, she said.

The study brings up many “intriguing kinds of things that we don't totally understand,” such as differences in risk factors and responses to UV radiation between men and women and between polymyositis and dermatomyositis.

These types of “interesting epidemiologic observations” may help in the future to understand more about the differences in pathogenesis, Dr. Werth said in an interview.

In the cross-sectional, retrospective study, Dr. Lori A. Love of the National Institute of Environmental Health Sciences and her coinvestigators gathered clinical data and serum samples from 202 PM and 178 DM patients at referral centers across the United States.

The investigators detected myositis-specific autoantibodies in 172 patients (45%), some of which were found in both polymyositis and dermatomyositis patients, whereas others were found only in each particular phenotypic type of myositis, such as anti-SRP in 21 PM patients and anti-Mi-2 in 23 DM patients.

Polymyositis occurred in a significantly greater proportion of black patients (66%) than among nonblack patients (48%), the study showed.

Most (86%) of the patients with anti-SRP antibodies were black, Dr. Love and her associates reported (Arthritis Rheum. 2009;60:2499-504).

The proportion of patients in the study who had anti-Mi-2 autoantibodies was significantly associated with the UV Index for the seven regions (comprising 37 states) that the investigators categorized according to shared geoclimatic factors. However, the UV Index was not associated with the proportion of patients with DM. Both of these comparisons proved to be significant for women but not for men.

Evidence from a previous study has shown that the dose of UV radiation required to induce immunosuppression is three times higher in women than in men, which may mean “other mechanisms would need to be operative to potentially explain how UV radiation preferentially results in the development of dermatomyositis and anti-Mi-2 autoantibodies in women,” the investigators wrote.

They noted that “it is tempting to speculate that the development of DM and DM-specific anti-Mi-2 autoantibodies, which are associated with certain major histocompatibility loci, is related to UV-induced increased expression of target autoantigens combined with altered immune responses in genetically susceptible individuals.”

The fact that not all dermatomyositis patients have anti-Mi-2 autoantibodies but still develop dermatomyositis means that other environmental risk factors outside of UV radiation must be operating to contribute to the development of the disease, said Dr. Steven Ytterberg of the division of rheumatology at the Mayo Clinic, Rochester, Minn.

It would be worthwhile to determine if DM patients with anti-Mi-2 autoantibodies are more likely to get clinical disease flares from UV radiation exposure than are those who do not have the autoantibodies. Dermatomyositis patients who are negative for anti-Mi-2 may have a different environmental risk factor, Dr. Ytterberg said in an interview.

The investigators noted that the study may be limited by the following: referral bias, because patients with myositis who are seen at referral centers may not be representative of the larger population of patients with myositis; the use of state-level UV radiation intensities, which can vary considerably from one part of a state to another; the lack of accounting for individual-level exposure; differences in UV radiation exposure at different locations over time; and the use of personal photoprotective measures.

The study was funded in part by the intramural research programs of the National Institute of Environmental Health Sciences.

Dr. Werth and Dr. Ytterberg said they had no relevant disclosures.

The intensity of UV radiation exposure may be tied to the preva-lence of dermatomyositis in women, such as this hand involvement.

Source Courtesy Dr. Victoria P. Werth