Background/Purpose: JDM is an autoimmune systemic vasculopathy characterized by myositis and skin rash.  Some myositis specific antibodies (MSAs) are associated with clinical manifestations in JDM, including extensive photosensitive rash and a chronic disease course. Prior research demonstrates a link between UV radiation (UVR) and certain MSAs. However, it is unclear if UVR worsens disease severity in JDM. We investigated the association between UVR and development of calcinosis, which we used as a proxy for severe disease. Understanding the role of UVR in disease severity may help clinicians develop interventions to limit UV exposure and poor outcomes in JDM.

Methods: This was a cross-sectional study of JDM subjects in the U.S. multi-center Childhood Arthritis & Rheumatology Research Alliance (CARRA) registry enrolled from 2010-15. We excluded subjects missing date of symptom onset or zip code. Mean UV index (UVI) in the calendar month prior to symptom onset in each subject’s zip code was calculated from daily satellite solar noon measurements. The primary outcome was history of calcinosis. Chi-squared and Kruskal-Wallis tests were used to compare subject characteristics stratified by UV quartiles. Multivariate logistic regression was used with adjustment for sex, race, age, interval to diagnosis, disease duration, and latitude. Race was dichotomized as black or non-black. Interaction between race and UVI was evaluated.

Results: Among subjects (n=522),11% identified as black and 89% as non-black, of which 79% identified as white. Overall, mean UVI was 4.9 (±2.6) and 11% had calcinosis. Stratified by UV quartiles, clinical and demographic characteristics were similar. In a multi-variate analyses, there was no significant relationship between mean UVI and calcinosis (see Table 1 for OR’s). Black race was associated with a 3-fold greater odds of calcinosis. However, when accounting for a statistically significant interaction between race and UVI, black subjects were less likely to develop calcinosis at the mean UVI. At higher UVI levels, the odds of calcinosis steadily increased in the non-black subjects. Additional statistically significant risk factors for calcinosis in our model included male sex, older age at disease onset, longer disease duration, and delay in diagnosis.

Conclusion:  In the CARRA JDM registry, we found that black subjects living in areas with lower UVI, had a 3-fold greater odds of calcinosis compared to non-black subjects. However, non-black subjects living in areas with moderate to high UVI, had increased risk of calcinosis beyond those of black subjects suggesting that lighter skinned individuals with JDM may be more susceptible to UVR and subsequent development of calcinosis. Our data suggests UVR is an important factor associated with calcinosis but also highlights the complex interplay between genes and environment present in autoimmune conditions like JDM.