Dermatomyositis (DM) has been associated with geospatial differences in ultraviolet (UV) radiation, but the role of individual determinants of UV exposure prior to diagnosis is unknown. The objective was to examine the role of those individual determinants.
We analyzed questionnaire data from 1,350 adults in a US national myositis registry (638 with DM, 422 with polymyositis [PM], and 290 with inclusion body myositis [IBM] diagnosed at ages 18-65 years), examining the likelihood of DM compared with PM and IBM diagnosis, in relation to self-reported sunburn history and job- and hobby-related sun exposures in the year prior to diagnosis. We estimated odds ratios (ORs) and 95% confidence intervals (95% CIs) using logistic regression adjusted for age, skin tone, and sex, to determine the association of individual UV exposures with DM diagnosis. We also evaluated the proportion of DM by maximum daily ambient UV exposure, based on UVB erythemal irradiances for participant residence in the year prior to diagnosis.
DM was associated with sunburn in the year before diagnosis (2 or more sunburns OR 1.77 [95% CI 1.28-2.43] versus PM/IBM; 1 sunburn OR 1.44 [95% CI 1.06-1.95]) and with having elevated job- or hobby-related sun exposure (high exposure OR 1.64 [95% CI 1.08-2.49] or moderate exposure OR 1.35 [95% CI 1.02-1.78] versus low or no exposure). Ambient UV intensity was associated with DM in females (β = 3.97, P = 0.046), but not overall.
Our findings suggest that high or moderate personal exposure to intense sunlight is associated with developing DM compared with other types of myositis. Prospective research on UV exposure as a modifiable risk factor for DM is warranted.