Environmental factors preceding illness onset differ in phenotypes of the juvenile idiopathic inflammatory myopathies

Objective. To assess whether certain environmental factors temporally associated with the onset of juvenile idiopathic inflammatory myopathies (JIIMs) differ between phenotypes. Methods. Physicians completed questionnaires regarding documented infections, medications, immunizations and an open-ended question about other noted exposures within 6 months before illness onset for 285 patients with probable or definite JIIM. Medical records were reviewed for 81% of the patients. Phenotypes were defined by standard clinical and laboratory measures. Results. Sixty per cent of JIIM patients had a reported exposure within 6 months before illness onset. Most patients (62%) had one recorded exposure, 26% had two and 12% had three to five exposures. Patients older than the median age at diagnosis, those with a longer delay to diagnosis and those with anti-signal recognition particle autoantibodies had a higher frequency of documented exposures [odds ratios (ORs) 95% CI 3.4, 31]. Infections were the most common exposure and represented 44% of the total number of reported exposures. Non-infectious exposures included medications (18%), immunizations (11%), stressful life events (11%) and unusual sun exposure (7%). Exposures varied by age at diagnosis, race, disease course and the presence of certain myositis autoantibodies. Conclusion. The JIIMs may be related to multiple exposures and these appear to vary among phenotypes.