Occupational and Hobby Exposures Associated with Myositis Phenotypes in a National Myositis Patient Registry.

Objective: To investigate occupational and hobby exposures to silica, solvents, and heavy metals and odds of idiopathic inflammatory myositis (IIM) phenotypes, dermatomyositis (DM) and polymyositis (PM) versus inclusion body myositis (IBM), lung disease plus fever or arthritis (LD+), and systemic autoimmune rheumatic disease-overlap myositis (OM).

Methods: The sample included 1390 patients (598 DM, 409 PM, and 383 IBM) ages ≥18 years from a national registry. Of these, 218 (16%) were identified with LD+, i.e., self-reported lung disease with fever and/or arthritis, and 166 (12%) with OM. Questionnaire data on jobs, hobbies, and exposures before diagnosis were evaluated using a rules-based protocol and expert assessment of silica dust, solvents, and heavy metals exposure. We calculated adjusted odds ratios (OR) and 95% confidence intervals (CI) and explored joint effects with smoking.

Results: High silica exposure was associated with an increased odds of having DM (OR=2.02; 95%CI 1.18-3.46, compared to no exposure; p-trend=0.004), LD+ (1.75; 1.10-2.78; p-trend=0.005, versus no LD), and OM (2.07; 1.19-3.61; p-trend=0.020). Moderate to high heavy metals exposure was associated with greater odds of having LD+ (1.49; 1.00-2.14; p-trend=0.026) and OM (1.59; 0.99-2.55, p-trend=0.051). Greater odds of LD+ were seen among smokers with moderate to high silica exposure versus non-smokers with low or no exposure (high-certainty assessment, 2.53; 1.31-4.90; p-interaction=0.061).

Conclusion: These findings, based on a systematic exposure assessment, suggest that occupational and hobby exposures to silica and heavy metals contribute to adult IIM phenotypes, including DM, OM, and LD+, a possible marker for anti-synthetase or other autoantibody-associated lung disease.