Mortality trends in polymyositis and dermatomyositis: A general population-based study

Objective: To evaluate mortality trends in polymyositis (PM) and dermatomyositis (DM) between January 1, 1997, and December 31, 2014. Methods: Using an administrative health database from the province of British Columbia, Canada, we identified all patients with incident PM/DM and up to 10 age-, sex-, and index date matched non-PM/DM individuals. Study cohorts for both PM and DM were divided into two subgroups based on the year of diagnosis (i.e., early cohort [1997-2005] and late cohort [2006-2014]). Mortality rates, hazard ratios (HRs), and rate differences were compared between these cohorts. Results: Mortality rates (per 1000 person-years) in the early cohorts for PM and DM patients were higher than those in the late cohorts (for PM: 58.6 vs. 39.4; for DM: 80.6 vs. 51.3), whereas smaller improvements were observed in the comparison cohorts (for non-PM: 15.5 vs. 12.5; for non-DM: 14.1 vs. 11.5). Corresponding to these two time periods, multivariable HRs for PM were 2.4 (95% CI, 1.7 to 3.4) and 2.0 (95% CI, 1.4 to 2.9), respectively (P-value for interaction=0.62). The corresponding absolute mortality rate differences were 32.6 (95% CI, 20.8 to 44.4) and 18.6 (95% CI, 9.2 to 28.0), respectively (P-value for interaction=0.02). Similar results with higher HRs and risk differences were seen in DM. Conclusions: In this general population study, we found a declining excess mortality in PM or DM patients in recent years, although there was a considerable residual premature mortality gap in the late cohort. (C) 2020 Elsevier Inc. All rights reserved.