Background Dermatomyositis (DM) and polymyositis (PM) are associated with significant mortality and morbidity. However, mortality trends for these two diseases are unknown, especially in the general population context.
Objectives To address this knowledge gap, we assess mortality trends for individuals with PM and DM between January 1, 1997 and December 31, 2012 in the general population.
Methods Using an administrative health database from province of British Columbia, Canada, we identified all incident cases of both PM and DM and up to 10 non-disease controls matched on sex-, age- and entry-time for each. Study cohorts for both PM and DM were divided into two subgroups based on the year of diagnosis (ie., 1997–2004 and 2005–2012).Mortality rates were calculated, as well as hazard ratios (HR) using a Cox proportional hazard model. HRs were adjusted for potential confounders (e.g., number of hospitalization and outpatient visits, Charlson's comorbidity index, glucocorticoid use, cardiovascular drugs, cox-2 inhibitors).
Results Mortality rates (cases per 1000 person-years) in the early cohorts (ie.,1997–2004) for PM and DM patients were considerably higher than those in the later cohorts (ie., 2005–2012) (for PM: 226.1 vs 73.3; for DM: 287.0 vs 56.9). In contrast, smaller improvements were observed in the comparison groups (for PM: 28.9 vs 16.2; for DM: 31.0 vs 13.5). Corresponding to these two time periods, HRs for mortality for PM were 5.6 (95% CI, 3.2–9.9) and 3.1 (95%CI, 1.8–5.3), respectively, and 8.0 (95% CI, 4.0–16.0) and 2.9 (95%CI, 1.7–5.2) for DM, respectively. Testing for difference between incident cohorts via an interaction term were all significant (see table).
Conclusions This population-based study shows that the survival of PM and DM patients has improved in recent years, suggesting that new treatment strategies and improved management of PM and DM and its associated complications have led to significant improvements in PM- and DM-associated mortality.
Disclosure of Interest None declared