Background: The reported mortality rates of patients with polymyositis and dermatomyositis are highly variable worldwide. The excess mortality of patients with polymyositis/dermatomyositis has not been evaluated in an Israeli population.

Objectives: To investigate the overall mortality in a large and well-established cohort of patients with polymyositis/dermatomyositis as compared to the mortality expected in the matched general population in a tertiary medical center.

Methods: In this retrospective cohort study, the mortality of 166 patients with polymyositis/dermatomyositis was compared to age- and sex-matched control subjects in the general population. All-cause standardized mortality ratios (SMRs) were estimated.

Results: Overall, 47 (28.3%) deaths were observed among patients with polymyositis/dermatomyositis during a mean follow-up period of 5.8 ± 4.8 years, which was 7 times higher than in the control group (SMR 7.4, 95% confidence interval [95%CI] 5.5–9.8). The SMRs were comparable in patents with polymyositis (7.7, 95%CI 4.8–12.3) and dermatomyositis (7.2, 95%CI 5.0–10.3). The 1-, 5-, 10-, and 15-year overall survival rates were 90.0%, 82.8%, 51.5%, and 26.1%, respectively, in patients with polymyositis, and 80.3%, 59.6%, 40.0%, and 17.1%, respectively, in patients with dermatomyositis.

Conclusions: The overall mortality among Israeli patients with polymyositis/dermatomyositis is 7.4 times greater than for the general population. Although long-term mortality was comparable between patients with dermatomyositis and polymyositis, patients in the former group died at a notably earlier stage.