We aimed to determine the population-based incidence, prevalence, and mortality of dermatomyositis (DM) using European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) criteria.
This population-based cohort study included incident DM from 1/1/1995 to 12/31/2019. We manually reviewed all individuals with at least one code for DM or polymyositis to determine if they met EULAR/ACR criteria, subspecialty physician diagnosis, and/or Bohan & Peter criteria. We age- and sex-adjusted incidence and prevalence estimates to the United States Non-Hispanic White year 2000 population and estimated prevalence on 1/1/2015. Standardized mortality ratios (SMR) with 95% confidence intervals (CI) compared observed to expected mortality adjusting for age, sex, and year.
We identified 40 cases of verified DM, with 29 cases incident in Olmsted County from 1995 to 2019. Mean age was 57 years, 26 (90%) were female, and 12 (41%) had clinically amyopathic DM (CADM). Median follow-up time was 8.2 years. The overall adjusted incidence of DM was 1.1 (95% CI 0.7 to 1.5) per 100,000 person-years, and prevalence was 13 (95% CI 6 to 19) per 100,000. The standardized mortality ratio was significantly elevated among the myopathic DM cases (3.1, 95% CI 1.1 to 6.8) but not CADM cases (1.1, 95% CI 0.2 to 3.3). The positive predictive value of two or more DM codes was only 40/82 (49%).
This population-based study found DM incidence and prevalence were higher than previously reported. Mortality was significantly elevated for myopathic DM but not for CADM.