Survival Trends and Causes of Death in Dermatomyositis and Polymyositis: A 19-year Longitudinal Study in Taiwan

Dermatomyositis (DM) and polymyositis (PM) are rare idiopathic inflammatory myopathies associated with substantial morbidity and mortality. However, data on mortality patterns and prognostic factors in Asian populations, particularly in Taiwan, remain limited. We conducted a retrospective cohort study of 2,264 adult patients diagnosed with DM or PM between 2001 and 2019 using electronic medical records from the largest tertiary referral center in Taiwan. Mortality data were linked with the National Death Registry, and standardized mortality ratios (SMRs) were calculated relative to the general population. During 21,991 person-years of follow-up, 635 deaths were recorded (319 DM, 316 PM), with 5-year mortality rate of 18.0%. Malignancy and pneumonia were the leading causes of death, with significantly elevated SMRs. Patients diagnosed before age 45 had the highest relative risk of death, with SMRs of 6.36 for males and 17.94 for females. Survival analysis revealed significantly reduced survival in patients with malignancies or major infections (log-rank p < 0.0001). Cox regression identified older age at onset, male sex, malignancy, and major infection as independent risk factors for mortality. These findings highlight the persistently high mortality burden in DM and PM patients in Taiwan and underscore the need for early malignancy screening, infection prevention, and tailored management strategies to improve long-term outcomes.