The Prospective Registry Of MyositIS (PROMIS): II. Temporal shifts in causes of death among patients with idiopathic inflammatory myopathies

BACKGROUND: Idiopathic inflammatory myopathies (IIMs) are heterogeneous autoimmune diseases with variable long-term outcomes. OBJECTIVE: To determine the prognosis of IIM. METHODS: This multicenter, prospective cohort study included Chinese patients with IIM. We calculated the standardized mortality ratios adjusted for age and sex, analyzed causes of death, and identified risk factors for all-cause mortality using a multivariable Cox proportional hazards model. RESULTS: A total of 4534 patients were included, with 2902 dermatomyositis, 592 polymyositis, 927 anti-synthetase syndrome, and 113 immune-mediated necrotizing myopathy. Five hundred ten patients died with a median follow-up time of 46 months. The overall standardized mortality ratio was 6.2 (95% CI: 5.7-6.7). Cumulative survival rates at 1, 3, and 10 years were 92.6%, 88.6%, and 80.5%, respectively. Leading causes of death included interstitial lung diseases (18.8%), malignancies (18.8%), cardiovascular diseases (18.8%), and infections (18.6%), which shifted over time (from interstitial lung disease/infection to malignancies/cardiovascular diseases). Risk factors for mortality included male, lymphopenia, high serum ferritin, anti-melanoma differentiation-associated gene 5, anti-transcription intermediary factor 1 gamma (anti-TIF1γ), and anti-Ro 52 antibodies. LIMITATIONS: Underestimation of anti-synthetase syndrome and immune-mediated necrotizing myositis. CONCLUSION: IIM patients had significantly higher mortality than the general population, with variable causes of death and distinct risks based on myositis-specific antibodies. Myositis-associated autoantibodies-based classification may provide deeper insights into pathogenesis and management of IIM.