Remission rates and predictors in idiopathic inflammatory myopathy subgroups: Insights from a single-center cohort

Objective We evaluated remission rates and predictors across idiopathic inflammatory myopathy (IIM) subgroups using data from a prospective registry. Methods Adult IIM patients with ≥ 1 year of disease duration, enrolled between 2000 and 2019, were analyzed. Subgroups included dermatomyositis (DM), antisynthetase syndrome (ASyS), and immune-mediated necrotizing myopathy (IMNM). Remission was defined as the absence of disease activity by expert assessment. Drug-free remission (DFR) and International Myositis Assessment and Clinical Studies Group (IMACS) remission (≥ 6 months of DFR) were also evaluated. Cumulative incidence of remission and flare was estimated using the Cumulative Incidence Function. Remission predictors were evaluated using cause-specific Cox proportional hazards models. The association between remission and mortality was assessed using Cox models with remission treated as a time-dependent covariate. Results The cohort (n = 393) was 67.2% female with a mean age of 50.1 years. At 10 years, cumulative probabilities of remission, DFR, and IMACS remission were 40.3%, 23.3%, and 18.1%, respectively. Remission rates were highest in DM (47.4%) and lowest in ASyS (30.1%). Median time to first remission was 3.7 years. The 10-year cumulative incidence of flare following remission was 40.6%. Anti-Mi-2 antibody predicted a higher likelihood of remission (HR 2.08, p = 0.020). Remission and DFR were associated with improved survival. Conclusion Remission rates differed across IIM subgroups, being highest in DM and lowest in ASyS. Anti-Mi-2 antibody was associated with a higher likelihood of remission.