Subtype-specific mortality in idiopathic inflammatory myopathies: A hospital-based cohort

The aim of our study is to compare mortality rates, causes of death and associated risk factors for idiopathic inflammatory myopathies (IIM) and their various subtypes in a hospital-based cohort, specially IMNM (immune-mediated necrotizing myopathy).

This retrospective study was conducted using the MIIRTALITY cohort, including patients followed for IIM from 2010 to 2022. They were then categorized into five subtypes: dermatomyositis (DM), polymyositis (PM), antisynthetase syndrome (ASS), immune-mediated necrotizing myopathy (IMNM) and overlap myositis (OM). Survival analysis based on IIM subtypes was performed using the Kaplan-Meier method. Cox proportional hazards models were used to determine baseline variables associated with mortality.

During the study period, 33 of the 225 patients enrolled in this study died. IMNM have a mortality rate of 1.7 per 100 person-year. The poorest rate of survival was found in patients with DM (HR 3.32; 95% CI 1.61-6.86; p = 0.001), and the lowest mortality rate, when compared to the rest of IIM, was found in patients with ASS (HR 0.41; 95% CI 0.19-0.88). The presence of malignancy was associated with a markedly increased risk of death (HR 12.2; 95% CI 3.09-48.13; p < 0.001). Joint involvement and classification as a non-DM IIM subtype were associated with a reduced risk of death (HR 0.37; 95% CI 0.18-0.76; p = 0.006 and HR 0.06; 95% CI 0.01-0.36; p = 0.002), respectively.

Dermatomyositis had the highest mortality among IIM subtypes in our hospital-based cohort, ASS was associated with better survival, highlighting the importance of differentiating IIM subtypes so as to personalize treatment and follow-up strategies. In our hospital-based cohort, IMNM mortality was not higher than that of others subtypes. These findings underscore the importance of distinguishing IIM subtypes to personalize treatment and follow-up strategies.