Background/Purpose: Idiopathic Inflammatory Myopathies (IIM) are a group of heterogeneous connective tissue diseases including dermatomyositis (DM), polymyositis (PM), anti-synthetase syndromes (ASS), immune-mediated necrotizing myopathies (NM), and overlap syndromes (OS). These diseases are the most severe connective tissue diseases, with a high mortality rate of 30%. These diseases represent the connective tissue disorders with the highest mortality risk compared to the general population, with reported standardized mortality ratios ranging from 1.56 to 7. No study has evaluated the SMRs for OS and IMNM.The aim of this study was to evaluate the comparative mortality figure in IIM and its subgroups in a real-life setting.

Methods: A retrospective study was conducted using the MIIRTALITY cohort, including patients followed for IIM from 2010 to 2022. Patients were included if they had more than one year of follow-up or early death, were diagnosed between 2010 and 2020, and met the 2017 EULAR and/or 2019 ENMC classification criteria. They were then categorized into five subgroups: DM, PM, ASS, NM, and OS. Crude mortality rates were calculated for the study population, and expected mortality rates were obtained from the French National Institute of Statistics and Economic Studies (INSEE). Comparative Mortality Figures (CMFs) were computed as the ratio of observed to expected deaths, adjusting for differences in age structure between the study and reference populations. CMFs were preferred over standardized mortality ratios (SMRs) due to the limited size of the IIM subgroups.

Results: A total of 225 patients were included: 83 with dermatomyositis (DM; 36.9%), 14 with polymyositis (PM; 6.2%), 55 with antisynthetase syndrome (ASS; 24.4%), 24 with immune-mediated necrotizing myopathy (IMNM; 10.7%), and 49 with overlap syndrome (OS; 21.8%). The median age at diagnosis was 59 years [IQR 46–69], with a predominance of female patients (n = 133, 59.1%). The median follow-up duration was 4 years [IQR 2–7]. An associated malignancy was identified in 29 patients (12.8%).During follow-up, 33 patients died, corresponding to an overall mortality rate of 14.7%. The Comparative Mortality Figure (CMF) for the total IIM cohort was 3.49 (95% CI: 2.25–5.40). CMFs by subgroup were as follows: DM, 5.45 (95% CI: 3.42–8.67); PM, 24.23 (95% CI: 3.89–151.08); ASS, 1.51 (95% CI: 0.48–4.79); IMNM, 1.44 (95% CI: 0.35–5.90); and OS, 2.58 (95% CI: 1.14–5.89).

Conclusion: Patients with DM, PM, and OS demonstrated a significantly increased risk of mortality compared to the general population. No excess mortality was observed in patients with ASS or IMNM.

« Back to ACR Convergence 2025

ACR Meeting Abstracts - https://acrabstracts.org/abstract/mortality-in-idiopathic-inflammatory-myopathy-in-the-toulouse-cohort-miirtality/