Background/Purpose: Idiopathic inflammatory myopathies (IIMs) are rare autoimmune diseases characterized by muscle weakness, often involving other organs such as the skin, lungs, and heart. Defined subtypes include dermatomyositis (DM), anti-synthetase syndrome (ASS), polymyositis (PM), immune necrotizing myopathy (IMNM), and inclusion body myositis (IBM). ASS exhibits distinct clinical, serological, and prognostic features.This study aims to compare the prognosis and clinical characteristics of patients with ASS and other IIMs (OIMM) in our cohort.

Methods: Data of 122 IIM patients fulfilled Bohan and Peter criteria and 2017 myositis classification criteria with myositis-specific antibody results who were followed up in our clinic between 1991 and 2024 were retrospectively analysed. The patients were divided into two groups, those with ASS and those with OIMM and their clinical and laboratory characteristics damage progress and survival rates were compared.

Results: A total of 35 patients (28.7%) were diagnosed with ASS. In this cohort, 85.7% of ASS and 59.8% of OIIM were female (p = 0.011). The median age at diagnosis was 47 years in ASS and 46 years in OIMM. The mean follow-up period was 84.48±77.95 months. In these patients, anti-Jo-1 was positive in 88.6%, anti-PL-7 in 8.6%, and anti-KS in 2.8%. The frequency of mechanic’s hand (ASS: 11.4%; OIMM: 1.1%; p = 0.024), arthritis (ASS: 51.4%; OIMM: 21.8%; p = 0.003), and ILD (ASS: 68.6%; OIMM: 21.8%; p< 0.001) were significantly higher in the ASS. Dysphagia was frequent in the OIMM (ASS: 8.6%; OIIM: 37.9%; p = 0.003). Anti-Ro-52 positivity was also higher in the ASS (ASS: 42.9%; OIIM: 21.8%; p = 0.034). At the time of diagnosis, median CRP, leukocyte, and neutrophil values were higher in the ASS. The median myositis damage index (MDI) of the ASS group was higher than the OIMM in the sixth month of the follow-up (median MDI: 3 vs. 2, p = 0.046) Comparing the ASS group with other autoantibody based subgroups, a difference was observed between the ASS and the TIF-1 gamma-positive patients in terms of damage progression at the sixth month (median MDI: 3 vs 1.5, p = 0.033) While ILD was observed at a high prevalence in the ASS malignancy was predominant in anti-TIF-1gamma positive patients (ILD: 72.7% vs 3%, p < 0.001; malignancy: 20% vs 35.3%, p = 0.045) In the last assessment there was no difference between the OIMM and ASS for MDI. The mortality rate was 14.3% in the ASS and 14.9% in the OIIM (Figure 1) It was found that there was no difference in survival rates between the ASS and OIMM.

Conclusion: The ASS has significant clinical differences from OIMM. Among these patients, mechanic’s hand, arthritis, and ILD are more prevalent, whereas dysphagia is less common. Inflammatory markers like CRP, leukocyte, neutrophil levels, and anti-Ro-52 positivity are more frequent at baseline in the ASS. In the early follow-up period, higher organ damage was developed in patients with the ASS compared to the OIIM. This difference was due to the rapid development of significant ILD in most of the patients with ASS. These findings highlight the unique clinical features and different disease progression trajectories of ASS, providing insight into possible differences in the management strategies for IIM subtypes.

Figure 1: Comparison of survival rates by Kaplan-Meier analysis (Mantel Cox Log Rank test χ²=0.679 df=1, p=0.410).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparison-of-organ-damage-and-survival-in-anti-synthetase-syndrome-and-other-idiopathic-inflammatory-myopathies-an-analysis-of-patients-from-turkey/