Presence of Myositis-Specific Autoantibodies May Predict Favorable Outcomes to Rituximab in Patients with Idiopathic Inflammatory Myositis: Retrospective Observational Study.

Objective: This study aimed to evaluate the autoantibody profile, including myositis-associated autoantibodies (MAAs) and myositis-specific autoantibodies (MSAs), and their influence on outcomes of rituximab (RTX) treatment in patients with IIM.

Methods: This retrospective observational study included data from patients with idiopathic inflammatory myositis (IIM) who met at least one of the following criteria: Bohan and Peter, ACR/EULAR 2017, and ENMC criteria.

Results: Fifty-three patients, 72% of whom were female, were included. Among them, 32.1% had a clinical diagnosis of dermatomyositis, 35.8% antisynthetase syndrome (ASS), 15.3% overlap syndrome, 11.3% polymyositis, and 5.7% had immune-mediated necrotizing myopathy. RTX was used in 49% of the patients, and nearly half of them (46%) had ASS. Remission was achieved in 77%, a partial response was observed in 11.5%, and unresponsiveness/active disease was observed in 11.5% of patients receiving RTX. Relapse was lower, and mortality tended to be lower in patients receiving RTX. In multivariate analysis, MSA positivity was associated with remission in those receiving RTX.

Conclusion: In our study, RTX was safe and effective in patients with IIM who had an inadequate response or severe disease at admission. Furthermore, the presence of MSAs may predict a favorable response to RTX treatment in patients with IIM.