Real-life effectiveness of rituximab in different subsets of idiopathic inflammatory myopathies

Objective: Idiopathic inflammatory myopathies (IIM) are heterogeneous autoimmune diseases including dermatomyositis (DM), polymyositis (PM), immune-mediated necrotizing myopathy (IMNM), and anti-synthetase syndrome (ASS). Treatment typically involves high-dose corticosteroids (CCS) and conventional synthetic disease-modifying antirheumatic drugs (csDMARD). Rituximab (RTX) has shown effectiveness in refractory cases. Our real-life study aimed to assess the safety and effectiveness of RTX treatment in IIM patients. Methods: We conducted a retrospective study including patients with IIM refractory to both high-dose CCS and csDMARD. Patients were treated with a full RTX dose (2 g every 6 months). Laboratory and clinical data, along with the total improvement score (TIS), were assessed to evaluate RTX effectiveness and safety. Data were analyzed using GraphPad Prism (v. 9.5.1). Results: A total of 41 patients received the full RTX dose (15 DM, 15 ASS, 5 PM, and 6 IMNM). This treatment regimen significantly reduced daily CCS usage from 15 mg [interquartile range (IQR) 12.5-25 mg] at baseline to 5 mg (IQR 5-5 mg) after 1 year of treatment (p<0.001). Additionally, over 90% of patients achieved at least a minimal TIS at 12 months, which was maintained at 24 months. At 1 year, RTX persistence was 68.3%. Although reductions in serum immunoglobulins (Ig)A and IgM levels were observed, no cases of severe hypogammaglobulinemia (IgG<400 mg/dL) occurred. The most common reason for treatment interruption was an adverse skin reaction (6 cases) during RTX infusion, while infections most frequently involved the respiratory tract (5 cases). Conclusions: RTX demonstrated effectiveness in various subsets of IIMs, often leading to clinical improvement and significantly reducing the CCS dose.