Presence of myositis specific autoantibodies including anti synthetase antibodies predict favorable outcomes to rituximab in patients with idiopathic inflammatory myositis: Retrospective observational study

Background: Idiopathic inflammatory myositis (IIM) is a group of disorders that mainly affect skeletal muscle, joints, skin, and lungs. Objectives: This study aimed to evaluate the autoantibody profile including myositis-associated autoantibodies (MAAs) and myositis-specific autoantibodies (MSAs) and their influence on outcomes, response rates, and associated factors to Rituximab (RTX) treatment in patients with IIM who followed up in a single tertiary center. Methods: Data from the patients with IIM who follow-up between 2019 and 2023 years and met the Bohan and Peter and/or the ACR/EULAR 2017 and/or the ENMC criteria were retrospectively reviewed. RTX was initiated in patients who had an inadequate response to at least one immonomudulatory/immunosuppressive treatment (refractory group) or as a first-line treatment in patients who had critical/severe disease manifestations such as respiratory failure due to severe intertitial lung disease (ILD), respiratory muscle involvement, and dysphagia. RTX was administered at a dose of 1 g every 6 months on days 0-15, and the dose was repeated at month 6 in patients who responded to treatment. Remission was defined as the patients who met all of the following criteria during at least 6 months: i) absence of a sign of muscle inflammation by manual muscle test (normalization of muscle strength in patients without damage) alongside muscle enzymes (normalization in CK and LDH levels), ii) improvement or no progression in respiratory symptoms alongside pulmonary function tests (less than 10% decline in FVC and/or DLCO) in patients who had ILD at baseline, iii) disappearance of active skin lesions among dermatomyositis (DM) patients iv) resolution of other features attributed to several manifestations such as arthritis, heart involvement and gastrointestinal symptoms if present.