Myositis-specific antibodies and clinical characteristics in patients with autoimmune inflammatory myopathies: reported by the Argentine Registry of Inflammatory Myopathies of the Argentine Society of Rheumatology

Introduction/objectives To describe clinical features in patients with inflammatory myopathies (IMs) from the Argentine Registry of Inflammatory Myopathies, and their relationship with myositis-specific antibodies (MSAs). Methods This cross-sectional study included 360 adult patients with dermatomyositis (DM), polymyositis (PM), and inclusion body myositis. Demographics, clinical, and serological characteristics were retrospectively recorded (2016-2019). MSAs were determined by immunoblotting. Patients who were positive for anti-Jo-1, Mi-2, and MDA5 were compared against a group of patients, taken as reference group, who were negative for all MSAs. Results Women 72%, median age at diagnosis was 47.3 years (18-82). The most frequent subtypes were DM (43.9%) followed by PM (30%).The most frequent MSAs were anti-Jo-1 (51/317), 16.1%; MDA5 (12/111), 10.8%, and Mi-2 (23/226), 10.2%. Anti-Jo-1 was associated (p < 0.05) with a higher frequency of chronic disease course, interstitial lung disease (ILD), arthritis, and mechanic's hands. Anti-Mi-2 was found in patients who had higher frequency of skin manifestations and higher CK values (p < 0.001). Patients with anti-MDA5 had normal or low CK levels. Anti-MDA5 was associated (p < 0.05) with skin manifestations, arthritis, and ILD. The rest of MSAs had frequencies lower than 8%. Anti-TIF1 was found in eight DM patients and one had cancer. Anti-SRP was found in seven patients who had PM and elevated CK. Conclusion Anti-Jo-1 was the most frequent MSA, and was associated with ILD; MDA5 was associated with CADM and ILD, and Mi-2, with classical DM. Despite the different prevalence with respect to other cohorts, the clinical characteristics for each MSA group were similar to the data reported in other studies. Key Points center dot This study describes the prevalence of MSAs in the Argentine Registry of IMs. center dot Anti-Jo-1 and anti-MDA5 were associated with ILD. center dot Anti-Mi-2 was the third most frequent MSA, associated with classical DM.