Anti-mitochondrial antibody-positive myositis: A systematic review of 123 cases

Anti-mitochondrial antibody (AMA)-positive myositis is an under-recognized subtype of idiopathic inflammatory myopathies (IIMs). A systematic literature review was conducted to clarify the clinical and pathological features of AMA-positive myositis. PubMed/Medline and Scopus databases were searched up to April 2025, and individual data was analyzed. From 50 articles, 123 patients were included (age 54.5 years; female 66.7%; disease duration 18.0 months), with limb muscle weakness, axial myopathy, muscle atrophy, and respiratory failure reported in 90.7%, 64.9%, 58.4%, and 36.7%, respectively. Coexistence (58.5%) of cardiac involvements (CIs) (arrhythmias, 94.1%; cardiomyopathy, 74.6%; myocarditis, 45.0%; pulmonary hypertension, 40.0%) correlated with long disease duration, respiratory disturbance, and primary biliary cholangitis (PBC), but inversely correlated with initial muscular presentations and dermatomyositis-specific rash. PBC coexisted in 52.5%, who demonstrated significantly more CIs and extra-muscular autoimmune disorders than those without PBC but fewer cancers. Muscle histopathology detected necrotic and regenerating fibers (87.3%), variation in muscle fiber size (83.0%), major histocompatibility complex class I expression (72.7%), and membrane attack complex deposition (65.5%). Glucocorticoids and immunomodulatory/immunosuppressive agents were introduced in 92.1% and 39.1%, respectively. Muscle strength improved in 77.5%; however, 20.7% relapsed. CIs deteriorated in 46.0%, 44.1% of which required electronic devices. Death occurred in 7.3% within 15.0 median months. AMA-positive myositis represents an independent phenotype among IIMs and pathologically immune-mediated necrotizing myopathy-like findings. Concurrent PBC or CIs are associated with characteristic muscular and extra-muscular domains, which are sometimes difficult to manage. Understanding unique disease behaviors may aid in early diagnosis and improve clinical management of AMA-positive myositis.