We analyzed the prevalence of anti-mitochondrial
autoantibodies (AMA) in adult- and juvenile-onset
myositis longitudinal cohorts and investigated phenotypic differences in
myositis patients with AMA. We screened sera from
myositis patients including 619 adult- and 371 juvenile-onset
dermatomyositis (DM, JDM),
polymyositis (PM, JPM),
inclusion body myositis (IBM), or amyopathic DM patients and from healthy controls, including 164 adults and 92 children, for AMA by ELISA. Clinical characteristics were compared between
myositis patients with and without AMA. AMA were present in 5% of adult
myositis patients (16 of 216 DM, 10 of 222 PM, 4 of 140 IBM, 1 of 19 amyopathic DM), 1% of
juvenile myositis patients (3 of 302 JDM, 1 of 25 JPM), and 1% of both adult and juvenile healthy controls. In patients with adult-onset
myositis, AMA were associated with persistent
muscle weakness, Raynaud's phenomenon,
dysphagia, and
cardiomyopathy. Adult
myositis patients with AMA may have more severe or treatment refractory disease, as they more frequently received
glucocorticoids and
intravenous immunoglobulin. In
juvenile myositis, children with AMA often had falling episodes and
dysphagia, but no other clinical features or medications were significantly associated with AMA. AMA are present in 5% of adult
myositis patients and associated with
cardiomyopathy,
dysphagia, and other signs of severe disease. The prevalence of AMA is not increased in patients with
juvenile myositis compared to age-matched healthy controls. Our data suggest that the presence of AMA in adult
myositis patients should prompt screening for cardiac and swallowing involvement. Key Points • Approximately 5% of a large North American cohort of adult
myositis patients have anti-mitochondrial
autoantibodies. • Adults with anti-mitochondrial
autoantibodies often have chronic weakness, Raynaud's,
dysphagia,
cardiomyopathy, and more severe disease. • Anti-mitochondrial
autoantibodies are rare in
juvenile myositis and not associated with a specific clinical phenotype.