Background/Purpose: We analyzed the prevalence of anti-mitochondrial autoantibodies (AMA) in both juvenile-(JM) and adult-onset myositis cohorts and investigated phenotype differences between juvenile and adult myositis patients with or without AMA.
Methods: We screened sera from myositis patients who were classified as dermatomyositis (DM), polymyositis (PM), or inclusion body myositis (IBM) based on Bohan and Peter or Grigg criteria, including 342 juvenile-onset (JM) and 619 adult-onset patients (216 DM, 222 PM, 140 IBM, and 19 amyopathic DM (ADM)), and from healthy controls, including 92 children and 164 adults, for AMA by ELISA. Clinical characteristics were compared between myositis patients with and without AMA.
Results: AMA were present in 1% (4/342) of JM patients, 5% (32/619) of adult myositis patients (16 DM, 10 PM, 4 IBM, and 1 ADM), and 1% of both juvenile and adult healthy controls. Of the 4 JM patients with AMA, 3 had DM and 1 had PM. Three of the four AMA+ JM patients had dysphagia and all 4 patients had a moderate to severe disease onset. There were no other clinical features or medication usage associated with AMA in JM patients. In the 619 adult myositis patients, AMA were associated with cardiomyopathy (16% vs 5%, p=0.01). Additional clinical data available in 480 of the 619 patients followed longitudinally showed that AMA were associated with persistent muscle weakness over an average of 6 visits (90% vs 62%, p=0.005), Raynaud’s phenomenon (43% vs 14%, p< 0.001), and dysphagia (63% vs 36%, p=0.003). Adult patients with AMA also more frequently received glucocorticoids (90% vs 67%, p=0.04) and intravenous immunoglobulin (60% vs 29%, p=0.003).
Conclusion: AMA are present in 1% of JM and 5% of adult myositis patients. In juvenile myositis AMA are not disease specific; however, patients often had dysphagia similar to adult-onset myositis patients with AMA. In adult-onset myositis patients, AMA are also associated with chronic muscle weakness, cardiomyopathy and Raynaud’s. Our data suggest that AMA may have a role in disease management in myositis, and their presence necessitates cardiomyopathy screening in adult-onset, but not juvenile-onset myositis patients.
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