Anti-mitochondrial
antibodies, the characteristic markers of
primary biliary cirrhosis, have been detected in most patients with this disease. However, the prevalence of these
antibodies in
inflammatory myopathies and their clinical and histopathological significance has not been determined. Sera from 212 consecutive patients with
inflammatory myopathies were screened for anti-mitochondrial
antibodies by
enzyme-linked
immunosorbent assay. The clinical and histopathological features of anti-mitochondrial antibody-positive patients were analysed and statistically compared with those of anti-mitochondrial antibody-negative patients. Twenty-four patients positive for anti-mitochondrial
antibodies (seven patients with and 17 patients without
primary biliary cirrhosis) were identified (11.3%). Thirteen patients had a clinically
chronic disease course of >12 months before their diagnosis at hospitals. Six of these 13 patients (four asymptomatic patients with increased
creatine kinase levels and two patients with
arrhythmia) had not been aware of
muscle weakness, but all 13 patients had
muscle atrophy at initial presentation. As complications, eight patients had cardiac involvement including arrhythmias (five patients with
supraventricular tachycardia; two with
ventricular tachycardia; and one patient with
atrioventricular block), six patients had moderately decreased ejection fraction and six patients had decreased vital capacity, two of whom required respiratory support. Regarding muscle histopathological findings, in addition to
inflammation, 13 patients had chronic myopathic changes and six had granulomatous lesions. Statistical analysis showed that the clinical features of a
chronic disease course, cardiac involvement and
muscle atrophy, and the histopathological features of chronic myopathic changes and granulomatous
inflammation, were significantly more frequently observed in patients with anti-mitochondrial antibody-positive
inflammatory myopathy than in patients who were negative for anti-mitochondrial
antibodies. Except for cardiac involvement, which is more frequently observed in patients with
primary biliary cirrhosis, no significant differences in clinical or histopathological features were found between patients with or without
primary biliary cirrhosis. Our study revealed that
inflammatory myopathies associated with anti-mitochondrial
antibodies were frequently found in patients with the clinical features of a
chronic disease course,
muscle atrophy and cardiopulmonary involvement, and the characteristic histopathological feature of granulomatous
inflammation. Our study suggests that
inflammatory myopathies associated with anti-mitochondrial
antibodies form a characteristic subgroup.