Myositis with antimitochondrial antibodies diagnosed by rectus abdominis muscle biopsy.

INTRODUCTION: Antimitochondrial antibodies are autoantibodies detected in 90% of primary biliary cirrhosis (PBC) patients. Some PBC cases are complicated by myositis, which is difficult to confirm due to minimal histological evidence of inflammation in limb muscles. METHODS: Our aim was to determine the extent of inflammatory changes in a truncal muscle biopsy specimen from a PBC patient. RESULTS: A 48-year-old woman with a 5-year history of atrial fibrillation and chronic heart failure was evaluated for elevated serum creatine kinase level. Antimitochondrial M2 antibodies were detected, and PBC was diagnosed. A biceps brachii biopsy specimen showed mild, non-specific myogenic changes; a second biopsy was performed on the rectus abdominis muscle, which showed typical inflammatory changes. Myositis with antimitochondrial M2 antibodies was confirmed. CONCLUSIONS: In myositis patients with antimitochondrial M2 antibodies, muscles of the extremities are involved to a lesser extent. Radiological and histological examination focusing on truncal muscles, including a biopsy, is important.