Myositis with antimitochondrial antibodies diagnosed by rectus abdominis muscle biopsy

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.

Our aim was to determine the extent of inflammatory changes in a truncal muscle biopsy specimen from a PBC patient.

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.

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.