Diagnostic yield associated with multiple simultaneous skeletal muscle biopsies.

Certain skeletal muscle disorders, such as inflammatory myopathies, may show regional variability, prompting consideration of simultaneous biopsy of more than 1 muscle to increase the likelihood of diagnosis. There are few data in the literature to support this approach. This study is a retrospective 8-year review of 99 cases (52 men; mean age, 61.8 years) who had multiple muscles biopsied simultaneously. The most common clinical symptoms prompting biopsy included weakness in 83 cases and myalgia in 15. The most common diagnoses were as follows: neurogenic atrophy, 48; inflammatory myopathy, excluding inclusion body myositis, 29; and type II muscle fiber atrophy, 24. Diagnoses were the same in both biopsied muscles in 54 cases (55%). In 17 cases, a diagnosis was made from only 1 biopsy. Of 29 inflammatory myopathies and vasculitis (excluding inclusion body myositis), a diagnosis could be made from only 1 of the 2 biopsies in 10 cases (34%). In a significant subset of cases, a potentially treatable inflammatory myopathic condition might have been missed if only 1 site had been biopsied, justifying biopsy of 2 sites in suspected cases of inflammatory myopathy.