Diagnostic outcome of muscle biopsy

Introduction: We reviewed the diagnostic yield of muscle biopsy according to the presence or absence of muscle weakness, hyperCKemia, and electromyogaphic (EMG) abnormalities. Methods: In a retrospective study, 698 muscle biopsy reports were analyzed. Logistic regression models for myopathy and specific myopathy were fit, and receiver-operating characteristic (ROC) curves were generated to assess prediction accuracy. The probability of finding specific myopathy was considered the main indication of a positive muscle biopsy. Results: Isolated hyperCKemia was poorly predictive of either myopathy or specific myopathy. Combined myopathic EMG, proximal weakness, and hyperCKemia were predictive. The predictability increased proportionally to the creatine kinase (CK) level in patients with proximal weakness and myopathic EMG. Cross validation showed accuracy around 70% for a probability threshold of 50%. Conclusions: The presence of hyperCKemia, proximal weakness, and myopathic EMG together were associated with highly positive diagnostic outcome of muscle biopsy. Isolated hyperCKemia had a poor diagnostic yield.