Yield of Muscle Biopsy in Patients with Findings of Myopathy on Electrodiagnostic Testing

Background The evaluation of neuromuscular diseases includes detailed clinical assessment, blood testing, electrodiagnostic studies (EDS), biopsy, and genetic tests. EDS alone cannot provide a specific diagnosis. Further testing in the form of genetic tests or muscle biopsy (MB) is required. Objective The objective of the study is to evaluate the yield of MB in patients with findings of myopathy on electrodiagnostic testing and assess the factors affecting an abnormal biopsy outcome. Methods Electromyography (EMG)/nerve conduction studies (NCS) performed for suspected myopathy over 5 years from 2011 to 2016, at the neurophysiology department of a tertiary care center in Pakistan, were reviewed. Based on inclusion criteria, records of 58 patients were retrospectively reviewed. Results After an EMG/NCS diagnosis of myopathy, the frequency of MB testing was only 10.1%. The median age of patients was 26.5 years. The clinically suspected diagnosis was categorized into hereditary myopathy (n = 15, 25.9%) and acquired myopathy (n = 18, 31%). The positive predictive value of EMG is 77.2%. Twenty-eight (48.2%) patients had abnormal MB whereas 20 (34.4%) revealed normal findings. Factors significantly influencing an abnormal outcome of biopsy included moderate-to-severe elevation of creatine kinase (>2,000 U/L),presence of denervation changes, and severe myopathy on EMG. Conclusion Even though the overall yield of MB testing may not be very high in our setting due to the unavailability of special techniques and expertise, certain factors can help to improve the diagnostic yield. Clinicians should encourage MB testing, especially in cases with strong clinical, laboratory and electrodiagnostic suspicion, and absence of genetic testing for suspected myopathy.