[How I investigate...a myopathy with a muscle biopsy]

Muscle biopsy is a valuable tool in the diagnosis of many neuromuscular disorders. It is an invasive investigation that will be considered after careful clinical examination, supplemented by biological and electrophysiological studies. The biopsy procedure and the subsequent processing of specimen in the laboratory significantly influence the information provided by the microscopic examination of muscle tissue. They are reviewed in details in this article. Close collaboration between clinicians and neuropathologists in the setting of an optimized procedure will further increase the diagnostic yield of muscle biopsy.