Histological examination of muscle tissue is used to establish a diagnosis of neuromuscular disease, to investigate patients with systemic disease, to exclude treatable diseases in patients with progressive muscular wasting, and allows biochemical investigations of muscle tissue. The choice of muscle biopsy is important. Deltoid, biceps brachii and quadriceps femoris muscles are mostly used and specimens are usually obtained by an open biopsy. The interpretation of the muscle biopsy must be considered in relation to the clinical problem. Enzyme histochemical methods allow study of sub-cellular structures and are therefore particularly useful in diagnosis. They are standardized and a routine series should be used in each specimen. In routine diagnostic work electron microscopy is of relatively little value. It is first important to inspect the size, shape and fibre type distribution to get an impression of whether the biopsy is normal or abnormal. Then more characteristic features of either neuropathies or myopathies are looked for. Regarding prognosis it is difficult to draw conclusions from the muscle biopsy. Biochemical assays may be useful in establishing precise diagnosis, especially in glycogenoses and mitochondrial disorders.
