Electron microscopy in the diagnosis of skeletal muscle disorders: Its utility and limitations

Electron microscopy (EM) has a substantial role in the diagnosis of skeletal muscle disorders. The ultrastructural changes can be observed in muscle fibers and other components of the muscle tissue. EM serves as a confirmatory tool where the diagnosis is already established by enzyme histochemistry staining. Although it is indispensable in the diagnosis of rare forms of congenital myopathies not appreciated by light microscope, such as cylindrical spiral myopathy, zebra body myopathy, fingerprint body myopathy, and intranuclear rod myopathy, in cases not subjected to histochemical staining, it is required for definitive diagnosis in certain groups of muscle disorders, which includes congenital myopathies, metabolic myopathies in particular mitochondrial myopathies and glycogenosis, and in vacuolar myopathies. It does not have diagnostic implications in muscular dystrophies and neurogenic disorders. In the recent past, despite the availability of advanced diagnostic techniques, electron microscopy continues to play a vital role in the diagnosis of skeletal muscle disorders. This review gives an account of ultrastructural features of skeletal muscle disorders, the role of EM in the diagnosis, and its limitations.