Morphological methods in the diagnosis of mitochondrial encephalomyopathies: the role of electron microscopy.

Mitochondrial encephalomyopathies (MEs) encompass a heterogeneous group of disorders that frequently present a diagnostic challenge to clinicians. Historically, MEs were diagnosed by finding ragged red fibers in the muscle biopsy and confirmatory evidence was provided by the presence of numerical and/or ultrastructural abnormalities in mitochondria. In most centers diagnosis involves clinical evaluation and the morphological, histochemical, and biochemical investigation of a skeletal muscle biopsy. However, with the availability of mitochondrial DNA analysis, the necessity and role of morphological methods and, in particular, electron microscopy has been questioned. The aim of this study was to delineate the role of electron microscopy in the diagnosis of MEs.