Ultrastructural diagnosis of mitochondrial encephalomyopathies revisited

Mitochondrial encephalomyopathies (MEs) are a heterogeneous group of multis ystem disorders with extreme variability in clinical phenotype. Due to thei r complex nature, accurate diagnosis requires a coordinated approach, based on clinical and various laboratory data. Despite the introduction of bioch emical assay of mitochondrial enzymes and the availability of mtDNA mutatio n analysis, the diagnosis of MEs still relies heavily on morphological meth ods. The latter include histology, histochemistry, and electron microscopy. A comparative study was undertaken to define the contemporary role of elec tron microscopy in the morphological diagnosis of MEs. Muscle biopsies from 20 patients with MEs, 9 children and 11 adults, were evaluated by histolog y, enzyme histochemistry, and electron microscopy. The results clearly demo nstrate that electron microscopy is of importance in providing essential di agnostic information in pediatric patients, but is of lesser value in the d iagnosis of adult cases, where it provides only supplementary information.