Mitochondrial myopathies are a type of myopathy associated with mitochondrial disease. On biopsy, the muscle tissue of patients with this disease category usually demonstrate 'ragged red' muscle fibers. These 'ragged red' fibers contain mild accumulations of glycogen and neutral lipids, and may show an increased reactivity for succinate dehydrogenase and a decreased activity for cytochrome c oxidase. Inheritance is maternal (non-Mendelian extranuclear). There are several subcategories of mitochondrial myopathies.