MERRF: a clinicopathological study. Relationships between myoclonus epilepsies and mitochondrial myopathies.

Myoclonus epilepsy associated with ragged-red fibers (MERRF) is a degenerative disease involving dentate nuclei of the cerebellum, globus pallidus, the posterior columns and spinocerebellar tracts of the spinal cord, and skeletal muscles. Abnormal mitochondria were observed in the cells of the cerebellar cortex and of the dentate nuclei. The main symptoms of this disease include cerebellar ataxia and myoclonus in addition to muscular wasting. Patients with MELAS occasionally have myoclonus, but they never have myoclonus as their initial symptoms. Most of the patients with both clinical features of MERRF and MELAS were regarded as belonging to the category of MELAS.