Neuropathology of myoclonus epilepsy associated with ragged-red fibers (Fukuhara's disease).

The post-mortem findings are reported of two patients with myoclonus epilepsy associated with ragged-red fibers (MERRF, Fukuhara's disease), whose clinical findings have been described in detail previously. In addition to the mitochondrial myopathy, both patients had consistent lesions in the central and peripheral nervous systems: (1) degeneration of the dentatorubral and pallidoluysian systems, (2) spinal cord lesions resembling Friedreich's ataxia, and (3) degeneration of the substantia nigra, cerebellar cortex, inferior olivary nucleus, locus ceruleus, gracile and cuneate nuclei, and the pontine tegmentum. The nature and distribution of the lesions are different not only from the other mitochondrial encephalomyopathies but also from other known diseases. It is concluded that MERRF is a disease entity.