[Fukuhara disease].

MERRF is an acronym of myoclonus epilepsy associated with ragged-red fibers and was first reported as a new nosological entity belonging to mitochondrial encephalomyopathies in San Remo symposium on "Mitochondrial Pathology" in 1982. MERRF was named Fukuhara disease by Rowland (1983). The first reported patient had been diagnosed as having Ramsay Hunt syndrome associated with Friedreich's ataxia. However, nowadays, the previously reported cases as having Ramsay Hunt syndrome associated with Friedreich's ataxia are regarded as having been suffered from MERRF. The history in establishing the nosological entity of MERRF was described. Patients with MERRF develop myoclonus, epileptic seizures, cerebellar ataxia, dementia, sensorineural hearing disturbance, optic atrophy, muscular wasting, and foot deformities at the advanced stage. Pathological findings show degeneration of the dentate nuclei, globus pallidus, and red nuclei, substantia nigra, inferior olivary nuclei, cerebellar cortex, and spinal cord. The posterior columns, the spinocerebellar tracts, and Clark's columns are degenerating in the spinal cord. The pyramidal tracts never show a severe degeneration as in Friedreich's ataxia. The skeletal muscles show mitochondrial abnormalities histologically and electron microscopically. Clinical features of MERRF are not necessarily uniform in the early stage and muscle biopsy findings are also very mild in some patients with MERRF, necessitating genetic analysis for diagnosis. Most of patients show a point mutation (A --> G) of nt 8344 in mitochondrial DNA.