[Myoclonus epilepsy associated with ragged-red fibers--report of a patient with negative myoclonus].

A 21-year-old woman, who had no particular familial history, was admitted to our hospital because of hand tremor and gait disturbance. On neurological examination, she showed muscle weakness in the proximal extremities. There was an ataxia on heel-to-shin testing. Action and postural myoclonus involving the extremities were also noted. In addition, with dorsiflexion of the hands, asterixis-like movement was manifested. Pyruvate was 1.0 mg/dl and lactate was 24.1 mg/dl in cerebrospinal fluid. Brain CT scan revealed mild cerebellar atrophy. EEG showed synchronous diffuse slow wave. Median nerve SEPs showed a large N20-P25 component (20 microV). Median nerve C-reflex was not evoked. With dorsiflexion of the hands, the asterixis-like movement was induced with brief cessation of surface EMG activity in the forearm muscles, as shown by the accelerometer trace. Biopsy specimens of the biceps brachii muscle revealed numerous ragged-red fibers. By PCR-RFLP method with use of a mismatched primer, we analyzed mitochondrial DNA extracted from peripheral leukocytes. The A to G mutation at nucleotide position 8,344 in a tRNA(Lys) gene of a mitochondrial genome was detected. In this patient, clonazepam was effective on the asterixis-like movements. From existence of positive myoclonus, giant SEPs and efficacy of clonazepam, we considered this movement to be negative myoclonus. Our study indicated the possibility that such an involuntary movement could be induced by certain posture in patients with MERRF.