[Rhythmic skeletal myoclonus without palatal myoclonus].

We reported a case of 89-year-old woman showing rhythmic skeletal myoclonus mainly on the right upper limb. This myoclonus appeared five days after the cerebral infarction. It was seen constantly both at rest and in posture, and decreased during voluntary movement. When the patient was under emotional stress, it spread to the submandibular, neck and trunks of upper limb. During sleep, this movement completely disappeared. There was no myoclonus in palato-pharyngo-laryngo-oculo-diaphragmatic muscle group. In the examination of the surface electromyography, the movement was not reciprocal between extensor and flexor muscles, and its cycle was about 3.5 Hz. It was different from the intention tremor because it did not increase during the movement phase on the finger nose test. The examination of MRI revealed a small infarction including right dentate nucleus and right superior cerebellar peduncle, and from which an infarction of the superior cerebellar artery territory was considered. Only a few cases of rhythmic skeletal myoclonus without palatal myoclonus have been reported in the literature. All of these cases had small infarction of the same region as the above case. Their myoclonus began 5 to 15 days after the onset of cerebral infarction. These periods were markedly shorter than that of intention tremor and palatal myoclonus. This fact suggest that the rhythmic skeletal myoclonus has a different mechanism from that of the palatal myoclonus.