Evolution of segmental myoclonus during sleep: polygraphic study of two cases.

We describe the sleep evolution of two cases of segmental myoclonus. The first patient had symptomatic palatal myoclonus which, as in most reported cases, persisted during sleep with a slight but significant reduction in frequency. The second patient presented apparently essential spinal myoclonus, which disappeared on falling asleep and recurred for short periods during arousals. This patient also had nocturnal myoclonus involving the legs, as well as those muscles affected by spinal myoclonus. The physiopathological significance of this unusual association is discussed.