Olivopontocerebellar degeneration, abnormal sleep, and REM sleep without atonia.

Polygraphic studies during sleep performed in two patients with olivopontocerebellar degeneration (OPCD) revealed an abnormal control of muscle tone. It was demonstrated by bursts of EMG activity during sleep and progressive disappearance of muscle atonia during sleep. Muscle atonia disappeared during rapid eye movement (REM) sleep, permitting movements and expression of feelings probably associated with REM sleep-related oneiric activity. Patients, unaware of their nocturnal sleep disturbance, complained only of the resulting daytime tiredness and sleepiness.