Motor disorders in sleep.

Sleep is normally a time of motor quiescence. Motor disorders may, however, arise during the different phases of sleep. Nocturnal myoclonus or periodic leg movements in sleep usually occur during light sleep and may be considered the motor accompaniment of the cyclic fluctuations in excitability typical of such stages. Nocturnal frontal lobe epilepsy also occurs during NREM sleep and may be misdiagnosed as parasomnia. REM behavior disorders are instead dissociated episodes of REM sleep without atonia, often associated with or even heralding Parkinson's disease or multiple system atrophy.