Periodic, aperiodic, and rhythmic motor disorders of sleep.

A variety of spontaneous movements can occur during sleep. Most are unassociated with identifiable CNS pathology and are presumed to be caused by sleep-related modulation of CNS motor control systems. Individual dyskinesias occurring during sleep can be characterized not only by their frequency, rhythmicity, and anatomic predilections, but also by the stage of sleep in which they characteristically occur. Wake-pattern movement disorders improve during sleep but, contrary to common belief, they do not entirely disappear. Instead, these disorders reemerge in attenuated form, often during nonrapid eye movement sleep. The identification and proper characterization of the various sleep-related dyskinesias are greatly aided by careful polysomnographic study.