Nocturnal myoclonus observed in a patient with neuroleptic-induced akathisia.

An all-night polysomnogram was twice recorded in a patient with neuroleptic-induced akathisia (NIA). The polysomnogram revealed nocturnal myoclonus. After disappearance of akathisia by the administration of clonazepam, we recorded the second polysomnogram. At the second examination, sleep efficacy increased and the total number of nocturnal myoclonus decreased remarkably. The mean inter-movement interval of nocturnal myoclonus prolonged. These findings suggest a close relationship between the mechanisms of neuroleptic-induced akathisia and nocturnal myoclonus.