Propriospinal myoclonus at sleep onset

**Definition:** Propriospinal myoclonus at sleep onset consists of sudden myoclonic jerks of the trunk, hips, and knees in a fixed pattern that occur during the transition from wakefulness to sleep and, more rarely, during nighttime awakenings or upon awakening in the morning. The jerks arise mainly in spinally innervated muscles and thereafter propagate to rostral and caudal muscles at a low speed, typical of propriospinal pathways. The movements result in clinically significant difficulty with sleep initiation or maintenance.