Propriospinal myoclonus upon relaxation and drowsiness: a cause of severe insomnia.

Three patients, aged 71, 50, and 41 years, presented with myoclonic activity arising in the relaxation period preceding sleep onset and causing severe insomnia. Polygraphic studies showed that the myoclonic activity began in spinally innervated muscles, propagating at low speed to rostral and caudal muscular segments. Myoclonus arose whenever patients relaxed mentally and showed diffuse electroencephalographic alpha activity and was independent of posture. The jerks disappeared during sleep. Clonazepam afforded symptomatic improvement. Propriospinal myoclonus arising from a spinal generator may be facilitated by changes in supraspinal control related to vigilance levels. When arising during relaxation and drowsiness, it may cause severe insomnia.