Characteristics of rapid eye movement sleep behavior disorder in narcolepsy

Abstract

Rapid eye movement (REM) sleep behavior disorder (RBD) is characterized by dreamenacting behavior and impaired motor inhibition during REM sleep (REM sleep without atonia, RSWA). RBD is commonly associated with Parkinsonian disorders, but is also reported in narcolepsy. Most patients with narcolepsy with cataplexy lack the hypocretin neurons in the lateral hypothalamus. In contrast, RBD, RSWA, and hypocretin deficiency are rare in narcolepsy without cataplexy. Phasic motor activity in REM and non-REM (NREM) and dreamenacting behavior (RBD) coexist with cataplexy in narcolepsy because of hypocretin deficiency. Thus, hypocretin deficiency is linked to the two major disturbances of REM sleep motor regulation in narcolepsy: RBD and cataplexy. Moreover, it is likely that hypocretin deficiency independently predicts periodic limb movements in REM and NREM sleep, probably via involvement of the dopaminergic system. This supports the hypothesis that an impaired hypocretin system causes general instability of motor regulation during wakefulness, REM and NREM sleep in human narcolepsy. We propose that hypocretin neurons are centrally involved in motor tone control during wakefulness and sleep in humans and that hypocretin deficiency causes a functional defect in the motor control involved in the development of cataplexy during wakefulness and RBD/RSWA/ phasic motor activity during REM sleep.