REM sleep behavior disorder - past, present, and future

Abstract

The REM sleep behavior disorder (RBD) is a fascinating experiment of nature predicted by animal experiments nearly 40 years ago. Active paralysis of somatic muscles is one of the defining features of REM sleep. In the catmodel of REM sleep behavior disorder, bilateral perilocus ceruleus lesions result in loss of the expected atonia of REM sleep, resulting in dream-enacting (oneiric) behaviors. In humans, REM sleep behavior disorder presents as complex behaviors arising from REM sleep, as the persistence of muscle tone during REM sleep permits the acting out of dreams, often with violent or injurious consequences to the patient or bed partner. These behaviors include talking, yelling, swearing, grabbing, punching, kicking, jumping, or running out of the bed and may result in lacerations, ecchymoses, or fractures. The acute, or transient, form is usually drug-induced (most commonly tricyclic antidepressants [TCAs] or serotonin-specific reuptake inhibitors [SSRIs]). REM sleep behavior disorder may also be a manifestation of narcolepsy. The chronic form is seen predominantly in men (80-90%) over 50 years of age. Initially felt to be idiopathic, it is now becoming apparent that spontaneous REM sleep behavior disorder is often a harbinger of degenerative neurological conditions, most commonly one of the synucleinopathies (Parkinson's disease, multiple system atrophy, or dementia with Lewy body disease). Interestingly, the symptoms of REM sleep behavior disorder precede any other manifestations of the underlying neurodegenerative disorders by an average of over 10 years. It is readily diagnosed by formal sleep studies which reveal persistence of muscle tone during REM sleep. Most cases of REM sleep behavior disorder respond dramatically to clonazepam administered at bedtime.