REM Sleep Parasomnias

Rapid eye movement (REM) sleep is characterized by numerous physiologic variables that usually occur in concert to produce the fully declared REM sleep. The majority of the REM sleep parasomnias reflect state dissociation, a condition seen when not all of the elements usually comprising REM sleep are present, resulting in fascinating clinical phenomena. The most common and best-studied REM sleep parasomnia is the REM sleep behavior disorder (RBD). In patients with RBD, somatic muscle atonia-one of the defining features of REM sleep-is absent, permitting the acting out of dream mentation, often with violent or injurious results. RBD is overwhelmingly a disorder affecting older men, many of whom eventually develop neurodegenerative disorders. Increasingly, medications prescribed for psychiatric symptoms (predominantly selective serotonin reuptake inhibitors), are the cause of RBD. The vast majority of patients with RBD respond to clonazepam. Further study of the REM parasomnias will serve to teach us much about sleep and the function of the central nervous system.