The term parasomnia refers to a group of disorders of arousal, partial arousal, and sleep-stage transition. A feature of many of the parasomnias is the occurrence of abnormal muscle activation behaviors occur during sleep. These behaviors may be associated with REM or NREM sleep. Behaviors occurring predominantly during the first third of the night are likely to be related to Stages 3 and 4 sleep because this is the time of night when SWS predominates and are largely considered disorders of arousal. Somnambulism or sleep walking, sleep terrors, and confusional arousals are commonly occurring parasomnias during SWS. Usually, these disorders affect children and adolescents, and resolve during adulthood. However, these disorders may carry over into adulthood or arise secondary to medications. Sleep walking may result in significant sleep-related injuries because patients may walk through windows or fall down stairs during their nocturnal wanderings.
Sleep complaints that occur during the transition from wakefulness to sleep often affect otherwise healthy individuals and include sleep starts, sleep talking, and rhythmical movement disorders such as head banging, body rocking, and head rolling. The hallmark of this group of disorders is their occurrence at sleep onset, with some also occurring during wakefulness.
The parasomnias associated with REM sleep include nightmares, sleep paralysis, and RBD. y REM-related parasomnias are more likely to occur later in the night, when REM sleep predominates. RBD usually affects older men, in contrast to the other REM- and NREM-related parasomnias. RBD may occur as an idiopathic disorder or arise secondary to neurological disorders in which there is pathology involving brain stem nuclei. RBD is considered a primary disorder of REM sleep that parallels oneiric activity in animals following selective lesions of the pontine nuclei controlling motor atonia. Patients with narcolepsy, another disorder of REM sleep, may also show features of RBD.
Additional sleep-related behavior disorders that may be confused with those described earlier include paroxysmal nocturnal dystonia and nocturnal epilepsy. These disorders appear as paroxysmal, stereotyped behaviors with sudden onset and resolution reflecting abnormal cortical activity rather than alterations in brain stem centers controlling REM sleep, or arising from NREM sleep.
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