REM Sleep Behavior Disorder

Definition and Prevalence
REM sleep behavior disorder (RBD) is a disorder in which the muscle atonia typical of the REM state is absent, causing motor disinhibition presenting as vigorous movements that may be violent or aggressive toward the patient or the bed partner. Vivid dreams are often remembered on awakening and are consistent with the observed behavior. Most often the patients report not being the aggressors in the dream, but being the defenders of themselves or their family members. The harmful behavior is uncharacteristic of the waking individual.

RBD is considered a neuropathologic disorder, al-though most often it is idiopathic. It has been associated with neurodegenerative impairments such as dementia, parkinsonism, Guillain-Barre syndrome, olivo-ponto-cerebellar degeneration, and subarachnoid hemorrhage. Some patients exhibit other sleep disorders, including narcolepsy and PLMS. It is also associated with psychiatric disorders such as depression and drug and alcohol abuse and withdrawal.

The prevalence of REM behavior disorder (RBD) in the population has not been estimated; however, those diagnosed with the disorder are predominantly older men.

Consequences
The majority of the patients report injuries to themselves and to their spouses, including ecchymoses, lacerations, and fractures.

Clinical Presentation
Episodes usually begin during the second half of the night when REM is most abundant, but usually no earlier than 60 to 90 min after sleep onset, which is when the first REM period is expected to occur.

RBD may become more frequent over time. Patients may experience an episode once every 2 to 3 weeks, or as many as four episodes a night for several nights in a row. Some experience a nightly episode. There have been no reports of spontaneous remission.

One-fourth of the patients report a prodrome in their history, which involved behavioral disinhibition of dreams, or other parasomnias, including sleeptalking, yelling, and limb jerks. Sleep recordings show elevated percentages of REM sleep, as well as a shortened REM latency.

Diagnosis and Differential Diagnosis
A detailed history of the sleep disorder, from both the patient and the bed partner, should include the timing and frequency of the episodes and the type of the behavioral disturbance. Mahowald and Schenck have suggested minimal criteria for diagnosing RBD, including a history or videotape recording of abnormal sleep behavior, with an EMG recording showing elevated muscle tone and/or phasic limb twitching.

Differential diagnoses include night terrors and sleepwalking, which are also disruptive behavioral enactments during sleep; however, unlike RBD, these are parasomnias that occur during non-REM sleep, often in the early part of the night.