Overview of RBD
Patients with rapid eye movement behavior disorder (RBD) act out dramatic and/or violent dreams during rapid eye movement (REM) stage sleep. Another feature of RBD is shouting and grunting while sleeping.
RBD is a type of parasomnia, which is a condition that occurs during sleep and creates a disruptive event. It is similar to other sleep disorders that involve motor activity, such as sleepwalking and restless legs syndrome/periodic limb movement disorder (RLS/PLMD).
Unlike these conditions, RBD movements occur during REM sleep, which is usually characterized by a state of atonia, or sleep paralysis. Diagnosis and treatment of RBD involve polysomnography, drug therapy, and the exclusion of potentially serious neurological disorders.
RBD is usually seen in men 60 years old or older, but the condition also occurs in younger people and in women. Incidents of REM behavior disorder are often described anecdotally to family members and not to physicians, so statistics of incidence are inexact.
Physiology and Causes of RBD
Rapid eye movement behavior disorder is an uncommon sleep disorder first described in 1986. There is no known cause for RBD. It is, however, known to occur during rapid eye movement sleep, which is characterized by brain activity patterns that resemble wakefulness and which has been documented with polysomnography and other sleep tests.
Most dreaming occurs during REM sleep. Another characteristic of REM sleep is a general state of atonia, or muscle paralysis. So, while the brain is very active during REM sleep, the body is usually still.
The basic mechanism for REM sleep paralysis is found in the brainstem, the part of the brain that connects the spinal cord to the cerebral hemispheres, and that consists of the pons, midbrain, and the medulla oblongata. Although physicians do not thoroughly understand the complex processes, it is known that the brainstem undergoes changes in REM sleep that result in paralysis of the body's voluntary muscles.
Certain neurotransmitters, like acetylcholine (Ach), become dormant and do not communicate motor activity. The absence of muscular contraction during REM can be seen as a drop on the electromyogram (EMG) during polysomnography. An electroencephalogram (EEG) shows elevated brain activity during REM.
Physicians and sleep technicians hypothesize that the brain naturally and purposely prevents motor activity during REM sleep to ensure restful, inactive sleep during the most electrically active stage of sleep. In this context, sleep paralysis describes a normal state of sleep, unlike sleep paralysis experienced in narcolepsy, which affects people while they are trying to stay awake.
Motor Activity and REM Sleep
In RBD, neurotransmitters are not blocked, and the voluntary muscles become tonic, or tensely contracted, allowing a sleeping person to move his or her muscles during REM. Rapid eye movement behavior disorder is characterized by significant submental (under the chin) and limb muscle tone. The combination of heightened cerebral activity and muscular tonicity results in physically acting out dreams that involve excited and sometimes violent movement.
The body can be rigid and extremely tense during episodes of RBD. For example, a person might straighten his or her leg, flexing it intensely for several seconds or a minute. Often, sleepers curl up slightly, while flexing their limbs and chin.
People with RBD typically remember little nothing of this activity, unless they fall out of bed, bump into the furniture, or injure themselves and wake up. But they can usually remember and tell the dreams they were having during an episode.
Dreams that involve physical or violent activity—such as fighting, dancing, running, chasing, attacking, being attacked, running from an assailant—are more likely to trigger RBD activity. Sleepers with RBD sometimes injure their bed partners. Some people have been known to leave the bed, run into a wall, run through a window, or run down the stairs. But RBD activity is usually confined to the bed and the surrounding area.