Normal sleep has two distinct states: non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. NREM sleep is divided into three stages. During REM sleep, rapid eye movements occur, breathing becomes irregular, blood pressure rises, and there is a loss of muscle tone (paralysis). However, the brain is highly active, and the electrical activity recorded in the brain by EEG during REM sleep is similar to that recorded during wakefulness. REM sleep is usually associated with dreaming. REM sleep accounts for 20%-25% of the sleep period.
In a person with REM sleep behavior disorder (RBD), the paralysis that normally occurs during REM sleep is incomplete or absent, allowing the person to "act out" their dreams. RBD is characterized by the acting out of dreams that are vivid, intense, and violent. Dream-enacting behaviors include talking, yelling, punching, kicking, sitting, jumping from bed, arm flailing, and grabbing. An acute form may occur during withdrawal from alcohol or sedative-hypnotic drugs.
RBD is usually seen in middle-aged to elderly people (more often in men).
Causes of REM Sleep Disorder
The exact cause of REM sleep behavior disorder (RBD) is unknown, although the disorder may occur in association with various degenerative neurological conditions such as Parkinson's disease, multisystem atrophy (also known as Shy-Drager syndrome), and diffuse Lewy body dementia. In 55% of persons the cause is unknown, and in 45%, the cause is associated with alcohol or sedative-hypnotic withdrawal, tricyclic antidepressant (such as imipramine), or serotonin reuptake inhibitor use (such as fluoxetine, sertraline, or paroxetine) or other types of antidepressants (mirtazapine).
RBD often precedes the development of these neurodegenerative diseases by several years. In one study, 38% of patients diagnosed with RBD subsequently developed Parkinson's disease within an average time of 12-13 years from the onset of RBD symptoms. Also, RBD is seen in 69% of those with Parkinson's disease and multisystem atrophy. The relationship between RBD and Parkinson disease is complex; however, not all persons with RBD develop Parkinson's disease.