Normal dreaming occurs during the deepest sleep states. Obviously, if experiencing a frightening dream, sleeping people could be injured if they jumped out of bed and started to run. Fortunately, the brain has a natural protective mechanism during dreaming: body paralysis. During the primary sleep stage in which dreaming occurs, the body’s muscle tone is shut off and muscles become limp. Only the eye muscles are spared, still able to move during a dream. This state in which dreaming takes place is rapid eye movement (REM) sleep. Restated, during REM sleep, a switch is thrown in the brain stem that shuts off body movement during dreaming. People with Lewy disorders of all types often lose this switch function. In other words, they can still move during the dreams of REM sleep. In the midst of a dream, they may act out by yelling, kicking, or hitting the air. This behavior is termed dream enactment behavior. When it is a recurring event it is termed REM sleep behavior disorder. REM sleep behavior disorder occurs in people with Lewy disorders—Parkinson’s disease, DLB, or PDD. It also occurs in another disorder in which alpha-synuclein is abnormally deposited in the nervous system, multiple system atrophy (MSA). Recall from Chapter 2 that alpha-synuclein is present in Lewy bodies and is thought to be a causative factor in all of these conditions. REM sleep behavior disorder may be present years or even decades before the occurrence of DLB, PDD, Parkinson’s disease, or multiple system atrophy. It is often one of the first signs of these disorders, predating most other manifestations. That does not mean that everyone who acts out their dreams will eventually develop Parkinson’s disease, DLB, or MSA. However, it does confer an increased risk. It should be noted that certain medications may provoke REM sleep behavior disorder, such as the commonly used antidepressants. Also, sleepwalking in children should not be confused with this disorder. Sleepwalking occurs in a different sleep stage and is not thought to be a forerunner of Lewy body conditions.
REM sleep behavior in Parkinson disease: Frequent, particularly with higher age
