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REM Behavior Disorder: Another Kind of Sleepwalking
Abstract & Commentary
By Charles P. Pollak, MD, Professor, Clinical Neurology, Weill College of Medicine. Dr. Pollak is a stockholder for Merck, and is on the speaker's bureau for Merck.
Synopsis: 'Idiopathic' RBD patients with olfactory impairment might present with stage 2 preclinical alpha-synucleinopathy.
Sources: Stiasny-Kolster K, et al. Combination of 'Idiopathic' REM Sleep Behavior Disorder and Olfactory Dysfunction As Possible Indicator For Alpha-Synucleinopathy Demonstrated By Dopamine Transporter FP-CIT-SPECT. Brain. 2005;128:126-137.
Sleepwalkers usually awaken in the morning with little or no recall of walking during the night. They infer that they walked from the evidence that they find, such as an open front door or open containers of food. In REM Sleep Behavior Disorder, by contrast, the sleeper awakens from a vividly recalled dream. Not only that, but he may be confronted with evidence that some of the dreamed events actually took place. His wife, for example, may bear the marks of blows that he inflicted while defending himself in a fight that was entirely fictive. If she was awakened by his shouts, she may have witnessed the combative movements that resulted in her injury. In short, she may recount an enacted dream. It might be thought by a neurologist that the enactment of a dream, at least one occurring during REM sleep as most do, would be obviated by the inhibition of spinal muscle activity that normally accompanies REM sleep. Since 1986, however, when the first series of adults with RBD was described, it has become clear that REM atonia can be partially lost, resulting in motor activity that corresponds exactly to events later recalled as part of a dream narrative. A polysomnogram will reveal increased tonic EMG activity, as well as increases in phasic bursts during otherwise typical REM sleep. Such increases have recently been quantified to assess the severity of RBD. Sleep architecture is usually well preserved.
RBD has an interesting history. It was originally described by Michel Jouvet, a neurosurgeon and sleep specialist who placed lesions in the region of the locus coeruleous of the cat in an effort to localize areas of the CNS essential for REM sleep. Once the cat had fallen asleep, Jouvet observed behaviors that were part of a cat's waking behavioral repertoire, such as movements that are normally made when toying with a mouse or grooming. Because such behavioral stereotypes were limited to REM sleep, Jouvet speculated that the animal was "acting out its dream." Subsequently, Schenck & Mahowald at the University of Minnesota, described what appeared to be the human equivalent in a series of patients, most of them older men.
In a recent analysis of the dreams of RBD patients and controls, RBD dreams were found to be more aggressive, to contain animals, and less likely to be sexual. A questionnaire revealed normal levels of daytime aggressiveness. Stiasny-Kolster and colleagues speculate that aggressive dreams and vigorous motor activity are 2 manifestations of hyperactivity of a common neuronal generator. Both the dreams and excessive motor activity can be reduced with clonazepam.
It was observed that RBD was associated with certain neurodegenerative disorders: Parkinson disease (PD), multiple-system atrophy (MSA), dementia with Lewy bodies (DLB), spinocerebellar atrophy type 3 (SCA3; Machado-Joseph disease), and progressive supranuclear palsy (PSP). These share the presence of -synuclein-positive intracellular inclusions, and sometimes developed several years before the onset of PD.
According to a new neuropathological staging, PD progresses from the olfactory nucleus or bulb to the lower brainstem (medulla and pontine tegmentum) and only later to the dopaminergic neurons of the midbrain substantia nigra pars compacta. It has long been known that olfactory dysfunction is a common and very early feature of PD. A second early feature of PD is RBD, which is followed by the development of PD 12.7 years later (average) in 65% of cases. More generally, RBD is strongly predictive of the eventual development of an -synucleinopathy (PD, MSA or dementia with Lewy Bodies), rather than a parkinsonian or dementing disorder such as PSP, corticobasal degeneration, Alzheimer's disease, or Pick's disease. Lewy bodies have been found in the same brainstem areas as in PD. Taken together, these findings imply that olfactory deficits should be a feature of RBD, and Stiasny-Kolster et al have now found that this is indeed so.
They studied 30 men and women, mean age 48 years, with either RBD or subclinical RBD (ie, PSG evidence of REM sleep without atonia and without violent behavior). Nearly all (96.7%) of the RBD patients had a pathologically increased olfactory threshold, and many were also unable to discriminate odors or identify them correctly. Two-thirds of the RBD patients were unaware of an olfactory deficit before testing. Eleven of the 30 patients also agreed to undergo I-123_FB-CIT SPECT studies. The results were consistent with a continuum of striatal dopamine transporter deficiency, with the lowest values being found in PD, followed by RBD, then by subclinical RBD.
RBD can be easily recognized by the practicing neurologist. The diagnosis can be strongly presumed from the clinical features alone, and proof is readily obtained with a confirmatory polysomnogram that reveals the loss of muscle atonia normally associated with REM sleep. The loss of atonia may be attributed to the disruption of inhibitory systems in the medial medulla. Treatment with clonazepam 0.5mg is fortunately nearly always effective and greatly appreciated by patient and family. It then remains for the neurologist to keep a watch for the possible likely development of PD or another synucleinopathy.