Residency · Residency · Neurology

REM Sleep Behavior Disorder and Parasomnias

Introduction

Parasomnias are undesirable physical or experiential events that occur during entry into sleep, within sleep, or during arousal from sleep. They are classified by the sleep stage from which they arise: NREM parasomnias (disorders of arousal), REM parasomnias (most notably REM sleep behavior disorder), and other parasomnias. REM sleep behavior disorder (RBD) is of particular importance to neurologists because of its strong association with alpha-synucleinopathies.

Normal REM Sleep Physiology

REM sleep is characterized by rapid eye movements, low-voltage desynchronized EEG, and skeletal muscle atonia. This REM atonia is mediated by glycinergic and GABAergic inhibition of spinal motor neurons, originating from the sublaterodorsal nucleus (equivalent to the subcoeruleus in humans) and the ventromedial medulla. Dreaming is most vivid and narrative during REM sleep. Loss of the normal REM atonia mechanism is the fundamental abnormality in RBD.

REM Sleep Behavior Disorder

Clinical Features

Dream enactment behavior is the hallmark of RBD: patients act out their dreams during REM sleep with vocalizations such as shouting, swearing, or laughing, and complex motor behaviors including punching, kicking, running, and leaping out of bed. Dreams are often vivid and violent, involving being chased, fighting, or defending against attack. Patients may injure themselves or their bed partners. Behaviors are typically stereotyped and occur in the latter half of the night when REM density is greatest. Patients are usually unaware of their behavior until awakened or informed by a bed partner.

Diagnosis

Video-polysomnography (v-PSG) is required for definitive diagnosis. The key finding is REM sleep without atonia (RSWA), identified as excessive phasic or tonic EMG activity on chin and limb EMG channels during REM sleep, often with video-captured dream enactment. RBD mimics must be excluded, including severe obstructive sleep apnea (pseudo-RBD from arousals), nocturnal seizures, NREM parasomnias, and PTSD-related nightmares.

Association with Neurodegenerative Disease

Isolated RBD (iRBD, formerly idiopathic RBD) is the strongest known prodromal marker for alpha-synucleinopathies. Longitudinal studies demonstrate that greater than 80-90% of iRBD patients will develop a defined alpha-synucleinopathy within 10-15 years: approximately 45% develop Parkinson disease, approximately 25% develop dementia with Lewy bodies, and approximately 5-10% develop multiple system atrophy. The mean interval from RBD onset to phenoconversion is approximately 10-14 years. Biomarkers of impending phenoconversion include olfactory dysfunction, constipation, subtle motor signs, dopamine transporter (DaT) imaging abnormalities, and cognitive decline.

Management of RBD

Environmental safety measures are the first priority: removing bedside objects, padding the floor, using bed rails or placing the mattress on the floor, and separating bed partners if necessary. Melatonin is the first-line pharmacotherapy at 3-12 mg at bedtime, restoring REM atonia with minimal side effects. Clonazepam at 0.25-2 mg at bedtime is effective in reducing dream enactment but carries risks of sedation, falls, and worsening of OSA. Medications that exacerbate RBD should be avoided or minimized, including SSRIs, SNRIs, tricyclic antidepressants, and beta-blockers. Counseling regarding the association with neurodegenerative disease should be handled with sensitivity, and neuroprotective trials for iRBD patients are underway.

NREM Parasomnias (Disorders of Arousal)

General Features

NREM parasomnias arise from slow-wave sleep (N3), typically during the first third of the night. They involve partial arousal from deep sleep with impaired consciousness, amnesia for the event, and automatic behavior. These are more common in children, with prevalence decreasing with age. Precipitants include sleep deprivation, alcohol, stress, fever, obstructive sleep apnea, and medications such as sedatives and lithium.

Sleepwalking (Somnambulism)

Sleepwalking involves complex ambulatory behavior during sleep with eyes open but a glassy, unfocused appearance. Activities may range from routine behaviors like walking, eating, or opening doors to dangerous ones such as leaving the house or driving. Patients carry a high injury risk, are difficult to awaken, and are confused if aroused.

Sleep Terrors (Night Terrors)

Sleep terrors present as sudden arousal from N3 sleep with intense fear, screaming, and autonomic activation including tachycardia, diaphoresis, and mydriasis. The patient is inconsolable, unresponsive to the environment, and amnestic for the episode. They are distinguished from nightmares, which occur during REM sleep, produce vivid dream recall, and rarely involve motor behavior.

Confusional Arousals

Confusional arousals involve disoriented behavior on awakening from sleep without significant ambulation or autonomic activation. They may include inappropriate speech, slow responses, or combative behavior if the patient is physically restrained.

Treatment of NREM Parasomnias

Management begins with addressing predisposing factors, ensuring adequate sleep, and treating comorbid sleep disorders, especially OSA. Safety precautions include locking doors and windows, installing alarm systems, and removing hazardous objects. Pharmacotherapy for frequent or dangerous episodes includes clonazepam 0.25-1 mg at bedtime or low-dose SSRI. Anticipatory awakening, which involves waking the patient 15-30 minutes before the typical event time, is especially useful in children.

Other Parasomnias

Sleep-Related Eating Disorder

Sleep-related eating disorder involves recurrent episodes of involuntary eating during partial arousals from NREM sleep. It is associated with sedative-hypnotic medications, especially zolpidem, and may involve consumption of unusual or inedible items. Treatment involves discontinuing offending medications, and topiramate may be helpful.

Exploding Head Syndrome

Exploding head syndrome is the perception of a loud noise or explosion in the head during sleep-wake transition. It is benign and painless but causes significant distress. Reassurance is typically sufficient treatment.

Sleep Paralysis

Sleep paralysis is a transient inability to move or speak during sleep-wake transitions lasting seconds to minutes, often accompanied by hallucinations and anxiety. Isolated episodes are common with a prevalence of 6-8%, while recurrent episodes may be associated with narcolepsy. Treatment includes sleep hygiene and reassurance, with SSRIs reserved for recurrent cases.

Clinical Pearls

REM sleep behavior disorder in an older adult without a known neurological diagnosis is a prodromal marker for an alpha-synucleinopathy, and these patients warrant longitudinal follow-up for early signs of Parkinson disease, DLB, or MSA. SSRIs and SNRIs are among the most common medications that trigger or worsen RBD, and this should be considered in patients who develop dream enactment after starting antidepressants. NREM parasomnias and RBD occur at different times of night: NREM parasomnias typically occur in the first third when N3 predominates, while RBD occurs in the latter half when REM predominates. Melatonin is preferred over clonazepam as first-line RBD therapy due to its favorable side-effect profile, especially in elderly patients at risk for falls. Video-PSG is essential for diagnosing RBD because clinical history alone is insufficient, as OSA-related arousals can mimic dream enactment behavior.

References

1. St Louis EK, Boeve BF. REM sleep behavior disorder: diagnosis, clinical implications, and future directions. Mayo Clin Proc. 2017;92(11):1723-1736.
2. Postuma RB, Iranzo A, Hu M, et al. Risk and predictors of dementia and parkinsonism in idiopathic REM sleep behaviour disorder: a multicentre study. Brain. 2019;142(3):744-759.
3. Galbiati A, Verga L, Giora E, Zucconi M, Ferini-Strambi L. The risk of neurodegeneration in REM sleep behavior disorder: a systematic review and meta-analysis of longitudinal studies. Sleep Med Rev. 2019;43:37-46.
4. Fleetham JA, Fleming JAE. Parasomnias. CMAJ. 2014;186(8):E273-E280.

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