During normal REM sleep, the body is paralysed. A brainstem mechanism called REM atonia actively suppresses spinal motor neurons, preventing us from physically acting out our dreams. In REM sleep behaviour disorder (RBD), this paralysis mechanism fails, and the sleeper moves, vocalises, and sometimes violently enacts dream content, often involving chasing or being chased, fighting, or escaping threat. The condition is medically significant beyond the sleep disturbance and injury risk it creates.
Recognising RBD
The typical presentation is complex motor behaviour during sleep reported by a bed partner: kicking, punching, grabbing, shouting, or falling out of bed. The episodes typically occur in the second half of the night when REM sleep predominates. The sleeper can often be woken during an episode and will recall a vivid dream consistent with the observed behaviour. This distinguishes RBD from other parasomnias such as sleepwalking, which occurs in deep NREM sleep and involves no dream recall.
The Parkinson's Disease Connection
Idiopathic RBD (RBD without a clear secondary cause) is one of the most powerful prodromal markers of alpha-synuclein neurodegenerative disease yet identified. A 2013 meta-analysis found that approximately 81% of people diagnosed with idiopathic RBD will develop Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy within 12 to 20 years. This is consistent with Braak's hypothesis that Parkinson's pathology originates in the brainstem structures controlling REM atonia before it reaches the substantia nigra and produces motor symptoms.
Diagnosis
Definitive diagnosis of RBD requires polysomnography (a formal sleep study) demonstrating REM sleep without atonia and motor events during REM. A video-polysomnogram allows correlation of movements with the sleep stage. Questionnaire-based screening tools, including the REM Sleep Behaviour Disorder Single-Question Screen (RBD1Q) and the Munich RBD Questionnaire, are validated screening instruments that a GP can use before referring for polysomnography.
Causes and Risk Factors
- Idiopathic RBD: no identifiable cause; high risk of synucleinopathy
- Medications: SSRIs and SNRIs (antidepressants) are the most common secondary cause; they can induce RBD or unmask subclinical RBD
- Parkinson's disease: approximately 30 to 60% of Parkinson's patients have RBD at some stage of their disease
- Narcolepsy: RBD occurs in a significant proportion of narcolepsy patients
- Brainstem structural lesions: stroke or multiple sclerosis affecting pontine tegmentum
Management
- Safety first: padded bed rails, mattress on the floor, removal of sharp objects and lamps from bedside, separate sleeping arrangements if injury risk is significant
- Melatonin: 3 to 12mg at bedtime is first-line pharmacological treatment; reduces the frequency and severity of RBD events in most patients; mechanism may involve enhancement of REM atonia pathways
- Clonazepam: effective but associated with dependency, cognitive effects, and worsening sleep apnea; now generally second-line
- SSRI review: if an antidepressant is suspected as the cause, switching to a different class may resolve RBD
- Parkinson's disease monitoring: people with idiopathic RBD should be followed clinically for prodromal Parkinson's features and considered for neuroprotective trial enrolment if available
Sources
- Schenck CH, et al. (2013). Delayed emergence of a parkinsonian disorder or dementia in 81% of older males initially diagnosed with idiopathic REM sleep behavior disorder. Sleep Medicine, 14(8), 744-748.
- Postuma RB, et al. (2012). Idiopathic REM sleep behavior disorder in the transition to degenerative disease. Movement Disorders, 28(2), 149-159.
- Aurora RN, et al. (2010). Best practice guide for the treatment of REM sleep behavior disorder. Journal of Clinical Sleep Medicine, 6(1), 85-95.