RespiratoryTier 2Disease (DEADMAN)

Sleep disorders - REM sleep behavioural disorder

Description

Loss of the normal REM atonia -> the patient enacts dream content
Dream enactment is complex, purposeful and matches the reported dream - punching, kicking, shouting, leaping from bed
- Dreams are typically confrontational - being attacked, chased, defending a spouse
Rapid, complete return to lucidity on waking, with clear dream recall
Occurs in the second half of the night (REM-dense)

Classification

Isolated (idiopathic) RBD - a misnomer; almost all are prodromal neurodegenerative disease
Secondary RBD - established synucleinopathy, narcolepsy type 1, brainstem lesion, drug-induced

Distinguishing from the mimics

	RBD	NREM parasomnia (sleepwalking/terrors)	Nocturnal frontal lobe epilepsy
Timing	Second half	First third	Any, often clustered
Age	>50, M>F	Childhood	Any
Behaviour	Enacted dream, stays near/in bed	Confused, walks, leaves bed	Stereotyped, brief, dystonic/hyperkinetic
Recall	Vivid, matches action	None	Variable
Arousal	Immediate lucidity	Confused, amnesic	Rapid
Frequency/night	1-2	1	Many

Prevalence ~0.5-1.3% of adults over 60
M>F ~2-9:1 (women present with less violent behaviour and are under-recognised)
Mean onset 50-70 years
In established Parkinson disease ~30-50%; dementia with Lewy bodies ~70-80%; multiple system atrophy ~90-100%
Narcolepsy type 1: ~30-60% - younger onset, both sexes equally, not prodromal of neurodegeneration
Injury to the patient or bed partner in ~30-60% by the time of diagnosis

Normal REM atonia

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Subcoeruleus/subcoeruleus alpha nucleus (pons)

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Degeneration of the pontine subcoeruleus and its medullary projections -> loss of that inhibition -> movement during REM

Why it predicts synucleinopathy

Braak staging: alpha-synuclein pathology ascends from the olfactory bulb and dorsal motor vagal nucleus -> pontine/medullary tegmentum (Braak stage 2) -> substantia nigra (stage 3) -> cortex
The brainstem REM circuitry is affected years before the nigrostriatal degeneration that causes parkinsonism
-> RBD is the most specific clinical prodromal marker of an alpha-synucleinopathy - Parkinson disease, dementia with Lewy bodies, multiple system atrophy
It is NOT a feature of tauopathies (PSP, corticobasal degeneration, Alzheimer disease) - which is diagnostically useful

Secondary/drug-induced

SSRIs, SNRIs, mirtazapine, TCAs, beta-blockers, tramadol (can unmask or precipitate)
Alcohol withdrawal, brainstem lesions (stroke, MS, tumour), anti-IgLON5 disease, paraneoplastic (anti-Ma2)
Narcolepsy type 1 - hypocretin/orexin loss

Clinical

History from the bed partner is essential; ask specifically about injuries, bruising, furniture damage, sleeping separately
Screening questions: "Have you ever been told you act out your dreams?", "Have you ever hurt yourself or your partner while asleep?"

Polysomnography is required for diagnosis

REM sleep without atonia (RSWA) on chin and limb EMG - the mandatory finding
Video documentation of dream enactment, or a history of injurious/potentially injurious behaviour
PSG also excludes severe OSA, which causes "pseudo-RBD" arousal-related enactment (and is treated with CPAP, not clonazepam)
ICSD criteria: repeated episodes of sleep-related vocalisation or complex motor behaviour + documented during REM on PSG or presumed from history + RSWA

Look for prodromal features at diagnosis, and at every review

Hyposmia (formal smell testing), constipation, orthostatic hypotension, erectile dysfunction, urinary symptoms
Subtle motor signs: bradykinesia, reduced arm swing, micrographia
Cognitive screening (especially visuospatial, executive), depression, colour vision
DaT-SPECT, cardiac MIBG scintigraphy, skin biopsy for phosphorylated alpha-synuclein - research/selected use, not routine
Review the drug chart for antidepressants

1. Safety of the sleep environment - this comes first

2. Review precipitants

Cease or substitute the offending antidepressant where clinically possible (bupropion and agomelatine are less implicated)
Treat coexisting OSA with CPAP - alone this resolves a proportion of cases
Avoid alcohol and sleep deprivation

3. Pharmacotherapy - AASM 2023, all recommendations conditional

Drug	Note
Clonazepam 0.25-1 mg nocte	Long-standing first choice; falls, sedation, confusion, worsening OSA - a real concern in this elderly population
Immediate-release melatonin 3-12 mg nocte	Similar conditional recommendation; much better tolerated -> preferred in the frail, in those with cognitive impairment, and where OSA coexists
Transdermal rivastigmine	Conditionally recommended for isolated or secondary RBD
Pramipexole	Conditionally recommended in isolated RBD

The guideline deliberately does not rank clonazepam above melatonin - choose on comorbidity and falls risk
Avoid: quetiapine and other sedating antipsychotics are not indicated; patients with underlying DLB have severe neuroleptic sensitivity

4. Counselling about the prognosis

A difficult but necessary conversation. Disclose in a staged way, at the patient's pace, with time and follow-up
Explain that there is currently no neuroprotective therapy - and offer enrolment in prodromal cohorts and trials, where RBD patients are the key recruitment population
Longitudinal follow-up: annual motor, cognitive and autonomic review; driving assessment as features emerge

Parkinson disease, dementia with Lewy bodies, multiple system atrophy (pure autonomic failure too)
Narcolepsy type 1 - the exception: not a neurodegenerative marker
Antidepressants - SSRIs, SNRIs, mirtazapine, TCAs; beta-blockers; tramadol
Anti-IgLON5 disease (a tauopathy with prominent parasomnia and bulbar features), paraneoplastic encephalitis
Brainstem stroke, multiple sclerosis, pontine tumour
Obstructive sleep apnoea (mimics it)
Hyposmia, constipation, orthostatic hypotension, depression - the prodromal cluster
Prior pesticide exposure, head injury, farming, shift work (epidemiological associations)

~6-8% per year phenoconvert to an overt alpha-synucleinopathy
~80% within 15 years; longer cohorts approach 90%+
Median latency from RBD onset to diagnosis ~10-15 years, occasionally >25 years
Which disease develops is not predictable at onset, though:
- Hyposmia and colour vision loss -> Parkinson disease/DLB
- Prominent early autonomic failure -> MSA
- Early visuospatial and cognitive impairment -> DLB
RBD in established Parkinson disease predicts a worse phenotype: earlier cognitive decline and dementia, more autonomic dysfunction, more falls, more hallucinations
RBD symptoms themselves often improve as the disease advances (further motor degeneration)

Complications

Injury to patient and bed partner - fractures, subdural haematoma, lacerations, strangulation; the reason environmental modification is not optional
Marital and relationship strain, separate sleeping arrangements
Sedative-related falls and cognitive impairment from treatment
Psychological impact of prognostic disclosure

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