Secondary Causes of REM Sleep Behavior Disorder
Secondary RBD can be caused by neurodegenerative disorders (especially α-synucleinopathies), other neurological conditions, medications (particularly antidepressants), substance withdrawal states, and other sleep disorders. 1
Neurodegenerative Disorders (α-Synucleinopathies)
The strongest association exists with α-synucleinopathies, which represent the most common secondary causes:
- Parkinson Disease (PD): Found in 15-33% of PD patients 1
- Dementia with Lewy Bodies (DLB): Present in 40% of DLB patients; RBD is now a suggestive diagnostic feature for DLB 1
- Multiple System Atrophy (MSA): Occurs in 70% of MSA patients 1
Critical prognostic point: 38-65% of patients with presumed idiopathic RBD will develop a synucleinopathy within 10-29 years after RBD presentation 1. This makes RBD a prodromal marker for these conditions.
Less common tauopathies have rare associations (though not definitively proven):
Other Neurological Disorders
Structural and inflammatory brain conditions can cause secondary RBD 1:
- Spinocerebellar ataxia
- Limbic encephalitis
- Brain tumors (particularly brainstem)
- Multiple sclerosis
- Guillain-Barré syndrome
- Stroke (especially brainstem stroke) 2
These represent "acute" or "incidental" forms of RBD that occur within the context of subacute or acute-onset disorders 3.
Medication-Induced RBD
Antidepressants are the most common medication trigger 2:
- SSRIs: Paroxetine, fluoxetine (demonstrated to induce REM sleep without atonia even in patients without RBD) 1
- SNRIs: Venlafaxine 1
- Tricyclic antidepressants (TCAs) 2
- MAO inhibitors 2
- Mirtazapine 1
Population studies show an increased risk ratio for antidepressant use in patients with early-onset RBD 1.
β-Blockers have also been reported to cause RBD 1, 2.
Substance Withdrawal States
RBD occurs during REM rebound associated with:
Caffeine use has also been described as a trigger 2.
Associated Sleep Disorders
Narcolepsy type 1 (orexin deficiency disorder) has a strong association with secondary RBD 1, 4, 5. This typically presents in younger patients (adolescents and young adults) compared to other secondary causes.
Obstructive sleep apnea (OSA) can mimic RBD clinically through vigorous arousals, though polysomnography clarifies the diagnosis 1. OSA may also be comorbid with true RBD, complicating diagnosis and treatment 6.
Periodic limb movements of sleep may be associated with RBD 1.
Key Clinical Pitfalls
Important caveat: What appears to be "idiopathic" RBD may actually be cryptogenic, as autopsy studies have demonstrated Lewy bodies in presumed idiopathic cases 1. This underscores the importance of long-term neurological monitoring.
Diagnostic approach: When evaluating secondary RBD, polysomnography is mandatory to confirm REM sleep without atonia and distinguish true RBD from mimics like OSA-related arousals, non-REM parasomnias, or nocturnal seizures 1, 6. If secondary RBD is suspected, obtain brain MRI to evaluate for structural lesions, particularly in the brainstem 2.
Age and presentation matter: Secondary RBD in older adults (>50 years) suggests α-synucleinopathy, while younger patients should prompt evaluation for narcolepsy or structural lesions 4.