REM sleep behaviour disorder in older individuals: epidemiology, pathophysiology and management.

Rapid eye movement (REM) sleep behaviour disorder (RBD) is a sleep disorder in which patients appear to be enacting their dreams while in REM sleep. The behaviours are typically violent, in association with violent dream content, so serious harm can be done to the patient or the bed partner. The disorder predominantly affects older adults, and has an estimated prevalence in adults of 0.4-0.5%. However, the frequency is much higher in certain neurodegenerative diseases, especially Parkinson's disease, dementia with Lewy bodies and multiple systems atrophy. RBD can occur in the absence of diagnosed neurological diseases (the 'idiopathic' form), although patients with this form of RBD may have subtle neurological abnormalities and often ultimately develop a neurodegenerative disorder. Data from animal models and cases of RBD developing after brainstem (pontine tegmentum, medulla) lesions have led to the understanding that RBD is caused by a lack of normal REM muscle atonia and a lack of normal suppression of locomotor generators during REM sleep. Clonazepam is used as first-line therapy for RBD and melatonin as second-line therapy, although evidence for both of these interventions comes from uncontrolled case series. Because the risk of injury to the patient or the bed partner is high, interventions to improve the safety of the sleep environment are also often necessary. This review describes the epidemiology, pathophysiology and treatment of RBD.