Idiopathic rapid eye movement sleep behaviour disorder

Abstract

Rapid eye movement (REM) sleep behaviour disorder (RBD) is a parasomnia characterised by elaborate behaviours during REM sleep usually associated with action-filled dreams. Typical behaviours are screaming, grasping, punching, kicking and occasionally jumping out of bed, which are potentially harmful for the patient and their bed partner. Polysomnographic (PSG) recording reveals a loss of atonia and an excessive phasic motor activity during REM sleep. RBD affects mainly men over 50 years and its prevalence in the general population is estimated around 0.5%. It may occur in acute or chronic forms. The latter may be isolated (idiopathic RBD), or associated with other neurological diseases (symptomatic RBD), especially with a group of neurodegenerative disease called alpha-synucleinopathies, which includes Parkinson's disease, dementia with Lewy bodies (DLB) and multiple system atrophy. The idiopathic form accounts for up to 60% of the cases reported in the literature. Small clinical follow-up studies revealed that a proportion of these patients will eventually develop a parkinsonian syndrome and/or a DLB in the years following the RBD diagnosis, while some patients will remain idiopathic for decades. Recent studies found evidence of neural dysfunction during both wakefulness and sleep in iRBD, such as an impairment of the cortical activity, specific neuropsychological deficits, signs of autonomic dysfunction, deficit of colour discrimination, subtle abnormalities in quantitative measures of motor and gait speed and an olfactory impairment. The notion of "idiopathic" RBD is currently challenged and the use of a more conservative term of "cryptogenic" RBD has been suggested.