Neurophysiological assessment of REM sleep behaviour disorder

Abstract

REM sleep behaviour disorder (RBD) is characterized by violent dream-enacting behaviours associated with nightmares and increased EMG activity during REM sleep. RBD may be secondary to neurological diseases, particularly Parkinson’s disease, dementia with Lewy bodies, or multiple system atrophy. The majority of patients with idiopathic RBD will develop one of these synucleinopathies, indicating that this parasomnia represents in most instances the prodromal state of a neurodegenerative disease. RBD is also a treatable condition associated with injury potential. Thus, a correct diagnosis of RBD has relevant prognostic and treatment implications. Video-polysomnography (video-PSG) is mandatory for a definite RBD diagnosis. Video-polysomnography will rule out other conditions that can mimic RBD, such as obstructive sleep apnoea or periodic limb movement disorder. Video-polysomnography is also essential to record REM sleep-related behaviours or demonstrate REM sleep without atonia (RWA). RWA is defined as either excessive tonic or phasic EMG activity during REM sleep. However, excessive EMG activity is usually based on the scorer’s subjective impression and objective quantification is not routinely performed. Several manual and computer-assisted scoring methods of EMG activity in the chin and limb muscles have been developed, and recently quantitative EMG cut-off values for RBD diagnosis have been proposed.