REM sleep behaviour disorder in patients without synucleinopathy

REM sleep behaviour disorder (RBD) is a parasomnia characterised by the loss of muscle atonia in REM sleep, leading to dream enactment behaviours with or without vocalisations. ‘Idiopathic’, or perhaps more accurately isolated, RBD occurs in the absence of an underlying neurological disorder and has a prevalence of 0.38% to 1.15% in the general population aged over 60 years.1 2 It is recognised that RBD frequently represents an early prodromal marker of an emerging synucleinopathy (Parkinson’s disease, dementia with Lewy bodies or multiple system atrophy), with over 70% of individuals developing one of these diseases over a 12-year follow-up.3 However, RBD does not occur exclusively with synucleinopathies. We set out to perform a systematic review to describe the spectrum of other neurological disorders associated with RBD. We searched PubMed on 1st December 2019 to identify all previous reports of polysomnography-confirmed RBD cases occurring in association with neurological conditions (online supplementary figure). The search terms ‘rapid eye movement sleep behaviour disorder’ OR ‘rapid eye movement sleep behavior disorder’ OR ‘RBD’ were used. Only …