The sleeping brain in Parkinson's disease: A focus on REM sleep behaviour disorder and related parasomnias for practicing neurologists

Sleep disorders are identified as common non-motor symptoms of Parkinson's disease (PD) and recently this recognition has been expanded to include parasomnias, encompassing not only REM sleep behaviour disorder (RBD), but also other non-REM forms. RBD, a prototypical parasomnia in PD, exists even in the prodromal stage of the disease, and is characterized by the presence of dream enactment behaviours occurring alongside a loss of normal skeletal muscle atonia during REM sleep. In contrast, non-REM parasomnias are more frequently observed in the late stage PD. However, the development of these disorders often overlaps and it is not uncommon for PD patients to meet the criteria for more than one type of parasomnias, thus making a clinical distinction challenging for practicing neurologists who are not sleep specialists. Indeed, clinical recognition of the predominant form of parasomnia does not just depend on video-polysomnography, but also on an individual physician's clinical acumen in delineating pertinent clinical history to determine the most likely diagnosis and proceed accordingly. In this review article, we highlight the various forms of parasomnias that have been reported in PD, including, but not limited to, RBD, with a focus on clinical symptomatology and implications for clinical practice. In addition, we review the differences in PD-related parasomnias compared to those seen in general populations. With advances in sleep research and better technology for ambulatory home monitoring, it is likely that many unanswered questions on PD-related parasomnias will soon be resolved resulting in better management of this nocturnal challenge in PD.