Intraindividual variability of REM sleep behavior disorder in Parkinson's disease: a comparative assessment using a new REM sleep behavior disorder severity scale (RBDSS) for clinical routine.

The International Classification of Sleep Disorders (ICSD-2) defines REM sleep behavior disorder (RBD) as REM sleep without atonia (RWA) plus either sleep related injuries, potentially injurious or disruptive behaviors documented by medical history or polysomnography.1 RBD was first described as a REM parasomnia with dream-enacting behaviors and loss of physiological REM sleep muscle atonia,2 including vocalizations, scenic behavior, or violent movements.3 In clinical practice, diagnosis and adequate treatment of abnormal nocturnal behaviors is of great importance for the well-being of the patient as well as for care-givers and the family. Moreover, the correct diagnosis of RBD may enable us in the future to identify PD patients in the early pre-motor stage of the disease for treating them with new neuroprotective agents.4 We therefore have to know the clinical variability of RBD in PD and need a classification of its severity. RBD in firmly diagnosed moderate to advanced Parkinson's disease (PD) patients is frequent and needs to be differentiated from psychotic phenomena and other distressing sleep-disruptive symptoms such as nighttime akinesia or periodic limb movement disorder (PLMD). Despite careful evaluation of a patient's history, including their sleep habits and questioning of bed partners, clinical diagnosis of the nocturnal disturbance is often not correct, and calls for video-supported polysomnography (PSG), as required for the diagnosis of RBD according to the ICSD-2.1 Various studies have attempted to characterize and quantify RBD, including electromyographic measurements of tonic and phasic muscle activity during REM sleep5; differentiation between simple and complex movements6,7; grading of RBD intensity as mild, moderate or severe8; and qualitative descriptions of RBD manifestations in video-supported polysomnography.9 A detailed analysis of the number and types of motor events occurring during REM sleep uses a complex and thorough, but time-consuming video classification system.10 Many of these methods may yield interesting scientific information about the complex phenomenology of RBD; however, they do not appear feasible for use in clinical practice or for comparative studies. BRIEF SUMMARY Current Knowledge/Study Rationale: The study aims at investigating the phenomenology of REM sleep behaviour disorder (RBD) in Parkinson's disease (PD) patients. For this a polysomnographic severity scale was developed, rating REM sleep behaviour disorder clinically on an event-to-event basis. Study Impact: The newly developed REM sleep disorder severity scale (RBDSS) is a suitable and valid instrument for assessing RBD in PD. There is a significant intraindividual night-to-night variability in the expression of RBD in PD patients, to be considered when evaluating their nighttime sleep disturbances. To look into night-to-night variability of RBD and for use in further comparative studies, we developed a simple video-polysomnographic rating scale for RBD to be used in PD patients.