The study, published in Nature Portfolio is one of the few studies characterizing RBD semiology and the first to demonstrate which movements are limited. This is distinct from other sleep disorders and may serve as a useful biomarker to differentiate RBD.
RBD is a rare sleep disorder characterized by re-enactment of dreams during the rapid eye movement stage of the sleep, sometimes with violent abnormal movements, vocalizations, or experiences. Importantly, it can also predict the later occurrence of neurodegenerative disorders, such as Parkinson’s disease.
In the present study researchers retrospectively analysed clinical assessments and videos from diagnostic sleep studies of 38 RBD patients that were performed at the Sleep Disorders Centre at Guy’s and St Thomas’ Hospital in 2019. Upon confirming eligibility, they classified RBD events into distinct groups based on the types of movements. In total, 737 RBD events and 1011 distinct movements of different lengths of time were detected and subsequently described and classified.
‘We are delighted to add to a growing armamentarium of biomarkers to alert us to the early stages of this devastating neurodegenerative process that leads to Parkinson’s disease and dementia. Sleep and its physiology provide us with a precious window into the brain’s inner workings, and here at the King’s Health Partners we work jointly with the Parkinson Foundation International Centre of Excellence to ensure our findings have a true translational value for our patients.’ – Dr Ivana Rosenzweig, clinical senior lecturer at King’s IoPPN and the study’s lead author
The authors noted wide-ranging movements in 675 RBD events and detected significantly fewer vocalisation events, only 62. Limb movements were common - 44% and 80% of detected movements were in the lower or upper limbs, respectively. They were described as fast, repetitive, and jerky. Movements of the head and neck were also frequent (19%). However, only 4.88% of all recorded RBD movements were truncal (in the chest, abdomen, pelvis or back). Some patients were observed rolling in bed but only four patients in total exhibited movement resembling that of sitting upright.
Based on these results, the authors argue that RBD movements that occur while dreaming may be independent of spatial co-ordinates of the ‘outside world’ and instead rely on virtual space maps generated by the brain.
While rare, RBD is an important sleep disorder, especially because it is increasing seen as an early sign of neurodegenerative disorders, such as Parkinson’s disease, multiple systems atrophy, and Lewy body dementia. It can occur several years or even decades before any other motor signs characteristic of these diseases. If identified, it thus presents a precious period for preventative intervention, illustrating how understanding sleep’s basic physiological components has enticing and potentially wide-reaching clinical implications.
The study made possible thanks to funding from the Wellcome Trust and has been made available as open access.
Wasserman, D., Gullone, S., Duncan, I. et al. Restricted truncal sagittal movements of rapid eye movement behaviour disorder. npj Parkinsons Dis. 8, 26 (2022). https://doi.org/10.1038/s41531-022-00292-0
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