Motor features that distinguish isolated REM sleep behavior disorder patients from healthy controls: A systematic review

Individuals with isolated REM sleep behavior disorder (iRBD) are at high risk of developing α-synucleinopathies, particularly Parkinson's disease (PD) and dementia with Lewy bodies (DLB). With the development of potential neuroprotective treatments for synucleinopathies, including PD, identifying clinical features that can allow for tracking subtle changes in prodromal disease and thereby monitoring risk of phenoconversion in iRBD is paramount. Subtle motor deficits have been suggested to be present in iRBD, making them potentially important clinical markers for predicting future phenoconversion. This review aims to summarize existing literature that has investigated differences in motor function between iRBD and healthy individuals, as well as progression of motor decline in iRBD. 39 eligible studies were included in this review. The results suggest that quantitative motor assessments may be more sensitive to motor impairments in this population than clinical scales. Moreover, dual-tasking tended to unmask subtle motor deficits in individuals with iRBD, particularly in gait, balance, and tapping assessments. Longitudinal studies demonstrate that motor function worsens over time in iRBD, with earliest signs of motor deficits and clear progression in tapping assessments in particular. Larger longitudinal studies that use quantitative methods of motor assessments are needed to better characterize motor progression in iRBD, and confirm the reliability of different motor markers for predicting phenoconversion of iRBD into PD and other synucleinopathies.