Correlations with REM sleep behavior disorder severity in isolated rapid eye movement sleep behavior disorders patients.

Objectives: The pathogenesis of isolated rapid eye movement sleep behavior disorders (iRBD) is poorly understood. The severity of RBD may reflect its pathogenesis.
Methods: We compared motor function and non-motor symptoms (NMSs) between iRBD patients and healthy volunteers. We correlated motor function, NMSs, and striatal dopaminergic activity with RBD severity using video-polysomnography.
Results: Twenty-one iRBD patients and 17 controls participated. The Unified Parkinson's Disease Rating Scale part III scores were higher in patients compared to controls ( p  < 0.001). There was no difference in upper extremity function between patients and controls (right, p  = 0.220; left, p  = 0.209), but gait was slower in iRBD patients (walking time, p  < 0.001; number of steps, p  < 0.001). The mean value of the Korean version of the Mini-Mental State Exam and Clinical Dementia Rating were lower in patients ( p  = 0.006, p  = 0.003, respectively). Patients with were also more depressed ( p  = 0.002), had decreased olfactory function ( p  < 0.001), reported more frequent sleep/fatigue episodes ( p  < 0.001), worse attention/memory capacity ( p  < 0.001), gastrointestinal problems ( p  = 0.009), urinary problems ( p  = 0.007), and pain ( p  = 0.083). Further, iRBD patients reported more frequent sleep-related disturbances ( p  = 0.004), but no difference in daytime sleepiness ( p  = 0.663). Disease severity was correlated with pain ( r  = 0.686, p  = 0.002) and visuospatial function ( r = -0.507, p  = 0.038). There were no correlations between RBD severity and striatal dopaminergic activities ( p  > 0.09).
Conclusions: iRBD is a multisystem neurodegenerative disorder, and gait abnormalities may be a disease characteristic, possibly related to the akinetic-rigid phenotype of Parkinson's disease. The correlation between pain/visuospatial dysfunction and RBD severity may be related to its pathogenesis.