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.