The motor anomalies seen in isolated REM sleep behavior disorder

Background Isolated REM sleep behavior disorder (iRBD) is known to be an early feature in some PD patients. Quantitative tools are needed to detect early motor anomalies in iRBD. Methods A motor battery was used to compare iRBD patients with controls. This included two online keyboard-based tests, the BRadykineisa Akinesia INcoordination (BRAIN) test and the Distal Finger Tapping (DFT) test, a timed handwriting task and two motor assessments (10-meter walking and finger tapping) carried out both alone and during a mental task. This battery was compared with the motor section of the MDS-MDS-UPDRS-III. ROC analyses were used to measure diagnostic accuracy. Results We included 33 patients with video-PSG-confirmed iRBD and 29 age and sex matched controls. The iRBD group performed the BRAIN test and DFT test more slowly (p<0.001, p=0.020 respectively) and erratically (p<0.001, p=0.009 respectively) than controls. Handwriting speed was 10 seconds slower in iRBDs than controls (p=0.004). Unlike controls, under a mental task the iRBD group decreased their walking pace (p<0.001) and had a smaller amplitude (p=0.001) and slower (p=0.007) finger tapping than tasks in isolation. The combination of BRAIN & DFT tests with the effect of mental tasks on walking and finger tapping showed 90.3% sensitivity for 89.3% specificity (AUC 0.94, 95% CI 0.88-0.99), which was higher than the MDS-UPDRS-III (minus action tremor) (69.7% sensitivity, 72.4% specificity; AUC 0.81, 95% CI 0.71-0.91) for detecting motor abnormalities. Conclusion This study suggests that speed, incoordination, and dual task motor deterioration might be accurate indicators of incipient PD in iRBD.