Is REM sleep Behaviour Disorder (RBD) a risk factor of dementia in idiopathic Parkinson's disease?

Objective To study the sequence of occurrence of REM-sleep behaviour disorder (RBD) and dementia and their frequency among a population of patients with idiopathic Parkinson's disease (PD). Methods We performed a cross-sectional study on 65 PD patients seen in a movement disorder clinic and their bed partner, and asked them to complete the validated Mayo Sleep Questionnaire for RBD and sleep disorders. The diagnosis of PD with dementia (PD-D) was based on a clinical diagnosis of dementia; following DSM-IV criteria and MMSE score less than 25 and a battery of cognitive tests. Results From the 65 patients that completed the study, twenty-four met the clinical diagnosis of RBD. Ten of the 24 (42%) RBD patients met the clinical criteria of PD-D, whereas the remaining 14 patients were non-demented at the time of the study. The frequency of RBD was significantly higher in the PD-D group (n = 10, 77%) compared to the PD-ND group (n = 14, 27%, chi squared test: p = 0.0008). PD non-RBD had a lower occurrence of dementia (7.3%, 3 of 41) compared to those suffering from RBD (42%, 10 of 24). Of the 65 PD patients, 13 were diagnosed with PD-D and the remaining 52 were non-demented PD (PD-ND) patients. PD with RBD showed a faster decline in the number of dementia-free patients compared to the non-RBD patients (Log Rank test: p < 0.001). RBD preceded, coincided or followed the onset of the motor symptoms. Conclusion This study shows that RBD and dementia have a significant coincidence in the course of PD, and RBD not only precedes or coincides with the motor signs, but can occur during the course of the progression of the PD, suggesting a degenerative process of the dopaminergic and cholinergic neurons of the brainstem nuclei, progressing at a different pace in each patient.