In both its association with PD and its idiopathic form, RBD is an important risk factor for MCI. Except for visuoconstructional and visuoperceptual problems, RBD may be an important determinant of cognitive impairment in PD. Ann Neurol 2009;66:39-47.

Although we have found a slightly lower risk than other reports, the risk of developing neurodegenerative disease in idiopathic REM sleep behavior disorder is substantial, with the majority of patients developing Parkinson disease and Lewy body dementia.

This study shows that cognitive impairment in nondemented patients with Parkinson disease (PD) is closely related to the presence of REM sleep behavior disorder, a sleep disturbance that was not controlled for in previous studies assessing cognitive deficits in PD.

Idiopathic rapid eye movement sleep behaviour disorder is an important risk factor in the development of Parkinson's disease. Numerous potential predictive markers of Parkinson's disease may present before motor symptoms emerge, but testing of these markers in rapid eye movement sleep behaviour disorder has been performed only in small studies. There has been no comparison of markers between patients with idiopathic rapid eye movement sleep behaviour disorder and Parkinson's disease, and between men and women. We evaluated an array of potential Parkinson's disease predictive markers in 159 patients; including 68 with idiopathic rapid eye movement sleep behaviour disorder, 36 controls, 34 Parkinson's patients with rapid eye movement sleep behaviour disorder and 21 Parkinson's patients without rapid eye movement sleep behaviour disorder. Compared with controls, patients with idiopathic rapid eye movement sleep behaviour disorder demonstrated substantial olfactory loss (P < 0.001). Olfaction was more impaired in Parkinson's disease than idiopathic rapid eye movement sleep behaviour disorder and did not differ between Parkinson's patients with, or without, rapid eye movement sleep behaviour disorder. Numerous measures of motor function including the Unified Parkinson Disease Rating Scale alternate tap, Purdue Peg Board and Timed 'Up and Go' were impaired in idiopathic rapid eye movement sleep behaviour disorder compared with controls (P < 0.01). All of these motor measures were worse with Parkinson's disease than with idiopathic rapid eye movement sleep behaviour disorder, regardless of rapid eye movement sleep behaviour disorder status. Autonomic symptoms and systolic blood pressure drop were impaired in patients with idiopathic rapid eye movement sleep behaviour disorder compared with controls (P = 0.003). Orthostatic abnormalities in Parkinson's disease were found in the group with rapid eye movement sleep behaviour disorder (P < 0.001). However, Parkinson's patients without rapid eye movement sleep behaviour disorder were not different than controls and had less impairment than those with idiopathic rapid eye movement sleep behaviour disorder (P = 0.004) and Parkinson's patients with rapid eye movement sleep behaviour disorder (P < 0.001). Colour vision was impaired in idiopathic rapid eye movement sleep behaviour disorder compared with controls (P < 0.001). However, only Parkinson's patients with rapid eye movement sleep behaviour disorder had abnormalities significantly different than controls (P < 0.001), and there were significant differences between Parkinson's patients with or without rapid eye movement sleep behaviour disorder (P < 0.04). Idiopathic rapid eye movement sleep behaviour disorder patients had slightly increased harm avoidance scores on personality testing (P = 0.04). Other than slightly better performances among women in the Purdue Peg Board, there was no difference in any measure between men and women, suggesting similar pathogenic processes underlying rapid eye movement sleep behaviour disor...

One of the most devastating nonmotor manifestations of PD is dementia. There are few established predictors of dementia in PD. In numerous cross-sectional studies, patients with rapid eye movement (REM) sleep behavior disorder (RBD) have increased cognitive impairment on neuropsychological testing, but no prospective studies have assessed whether RBD can predict Parkinson's dementia. PD patients who were free of dementia were enrolled in a prospective follow-up of a previously published cross-sectional study. All patients had a polysomnogram at baseline. Over a mean 4-year follow-up, the incidence of dementia was assessed in those with or without RBD at baseline using regression analysis, adjusting for age, sex, disease duration, and follow-up duration. Of 61 eligible patients, 45 (74%) were assessed and 42 were included in a full analysis. Twenty-seven patients had baseline RBD, and 15 did not. Four years after the initial evaluation, 48% with RBD developed dementia, compared to 0% of those without (P-adjusted = 0.014). All 13 patients who developed dementia had mild cognitive impairment on baseline examination. Baseline REM sleep atonia loss predicted development of dementia (% tonic REM = 73.2 ± 26.7 with dementia, 40.8 ± 34.5 without; P = 0.029). RBD at baseline also predicted the new development of hallucinations and cognitive fluctuations. In this prospective study, RBD was associated with increased risk of dementia. This indicates that RBD may be a marker of a relatively diffuse, complex subtype of PD.