Electroencephalogram slowing in rapid eye movement sleep behavior disorder is associated with mild cognitive impairment

Background: Idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD) is a well-documented risk factor for synucleinopathies such as Parkinson disease (PD) and dementia with Lewy bodies (DLB). Moreover, approximately 50% of iRBD patients have mild cognitive impairment (MCI). The purpose of our study was to investigate waking electroencephalogram (EEG) abnormalities specific to iRBD patients with MCI. Methods: Forty-two polysomnographically confirmed iRBD patients, including 23 iRBD [+]MCI patients 19 patients without MCI (iRBD [-]MCI), and 37 healthy subjects participated in the study. All participants underwent a complete neuropsychologic assessment for MCI diagnosis and a waking quantitative EEG recording. Results: iRBD [+]MCI patients had a higher slow-to-fast frequency ratio than iRBD [-] MCI patients and controls in the parietal, temporal, and occipital regions. iRBD [+]MCI patients also had higher relative theta power in the parietal, temporal, and occipital regions and lower relative alpha power in the occipital region compared to iRBD [+]MCI patients and controls. Moreover, iRBD [+]MCI patients had higher relative theta power in the frontal and central areas and lower relative beta power in the central, parietal, and temporal regions compared to controls. The dominant occipital frequency also was slower in iRBD [+] MCI patients compared to controls. No between-group differences were observed between iRBD [-]MCI patients and controls. Conclusion: In iRBD patients, only those with concomitant MCI showed waking EEG slowing in the posterior cortical regions, providing a potential marker for an increased risk for developing DLB or PD. (C) 2013 Elsevier B. V. All rights reserved.