Mild cognitive impairment and abnormal brain metabolic expression in idiopathic REM sleep behavior disorder

Background: Mild cognitive impairment (MCI) is a common feature of isolated rapid-eye-movement sleep behavior disorder (iRBD). Here, we assessed cognitive functions and MCI in a prospective iRBD cohort and investigated their association with disease-specific brain metabolic patterns. Methods: Forty-four patients with polysomnography-confirmed iRBD performed a standardized battery of neuropsychological examinations every two years. We used previously established spatial covariance patterns from de novo drug-naive Parkinson's disease with concomitant RBD (denovoPDRBD-RP) and iRBD (iRBD-RP) using 18Ffluorodeoxyglucose PET scan. We compared those expressions between iRBD with normal cognition (iRBD-NC) and with mild cognitive impairment (iRBD-MCI), and evaluated whether they predict progressive cognitive deterioration. Results: Twenty iRBD patients (45 %) had MCI at baseline and 12 patients (27 %, about 7 % per year) had clinically significant cognitive deterioration after 4 years. The iRBD-MCI and iRBD-NC groups showed similar rates of cognitive change, but iRBD-MCI consistently performed worse in the domains of verbal memory and executive function. Elevated denovoPDRBD-RP expression predicted cognitive deterioration (hazard ratio = 5.98 [1.70-21.06]), whereas iRBD-RP did not. Conclusions: Increased disease-specific brain metabolic patterns are associated with iRBD-MCI and impending cognitive deterioration with the risk of progression to Lewy body dementia.

Automated summary

MCI is common in isolated RBD, with 45% of iRBD patients having MCI and a 27% risk of significant cognitive deterioration. Cognitive decline in iRBD-MCI group is particularly pronounced in verbal memory and executive function domains.