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.
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-naïve Parkinson’s disease with concomitant RBD (PDRBD-RP) and iRBD (iRBD-RP) using F-fluorodeoxyglucose 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.
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 PDRBD-RP expression predicted cognitive deterioration (hazard ratio = 5.98 [1.70-21.06]), whereas iRBD-RP did not.
Increased disease-specific brain metabolic patterns are associated with iRBD-MCI and impending cognitive deterioration with the risk of progression to Lewy body dementia.

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