Neurocognitive dysfunction associated with sleep quality and sleep apnea in patients with mild cognitive impairment.

OBJECTIVES: Sleep apnea syndrome (SAS) is considered a risk factor for cognitive decline in the elderly. The specific neurocognitive decline has been suggested as a predictive factor for dementia in patients with mild cognitive impairment (MCI). The authors aim to illustrate the sleep characteristics related to the specific neurocognitive decline in the community-dwelling elderly including patients with MCI.

DESIGN: Cross-sectional.

SETTINGS: Center for sleep and chronobiology in Kangwon National University Hospital.

PARTICIPANTS: Thirty patients with MCI and 30 age- and sex-matched normal elderly subjects were selected.

MEASUREMENTS: The authors administered seven tests in the Korean version of the Consortium to Establish A Registry of Alzheimer's Disease Neuropsychological battery and conducted nocturnal polysomnography. A p value below 0.05 was considered a statistical significance.

RESULTS: There was no significant difference in sleep parameters between the MCI and normal comparison (NC) groups. Sleep efficiency was positively correlated with Constructional Recall (CR) scores in both NC and MCI groups (r = 0.393 and 0.391, respectively). The amount of slow wave sleep (SWS) was also positively correlated with Boston naming test (BNT) scores in both groups (r = 0.392, 0.470, respectively). Stepwise multiple regression models showed that SWS and the apnea index were significant independent variables associated with the BNT score (Δβ = 0.43 and -0.34, respectively; adjusted R = 0.298) in the MCI group, and the amount of rapid eye movement sleep was a significant independent variable associated with the CR score (Δβ = 0.49; adjusted R = 0.217) in the NC group.

CONCLUSIONS: Our results show that poor sleep quality and greater severity of SAS were associated with impaired language function reflecting frontal-subcortical pathology in patients with MCI. This suggests that vulnerability to a specific brain damage associated with SAS could increase the risk for dementia.