Relationship of Sleep Quality and Cognitive Function in Patients with Mild Cognitive Impairment and Subjective Memory Impairment

ABSTRACT

Objectives@#To investigate the relationship between subjective sleep quality and cognitive function in patients with subjective memory impairment (SMI), a self-perceived cognitive decline without objective cognitive impairment, and amnestic mild cognitive impairment (aMCI). @*Methods@#We enrolled 246 patients with memory impairment (126 with SMI and 120 with aMCI) who fulfilled the Korean version of the Pittsburgh Sleep Quality Index (PSQI-K), a standardized battery of neuropsychological tests, and mood questionnaires. Based on the PSQI-K cutoff point of 5, patients were classified as good sleepers (GS) or poor sleepers (PS). @*Results@#There was no difference in the proportion of GS and PS between patients with SMI and aMCI [68 PS (54.0%) in SMI vs. 62 PS (51.7%) in aMCI, p>0.05]. Demographics did not differ between the SMI and aMCI groups. In both the SMI and aMCI groups, PS had worse sleep-wake parameters, such as sleep latency, total sleep time, and sleep efficiency, than GS and reported worse performance in all PSQI-K subcomponents. Neuropsychological data were not different between GS and PS, except for the Stroop word test in patients with aMCI. Depressive scores were worse in PS than in GS in both the SMI and aMCI groups. @*Conclusions@#We observed that cognitive function was not significantly different between GS and PS in both the SMI and aMCI groups, except in the Stroop word test in the aMCI group, while PS had more depressive mood than GS in both groups. This suggests that subjective sleep quality may depend on mood disturbances in patients with mild cognitive impairment.