Sleep disturbances and their correlation with memory impairment in patients with Alzheimer's disease and amnestic mild cognitive impairment

Background: Episodic memory impairment is the core clinical feature of patients with typical Alzheimer's disease (AD) at an early stage. Since sleep plays a very important role in memory consolidation, the relationship between memory impairment and sleep disorders in AD patients is worthy of investigation. Objective: To investigate sleep disturbances and their correlations with memory impairment in patients with AD and amnestic mild cognitive impairment (aMCI). Methods: Forty-three patients with AD, 43 patients with aMCI, and 43 cognitively unimpaired controls (CUCs) were recruited and subjected to memory assessment via the Hopkins Verbal Learning Test-Revised and objective sleep evaluation via polysomnography (PSG). Results: The total sleep time and the percentages of nonrapid eye movement (NREM) sleep stage 3 (N3) and the rapid eye movement (REM) were lower, while the percentages of NREM sleep stage 2 (N2) were greater in the AD and aMCI groups than in the CUC group (all p < 0.01). Compared with the CUC group, the AD group also presented a longer sleep latency and higher NREM sleep stage 1 (N1) percentage, apnea-hypopnea index (AHI), periodic limb movements during sleep index (PLMSI), and arousal index (AI). Both total learning scores and delayed recall scores were positively correlated with the N3 sleep percentage and negatively correlated with the AHI and PLMSI (all p < 0.01). Recognition scores were positively correlated with the N3 sleep percentage and negatively correlated with the AI (all p < 0.01). Conclusions: Our results suggest that sleep disturbance is correlated with learning and memory disability in AD and aMCI patients. PSG is useful for screening and monitoring AD.