Macro and microarchitectural features of sleep in Alzheimer’s dementia and mild cognitive impairment in a large clinical cohort

Abstract

AbstractBackgroundRecent work has characterized polysomnographic changes in Alzheimer’s Dementia (AD) that correlate with disease severity and precede clinical diagnosis. However, relatively small sample sizes and a paucity of studies examining sleep microarchitecture have been limitations. In this study we examined sleep micro‐ and microarchitectural features in large cohorts of patients with AD and mild cognitive impairment (MCI).MethodUsing a database of over 15,000 clinical PSGs with associated clinical metadata, 125 and 173 subjects were identified with mild AD and MCI, respectively. 260 age and sex matched subjects without neurological disease were identified as healthy controls (HC). Sleep staging results were based on AASM criteria, and micro‐architectural features were assessed using an algorithm trained to predict wake (1) or sleep (0) using spectral data from 3 seconds of EEG from a unique healthy adult cohort (Wake EEG Similarity Index, WESI).ResultSleep fragmentation was apparent in both the MCI and AD cohorts (relative to healthy controls), with AD subjects demonstrating significantly more severe PSG disturbances. Healthy controls demonstrated 400 minutes of total sleep time, in contrast to 374 minutes for MCI subjects and 362 minutes for healthy controls. Healthy subjects demonstrated 33 minutes of wake after sleep onset (WASO), compared to 60 and 67 minutes for MCI and AD subjects, respectively. As has been previously reported in smaller cohorts, wakeful bouts and N1 durations were significantly prolonged for AD and (to a lesser extent) MCI subjects, while N2, N3, and REM durations were reduced (with a pronounced reduction in AD N3 percentage). Sleep microarchitectural features assessed using WESI demonstrated that AD and MCI subjects had markedly higher relative wakefulness in all sleep stages except for N3, which showed the same sleep depth as HC.ConclusionWe confirm increased sleep fragmentation and loss of deeper sleep stages, correlating to disease severity. Spectral features of all sleep stages EXCEPT N3 appear more wakeful in AD and MCI subjects ‐ suggesting microarousals or impaired sleep maintenance contribute to sleep pathology. While N3 duration was markedly reduced, depth of sleep was comparable between populations. PSG findings offer promise as early diagnostic and therapeutic targets.