Sundowning and circadian rhythms in Alzheimer's disease

Objective: The goal of this study was to determine changes of circadian rhy thms induced by Alzheimer's disease and to explore relationships among rhyt hm disturbances, sundowning, and sleep disturbances in patients with Alzhei mer's disease. "Sundowning" is the occurrence or exacerbation of behavioral symptoms of Alzheimer's disease in the afternoon and evening. Method: Circadian rhythms of core body temperature and motor activity were measured in 25 patients with diagnoses of probable Alzheimer's disease and in nine healthy individuals. The subjects with Alzheimer's disease were div ided according to the occurrence of sundowning as determined by staff repor ts. Results: The subjects with Alzheimer's disease had less diurnal motor activ ity, a higher percentage of nocturnal activity, lower interdaily stability of motor activity, and a later activity acrophase (time of peak) than did t he healthy individuals. They also had a higher mesor (fitted mean) temperat ure, higher amplitude of the fitted cosine temperature curve, and later tem perature acrophase than did the healthy subjects. The severity of sundownin g was associated with later acrophase of temperature, less correlation of c ircadian temperature rhythm with a 24-hour cycle, and lower amplitude of te mperature curve. Conclusions: These data indicate that Alzheimer's disease causes disturbanc es of circadian rhythms and that sundowning is related to a phase delay of body temperature caused by Alzheimer's disease.