Definition and Prevalence
Dementia is highly associated with sleep disruption. Sleep-wake patterns in dementia are often polyphasic, with frequent nighttime awakenings and redistribution of sleep episodes throughout the day. Ancoli-Israel and colleagues have reported that many institutionalized demented patients were neither awake nor asleep for a full hour in the day or night, and that while the mildly to moderately demented patients had extremely fragmented sleep at night, the severely demented patients were extremely sleepy during the day and night.
Sleep structure is also altered in demented patients compared to healthy elderly individuals, with significantly lower amounts of stages 3 and 4 and REM sleep and significantly more awakenings, as well as more time spent awake during the night. Increased stage 1 sleep and decreased sleep efficiency have also been reported. REM latency has been found to increase in dementia patients, possibly due to the general reduction in the amount of REM found in these patients.
The neuronal degeneration seen in Alzheimer’s disease is most likely the cause of these sleep changes. Neuronal structures that are damaged in this population and are implicated in sleep regulation include the basal forebrain and the reticular formation of the brainstem. As sleep changes are already evident in the early, mild stages of dementia, they may serve as markers of early dementia in clinical assessment.
Nocturnal awakenings, often accompanied by agitation, confusion, and wandering, are typical in demented patients. These events are often referred to as “sundowning” behaviors, and as they typically occur at the same time of day, it has been suggested that they are related to a circadian rhythm disorder.
Support for this hypothesis has come from studies using bright light treatment for circadian rhythm disorders. Satlin et al. used bright light therapy in the evening to improve sleep and behavioral disturbances in Alzheimer’s disease patients. Mishima et al. found similar results using morning bright light therapy. Lovell et al. reported that bright light therapy in the morning hours decreased agitated behaviors in the late afternoon in a group of institutionalized demented patients.
In a recent study, Martin et al. challenged the idea of sundowning by showing that peak levels of agitation occur during various times of the day, but more often in the afternoon, rather than in the evening or night. However, they did find associations between circadian rhythms of activity, agitation, and light exposure, indicating that sleep disruption in demented individuals may be amenable to treatment using bright light exposure.
Ancoli-Israel et al. have reported a strong relationship between demented patients and sleep apnea, with the most severe apnea in the most severely demented group of patients. This positive association has been confirmed by several research studies, as summarized by Ancoli-Israel and Coy. In a review of the literature, the prevalence of SDB in demented patients ranged between 33% and 70%. In a recent study of institutionalized Alzheimer’s disease patients, the prevalence of SDB was 80% with RDI of 10 or more and 48% with an RDI of 20 or more.
Cognitive impairment is a common symptom in both dementia and SDB patients. In SDB, cognitive impairment is associated with the nocturnal hypoxemia, as well as the sleep fragmentation. In an epidemiologic study, Dealberto et al. (24) found a strong relationship between symptoms of SDB and cognitive impairment. Bliwise has suggested that SDB may contribute to cognitive decline in demented elderly, together with cerebrovascular disease and hypertension. Furthermore, he suggests that treatment of SDB may reverse the cognitive decline in demented patients or at least slow the dementia process. In a pilot study, Shochat et al. examined the possibility of treating demented patients with SDB using CPAP. They concluded that CPAP may be tolerated and may partially reverse cognitive decline (e.g., global mental functioning and memory) in some mildly demented patients.
In summary, severe sleep disturbance is commonly found in the demented elderly population, which may be the result of neurodegenerative processes in areas in the brain that regulate sleep/wake and possibly circadian rhythm mechanisms. The high presence of SDB in this population may indicate that neuronal damage is also contributing to the respiratory difficulties during sleep, and these respiratory disturbances may be contributing to the cognitive impairment associated with the dementia.
Revision date: July 8, 2011
Last revised: by Tatiana Kuznetsova, D.M.D.