The relationship between dementia severity and rest/activity circadian rhythms

Abstract

Patients with dementia have been shown to have disturbed sleep/wake rhythms. There is evidence of impairment in endogenous generation of rhythms and deficient environmental cues in this population. This study sought to examine patterns of rest/activity rhythms as they relate to dementia severity. Three days of actigraphy were collected from 150 nursing-home patients with dementia and used to compute rhythm parameters. Dementia severity was estimated with the Mini-Mental State Examination (MMSE). The relationship between rhythm parameters and dementia severity was examined. Rhythm parameters were not associated with dementia in the sample as a whole, but relationships emerged when the sample was divided on the basis of overall rhythm robustness (F-statistic). Within the group with less robust rhythms, those with stronger rhythms had less severe dementia. In the group with more robust rhythms, milder dementia was associated with having an earlier acrophase (timing of the peak of the rhythm) and narrower peak of the rhythm (shorter duration of peak activity). These results suggested a three-stage model of rest/activity rhythm changes in dementia in which dementia patients have a rapid decline in rhythmicity followed by a slight return to stronger rhythms. In the later stages of dementia, rhythms decline even further.

Keywords: actigraphy; circadian rhythms; dementia.

Figure 1

Distribution of Mini-Mental State Examination (MMSE) scores for all participants (n = 150).

Figure 2

Scatter plot of the acrophases (timing of the peak of the rhythm) expressed as clock time versus the value of the goodness-of-fit F-statistic. A vertical line indicates the median F-statistic of 58.

Figure 3

Plot of the relationship between Mini-Mental State Examination (MMSE) score and the goodness-of-fit F-statistic. The dashed line indicates the hypothesized relationship, according to which rhythms would remain robust until the more severe stages of dementia. Once neuronal damage passes a critical threshold, there is a rapid decline in rhythmicity. In contrast, the solid line represents the actual relationship observed in those with less robust rhythms.

Figure 4

Scatter plot of the relative timing of rhythms (acrophases) versus the dementia severity (Mini-Mental State Examination; MMSE) in subjects whose F-statistic was above the median, indicating more robust rhythms.