Phenotyping apathy in individuals with Alzheimer disease using functional principal component analysis

To determine if there is a specific pattern of gross motor activity associated with apathy in individuals with Alzheimer disease (AD).

Examination of ad libitum 24-hour ambulatory gross motor activity patterns.

Community-dwelling, outpatient.

Ninety-two individuals with AD, 35 of whom had apathy.

Wrist actigraphy data were collected and examined using functional principal component analysis (fPCA).

Individuals with apathy have a different pattern of gross motor activity than those without apathy (first fPCA component, p <0.0001, t = 5.73, df = 90, t test) such that there is a pronounced decline in early afternoon activity in those with apathy. This change in activity is independent of depression (p = 0.68, F[1, 89] = 0.05, analysis of variance). The decline in activity is consistent with an increase in napping. Those with apathy also have an early wake and bedtime (second fPCA component, t = 2.53, df = 90, p <0.05, t test).

There is a signature activity pattern in individuals with apathy and AD that is distinct from those without apathy and those with depression. Actigraphy may be a useful adjunctive measurement in the clinical diagnosis of apathy in the context of AD.