Associations between apathy and global cognition in a 5‐year follow‐up of individuals with Alzheimer's disease

Apathy is a common neuropsychiatric symptom in Alzheimer's disease (AD) associated with cognitive and functional impairment. Longitudinal studies have examined the associations between apathy and cognition in AD and other dementias, but more information is needed to understand whether the relationships are consistent longitudinally, and whether apathy relates to decline in AD-related cognitive domains or to drop-out rates in the follow-up. We used data from 236 people (age M = 75.15 and 51.3% female at baseline) with very mild or mild AD from the Finnish ALSOVA study with up to 5 years of follow-up. Global cognition was measured with the Consortium to Establish a Registry for Alzheimer's disease-Neuropsychological Battery, apathy with the Neuropsychiatric Inventory, and disease severity with the Clinical Dementia Rating-Sum of Boxes. Associations between cognition and apathy were examined with correlation analyses, linear regression analyses and linear mixed models. In longitudinal analyses, we found that apathy was associated with worse global cognition (B = -0.39, SE = 0.12, p = .001) after adjusting for disease severity. However, apathy and global cognition were not consistently associated with one another in cross-sectional analyses. Older age (OR = 0.95, p = .02), but not apathy, was associated with a lower likelihood of participating in the final follow-up visit. In conclusion, apathy associates with worse global cognition longitudinally, but when examined cross-sectionally, the apathy-cognition associations are inconsistent. Apathy at baseline does not seem to affect drop-out rates in a long follow-up of individuals with very mild or mild AD.