Cognitive domains and trajectories of functional independence in nondemented elderly persons

Cognitive impairment in general is known to predict functional disability, but it is not clear whether performance on specific cognitive domains predicts future disability trends among nondemented elderly persons.

In a representative elderly community-based cohort over up to 10 years of follow-up, we examined predictors of longitudinal trajectories in ability to perform Instrumental Activities of Daily Living (IADL) among nondemented elderly persons. We used trajectory analyses to identify homogeneous groups with respect to trends over time in the numbers of IADL disabilities and their association with baseline demographics, social engagement, depression, physical well-being, and general and domain-specific cognitive functions. We excluded from these analyses those individuals found to have dementia at baseline or at any time during follow-up.

Trajectory analysis revealed three homogeneous latent groups which we characterized as No Decline (no decline in abilities to perform IADL tasks over the course of study), Moderate Decline (some functional decline), and Sharp Decline (steep functional decline followed by death). Compared to the Sharp Decline group, the No Decline group was associated with higher baseline functions in all cognitive domains, and the Moderate Decline group was associated with higher baseline functions in all cognitive domains except psychomotor speed and naming. The Moderate and No Decline groups did not differ on any cognitive measure.

Among community dwelling elderly persons who remained free from dementia throughout the study, poorer scores in all cognitive domains predicted sharp functional decline followed by death.