Trajectories of cognitive and perceived functional decline in people with dementia: Findings from the IDEAL programme

Impaired cognition and instrumental activities of daily living (iADL) are key diagnostic features of dementia; however, few studies have compared trajectories of cognition and iADL.

Participants from the IDEAL study comprised 1537, 1183, and 851 people with dementia, and 1277, 977, and 749 caregivers at baseline, 12 and 24 months, respectively. Addenbrooke's Cognitive Examination-III and Functional Activities Questionnaire were used to measure cognition and iADL, respectively. Scores were converted to deciles.

Self-rated iADL declined on average by -0.08 (-0.25, 0.08) decile points per timepoint more than cognition. Informant-rated iADL declined on average by -0.31 (-0.43, -0.18) decile points per timepoint more than cognition.

Cognition and self-rated iADL declined at a similar rate. Informant-rated iADL declined at a significantly greater rate than cognition. Therefore, either cognition and perceived iADL decline at different rates or informants overestimate increasing iADL difficulties compared to both cognition and self-ratings.

Self-ratings of the degree of functional difficulties were consistent with cognition Decline in self-rated everyday activities was consistent with cognitive decline Informant-ratings of everyday activities declined more than cognition.