Trajectories of cognition and functional ability in people with dementia: Two‐year longitudinal results from the IDEAL programme

Abstract

AbstractBackgroundImpairment in both cognition and instrumental activities of daily living (iADL) are key diagnostic features of dementia. Few studies have compared trajectories of cognition and iADL. By comparing trajectories of cognitive decline with both self‐rated and informant rated iADL, the study determines whether these aspects are related or decline in parallel and where there is a difference between perceptions of change.MethodData from the Improving the experience of Dementia and Enhancing Active Life (IDEAL) study were used. The study comprises 1537, 1183, and 851 people with dementia, and 1277, 977, and 749 carers at baseline (T1), 12 months later (Time 2, T2), and 24 months later (Time 3, T3), respectively. Cognition was assessed with the Addenbrooke’s Cognitive Examination‐III (ACE‐III), higher scores indicate fewer cognitive difficulties. iADL was assessed using the Functional Activities Questionnaire (FAQ), higher scores indicate more iADL difficulties. Both self‐ratings (FAQ‐S) and informant ratings (FAQ‐I) were collected. Because of the differences in the scale and distribution of FAQ and ACE‐III, scores were converted to ranks to enable comparison of trajectories between the two measures; deciles were calculated at T1 and imposed on T2 and T3 scores.ResultAs ACE‐III decreased both FAQ‐S and FAQ‐I increased suggesting that people with dementia with more cognitive difficulties were rated as having greater iADL difficulties by both people with dementia themselves and their carers. FAQ‐S declined on average by ‐0.10 (‐0.26, 0.06) decile points per timepoint more than ACE‐III. As confidence intervals overlapped zero this suggests that FAQ‐S and ACE‐III ratings declined at a similar rate. FAQ‐I declined on average by ‐0.31 (‐0.43, ‐0.19) decile points per timepoint more than ACE‐III. The trajectory over the two years suggests that FAQ‐I ratings declined at a significantly greater rate than ACE‐III scores.ConclusionBoth cognition and iADL, whether self‐ or informant‐rated declined over two years. Trajectory analysis suggests that self‐rated iADL was generally concordant with cognitive decline, whereas informant‐rated iADL reflected more perceived decline 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.