Determinants of functional abilities in dementia

Abstract

Objectives: To determine the extent to which selected variables within demographic, psychometric, and memory domains can predict functional abilities in dementia.

Design: Hierarchical regression analyses were employed to predict functional abilities, while controlling for disease severity, using the Mini-Mental State Exam (MMSE).

Setting and participants: A total of 2368 inhabitants of Kungsholmen parish in Stockholm, Sweden, aged 75 years of age or older. Eighty-one subjects with confirmed dementia (MMSE, M = 17.9; SD = 5.26) were selected from the study population. The mean age was 84.5 years (SD = 5.58), and 72% were female.

Measurements: Participants received a battery of standardized neuropsychological instruments and selected experimental tasks that measured visuospatial ability as well as primary and episodic memory. Self-care was assessed using the Katz index of activities of daily living (ADL); instrumental activities of daily living (IADL) were assessed through the primary caregiver, who responded to questions related to functional competence of the participant.

Results: Hierarchical regression procedures revealed that disease severity was the strongest predictor of ADL and IADL performance. Controlling for disease severity, a measure of visuoperception (Poppelreuter's figures) also made a significant contribution to the explanatory variance in both ADL and IADL function. Beyond disease severity and visuoperception, years of schooling and disease duration were marginally predictive of IADL performance.

Conclusion: It is possible to predict functional abilities in dementia on the basis of individual difference variables. Multiple variables were initially correlated with ADL and IADL performance; however, after controlling for disease severity, visuoperception was the only predictor of ADL scores. In addition to visuoperception, IADL scores were also marginally predicted by education and disease duration. These findings highlight the importance of peripheral sensory processes in adaptive function in dementia. They also suggest that although many variables may be correlated with functional ability, their explanatory role, particularly with regard to self-care skills, is diminished in the presence of the disease.