Background: Cognition, abilities in activities of daily living (ADL), and behavioral disturbances in patients with Alzheimer's disease (AD) all influence the number of hours informal caregivers spend caring for their patients, and the burden caregivers experience. However, the direct effect and relative importance of each disease severity measure remains unclear.
Methods: Cross-sectional interviews were conducted with 1,222 AD patients and primary caregivers in Spain, Sweden, the U.K. and the U.S.A. Assessments included informal care hours, caregiver burden (Zarit Burden Inventory; ZBI), cognition (Mini-mental State Examination; MMSE), ADL-abilities (Disability Assessment for Dementia scale; DAD), and behavioral symptoms (Neuropsychiatric Inventory Questionnaire; NPI-severity).
Results: Multivariate analyses of 866 community-dwelling patients revealed that ADL-ability was the strongest predictor of informal care hours (36% decrease in informal care hours per standard deviation (SD) increase in DAD scores). Severity of behavioral disturbances was the strongest predictor of caregiver burden (0.35 SD increase in ZBI score per SD increase in NPI-Q severity score). In addition, the effect of ADL-abilities was, although attenuated, not negligible (0.28 SD increase in ZBI score per SD increase in DAD score). Decreasing cognition (MMSE) was associated with more informal care hours and increased caregiver burden in univariate, but not in adjusted analyses.
Conclusions: For patients residing in community dwellings, the direct influence of patients' cognition on caregiver burden is limited and rather mediated by other disease indicators. Instead, the patients' ADL-abilities are the main predictor of informal care hours, and both ADL-abilities and behavioral disturbances are important predictors of perceived caregiver burden, where the latter has the strongest effect. These results were consistent across Sweden, U.K. and the U.S.A.