To what degree does cognitive impairment in Alzheimer's disease predict dependence of patients on caregivers?

BACKGROUND: Patients with Alzheimer's disease experience a progressive loss of cognitive function, and the ability to independently perform activities of daily life. Sometimes a dependent stage is reached quite early in the disease, when caregivers decide that the patients can no longer be left alone safely. This is an important aspect of Alzheimer's for patients, their families, and also health care providers. Understanding the relationship between a patient's current cognitive status and their need for care may assist clinicians when recommending an appropriate management plan. In this study, we investigated the relationship of cognitive function to dependence on caregivers before the patients reach a severe stage of the disease. METHODS: Data were obtained on 1,289 patients with mild-to-moderate Alzheimer's disease studied in two randomised clinical trials of galantamine (Reminyl(®)). Cognition was assessed using the cognitive part of the Alzheimer's Disease Assessment Scale (ADAS-cog) and Mini-Mental State Examination (MMSE). Patients were considered dependent if they required >12 hours of supervision each day or had high care needs. The Disability Assessment for Dementia (DAD) scale was also used as a measure of dependence. Disability was predicted directly using MMSE and ADAS-cog and compared to predictions from converted scores. RESULTS: The odds ratio of dependence was significantly higher amongst the patients with worse cognitive impairment, adjusting for age, gender and antipsychotic medication use. For example, a 4-point difference in ADAS-cog score was associated with an increase of 17% (95% CI 11–23) in the adjusted odds for >12 hours of supervision, and of 35% (95% CI 28–43) for dependence. Disability predicted directly using actual ADAS-cog and scores converted from MMSE values had close agreement using the models developed. CONCLUSION: In patients with mild-to-moderate Alzheimer's disease, even relatively small degrees of poorer cognitive function increased the risk of losing the ability to live independently.