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BACKGROUND
Alzheimer's disease (AD) is clinically defined by the progressive impairment of memory and other cognitive abilities. As a result of cognitive decline, patients lose the ability to perform complex (instrumental) activities of daily living (ADL), and eventually basic ADL. Clinical assessment of cognition and functional abilities provides important indices of dementia severity. There are many instruments designed to assess these abilities in AD, several of which are used routinely in clinical trials. At a stage of moderate to severe dementia, patients with AD have marked impairment of recent memory and usually have lost the ability to carry out most instrumental ADL (IADL). They have a high risk of institutionalization. At this stage of dementia, patients are difficult to evaluate clinically and have received relatively little study in clinical trials. Typical measures, such as the Mini-Mental State Examination (MMSE) (Folstein et al., 1975) or Alzheimer's Disease Assessment Scale-cognitive (ADAS-cog) (Rosen et al., 1984), are suboptimal in moderate to severe AD, because patients' performance has reached a floor on many components. Functional abilities in these patients are usually measured by performance of basic ADL such as dressing, grooming, and bathing. Most basic ADL scales assess a limited range of activities. A clinical trial of vitamin E and selegiline in moderately severe AD (mean entry MMSE = 11) used clinical milestones such as death, institutionalization, and loss of basic ADL as primary outcome measures (Sano et al., 1997). Significant treatment effects were found regarding time to reach these milestones. However, there was no significant treatment-placebo difference regarding rates of cognitive change. It is possible that cognitive measures may not provide information under certain circumstances where ADL measures may do so. This question should be explored using instruments appropriate for patients with moderate to severe dementia.
For clinical trials in AD, outcome measures need to be reliable, comprehensive, reflect the abilities of the targeted patient population, have sensitivity to detect change over time, and be clinically meaningful. Because there are few detailed measures developed for research studies of moderate to severe dementia, we examined the performance and properties of an instrument specifically developed to assess ADL in this patient population, termed the Alzheimer's Disease Cooperative Study Activities of Daily Living scale for Severe impairment (ADCS-ADL-sev). In developing this...