A LONGITUDINAL-STUDY OF ALZHEIMERS-DISEASE - MEASUREMENT, RATE, AND PREDICTORS OF COGNITIVE DETERIORATION

Objective: This study measured the annual rate of cognitive change in patients with Alzheimer's disease and determined the effects of clinic al variables on that rate. It also compared the ability of two cogniti ve scales to measure change over the entire range of dementia severity . Method: The cognitive subscale of the Alzheimer's Disease Assessment Scale and the Blessed test for information memory and concentration w ere given to 111 patients with Alzheimer's disease and 72 nondemented elderly comparison subjects at 6-month intervals for up to 90 months. Longitudinal changes in scores on the cognitive subscale were measured with several different methods of data analysis. Results: For the pat ients with Alzheimer's disease, the annual rate of change in cognitive subscale scores showed a quadratic relationship with dementia severit y in which deterioration was slower for mildly and severely demented p atients than for patients with moderate dementia, Gender, age at onset , and family history of dementia had no effect on the rate of cognitiv e deterioration. The comparison group showed a slight improvement in c ognitive performance over time. All data analytic methods gave similar results. The cognitive subscale of the Alzheimer's Disease Assessment Scale was more Sensitive to change in both mild and severe dementia t han was the Blessed test. Conclusions: These results suggest that cogn itive deterioration is slow during the early and very late stages of A lzheimer's disease and more rapid during the middle stages. No clinica l variables other than degree of cognitive impairment and previous rat e of cognitive decline predicted rate of deterioration. These results have implications for treatment trials and attempts to identify subgro ups.