The Alzheimer's disease assessment scale: Patterns and predictors of baseline cognitive performance in multicenter Alzheimer's disease trials

Abstract

The cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog) is used as an efficacy measure in clinical drug trials of Alzheimer's disease (AD). We used data from 1,648 AD participants in two identical 26-week multicenter drug trials to examine the distribution of baseline ADAS-Cog scores in relation to selected demographic and clinical variables, Mini-Mental State Exam (MMSE), Global Deterioration Scale (GDS), and Geriatric Evaluation by Relative's Rating Instrument (GERRI) scores. At baseline, the mean (± SD) MMSE score was 18 ± 4, the ADAS-Cog score was 28 ± 11, and most subjects were in GDS stage 4 or 5. The ADAS-Cog score was statistically significantly correlated with MMSE (R = -0.76, p < 0.0001) and GERRI (R = 0.40, p < 0.0001) total scores. Correlations among the ADAS-Cog items ranged from 0.19 to 0.59 and all were statistically significant (p < 0.0001). In a multiple regression model, younger age, male gender, older age at onset of dementia, use of concurrent estrogen, and use of concurrent anti- inflammatory agents were statistically significantly associated with superior cognitive performance. We also present data on the distribution of ADAS-Cog scores in relation to subjects' age, level of education, MMSE score, and GDS stage. Because age, MMSE score, and GDS stage (and not the ADAS-Cog) are commonly used to select subjects for AD clinical trials, our data should improve the ability of sponsors to predict ADAS- inclusion criteria used. Our data also suggest that age, gender, age at onset of dementia, level of education, and use of estrogen (in women) or anti-inflammatory drugs are related to cognitive abilities in AD. Further studies are needed to assess how and when cognitive differences related to these variables arise.