A comparison of the original ADAS‐cognitive subscale and a novel extended version in mild cognitive impairment and Alzheimer’s disease.

Abstract

AbstractBackgroundThe Original Alzheimer’s disease Assessment Scale‐cognitive subscale (oADAS) is the gold standard for assessing cognition in Alzheimer’s disease (AD) medication clinical trials. One criticism is that this measure is not sensitive to pre‐dementia syndromes such as mild cognitive impairment (MCI), possibly due to ceiling effects for many of the subtests in the original ADAS‐cog (oADAS). In this study, we examined group differences between individuals with MCI, AD, and normal controls (NC) on the oADAS and a novel extended version of the ADAS (eADAS). We hypothesized the eADAS would be more sensitive than the oADAS at detecting differences between the groups after controlling for age, education, and sex.MethodThe oADAS was administered using standardized methods. The eADAS included short‐delay recall and recognition trials for the first wordlist, a short‐delay true‐false word recognition trial for the second word‐list, a letter‐digit timed psychomotor test, supermarket fluency, spontaneous clock drawing, three additional items to the object naming subtest, three additional figures to copy, and a similarities test. MCI and possible AD were diagnosed using established diagnostic criteria. The NC group was significantly younger and more educated than the MCI and AD groups. A 3×2 ANCOVA model with group as the between subject factor and ADAS type as the within subject factor was used. Total error scores from the oADAS and eADAS were converted to z‐scores.ResultThere was no main effect of ADAS type or ADAS type X education or ADAS type X group interactions. There were ADAS type x age and ADAS type x gender interactions (p’s = 0.01). Pairwise comparisons demonstrated that the NC group had lower total error scores compared to the MCI and AD groups and the MCI group had lower total error scores compared to the AD group for both the oADAS and eADAS (p’s<0.001).ConclusionThe results of the current study indicate that oADAS and eADAS are sensitive to group differences between MCI and AD, which was contrary to our hypothesis. We suggest more rigorous diagnostic criteria for MCI in the present study may explain some of the conflicting findings in the literature.