The Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS-Cog): Modifications and Responsiveness in Pre-Dementia Populations. A Narrative Review

Kueper, Jacqueline K.; Speechley, Mark; Manuel Montero‐Odasso · 2018 · OpenAlex-citations

DOI: 10.3233/jad-170991

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Summary

This narrative review evaluates the performance of the Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS-Cog) in pre-dementia populations, such as those with mild cognitive impairment (MCI) or normal cognition (NC), and examines modifications designed to improve its measurement properties. The ADAS-Cog was originally developed in the 1980s for assessing dementia, but its use has expanded to earlier disease stages. The authors argue that if the scale fails to detect meaningful changes in pre-dementia populations, clinical trials may incorrectly conclude that treatments are ineffective, compromising the understanding of disease progression. The study involved bibliographic searches of electronic databases (MEDLINE, Embase, Cinahl, PsychINFO, PsychTests, and Proquest Psychology) to identify studies using the original ADAS-Cog-11 in pre-dementia samples and to locate all modified versions. The review analyzed psychometric properties, including ceiling effects, reliability, measurement invariance, baseline discrimination, and responsiveness to disease progression, exposure-based differences, and treatment effects. Findings indicate that the original ADAS-Cog-11 is not an optimal outcome measure for pre-dementia studies. Seven of the eleven tasks demonstrate severe ceiling effects in MCI and NC samples, meaning many subjects score at the maximum level, limiting the ability to detect decline. Responsiveness to treatment effects is low; in a review of twenty clinical trials, the ADAS-Cog-11 detected statistically significant treatment effects in only 48% of cases. Furthermore, it frequently failed to detect associations with cognitive or imaging markers that other measures successfully identified. While the scale can discriminate between diagnostic groups at baseline, the magnitude of change scores detected in pre-dementia populations is very small. The review identified thirty-one modified versions of the ADAS-Cog. Modifications generally fall into two categories: altering scoring methodology (e.g., using Rasch analysis or Item Response Theory to weight tasks by precision) and adding new test items (e.g., assessing executive function, daily functioning, or memory). Modifications that alter scoring or add sensitive tasks appear most beneficial for improving responsiveness. However, these changes introduce heterogeneity across studies, which may limit the comparability of results between different trials. The authors conclude that while modifications improve performance, caution is required when selecting outcome measures for pre-dementia research due to the lack of standardization.

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• cognitive impairment