Target Symptoms and Outcome Measures: Cognition

Kirk, Andrew · 2007 · Crossref

DOI: 10.1017/s0317167100005552

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Summary

This review article addresses the adequacy of cognitive outcome measures used in dementia clinical trials, with a primary focus on the Alzheimer’s Disease Assessment Scale–Cognitive subscale (ADAS-Cog). The motivation stems from regulatory requirements for objective cognitive assessments in antidementia drug trials and the controversy surrounding the utility of approved therapies. The author evaluates whether the ADAS-Cog, designed specifically for Alzheimer’s disease (AD), is suitable for assessing patients with other dementias, such as vascular dementia, dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD). The paper analyzes the psychometric properties and clinical applicability of several instruments, including the ADAS-Cog, the Severe Impairment Battery (SIB), the Mini-Mental State Exam (MMSE), and the Modified Mini-Mental State Examination (3MS). The ADAS-Cog is an 11-item test scored out of 70 that assesses memory, orientation, language, construction, and praxis but omits attention, executive function, and agnosia. The review synthesizes existing literature to compare these tools across different disease severities and types, noting that while the ADAS-Cog differentiates AD patients from controls and distinguishes severity levels, it suffers from floor and ceiling effects and may not capture the specific cognitive deficits of non-AD dementias. Key findings indicate that the ADAS-Cog remains the most widely used measure for AD trials and has been applied in vascular and DLB trials, though its adequacy for FTD is questionable due to FTD’s distinct profile of language and executive impairment. For advanced dementia, the SIB is identified as the most widely used tool, offering analogous domains to the ADAS-Cog without the same floor effect. The MMSE and 3MS are deemed useful for patient stratification and trial entry but are limited as primary outcome measures due to ceiling effects in mild cases, floor effects in severe cases, and high inter-rater variability in the 3MS. The author notes that brief tests of frontal function, such as the Frontal Assessment Battery or Executive Interview, and aphasia batteries like the Western Aphasia Battery, may be necessary additions for FTD trials. The significance of this review lies in its conclusion that while the ADAS-Cog and SIB are appropriate for AD and advanced dementia respectively, cognitive measures better tailored to specific non-Alzheimer dementias are required. The author suggests that adding items assessing attention and executive function to the ADAS-Cog could improve its utility for vascular dementia, while entirely different tools are needed for FTD. This highlights a critical gap in current clinical trial methodologies, emphasizing the need for disease-specific cognitive assessments to accurately evaluate treatment efficacy across the spectrum of dementing illnesses.

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• cognitive impairment