Alzheimer's Assessment Scale May Lack Accuracy

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FROM ALZHEIMER'S & DEMENTIA

Portions of one of the most commonly used tests to measure cognitive performance in Alzheimer's disease trials may be too easy and may not accurately assess the range of patients' cognitive abilities or detect their change over time, according to two complementary studies.

Analyses of Alzheimer's Disease Assessment Scale--Cognitive Behavior Section (ADAS-Cog) scores measured in 193 patients with mild disease who participated in ADNI (the Alzheimer's Disease Neuroimaging Initiative) over the course of 2 years detected limitations of the scale that could be improved, reported Dr. Jeremy Hobart of the Clinical Neurology Research Group at Plymouth (England) University Peninsula Schools of Medicine and Dentistry, and his colleagues.

The investigators used observational data from ADNI to show that, out of 675 measurements made at time points of 0, 6, 12, and 24 months, data from ADAS-Cog total scores spanned the entire range of the scale and had no floor or ceiling effects that would reduce its ability to measure changes and differences in lower-functioning or higher-functioning patients, respectively However, 8 of the scale's 11 components (all except for word recall, word recognition, and orientation) had statistically significant ceiling effects with a skewed distribution of scores (Alzheimers Dement. 2012 [doi:10.1016/j.jalz.2012.08.005]). The mean age of patients was 74 years.

These results reproduce those that the investigators obtained in a previous psychometric evaluation of the ADAS-Cog in patients who participated in a randomized controlled clinical trial (J. Neurol. Neurosurg. Psychiatry 2010;81:1363-8). They noted that the results mean that "these components may underestimate cognitive performance differences in those with mild to moderate AD-type dementia. This may lead to problems in detecting clinical change."

Because often greater than three-fourths of the participants with mild Alzheimers disease in the ADNI study scored either 0 or 1 on the majority of ADAS-Cog components, Dr. Hobart and his associates remarked that this would mean that few or no cognitive problems were detected. …