Flaws in a test used in clinical trials to assess patients could be undermining the search for a drug to treat Alzheimer’s.
The scientists published their findings in two papers in the journal Alzheimer’s & Dementia.
In the past two years, there have been a number of clinical trials producing disappointing results for high-profile drugs, making some pharmaceutical companies abandon Alzheimer’s altogether. The flaws in the ADAS-Cog test could be partly responsible.
The ADAS-Cog test has been used as a key indicator on whether a drug is working. The test scores patients on 11 components using a variety of tasks associated with memory, language and praxis. Lower scores show a better cognitive performance, and so a disease that is less severe.
Any study using ADAS-Cog may have underestimated the changes in and differences between patients given the drug and controls. A large set of test scores was used to show ceiling effects in eight out of eleven ASAS-Cog components, meaning that there is an upper limit past which these parts of the test cannot properly capture the differences between patients.
The test isn’t detailed enough for the patients in the very early stages of the disease. In the second paper, researchers used complex mathematical algorithms were used to analyze how well ADAS-Cog performed as a measurement tool. They concluded that it has limitations with potentially serious implications for clinical trials.
ADAS-Cog was first published in 1984, when the concept of Alzheimer’s was more limited than today. And because of that, the test might not be able to pick up on the subtle improvements produced by the drugs being tested. Today, researchers are more interested in the early stages of the disease, when impairment is less obvious, and they believe the test should be improved to be more sensitive.
“Putting the Alzheimer’s cognitive test to the test I: Traditional psychometric methods” by Jeremy Hobart, Stefan Cano, Holly Posner, Ola Selnes, Yaakov Stern, Ronald Thomas, John Zajicek, Alzheimer’s Disease Neuroimaging Initiative, 18 December 2012, Alzheimer’s & Dementia.
“Putting the Alzheimer’s cognitive test to the test II: Rasch Measurement Theory” by Jeremy Hobart, Stefan Cano, Holly Posner, Ola Selnes, Yaakov Stern, Ronald Thomas, John Zajicek, Alzheimer’s Disease Neuroimaging Initiative, 18 December 2012, Alzheimer’s & Dementia.