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Alzheimer's disease dementia may be detectable via cognitive tests 18 years prior to diagnosis

Lower composite cognitive test scores were associated with the development of Alzheimer’s disease dementia during an 18-year follow-up study period, according to findings in Neurology.

“Cognitive test performance predicts development of subsequent [Alzheimer’s disease] dementia in European American populations. Several prospective studies suggest detectable cognitive deficits up to 10 years before clinical diagnosis of [Alzheimer’s disease] dementia and two studies suggest these deficits may be detected as long as 10 to 12 years before diagnosis,” study researcher Kumar B. Rajan, PhD, of Rush University Medical Center in Chicago, and colleagues wrote.

To further explore the relation of performance on brief cognitive tests to development of diagnosed Alzheimer’s disease dementia, researchers assessed data from the Chicago Health and Aging Project, a longitudinal, population-based study of health conditions among adults aged 65 years and older. Study participants (n = 2,125) completed cognitive tests approximately every 3 years over an 18-year follow-up period. Fifty-five percent of the study cohort was black. The study was conducted from 1993 to 2012.

Twenty-one percent of the study cohort developed clinical Alzheimer’s disease dementia during the study period.

Lower composite cognitive test scores were associated with the development of Alzheimer’s disease dementia during the study period.

The significance of the association between composite cognitive test scores and Alzheimer’s disease dementia diagnosis increased as time to diagnosis increased, from an odds ratio of 3.39 (95% CI, 1.72-6.67; P < .001) at 12 to 17.9 years before clinical diagnosis to 9.84 (95% CI, 7.41-13.06; P < .001) at 0.1 to 0.9 years before diagnosis.

These associations were larger among European Americans vs. black Americans.

Individual cognitive test scores for episodic memory, executive function and global cognition also significantly predicted development of Alzheimer’s disease dementia and showed similar trends over the 18-year study period, according to researchers.

“Our findings indicate that overall performance on a brief cognitive test battery and on tests measuring specific cognitive functions differ substantially on average between those who subsequently develop clinically evident [Alzheimer’s disease] dementia and those who remain free of [Alzheimer’s disease] dementia up to 18 years before diagnosis in a biracial population sample,” the researchers wrote. “The results confirm that average differences in cognitive test scores between those who develop clinically evident [Alzheimer’s disease] dementia and those who did not can be detected up to 12 years before clinical diagnosis among European Americans. Our results also extend this period to the entire observation period of 18 years.” – by Amanda Oldt

Disclosure: Rajan reports receiving financial support from the International Alzheimer’s Association and the NIH. Please see the full study for a list of all other authors’ relevant financial disclosures.