Cognitive Factors Preceding Alzheimer's Disease Examined

Study identifies four cognitive factors likely seen up to three years prior to disease onset
By Jeff Muise
HealthDay Reporter

THURSDAY, Oct. 15 (HealthDay News) -- The onset of Alzheimer's disease can be seen on tests for several cognitive factors up to three years prior to clinical diagnosis, according to a study in the October issue of the Archives of Neurology.

David K. Johnson, Ph.D., of the University of Kansas in Lawrence, and colleagues analyzed data on 444 seniors enrolled by the Alzheimer Disease Research Center between 1979 and 2006. To identify preclinical signs of Alzheimer's disease, the researchers evaluated four cognitive factors including global, verbal memory, visuospatial, and working memory. The trends were compared for individuals who developed Alzheimer's disease and those who did not.

The researchers note that sharp inflection points and subsequent downward trends were seen for all four cognitive factors. For global, the optimal inflection point prior to Alzheimer's disease diagnosis was two years. For verbal and working memory it was one year, and for visuospatial it was three years. The researchers had similar results when data comparisons were limited to subjects with autopsy-confirmed Alzheimer's disease.

"There is a sharp inflection point followed by accelerating decline in multiple domains of cognition, not just memory, in the preclinical period in Alzheimer disease when there is insufficient cognitive decline to warrant clinical diagnosis using conventional criteria. Early change was seen in tests of visuospatial ability, most of which were speeded," the authors write. "Research into early detection of cognitive disorders using only episodic memory tasks may not be sensitive to all of the early manifestations of disease."

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