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Alzheimer's Disease Preceded by Cognitive Decline

Dementia due to Alzheimer's disease preceded by five or six years of cognitive functional decline

WEDNESDAY, March 16 (HealthDay News) -- Dementia associated with Alzheimer's disease is preceded by five or six years of rapid cognitive decline in multiple functions, according to a study published in the March issue of the Archives of Neurology.

Robert S. Wilson, Ph.D., from the Rush Alzheimer's Disease Center in Chicago, and colleagues characterized the course of cognitive decline in the prodromal phase of Alzheimer's disease, in a 16-year observational study. A total of 2,071 individuals without dementia and 1,511 without cognitive impairment at baseline underwent annual clinical evaluations, including cognitive function testing and clinical classification of mild cognitive impairment, dementia, and Alzheimer's disease.

The investigators identified 462 individuals who developed Alzheimer's disease during the follow-up period. Five to six years before diagnosis, there was a 15-fold acceleration in the rate of global cognitive decline, with decline in semantic memory and working memory occurring slightly earlier than other cognitive functions (76 and 75 months before diagnosis, respectively). Cognitive decline preceded mild cognitive impairment by 80 months, and progressed more rapidly in amnestic (0.102 units per year) compared to non-amnestic (0.072 units in 62 months) subtypes.

"The rate of cognitive decline increased sharply about five to six years before dementia was diagnosed and showed a modest increase approximately four to six years before mild cognitive impairment was diagnosed. The results indicate that dementia in Alzheimer's disease is preceded by many years of progressively accelerating cognitive decline," the authors write.

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