Cognitive Decline Likely Due To Alzheimer’s Pathology

According to a report in the May 2002 issue of the Annals of Neurology, many cases of mild memory loss or other cognitive impairment in the elderly are accompanied by brain damage characteristic of Alzheimer's disease.

Researchers from the University of Kentucky's Sanders-Brown Center on Aging found a close correlation between the degree of memory loss and other cognitive impairment and levels of abnormal protein deposits in the brain called "neurofibrillary tangles."

"It seems that mild cognitive impairments are not a part of the normal aging process," said lead author Kathryn P. Riley, Ph.D. "Our findings and those of other researchers suggest that Alzheimer's pathology in the brain is affecting older adults long before the full symptoms of the disease appear."

Although these data support the recent understanding that mild cognitive impairments are a risk factor for Alzheimer's, the results also indicate that not everyone with such impairments will develop full-blown dementia, added Riley. The study underscores the importance of having a full evaluation of any suspected memory or other cognitive impairment.

For some time, researchers have suspected that normal aging was not the cause of mild losses of memory or other cognitive abilities, such as the ability to reason or solve problems, whether on psychological tests or in daily life. However it has been difficult to determine in living subjects whether these problems represent an earlier stage of Alzheimer's because the neurofibrillary tangles and other physical evidence of the disease are not visible with current brain imaging techniques.

Indeed, a definitive diagnosis of Alzheimer's cannot be given to a patient with severe cognitive problems until a pathologist identifies specific damage (neurofibrillary tangles and similar brain damage called "senile plaques") during an autopsy.

Riley and her colleagues had the benefit of studying some of the elderly subjects in the now-famous Nun Study. A decade ago, 678 School Sisters of Notre Dame, aged 75 to 102 years, agreed to frequent physical and psychological tests and to have their brains studied after death. A number of important insights into Alzheimer's disease have already been gleaned from this ongoing project.

The present study focused on 130 nuns who died in the intervening decade. The researchers compared the levels and distribution of neurofibrillary tangles in the nuns' brains with the results of cognitive tests taken within months before their deaths.

From the subjects in the earliest stages of neurofibrillary tangle deposition, to those in the latest stages, which are characterized by heavy and widespread tangle burdens, the degree of neurofibrillary tangles was paralleled by increasingly poor performance on the cognitive tests. The data also indicate that subjects with memory impairments in addition to other cognitive deficits had more of the tangles than subjects with non-memory cognitive deficits alone, and were more likely to be diagnosed with Alzheimer's disease over a four-year period.

"This information may be useful in light of newly developing treatments designed to delay the onset of cognitive impairment associated with Alzheimer's disease," said Riley. "Researchers and clinicians in the field of aging hope someday to be able to prevent mild cognitive impairments from progressing on to more severe conditions, and ultimately, to be able to prevent the impairments from occurring in the first place."

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