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Alzheimer's Disease Neuropathology May Not Affect Rate of Cognitive Decline in Oldest-Old Group


 

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Cognitive performance was not significantly affected by a greater presence of plaques or neurofibrillary tangles in nondemented adults ages 90 and older.

SAN DIEGO—Among nondemented adults ages 90 and older, no significant differences in cognitive performance were observed between those with high Alzheimer’s disease neuropathology and those with a low level of Alzheimer’s disease neuropathology, according to the results of a study presented at the 136th Annual Meeting of the American Neurological Association.

Archana B. Balasubramanian, PhD, from the Institute for Memory Impairments and Neurological Disorders at the University of California, Irvine, and colleagues measured and compared cognitive testing performance over time in older adults without dementia who had either high or low levels of Alzheimer’s disease neuropathology.

“Lower cognitive performance may be an indication of early neurodegenerative disease in the nondemented oldest-old,” the researchers hypothesized.

Overall, high plaques or high tangles were associated with lower cognitive test scores at each consecutive visit, but these results were not significant and rates of cognitive decline did not differ by level of Alzheimer’s disease neuropathology, as the researchers had initially hypothesized. These findings suggest that Alzheimer’s disease neuropathology may not be related to cognitive performance in nondemented older adults, and that other factors, such as health, lifestyle, or other brain pathology, may play a more important role in the rates of cognitive decline in the oldest-old.

Comparing Cognitive Testing Performance
Dr. Balasubramanian and coauthors included 58 participants from The 90+ Autopsy Study, a population-based study of aging and dementia. Participants were grouped into two categories based on high or low presence of neurofibrillary tangles and plaques. Thirty participants had a “low” presence of plaques, and 35 had a “low” presence of tangles. The median age at baseline across all groups was 95, and the median age at death was 98.

Participants completed cognitive tests every six months: the Modified Mini-Mental State Examination was used to measure global cognition, and the California Verbal Learning Test was used to measure memory. The investigators then analyzed testing results and assessed the overall effect of Alzheimer’s disease neuropathology on the level of cognitive performance.

“No significant differences in cognitive performance were found in participants with low versus high Alzheimer’s disease neuropathology,” the researchers reported. Although none of the trends reached significance, “participants with low plaques or low tangles showed greater learning effects and longer maintenance of learning on the Modified Mini-Mental State Examination and California Verbal Learning Test. High plaques or high tangles were associated with lower cognitive test scores overall at each visit,” the authors added.

“Learning effects contribute to nonlinear trajectories of cognitive performance in the nondemented oldest-old,” Dr. Balasubramanian’s team concluded. “When examining cognitive performance over multiple visits, learning effects must be taken into account.”

—Ariel Jones

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