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Racial Differences Characterize Cognitive Decline in Alzheimer's

A possible explanation is that differences in the prevalence of underlying causes of cognitive decline—such as cardiovascular disease and Parkinson's disease—may account for racial differences in the rate of decline among Alzheimer's patients.

The rate of cognitive decline in people with Alzheimer's disease appears to be slower among African Americans than among non-African Americans, according to a report in the November 2005 American Journal of Geriatric Psychiatry.

African Americans in the study had a lower level of cognition at baseline than non-African Americans, but declined at a 25 percent slower rate on average, said Lisa Barnes, Ph.D., and colleagues at Rush University Medical Center in Chicago.

"Because the rate of decline may be different, it suggests that the prognosis may be a little better for African-American patients," Barnes told Psychiatric News. "This could have implications for what clinicians tell patients about what the future will hold. At the same time, it may be harder to diagnose Alzheimer's in African Americans because it could take longer to identify that the changes are serious and indicative of Alzheimer's and not something else."

"[F]actors contributing to cognitive decline in African Americans differ in part from those factors that contribute to decline in non-African Americans."

Barnes is an assistant professor of neurological sciences and behavioral sciences at Rush University Medical Center.

She also said the findings have implications for how to interpret the effects of medication. "We might be overestimating the effects of our medications in African Americans, because they are declining more slowly anyway," she said.

But Barnes acknowledged that the surprising findings need to be replicated in other studies. Only one other study on racial differences in cognitive decline among Alzheimer's patients has appeared in the literature, according to the study authors.

In the study, older persons with clinically diagnosed Alzheimer's were recruited from the Rush Alzheimer's Disease Center and from adult day-care centers in the metropolitan Chicago area. Residence in the community was required, and those living in nursing homes and assisted-living facilities were excluded.

At six-month intervals for up to four years, subjects completed a battery of nine cognitive tests, from which a measure of global cognition was derived. Follow-up data were available on 452 participants, of whom 27 percent were African American.

Statistical models were constructed to control for the potentially confounding effects of age and education. Using these models, the researchers found that although African Americans scored lower on the global measure of cognition at baseline, they declined at a 25 percent slower rate. The three-year predicted rate of decline for any individual patient, using the statistical models, was slower for African Americans, such that by the third study year they had higher predicted scores than non-African Americans.

Barnes explained that several possible explanations for the findings were tested. One possibility was that the sample included some people who may not have had Alzheimer's, but when those individuals with "possible Alzheimer's" were excluded (and when a separate model that included those individuals was run on the course of possible Alzheimer's over time), the interaction between race and decline over time remained robust—African Americans declined significantly slower than non-African Americans.

Similarly, the researchers examined the possibility that lower cognitive scores at baseline may have caused them to underestimate the rate of decline among African Americans. Only 34 people obtained the lowest possible score at any evaluation, and this occurred with similar frequency among African Americans (8.8 percent) and non-African Americans (7.7 percent).

To examine the issue further, the researchers repeated the statistical model and excluded the 34 people, and the association of race with cognitive decline remained.

"We think a more likely explanation is that the factors contributing to cognitive decline in African Americans differ in part from those factors that contribute to decline in non-African Americans," the authors wrote. "For example, previous studies suggest that African Americans have a higher prevalence of cardiovascular disease and that Caucasians are more likely to develop Parkinson's disease, and both conditions can contribute to cognitive decline in persons with Alzheimer's. Large-scale biracial, longitudinal, clinicopathologic studies that can link risk factors, the clinical manifestations of disease, and pathologic changes in the brain are needed to investigate these and other possibilities."

An abstract of "Racial Differences in the Progression of Cognitive Decline in Alzheimer's Disease" is posted at <http://ajgp.psychiatryonline.org/cgi/content/abstract/13/11/959?>.

Am J Geriatr Psychiatry 2005 13 959[Abstract/Free Full Text]

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