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
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."
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
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
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
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
"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