No clear explanation for the difference, study says
THURSDAY, May 20 (HealthDay News) -- The incidence of the most common form of stroke has decreased significantly among whites but has increased slightly among blacks, according to a new regional survey designed to be representative of the United States as a whole.
Data from the Greater Cincinnati/Northern Kentucky Stroke Study showed an overall drop of 11.6 percent between 1999 and 2005 in the incidence of ischemic strokes, those caused by blood clots blocking a brain artery.
About 80 percent of strokes are ischemic. The others are hemorrhagic, caused by a burst blood vessel. The survey found no change in the incidence of hemorrhagic stroke.
A breakdown of the data showed a 14.4 percent decrease among white residents of the region, but a 4.6 percent increase among black residents, a rise that did not quite reach statistical significance.
The death rate for those who had ischemic strokes remained the same, about 10 percent, the survey found.
The good news from the survey is the overall decrease in incidence of stroke, said study author Dr. Dawn Kleindorfer, an associate professor of neurology at the University of Cincinnati. "This is the first time we've ever seen that," she said.
The bad news, of course, was the increase among blacks, who already had a significantly higher incidence of stroke.
There is no ready explanation for the findings, since the survey was designed just to measure incidence -- rather than underlying causes -- of stroke, Kleindorfer said. The most likely explanation for the overall decrease is better treatment of risk factors such as high blood pressure, obesity and high cholesterol levels, she said.
The reason for the difference between whites and blacks is also a matter of speculation, Kleindorfer said. "There are a lot of features that the survey cannot answer -- severity of the stroke, access to medical care, dietary differences," she said. "There are cultural differences, so completely teasing out the reasons would be challenging."
Blacks were more likely to have stroke risk factors, such as high blood pressure and diabetes, but were also more likely to be receiving treatment for them, the study found.
The survey findings, published in the May 20 online issue of Stroke, probably hold for the overall U.S. population, with one important exception, Kleindorfer said. "The [study] region is very representative of the United States as a whole in terms of income, education and percentage black," she said. "The big one missing is that there is no significant Hispanic population." Fewer than 3 percent of residents of the region studied were Hispanic.
Dr. Larry B. Goldstein, director of the Duke Stroke Center at Duke University, said the findings "are obviously concerning because they point out the differences between blacks and whites."
A study he did in collaboration with physicians at Yale University offers some clues to the racial disparity, Goldstein said. That study found no large differences in treatment for whites and blacks who had strokes, and no difference in hospital readmission rates for second strokes in the following year.
"What this is saying to me is that a lot of the difference has to do with overall risk factor control or treatment," he said.
Learn more about stroke symptoms and treatment from the U.S. National Library of Medicine.
SOURCES: Dawn Kleindorfer, M.D., associate professor, neurology, University of Cincinnati; Larry B. Goldstein, M.D., director, Duke Stroke Center, Duke University, Durham, N.C.; May 20, 2010, Stroke, online
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