Stroke Incidence Down, But Not for Blacks

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% between 1999 and 2005 in the incidence of ischemic strokes, those caused by blood clots blocking a brain artery.

About 80% 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% decrease among white residents of the region, but a 4.6% 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%, the survey found.

The good news from the survey is the overall decrease in incidence of stroke, says study author Dawn Kleindorfer, MD, an associate professor of neurology at the University of Cincinnati. "This is the first time we've ever seen that," she says.

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 says. 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 says.

The reason for the difference between whites and blacks is also a matter of speculation, Kleindorfer says. "There are a lot of features that the survey cannot answer -- severity of the stroke, access to medical care, dietary differences," she says. "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 online in Stroke, probably hold for the overall U.S. population, with one important exception, Kleindorfer says. "The [study] region is very representative of the United States as a whole in terms of income, education and percentage black," she says. "The big one missing is that there is no significant Hispanic population." Fewer than 3% of residents of the region studied were Hispanic.

Source: Brigham and Women's Hospital