New results from one of the first studies of the brains of members of the general public uncovered scores of participants who have the silent cerebral infarcts and have had no symptoms.
For years, silent cerebral infarcts have been found in patients who already have symptoms, such as those with transient ischemic attacks, or ministrokes, said George Howard, Dr. P.H., professor of public health sciences and neurology at the Wake Forest University Baptist Medical Center, writing in the May 7 issue of Stroke, Journal of the American Heart Association.
However, until this study, "Little was known about the prevalence and risk factors for silent cerebral infarcts in the general population."
Magnetic Resonance Imaging (MRI) exams of 1,737 participants in the Atherosclerosis Risk in Communities (ARIC) study found that 11 percent of the group had had a silent cerebral infarction. The percentage is so high that the investigators concluded that silent cerebral infarctions "represents a relatively common abnormality."
What causes it?
"Among the major cardiovascular risk factors considered, current cigarette smoking and hypertension (high blood pressure) were significantly associated with silent cerebral infarctions," said Howard. He said both smoking and high blood pressure had long been known as risk factors for stroke, so he was not surprised that both also increase the risk of silent cerebral infarctions.
In fact, the researchers found a stepwise relationship between smoking and silent cerebral ischemia "that parallels the relationship between smoking and carotid atherosclerosis."
Howard added, "The data showed a trend for a slight increase in the prevalence of silent cerebral infarcts among those exposed to second-hand smoke, a further increase for those who had smoked cigarettes in the past and the highest prevalence among those who are currently smoking cigarettes."
Furthermore, as the number of pack-years of smoking increased, so did the prevalence of silent cerebral infarction.
"Both are additional arguments for smoking avoidance and cessation," Howard said.
None of the other risk factors characteristically associated with stroke -- except high blood pressure ? were significantly associated with silent cerebral infarctions, he said. Those other factors include diabetes, partial blockage of the carotid artery, cholesterol levels, and advancing age.
Despite the study results, Howard said "The clinical implications of silent cerebral infarctions remain unclear."
In patients who have symptoms, he said the presence of silent cerebral infarctions is related both to subsequent strokes and to higher mortality rates.
"One could speculate that these lesions may be associated with a poor prognosis in the general population as well," he said. "However, there have been no prospective studies of the impact of silent cerebral infarction on the long term mortality and morbidity of the general population."
The 1,737 participants represented about 10 percent of the participants in the massive Atherosclerosis Risk in Communities study. ARIC, an National Institutes of Health-sponsored study conceived as a successor to the famed Framingham Heart Study, involves randomly selected participants in Forsyth County, N.C., Jackson, Miss., Hagerstown, Md. and suburban Minneapolis, Minn. All participants were between 45 and 65 when the trial began in 1986.
ARIC is an observational study. The health of the participants is monitored regularly, and physical condition, lifestyle, diet and other parameters are recorded, but diagnosis and treatment is left in the hands of personal physicians.
The participants in the current analysis were all from Forsyth County or Jackson. Experienced readers of the MRI results at an MRI Reading Center looked for infarcts that were at least 3 millimeters in diameter and that changed the MRI signal in characteristic ways.
Both the ARIC study, and the companion Cardiovascular Health Study among the elderly will provide such long term analysis, as they record illnesses and death over the years..
The research team also included investigators from the University of North Carolina at Chapel Hill, the National Heart, Lung and Blood Institute, and the Johns Hopkins University School of Medicine.
Contact: Robert Conn, Karen Richardson, Jim Steele or Mark Wright at 336-716-4587