'Silent Strokes' Strike One in 10 Healthy People

By Ed Edelson
HealthDay Reporter
Friday, June 27, 2008; 3:00 AM

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THURSDAY, June 26 (HealthDay News) -- If you're an older American with no major health problems, chances are about one in 10 that you've had a stroke and didn't know it.

It was probably not severe enough to cause recognizable symptoms, such as vision problems, facial weakness or trouble walking, but it was still a blockage of a brain artery, and it reduced your thinking powers just a bit.

That estimate comes from a new study of 2,040 people, average age 62, in the long-running Framingham Offspring Study. MRI scans showed that 10.7 percent of them had experienced what study author Dr. Sudha Seshadri, an associate professor of neurology at Boston University, called "a silent brain infarct."

It's the cerebral equivalent of what physicians call a myocardial infarct -- blockage of a blood vessel that causes damage to tissue. In the case of a silent stroke, the blockage and the damage occurs in the brain, without symptoms.

A silent stroke is different from a transient ischemic attack (TIA), a momentary loss of brain function, Seshadri said. A TIA causes some symptoms, while a silent stroke, by definition, doesn't. But both are warning signs to pay attention to the well-known risk factors for stroke, such as cholesterol levels, blood pressure, obesity and smoking, she said.

The incidence found in the Framingham Offspring study "was within the ballpark of what prior studies have suggested," Seshadri said. "But this was a group of people who were younger than in most of the prior studies. The fact that one in 10 persons had silent attacks that had subtle side effects on the brain is something we should be concerned about and should address."

The report was published in the online issue of Stroke.

The effects of a silent brain infarct show up on an MRI scan as "small lesions in various parts of the brain," Seshadri said. "We can't tell from that whether they had a symptomatic attack." And the MRI scans give no clues as to when the silent stroke occurred.

Testing showed that "on average, compared to age-matched controls, those with lesions do have subtle signs, such as loss of flexibility of talk," she said.