What You Do Know (Quitting Smoking, Lowering Blood Pressure) Can Help Prevent What You Don't Know (Silent Strokes)

May 07, 1998

DALLAS, May 8 -- How do you prevent something that you don't know is happening?

It's not a Zen question, but instead is the problem facing those who study "silent" strokes -- small "brain attacks," which affect as many as 11 percent of people 55 to 70 years old.

According a report in this month's Stroke: Journal of the American Heart Association, quitting smoking and lowering high blood pressure can help prevent this quiet problem.

In one of the first studies to examine what causes silent strokes -- strokes that do not exhibit any of the classic symptoms, but result from either blockages or bleeding in small blood vessels in the brain -- researchers found that people with high blood pressure were at twice the risk for developing a silent stroke as those with normal blood pressure. Smokers had nearly twice the risk for having a silent stroke. In addition, older people and African Americans were also at greater risk.

"The two biggest risk factors were smoking and hypertension, and not surprisingly, they're also the biggest risk factors for major strokes," says the study's lead author George Howard, Dr. P.H., professor of public health sciences and neurology at the Wake Forest University Baptist Medical Center, Winston-Salem, N.C. "People who currently smoke, people who were exposed to second hand smoke and people who had smoked in the past were all at greater risk for a silent stroke."

In the study, funded by the National Heart, Lung, and Blood Institute, researchers looked at the results of brain scans -- made by magnetic resonance imaging (MRI) -- of 1,737 people involved in the Atherosclerosis Risk in Communities Study and found that 11 percent of the population between the ages of 55-70 had suffered a silent stroke.

"The percentage surprised me," says Howard. "Basically, there could be millions of people out there with holes in their brain caused by 'silent' stroke.

"It's important to stress that these are 'little' strokes. They are not the same as a major stroke, which we all know to be damaging. I'm in the age range of the people most vulnerable to silent stroke, and I tell you, it almost makes me want to put my head in a MRI scanner to determine whether I've had one."

Between 10 and 40 percent of people who have had transient ischemic attacks -- mini-strokes -- have had silent strokes. TIAs exhibit the same warning signs and symptoms as a brain attack and often can lead to one.

Because these strokes are "silent," it's difficult to say exactly how many people have them, says Howard. He adds that one of the major questions is since people don't know they've had it, why should they care about a silent stroke?

"What has happened in many of these people is that they've had a first stroke, which is small and hits an 'unimportant' region of the brain," says Howard. "The prognosis is that they are about as likely to have a second stroke as someone who has had a clinically diagnosed stroke.

"It's like having a silent heart attack. If you do an echocardiogram, you find those who've had heart attacks and don't know it. People who've had silent heart attacks are at risk for a much more serious heart attack. It may be the same way with a silent stroke."

Silent strokes, which can take years to discover, may also play a role in the development of dementia in the elderly, according to Howard. Dementia is often attributed to Alzheimer's disease, but research is showing that it could also be caused by strokes, says Howard.

"Dementia can be related to vascular sources because if you get enough of these tiny strokes, you could well be on the road to dementia," says Howard.

The researchers found that among current and past smokers, a 20 pack-per-year difference in smoking exposure was associated with a 20 percent increase in the odds of having a silent stroke. In addition to smoking, high blood pressure was shown to double the odds of having a silent stroke.

The risk of developing a silent stroke as a result of smoking, or being exposed to smoke, rose with the amount of smoke the person had been exposed to. People who didn't smoke, but were exposed to environmental tobacco smoke had a six percent increase in the risk of having a silent stroke. In comparison, current smokers had a 88 percent increased risk.

"I'm not proposing that 100 million people get an MRI scan," Howard says. "What has to happen now is there needs to be a greater awareness of this and research as to what can be done about it."

Co-authors include Lynne E. Wagenknecht, Dr.Ph.; Jianwen Cai, Ph.D.; Lawton Cooper, M.D., M.P.H.; Michael A. Kraut, M.D.; and James F. Toole, M.D.

American Heart Association

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