F O R T L A U D E R D A L E, Fla., Feb. 16, 2001 -- A surprising 11 million Americans each year have strokes that are never detected because they cause no obvious symptoms, although over time they may lead to memory loss and other ills, a study concludes.
Doctors have long known that people can have insidious “silentstrokes”—tiny spots of dead cells inside the brain that do notcause classic stroke symptoms. But the new study suggests they areextremely common, occurring in about 4 percent of the U.S.population each year.
Besides the 11 million Americans who have silent strokesannually, about 750,000 more have ones that cause classic strokesymptoms, such as slurred speech, dizziness and numbness on oneside.
“Silent strokes are epidemic in this country,” said Dr. MeganC. Leary. While they occur in parts of the brain where they don’tcause symptoms right away, “the word ‘silent’ should be put inquotes, because their effects accumulate over the years.”
While a single silent stroke may have no impact, repeated oneslead to memory lapses, mood problems and difficulty walking. Theyare also a sign that people are especially prone to full-blownstrokes.
Leary and colleagues from UCLA Medical Center released theresults Friday at a meeting of the American Stroke Association inFort Lauderdale.
“It’s an alarming estimate,” said Dr. Robert J. Adams of theMedical College of Georgia. “It’s surprisingly high but verypossibly accurate.”
The researchers say silent strokes are rare before age 30. Butafter that, their prevalence doubles every 10 years. By the timepeople reach their 70s, one in three has a silent stroke everyyear.
The researchers also found that some people have more than onesilent stroke in a year. When these repeat ones are added together,Americans have almost 22 million silent strokes annually. Thismeans that only 3 percent of the total number of strokes in 1998,when the data were compiled, were actually diagnosed.
Leary based her estimate on two surveys involving brain scans onabout 5,500 Americans.
“What’s sad is that silent strokes and symptomatic strokes areamong the most preventable diseases in this country,” Leary said.
Doctors can see the scars left by silent strokes when theyperform routine brain scans. But ordinarily they do not search forthem. However, the new data raise the possibility that perhaps theyshould, since people who have one silent stroke are likely to havemany more.
Strokes can be prevented by keeping blood pressure undercontrol, lowering cholesterol, treating diabetes and stoppingsmoking. Leary said if people actually know they have had a silentstroke, they might be more willing to stick to blood pressuremedicines and cholesterol-lowering drugs that cut their risk.
The new data suggest that diagnosed strokes “may be just thetip of the iceberg,” said Dr. Ralph Sacco of Columbia University.But while they raise the possibility that doctors should look forsilent strokes and treat victims more aggressively, “we don’t havethe data to show that yet.”
In a separate study, Dutch doctors did brain scans on across-section of 1,077 elderly people. They found that one-quarterof them had signs of stroke, and 80 percent of these were silentstrokes.
“Up until now, we have not told people about silent strokesbecause we didn’t know what they mean,” said Dr. Sarah E. Vermeerof Erasmus Medical Center in Rotterdam. “Now we have evidence thatsilent strokes do count.”