Tom Murphy
RedwoodAge.com 

Researchers have found nearly 11 percent of middle-aged people had suffered "silent strokes" without knowing it, raising their risk for brain damage that can lead to dementia.

Silent strokes, also known as silent cerebral infarctions or SCIs, are brain injuries caused by a blood clot that stops the flow of blood to the brain.

“The findings reinforce the need for early detection and treatment of cardiovascular risk factors in midlife,” said  Dr. Sudha Seshadri, associate professor of neurology at Boston University School of Medicine.  “This is especially true since SCIs have been associated with an increased risk of incident stroke and cognitive impairment.”  

The study, reported in the journal Stroke, was based on MRI data from 2,000 people with an average age of 62 who were children of the original Framingham Heart Study. Members of the second generation has had clinical exams every four to eight years.

Of those who had no symptoms, 10.7 percent had SCIs. More than four in five of those had a single lesion. Prior estimates of SCIs ranged from 5.8 percent to 17.7 percent depending on age, ethnicity and other factors. 

Risky Living
The study correlated the Framingham Stroke Risk Profile, which estimates the probability of having a stroke over the next decade, to prevalence of SCI for the first time. Factors considered in the profile include smoking, heart disease, blood pressure, diabetes and atrial fibrillation (AF) - the most common type of heart arrhythmia. All the factors were associated with SCI. 

“In our data, AF increased the risk of prevalent SCI more than two-fold,” said Seshadri, who co-authored the paper with 13 other researchers. The work was funded by the National Heart, Lung and Blood Institute; the National Institute on Aging; and the National Institute of Neurological Disorders and Stroke.

Stroke and AF have the same risk factors. So people with high blood pressure that may cause AF also can lead to stroke, meaning AF may be a result of SCI rather than a cause. It isn't clear if screening for AF would help predict strokes.

The risk wasn't affected much by age or gender, but the study found hypertension and high levels of homocysteine - a sulf-containing amino acid - in the blood increased the risk. Most of those in the study were of European descent, so there were no findings on how race may play a role.