Wednesday, July 9, 2008

A 10% Prevalence of Silent Stroke Found in "Healthy" Adults

About 10% of apparently healthy middle-aged adults have experienced silent cerebral infarcts (SCI), according to the latest results from the Framingham Offspring Study. Furthermore, the study found risk factors typically associated with clinical stroke, including hypertension, elevated serum homocysteine, and carotid artery disease, are also associated with midlife SCI.

The study's findings are consistent with previous community-based studies, which have estimated the prevalence of SCI between 5.8% and 17.7%, depending on age, ethnicity, presence of comorbidities, and imaging techniques.
"Our study shows that, in a middle-aged population free of clinical disease, there is a distressingly high prevalence of subclinical disease, as evidenced by these silent infarcts, which we know increase the risk of clinical stroke and cognitive impairment," study investigator Sudha Seshadri, MD, from Boston University School of Medicine, in Massachusetts, told Medscape Neurology & Neurosurgery.
"These findings also reinforce the need for clinicians to aggressively detect and manage cardiovascular risk factors, perhaps even earlier than midlife," she added.
The study is published online June 26 in Stroke.
Atrial Fibrillation Link
In addition to the prevalence data, the investigators also found that stroke risk factors, including hypertension, elevated plasma homocysteine, carotid stenosis, and increased carotid artery intimal medial thickness, are also significantly associated with silent infarcts.
Another, somewhat surprising, finding, said Dr. Seshadri, was a significant link between atrial fibrillation (AF) and SCI, with the data revealing that AF increased the risk for prevalent SCI more than 2-fold.
According to Dr. Seshadri, this finding may be an indication that AF is a simultaneous outcome, rather than a cause of SCI.
"While it is possible that tiny emboli resulting from atrial fibrillation may be causing these silent infarcts, it is probable that some of the risk factors for AF are the same as those for SCI. Therefore, it may be that atrial fibrillation is a marker for silent infarcts, rather than a cause, and that the 2 conditions are occurring together," she said.
An offshoot of the Framingham Heart Study, a longitudinal study that began in 1948 with the goal of identifying common risk factors for cardiovascular disease, the Framingham Offspring Study, which began in 1971, includes the children and children's spouses of the original cohort.
With an average age of 62 years, the current sample included 2040 offspring who attended the sixth examination (1996-1998) and underwent volumetric brain magnetic resonance imaging (MRI) in 2001 and were free of clinical stroke.
In addition, subjects were assessed using the Framingham Stroke Risk Profile (FSRP), a validated instrument that predicts 10-year probability of incident stroke and includes age, systolic blood pressure, antihypertensive therapy, diabetes mellitus, cigarette smoking, cardiovascular disease, AF, and left ventricular hypertrophy.
Subjects also underwent carotid imaging and measurement of cholesterol concentrations as well as plasma homocysteine.
Need to Follow Guidelines
Among the 10.7% of study subjects who had MRI evidence of silent infarcts, 84% had a single lesion, most commonly located in the basal ganglia (52%). One third of the lesions were subcortical, and 10% were cortical lesions.
According to the study, the aggregate FSRP score was significantly associated with prevalent SCI. Of the FRSP variables, AF, hypertension, and systolic blood pressure were all associated with an increased risk for silent infarct.
Of the variables not included in the FRSP, plasma homocysteine, carotid stenosis of 25% or greater, and increased intimal medial thickness were also associated with a higher risk for prevalent SCI. Neither age nor sex modified the effect of any of the risk factors on SCI prevalence.
The finding that there is a link between elevated homocysteine may warrant consideration of including SCI as an outcome in future studies looking at the potential benefit of vitamin supplementation.
While the study's findings are not necessarily surprising, said Dr. Seshadri, they do underscore the need to follow guidelines for the early diagnosis and prevention of hypertension and atherosclerosis and their risk factors.
Unfortunately, she said, such guidelines have not been optimally implemented for a variety of reasons. "For instance, we know that over a lifetime, 9 out of 10 people will develop hypertension. When a condition is that common it tends to be regarded as the 'norm.' But we also know that the 10% of people who do not develop high blood pressure are healthier and live longer, better-quality lives. I would argue that even though a condition is regarded as the norm it should still be treated aggressively," she said.
The study was supported by the National Heart, Lung, and Blood Institute; the National Institute on Aging; and the National Institute of Neurological Disorders and Stroke. The study authors have disclosed no relevant financial relationships.
Stroke. Published online June 26, 2008.

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