Fall 2005

Cognitive Function May Be Indicator of Stroke Risk

While a severe stroke can obviously strongly affect cognition, there has been little study of the effects of very small, "silent" strokes on cognitive ability. UCSF researcher Jacob Elkins, M.D., is working to bridge this knowledge gap with a series of studies.

"Stroke plays an important role in dementia, but it is now becoming clear that more subtle forms of vascular injury in the brain may play an equally important role in cognitive decline," Elkins says.

Studies of large populations of elderly patients show that about one-third of those 65 and older have had at least one brain infarction, most of which were never recognized clinically. These subclinical infarcts can accumulate over time and they appear to cause cognitive deterioration.

Elkins and his colleagues are interested in doing a careful study of the cognitive deterioration in these patients and finding correlations with these patients' cerebrovascular disease.

Traditionally, when someone suffers a stroke, it is his or her overall function rather than cognitive decline that is used as a measure of the severity of the stroke. Now, Elkins says, cognitive change is becoming a sensitive outcome measure in studies of stroke prevention and treatment.

"In other diseases, we know that subclinical changes in organ function warn us of disease risk," Elkins says. For instance, left ventricular hypertrophy is a sign of heart attack risk, he notes. "Similarly, we hope that tests of changes in cognitive function might allow us to assess the risk of having a clinically significant stroke," Elkins says.

Another important element of these studies is understanding why silent strokes have a big negative impact on some people, while others don't seem to be much affected, Elkins says. For instance, those with higher educational levels seem to be more resilient to stroke damage in cognition, but it is not clear why this is so.

"The thought is that lots of brain activity makes the brain healthier through use, possibly by increasing alternative neural pathways that can be used if one pathway is knocked out," Elkins says. Another possibility is that some people may have higher levels of certain growth factors that come into play to repair neural tissue after stroke. "In any case," Elkins says, "these naturally occurring differences in cognitive decline after stroke could give us insight into what we can do after stroke to reduce its effects and improve recovery."

Elkins and his colleagues have identified a group of Kaiser Permanente patients in their late 80s who have been with the health care program for over three decades. This group's extensive health histories — records of how well they have controlled their blood pressure, for instance — make them a valuable research population for studying how exposure to vascular risk factors affects cognition over a long period. "We also will be able to collect DNA and find out if there are genetic factors that account for why they have done so well," Elkins says.

"What we really want to do in the future is move from observational studies to prospective, randomized trials, so that we can really reduce cognitive decline among those with cerebrovascular disease," Elkins says. "That will likely provide the key confirmation that there are causal links between silent stroke and dementia."

To contact Dr. Elkins, call (415) 353-3677.

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