February 12, 2000
Johns Hopkins scientists report a new way of monitoring brain damage that could significantly increase the number of stroke patients eligible for -- and helped by -- clot-breaking treatments.
At today's meeting of the American Stroke Association in New Orleans, neurologist Argye Hillis, M.D., explained how a quickly given battery of cognitive tests, combined with a rapid, readily available type of MRI scan, can single out stroke patients who would likely benefit from new techniques that restore brain blood flow.
"The method looks as though it will let us identify patients who still have salvageable brain tissue, in whom we might be able to recover brain function," says Hillis.
A quick and easy measure of salvageable tissue has been neurologists' goal ever since TPA (tissue plasminogen activator) and similar clot-breaking drugs appeared for stroke about a decade ago. For all the drugs' publicity, the number of eligible patients has remained surprisingly small --about 1 percent of those who get to the hospital.
To be both safe and effective, the clot-breaking drugs must be given during a "treatment window" within three hours of the stroke's onset, when actual brain tissue death is at its lowest point. Patients unlikely to benefit from the clot-breaking drugs have large areas of dead tissue, says Hillis, and it's the proportion of potentially salvageable "distressed" tissue to dead tissue that's important in deciding whether to try to restore blood flow.
"In some patients the amount of brain that's died is tiny, but they still have huge problems, for example, in comprehension or speech," she adds. "Those are the ones who may be helped, and they don't always fall right within the three-hour limit."
Hillis and a team of researchers administered simple cognitive tests, such as object naming, word reading and word-picture matching, to 40 stroke patients within12 hours of the onset of their symptoms. The tests were easy to give, says Hillis; she generally trotted alongside patients' gurneys, questioning them en route to the MRI suite.
The team compared results of the tests with images of the patients' brains taken through MR perfusion imaging, a type of MRI (magnetic resonance imaging) that highlights tissue "distressed" because of low oxygen and nutrients. The researchers also used a second MRI technique -- MR diffusion weighted imaging --that reveals brain tissue that has died.
The results show that the simple cognitive tests accurately reflect overall brain damage – in both dead and distressed tissue. By combining the tests with the MR diffusion scans, Hillis says, you get a picture of how much tissue is dead and how much is probably salvageable. "We believe the two together could help plan therapy quickly," says Hillis.
The cognitive tests could also help monitor treatment, she adds. The patients whose blood flow was therapeutically restored showed marked improvement in the tests.
Some patients ineligible for TPA might be candidates for other blood-restoring therapies, says Hillis, such as temporarily increasing blood pressure or carotid endarterectomy, a technique that surgically clears narrowing or blockage in the major neck artery to the brain.
"We're planning further studies to see how long people have salvageable tissue," says Hillis. Some stroke patients have regained brain functions when their circulation is restored as much as a week after stroke onset. The study was funded by the National Institute on Deafness and Communications Disorders and the National Stroke Association. Other researchers were Robert Wityk, M.D., Peter Barker, Ph.D., Norman Beauchamp, M.D., and Barry Gordon, M.D., Ph.D.
Related Web sites: http://www.amhrt.org/catalog/Stroke_catpage30.html for a discussion of various current stroke therapies.
The researchers have online files available showing clear scans of brain sections affected by stroke, distinguishing between dead and "distressed" tissue. Interviews with stroke patients can be arranged.