The risk of a full-blown stroke will remain high for at least a decade after a person has a slight brush with stroke, in the form of a transient ischemic attack or minor stroke, a new study says.

These patients have a nearly 13% increased risk of stroke over five years and a 20% increased risk over a decade, researchers report in the Journal of the American Medical Association.

"What was surprising to us is actually the magnitude of that risk beyond 90 days," researcher Faizan Khan, a postdoctoral fellow at the University of Calgary, told tctMD, a news service of the Cardiovascular Research Foundation.

"Given that most secondary prevention clinics only follow their patients for the first 90 days, we hope that our findings will … raise attention to this persistently high risk," he said.

A transient ischemic attack is a temporary blockage of blood flow to the brain, according to the American Stroke Association.

The clot causing the block typically dissolves on its own or is dislodged, with symptoms usually lasting less than five minutes.

A TIA doesn't cause permanent damage, but it's considered a "warning stroke" that shows a full-blown stroke could be in the offing, the ASA says.

Symptoms of a TIA are similar to those of a full-fledged stroke, including weakness, numbness or paralysis on one side of the body; slurred speech; difficulty understanding others; blindness in one or both eyes; dizziness; or a severe headache for no apparent reason.

Clinical practice currently focuses on stroke risk within the first 90 days following a TIA or minor stroke, based on research showing that the risk of a subsequent stroke is high during that period, researchers said in background notes.

However, studies have not conclusively evaluated the longer-term risk that these near-misses with stroke pose to a person's brain, researchers said.

To evaluate that risk, researchers pooled data from 38 prior studies involving more than 171,000 patients who suffered either a TIA or a minor stroke and whose health was followed for at least a year.

Results show the risk of a stroke is about 6% more within a year, but rises to 13% at five years and 20% at 10 years.

A patient's 10-year risk of a clot-driven stroke is about 18% higher, and they are about 3% more likely to suffer a fatal stroke within a decade, results show.

These results indicate that doctors should consider a TIA or minor stroke as a flashing red-light warning that a more serious stroke could be on its way, senior researcher Dr. Michael Hill, a professor of medicine at the University of Calgary, told tctMD.

"This is the time to pay attention and fix it, and fix it for good," Hill said.

--Dennis Thompson