A warning or mini-stroke occurs before one in every eight strokes, according to an Ontario study.

A transient ischemic attack or TIA is a mild stroke that causes stroke symptoms such as sudden numbness of the face, arm or leg. The symptoms last for less than 24 hours and then resolve on their own without disabling neurological effects.

Dr. Daniel Hackam of the University of Western Ontario in London, Ont., and his colleagues analyzed all patients hospitalized with a diagnosis of stroke between July 2003 and September 2007.

Stroke warning signs

  • Weakness, numbness or tingling in face, arms or legs, especially on one side of the body.
  • Trouble speaking or understanding speech.
  • Sudden blurring, double vision or loss of vision.
  • Sudden severe headache.
  • Dizziness, loss of balance.

Of the 16,400 patients reviewed, 2,032, or 12.4 per cent, had a TIA prior to the stroke that landed them in hospital, the team reported in Tuesday's issue of the journal Neurology.

"These results illustrate the need for better risk assessment tools for preventing strokes before they occur," Hackam said in a release.

"Other studies have shown that up to 80 per cent of strokes after TIA can be prevented when risk factors are managed intensively."

Go to emergency for minor stroke

People who did not have a TIA were more likely to have a more serious stroke than those who did have a warning stroke.

Among those with no warning stroke, 15.2 per cent died while in hospital compared with 12.7 of those who had a TIA. People who had strokes without a warning were also more likely to have a heart attack in hospital, 4.8 per cent, compared with 3.1 per cent among the other group.

People who had a warning stroke tended to be older and more likely to have diabetes, high blood pressure and heart problems.

It's possible that the blood vessels in people with warning strokes were "preconditioned to the lack of blood flow," which protected them from the full damage caused by the larger stroke, Hackam said.

He urged anyone who experiences a minor stroke to get to an emergency room immediately.

A study by researchers in Calgary in 2007 concluded that patients who have mini-strokes often suffer serious strokes within 48 hours. For every 25 TIA patients treated with drug therapy, one stroke may be prevented — but timing is crucial.

The study was supported by the Canadian Institutes of Health Research and Ontario Ministry of Health and Long-Term Care.