One out of every eight strokes is preceded by a "warning stroke" called a transient ischemic attack, finds new Canadian research published inthe journal Neurology.

Doctors have long known about TIAs or "mini-strokes," but how often they affect patients who go on to have full strokes has not always been clear. It had been estimated that about 10 per cent who have a mini-stroke will have a full-blown stroke within three months. But this study suggests the numbers are higher.

Mini-strokes, or TIAs, have the same symptoms as a full blown stroke, including sudden weakness, slurred speech and difficulty walking. The symptoms last only minutes or hours and since people recover within a day, many don't take them seriously.

But doctors say patients who suffer mini-strokes should seek immediate medical treatment, because intensive treatment can prevent a larger stroke.

For the study, researchers looked at 16,400 patients who went to Ontario hospitals after having a stroke over four years. Among the patients, 2,032, or 12.4 per cent, reported having the symptoms of a TIA prior to a major stroke.

The good news is that patients who have had a TIA seem more likely to survive a larger stroke. The researchers found that those with no warning symptoms before a major stroke were:

  • more likely to die while at the hospital (15.2 per cent compared to 12.7 per cent)
  • more likely to have a heart arrest while in the hospital (4.8 per cent compared to 3.1 per cent)
  • less likely to be able to go home after the hospital stay, rather than to a nursing home or rehabilitation center (40.1 percent compared to 43.1 percent).

Those with the warning stroke were typically older than those without warning strokes. They were also more likely to have diabetes, high blood pressure and heart problems.

Doctors don't know why TIA survivors fare better than those stroke patients with no warning sign, but they have theories.

"It's possible that the blood vessels of those with warning strokes were preconditioned to the lack of blood flow, which protected them from the full result of the larger stroke," said study author Dr. Daniel G. Hackam, of the University of Western Ontario in London, ON.

"Any person who experiences even a minor stroke should get to the emergency room immediately."

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

Previous research has shown that up to 80 per cent of strokes after TIA can be prevented when risk factors are treated with clot-busting drugs, medications to control blood pressure and improve cholesterol, or surgery in some cases.

Anyone who has had a TIA are at a higher risk for having a stroke immediately after the TIA and for a year later.

According to the Heart and Stroke Foundation, the warning signs for a TIA are the same for a stroke; they are:

  1. Weakness - Sudden loss of strength or sudden numbness in the face, arm or leg, even if temporary.
  2. Trouble speaking - Sudden difficulty speaking or understanding or sudden confusion, even if temporary.
  3. Vision problems - Sudden trouble with vision, even if temporary.
  4. Headache - Sudden severe and unusual headache.
  5. Dizziness - Sudden loss of balance, especially with any of the above signs.