NEW YORK (Reuters Health) – While the risk of stroke after a transient ischemic attack (TIA) is highest in the first few days, stroke risk remains elevated even when the TIA was 5 years in the past, according to a paper in the February issue of Stroke.

At the University of Washington in Seattle, Dr. Bruce M. Psaty and colleagues analyzed participants in an ongoing population-based case-control study to estimate short-term and long-term relative risks of incident ischemic stroke associated with clinically diagnosed TIA.

Their data covered 1914 patients with incident ischemic stroke and 9874 controls. Two hundred fifteen stroke patients (11.2%) and 252 controls (2.5%) had histories of a clinically diagnosed TIA.

After adjustment for age, gender, hypertension status, and calendar year, the risk of ischemic stroke was 4.21-fold higher in patients who had a clinically diagnosed TIA at any time in the past, compared to individuals without a clinical diagnosis of TIA. After adjustment for additional ischemic stroke risk factors, the stroke risk in patients with a history of a TIA was still 3.85-fold higher.

The short-term relative risk of ischemic stroke in individuals with TIA was particularly high, with odds ratios ranging from 30.4 for TIA diagnosed less than 1 month before the index date to 18.9 for 1 to 3 months and 3.16 for 4 to 6 months.

Longer-term risks were moderately high, the researchers note, with odds ratios ranging from 1.88 to 4.70 in intervals encompassing 7 months to 5 years before the index date. The odds ratio was 1.87 when the most recent TIA had been diagnosed more than 5 years before the index date.

When the intervals from the most recent TIA to the index date were collapsed into 2 categories, the odds ratios for stroke were 22.2 for patients with a TIA no more than 3 months earlier, and 2.58 for patients whose TIA was 4 or more months in the past.

The risks did not differ significantly for younger and older age groups, for women versus men, or for nonhypertensive women versus hypertensive women, the investigators say. (They note that all of the men in the study had treated hypertension.)

“Based on our results,” the authors conclude, “the opportunity for more effective stroke prevention would appear to be greatest in the short term, within the first 3 months after TIA diagnosis, but prevention opportunities would likely persist through the long term, even 5 or more years after clinically diagnosed TIA.”

Reference:
Stroke 2010.