Background and purpose: The relative risk of ischemic stroke associated with transient ischemic attack (TIA) is not well defined because most studies of stroke after TIA did not include comparison groups. We sought to estimate short-term and long-term relative risks of ischemic stroke associated with clinically diagnosed TIA.
Methods: We used data from a population-based case-control study. Cases were hypertensive men and women and postmenopausal women, ages 30 to 79, with incident ischemic stroke. Control subjects were sampled within strata of age, sex, hypertension status, and calendar year. The index date was the stroke date for cases and a random date for control subjects. Clinically diagnosed TIA was ascertained from medical records. We used logistic regression to calculate ORs.
Results: The study included 1914 stroke cases and 9874 control subjects. Clinically diagnosed TIA was present in 215 (11.2%) cases and 252 (2.5%) control subjects. Analyses focused on the most recent TIA before the index date. For TIA <1 month before the index date, the adjusted OR for stroke was 30.4 (95% CI, 10.4 to 89.4); for TIA 1 to 3 months before the index date, it was 18.9 (8.58 to 41.6); for TIA 4 to 6 months before the index date, it was 3.16 (1.27 to 7.82); and for TIA >5 years before the index date, it was 1.87 (1.22 to 2.85).
Conclusions: The relative risk of ischemic stroke was high for TIA diagnosed within the past 3 months and moderately high for TIA diagnosed >5 years in the past compared with no history of clinically diagnosed TIA.