Redefinition of transient ischemic attack improves prognosis of transient ischemic attack and ischemic stroke: an example of the will rogers phenomenon.

BACKGROUND AND PURPOSE The recent redefinition of transient ischemic attack (TIA) reclassifies patients with acute infarction on magnetic resonance imaging as ischemic stroke. Redefinition will improve the prognosis of both TIA and ischemic stroke, an epidemiological paradox known as the Will Rogers phenomenon. We sought to quantify the impact of this phenomenon. METHODS Incidence of TIA, risk of death/disability after stroke, rate of acute infarction on magnetic resonance imaging after TIA, and 90-day stroke risk after TIA with and without infarction on magnetic resonance imaging were determined based on published data. The impact on poststroke disability in the redefined cohort of patients with ischemic stroke was computed. A sensitivity analysis was performed to account for uncertainty in input variables. RESULTS Using the new TIA definition, the 90-day risk of stroke following TIA is 1%. In the United States, redefinition will increase annual ischemic stroke incidence from 691,650 to 747,755 and result in a 3.4% absolute reduction in poststroke disability. In a sensitivity analysis, this risk reduction varies from 1.5 to 6.5%, and is most dependent on the incidence of TIA. CONCLUSIONS Redefinition of TIA reduces stroke risk after TIA to approximately 1% at 90 days, and reduces the rate of poststroke disability by approximately 3.4%.