Long-term Incidence of Ischemic Stroke Following Transient Ischemic Attack: A Nationwide Study During 2014-2020.

Background: The short-term incidence of ischemic stroke after a transient ischemic attack (TIA) is high. However, data on the long-term incidence are not well known but are needed to guide preventive strategies. Methods: Patients with first-time TIA (index date) in the Danish Stroke Registry (January 2014-December 2020) were included and matched 1:4 with individuals from the background population and 1:1 with patients with a first-time ischemic stroke based on age, sex, and calendar year. The incidences of ischemic stroke and mortality from index date were estimated by Aalen-Johansen and Kaplan-Meier estimators, respectively, and compared between groups using multivariable Cox regression. Results: We included 21,500 patients with TIA, 86,000 patients from the background population, and 21,500 patients with ischemic stroke (median age 70.8 years [25th-75th percentile 60.8-78.7]: 53% men). Patients with TIA had more comorbidities than the background population, yet less than the control stroke population. The five-year incidence of ischemic stroke following TIA (6.1% [95% CI 5.7-6.5]) was higher than the background population (1.5% [95%CI 1.4-1.6], hazard ratio (HR) 5.14 [95%CI 4.65-5.69 ]), but lower than the control stroke population (8.9% [95%CI 8.4-9.4], HR 0.58 [95%CI 0.53-0.64]). The five-year mortality for patients with TIA (18.6 % [95%CI 17.9-19.3]) was higher than the background population (14.8% [95%CI 14.5-15.1 ], HR 1.26 [95%CI 1.20-1.32 ]), but lower than the control stroke population (30.1% [95% CI 29.3-30.9), HR 0.41 [95%CI 0.39-0.44]). Conclusions: Patients with first-time TIA had an ischemic stroke incidence of 6.1% during the 5-year follow-up period. Following adjustment for relevant comorbidities, this incidence was approximately five-fold higher than what was found for controls in the background population, and 40% lower than for patients with recurrent ischemic stroke.