Long-Term Incidence of Ischemic Stroke After Transient Ischemic Attack: A Nationwide Study From 2014 to 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 on the basis of 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]; 53.1% males). Patients with TIA had more comorbidities than the background population, yet less than the control stroke population. The 5-year incidence of ischemic stroke after TIA (6.1% [95% CI, 5.7-6.5]) was higher than the background population (1.5% [95% CI, 1.4-1.6], P<0.01; hazard ratio, 5.14 [95% CI, 4.65-5.69]) but lower than the control stroke population (8.9% [95% CI, 8.4-9.4], P<0.01; hazard ratio, 0.58 [95% CI, 0.53-0.64]). The 5-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], P<0.01; hazard ratio, 1.26 [95% CI, 1.20-1.32]) but lower than the control stroke population (30.1% [95% CI, 29.3-30.9], P<0.01; hazard ratio, 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. After adjustment for relevant comorbidities, this incidence was approximately 5-fold higher than what was found for controls in the background population and 40% lower than for patients with recurrent ischemic stroke.