Long-Term Risk of Dementia After TIA: A Population-Wide Matched Cohort Study

Long-term risk of dementia after TIA remains poorly characterized, despite a known impact on cognition. We aimed to quantify the rate, relative risk, and time course of incident dementia after TIA compared with a matched reference population (controls) and individuals with stroke.

We conducted a population-wide cohort study using linked administrative health data for the province of Ontario, Canada (2002-2022). Adults with a first TIA were identified from emergency department visits or hospital admissions and followed from 90 days after the index event. Individuals with prior dementia, prior stroke, early death, or long-term care admission were excluded. Patients with TIA were matched to population controls on age, sex, neighborhood-level deprivation, rurality, and vascular comorbidities. Patients with TIA were also matched to those with first stroke. Incident dementia was ascertained using a validated algorithm based on hospital diagnoses, physician claims, and dementia-specific medications. Cause-specific and subdistribution hazard models accounting for competing risk of death were used for 1-, 5-, and 10-year risk of dementia, with time-varying analyses.

Among 113,081 matched patients with TIA (mean age 70 years; 50% female), dementia was diagnosed in 19.3% over a mean follow-up of 7.11 years (SD 5.16). Dementia rates after TIA were consistently higher than in matched controls across all time horizons (overall rate 2.71 vs 2.03 per 100 person-years). The hazard ratio for dementia after TIA was highest within the first year (hazard ratio [HR] 1.75, 95% CI 1.66-1.85) and remained elevated over 20 years of follow-up (overall HR 1.34, 95% CI 1.31-1.36). Compared with stroke, the hazard of dementia was lower after TIA early on (1-year HR 0.67, 95% CI 0.64-0.70) but converged and became similar after 5 years of follow-up. Dementia incidence substantially exceeded stroke incidence, and adjustment for incident stroke minimally attenuated results.

TIA is associated with a large and sustained increase in dementia risk, approaching that observed after stroke over long-term follow-up. Dementia occurs far more frequently than incident stroke after TIA, highlighting cognitive decline as a major long-term complication and a target for prevention with new strategies that include and extend beyond stroke prevention.