Magnitude and Time-Course of Dementia Risk in Stroke Survivors

BACKGROUND AND OBJECTIVES: Survivors of stroke are at high risk of dementia, but it is unclear whether this elevated risk is due to other confounding factors. We sought to determine the magnitude and time course of dementia risk after stroke with robust comparison with matched nonstroke populations in an entire province. METHODS: We conducted a population-wide analysis of over 15 million people in Ontario, Canada, between 2002 and 2022. Using linked administrative databases, we identified adults hospitalized for ischemic stroke, intracerebral hemorrhage, or acute myocardial infarction (AMI). We performed 1:1 matching of people with stroke to all residents of Ontario (reference population) without stroke and separately to those with AMI, on age, sex, rural residence, neighborhood deprivation, and vascular comorbidities. We calculated the incident rate per 100 person-years and hazard ratios (HRs) for all-cause dementia between 90 days after stroke and 1 year, 5 years, 10 years, and total follow-up and evaluated time-varying HRs. In sensitivity analyses, we adjusted for new stroke in follow-up and the cumulative number of health care encounters. RESULTS: Of 175,980 stroke survivors, 174,817 (99.3%) were successfully matched to people in the reference population and 151,673 (90%) were matched to those with AMI. Over a mean follow-up of 5.6 years (SD 4.71, maximum 20 years), a total of 32,621 (18.7%) were diagnosed with dementia after stroke compared with 21,929 (12.5%) in the Ontario reference population. The rate of dementia per 100 person-years over total follow-up time was higher after acute stroke compared with the reference population (3.34 vs 1.89) and the AMI cohort (3.19 vs 1.75). The HR of dementia was higher in those with stroke compared with the reference population (1.76, 95% CI 1.73-1.79) and the AMI cohort (1.82, 1.79-1.85). HRs varied across time, with over 2.5-fold increase in dementia risk within 1 year, decreasing to 1.5-fold at 5 years and 1.3-fold at 20 years after stroke. Estimates were similar in sensitivity analyses. Recurrent stroke was associated with 3-fold increased dementia risk. DISCUSSION: In this population-wide study, almost one-fifth of stroke survivors were diagnosed with dementia, with an 80% higher risk of dementia after robust matching to those without stroke. Targeted dementia prevention efforts in acute and chronic survivors of stroke are needed.