Nationwide Trends in Incidence of Stroke and Transient Ischemic Attack in Younger and Older Adults in Norway 2001 to 2021.

BACKGROUND: There is conflicting evidence on the time trends of stroke incidence in younger adults. We aimed to explore time trends in the incidence of stroke, stroke subtypes, and transient ischemic attack in different age groups in Norway the past 2 decades. METHODS: In this nationwide registry-based cohort study, we identified incident stroke cases from hospitalizations with stroke (ischemic stroke, intracerebral hemorrhage and unspecified stroke), transient ischemic attack, or out-of-hospital deaths due to stroke. Included individuals were aged ≥15 years with no prior hospitalization for stroke during the past 7 years. Incidence per 100 000 population was age-standardized and presented by year, sex, and age group. Average annual percentage changes in incidence were estimated using weighted log-linear regression. RESULTS: From 2001 to 2021, we identified 229 857 incident total stroke cases (49.2% women) among 5 691 495 individuals in the Norwegian adult population. Incidence per 100 000 population decreased over time for all stroke subtypes in both men and women. However, the incidence of ischemic stroke for men aged <35 years increased annually by 1.6% (95% CI, 0.3-2.8). For intracerebral hemorrhage, the incidence was stable in younger men and women and the oldest women. For transient ischemic attack, both sexes experienced a sharp rise in the incidence until 2012, followed by a substantial decrease. CONCLUSIONS: Total stroke incidence declined from 2001 to 2021. However, less favorable time trends were observed in younger age groups, with a worrisome increase in ischemic stroke incidence among men aged 15 to 34 years. These trends are concerning and need further investigation.