Incidence and Post-Stroke Survival in the Normandy Stroke Population-Based Study (2017-2022): Impact of Time-Based Versus Tissue-Based Definitions

OBJECTIVES: The 11th edition of the International Classification of Diseases (ICD-11) incorporates a tissue-based definition of stroke and may alter estimates of incidence and outcomes. We assessed whether transitioning from a time-based to a tissue-based definition introduces age-dependent changes in stroke incidence and post-stroke survival. METHODS: The Normandy Stroke Study is a population-based study using multiple overlapping sources to identify stroke cases in Caen-Normandy-Metropole, France. Events occurring between May 15, 2017, and December 31, 2022, were classified using time-based (symptoms ≥24 hours) and tissue-based definitions (symptoms ≥24 hours or <24 hours with neuroimaging evidence of ischemic injury). RESULTS: Among 3,826 first-ever strokes meeting the tissue-based definition, median (IQR) age was 76 (64-85) years, and 1,932 (50.5%) were female. The age-standardized incidence rate of stroke (95% CI) was 161 (156-166) per 100,000 person-years (ESP2013), including 132 (128-137) for ischemic or undetermined stroke, 22 (20-24) for intracerebral hemorrhage, and 7 (6-8) for subarachnoid hemorrhage. Three-year mortality was 36.4% (95% CI 34.9-38.0). Compared with the time-based definition, the tissue-based definition increased stroke incidence by 6.5% and reduced 3-year mortality by 3.9%. The impact of the tissue-based definition on stroke incidence was greater at younger ages (all strokes: younger than 55 years = +8.5%; 55 years or older = +6.0%; ischemic stroke: younger than 55 years = +12.5%; 55 years or older = +7.3%). DISCUSSION: Adoption of a tissue-based definition modestly increased stroke incidence and post-stroke survival, with greater impacts at younger ages. Implementation of ICD-11 may introduce age-related differences in temporal trends, highlighting the importance of consistent definitions in stroke surveillance.