Design: Population-based stroke registry
Population: 3,826 first-ever strokes in Caen, France, 2017–2022
Primary outcome: Stroke incidence and three-year survival under time- vs tissue-based definitions
Effect: Tissue-based definition: incidence +6.5% overall, +12.5% for ischaemic stroke under 55

ICD-11 counts a transient event with imaging evidence of infarction as a stroke, rather than requiring symptoms for 24 hours or more. The Normandy Stroke Study applied both definitions to 3,826 first-ever strokes in Caen from 2017 to 2022.

The tissue-based definition raised measured stroke incidence by 6.5% and lowered three-year mortality by 3.9%, because the added events are milder. The increase was larger under 55 years: 12.5% for ischaemic stroke, against 7.3% in older people.

For clinicians, this means younger patients with brief symptoms and a positive scan are now classified, and should be managed, as stroke. For anyone reading trend data, an apparent rise in young stroke may partly be a change in definition.

Classify a transient event with imaging evidence of infarction as stroke, not TIA.
Manage these patients with full secondary prevention, as for any ischaemic stroke.
Expect more young patients to meet the stroke definition under ICD-11.
Interpret rising young-stroke statistics with the definition change in mind.

Why it matters

A coding change alters both individual labels and population trends.

The statistics, in plain English

A 6.5% increase in incidence means about 6 or 7 extra strokes counted per 100 under the old definition. These are milder events, which is why three-year mortality falls when they are included.