Underestimation of the early risk of recurrent stroke - Evidence of the need for a standard definition

Background - There is considerable variation in the definitions used for recurrent stroke. Most epidemiological studies exclude events within the first 28 days (eg, Monitoring Trends and Determinants in Cardiovascular Disease [MONICA]) or events within 21 days in the same territory as the presenting event ( eg, most stroke incidence studies). However, recurrence is most common during this early period and these restrictive definitions could underestimate the benefits of early prevention. Methods - We determined the 90-day risk of recurrence after incident ischemic stroke in 2 population-based cohorts ( Oxford Vascular Study [OXVASC] and Oxfordshire Community Stroke Project [OCSP]) with the 3 most common definitions: any stroke greater than or equal to24 hours after the incident event excluding early deterioration not caused by a stroke ( definition A); as above, but excluding any stroke within 21 days in the same territory as the incident event ( definition B); and any stroke greater than or equal to28 days after the incident event ( definition C). Results - 657 patients had 93 recurrent strokes between 24 hours and 90 days after the incident event. The 90-day recurrence risks (95% CI) using definition A were 14.5% (11.5 to 17.5) in the OCSP and 18.3% (10.8 to 25.8) in the OXVASC. The equivalent risks using definitions B and C were 8.3% (5.9 to 10.8) and 4.8% (2.8 to 6.7), respectively, in the OCSP and 7.0% (1.6 to 12.4) and 5.9% (1.0 to 10.9) in the OXVASC. The definition A risk of recurrence was particularly high after partial anterior (22.9%, 17.5 to 28.2) and posterior (19.5%, 13.0 to 25.9) circulation strokes. Conclusions - The 3 most widely used definitions of recurrent stroke yield markedly different 90-day risks. We suggest that, where possible, definition A be adopted as the standard to avoid underestimation of risk and to allow valid comparison of different studies.