Epidemiology of Transient Ischemic Attacks Using Time- or Tissue-Based Definitions

Available crude annual incidence rates of transient ischemic attack (TIA) range between 29.0 and 61.0 cases per 100 000 in Western countries. TIA is a known predictor of subsequent ischemic stroke with risk estimates within 3 months ranging between 7.5% and 17.3%; a half of those events were described to occur within 48 hours. TIA epidemiology may have changed in recent years as a consequence of improved identification and treatment of vascular risk factors. According to the traditional time-based definition, TIA is a focal neurological dysfunction of brief duration, presumed to be of vascular origin and confined to an area of the brain or eye perfused by a specific cerebral artery and of a duration <24 hours. Several studies have shown that diffusion-weighted imaging (DWI) alterations in clinically appropriate locations are present in about one third of patients with transient neurological symptoms, suggesting that the 24-hour criterion may allow the inclusion of patients with an acute ischemic cerebral tissue injury. A redefinition of TIA has alternatively been proposed. According to this tissue-based definition, TIA is a transient episode of neurological dysfunction caused by focal brain, spinal cord or retinal ischemia, without acute infarction. So far, to the best of our knowledge, no attempts were made to test the applicability of this definition in population-based studies. We, therefore, performed a prospective population-based study to obtain data on TIA incidence and prognosis according to the traditional time-based definition. We also deemed useful to evaluate if the tissue-based TIA definition was suitable for the same context.