Incidence of transient ischemic attacks in Oxfordshire, England

The Oxfordshire Community Stroke Project is a prospective register of all new cases of stroke and transient ischemic attack (TIA) in a population of 105,000 residents of Oxfordshire, England. Between November 1, 1981, and October 31, 1986, 184 patients presented for the first time to a general practitioner or hospital with a TIA. The crude annual incidence rate was 0.35/1000, 0.42/1000 standardized to the 1981 population of England and Wales. We estimate that each year approximately 21,000 patients in England and Wales (about half of whom are greater than 70 years old) consult a doctor for the first time with a TIA. Approximately 80% of our 184 patients had TIAs in the carotid distribution; the remainder had TIAs in the vertebrobasilar distribution or TIAs of uncertain vascular distribution. The incidence of TIA increased sharply with increasing age, and the overall incidence in men was very similar to that in women (incidence ratio 1.3). However, in middle age, men were much more likely to suffer a TIA than women (odds ratio 2.6), which probably explains the marked male predominance in most hospital-based studies and treatment trials in which the elderly, and thus women, are underrepresented. This has important implications for the design and interpretation of clinical trials of treatment for TIAs.