Transient Ischaemic Attack Rarely Precedes Stroke in a Cohort with Low Proportions of Large Artery Atherosclerosis: A Population-Based Study

BACKGROUND: Ischaemic stroke is reportedly preceded by transient ischaemic attack (TIA) in 15–30$ of all cases. The risk of stroke following TIA is highest in the presence of unstable atherosclerotic plaques in large arteries. The recent population-based Adelaide Stroke Incidence Study describes a population with a low proportion (16$) of stroke attributable to large artery atherosclerosis (LAA). We hypothesized that this population-based ischaemic stroke cohort would have a lower rate of preceding TIA than previously reported. METHODS: This paper is a prospective ascertainment of all suspected TIAs and strokes in a 12-month period from 2009 to 2010. Ischaemic stroke pathogenesis was classified by the TOAST criteria. Details of preceding TIA events were scrutinised. RESULTS: In this 12-month period, 318 stroke events in 301 individuals were recorded. Of the total 258 ischaemic strokes, 16$ (95$ confidence interval [CI] 12–22) were from LAA. Of 258 ischaemic stroke patients, only 11 (4$; 95$ CI 2–7) reported symptoms in the preceding 90 days consistent with TIA. Nine (82$) sought medical attention. The median ABCD(2) score in this group was 4.5 (IQR: 3–7), and the median time of event prior to stroke was 20 days (IQR: 4–32). CONCLUSION: In our population-based cohort, rates of TIA preceding ischaemic stroke were much lower than previously reported, probably reflective of effective secondary prevention (active TIA clinics) and primary prevention (limiting LAA prevalence). In our population, further enhancements in TIA care will be of limited yield.