Background: Incidence and predictors of ischemic stroke in patients with transient ischemic attack (TIA) have not been fully clarified outside Europe and North America. Aims: We undertook the present prospective, multicenter study to clarify the incidence, predictors, and etiology of ischemic stroke within one year of TIA onset in Japan. Methods: The study subjects were patients within seven days of TIA onset who were enrolled in a prospective register from 57 hospitals between June 2011 and December 2013. The primary endpoint was occurrence of ischemic stroke. Results: Of 1365 consecutive patients, 1245 were followed for one year after TIA onset; 101 (8.1%) experienced ischemic stroke during follow-up. The leading subtype of ischemic stroke was small-vessel occlusion (SVO) followed by large-artery atherosclerosis (LAA) attributable to intracranial artery diseases. When dividing ischemic stroke events between those occurring within the first 90 days after TIA onset and those occurring after the first 90 days, the leading subtype of ischemic stroke within the first 90 days after TIA onset was SVO, followed by LAA attributable to intracranial artery diseases. In comparison, the subtypes most commonly seen beyond the first 90 days after TIA onset were cardioembolic and LAA attributable to intracranial artery disease. The one-year risk of ischemic stroke increased significantly as ABCD2 score increased, at 6.2% for 0–3 points, 7.2% for 4–5 points, and 11.6% for 6–7 points. Conclusions: The one-year ischemic stroke risk after TIA was about 8% and was associated with the ABCD2 score. The most common subtype of subsequent ischemic stroke was SVO.
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