Posted by Carla Rothaus
What neuroimaging test is preferred for suspected TIA?
Approximately 20 to 25% of ischemic strokes are heralded by transient ischemic symptoms. Read the NEJM Clinical Practice Article here.
Q: What is the new definition of transient ischemic attack (TIA)?
A: An older, time-based definition of TIA (based on symptoms lasting <24 hours) has been revised owing to the identification of an infarct on brain imaging in many patients with symptoms that last more than 10 minutes and given that many patients who arrive at the hospital within 6 hours after the onset of symptoms are considered for urgent revascularization. The new definition of TIA is now “tissue-based.” An ischemic lesion is not visible on brain imaging in a patient with TIA, and a patient with transient symptoms who has even a tiny ischemic brain lesion on imaging is considered to have had a minor ischemic stroke. Since TIA and minor ischemic stroke generally have the same clinical manifestations (except for neuroimaging findings) and management, they are clinically considered together.
Q: Describe the importance of prompt recognition of a TIA.
A: Symptoms of a TIA, if recognized as such, provide a critical opportunity to quickly find and treat the cause in order to prevent a devastating stroke. Without treatment, the risk of stroke is as high as 20% at 3 months, and most of this risk occurs within the first 10 days, particularly within the first 2 days. Observational data indicate that prompt clinical diagnosis and immediate preventive measures are associated with a decrease of up to 80% in the 3-month risk of stroke.
Morning Report Questions
Q: What neuroimaging test is preferred for suspected TIA?
A: Immediate diffusion-weighted imaging assessed with magnetic resonance imaging (MRI) is the current preferred test for patients with a suspected TIA, since its sensitivity in detecting brain ischemia is much higher than that with computed tomography (CT). In up to 50% of patients with suspected TIA, a bright spot on diffusion-weighted imaging indicates ischemia; this finding is particularly useful when the transient symptoms are of borderline significance or when the symptoms are atypical. Although CT of the head generally cannot be used to diagnose ischemia, when diffusion-weighted imaging is not available, CT should be performed to rule out another cause of the symptoms. If diffusion-weighted imaging is negative and there is a strong clinical suspicion of TIA, perfusion-weighted imaging may be performed during the same MRI examination; in 30% of cases, a focal perfusion deficit is identified in the brain area corresponding to the symptoms.
Q: Is the optimal antithrombotic strategy for patients with TIA still under investigation?
A: Randomized trials are needed to determine the best antithrombotic strategy for patients with TIA (or minor ischemic stroke). Dual antiplatelet therapy of aspirin and clopidogrel for 21 days is considered by many experts to be the standard of care, yet clopidogrel is less effective or not effective in patients who are carriers of CYP2C19 loss-of-function alleles (as many as 20 to 40% of the population, depending on ethnic group), and screening for clopidogrel resistance has not been validated for clinical use. Ongoing randomized trials involving patients with previous TIA or stroke are assessing the benefits and risks of ticagrelor, an alternative, directly-acting antiplatelet agent that does not need to be metabolized, in combination with aspirin, as compared with aspirin alone, triple antithrombotic strategies (a dual antiplatelet agent plus a short-term oral anticoagulant), and an intravenous tissue plasminogen activator in patients with intracranial large-vessel occlusion.
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