Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 49-year-old-man is evaluated 1 day after having an episode of right arm weakness without pain that lasted 5 minutes. He is now asymptomatic. The patient has type 2 diabetes mellitus and dyslipidemia. Medications are aspirin, metformin, and atorvastatin.

On physical examination, blood pressure is 126/68 mm Hg, pulse rate is 86/min and regular, and respiration rate is 12/min. No carotid bruits or cardiac murmurs are heard on cardiac auscultation. All other physical examination findings are normal.

An electrocardiogram shows normal sinus rhythm with no ST-segment or T-wave changes.

Which of the following is the most appropriate initial imaging test?

A. Carotid duplex ultrasonography
B. CT angiography of the neck
C. MRI of the brain
D. Transesophageal echocardiography

MKSAP Answer and Critique

The correct answer is A. Carotid duplex ultrasonography.

This patient should have carotid duplex ultrasonography. He most likely has had a transient ischemic attack (TIA) referable to the left hemisphere and is at risk of ischemic stroke within the next 90 days, with the highest risk occurring within the first 2 days. Although his ABCD² score (based on patient Age, Blood pressure, Clinical presentation, Duration of symptoms, and presence of Diabetes mellitus) of 3 indicates a predicted stroke risk of 1.3% and the need for hospitalization and rapid evaluation, these scores are neither sensitive nor specific enough to identify patients at highest risk of stroke. Several studies have identified extracranial symptomatic internal carotid artery stenosis as an indicator of stroke risk of greater than 70% after TIA; this risk can be modified with carotid revascularization. Several modalities are available for imaging the internal carotid artery and identifying extracranial symptomatic stenosis, including duplex ultrasonography, CT angiography, and magnetic resonance angiography (MRA). Duplex ultrasonography has the benefit of being inexpensive, readily available, low risk, and noninvasive and thus is an appropriate early study. If the carotid duplex ultrasound shows high-grade stenosis, confirmation of this finding by CT angiography or MRA is required before surgical intervention. If the carotid duplex ultrasound is unrevealing, then additional vessel imaging of the neck is unnecessary.

CT angiography of the neck is more costly and less widely available than carotid duplex ultrasonography. Additionally, the radiation exposure makes CT angiography less desirable as an initial imaging test.

Brain MRI is not the initial test of choice because the presence or absence of a cerebral infarct will not immediately change medical management or affect the patient’s stroke risk. Cerebral imaging with either CT or MRI eventually may be required in this patient but should occur after an evaluation of the internal carotid artery that may lead to hospitalization and surgical intervention.

In patients with risk factors for stroke after a TIA, transesophageal echocardiography is (TEE) is unlikely to immediately change management, is invasive, and has low yield for finding an embolic source of stroke in patients who are in sinus rhythm. TEE can be considered in certain patients with stroke if they are young and have no apparent risk factors for stroke or if unusual causes are suspected, such as cardiac tumor, patent foramen ovale, aortic arch atherosclerosis, or endocarditis.

Key Point

• In a patient with a transient ischemic attack, carotid duplex ultrasonography is an inexpensive, readily available, and noninvasive imaging modality for identifying high-grade stenosis and the possible need for surgery.

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