The patient should undergo carotid ultrasonography. He most likely has experienced a transient ischemic attack (TIA), which implies the absence of retinal or cerebral infarction. His ABCD2 score, which is based on a patient's Age, Blood pressure, Clinical presentation, Duration of symptoms, and the presence of Diabetes mellitus, is 2 (one point for elevated blood pressure and one point for the symptom of slurred speech), which indicates a 2-day stroke risk of 1.3%. The antecedent transient monocular blindness in the left eye is concerning for extracranial atherosclerosis of the internal carotid artery. Hospital admission is recommended for all patients with TIAs who have an ABCD2 score of 3 or greater to expedite diagnostic testing and stroke subtyping; admission is also recommended for patients with a score of 0 to 2 if rapid outpatient evaluation cannot be performed.
Carotid ultrasonography to evaluate for symptomatic extracranial internal carotid artery stenosis is the most appropriate next diagnostic test in this patient with a TIA, given the high risk of early recurrence. Patients with greater than 70% extracranial internal carotid artery atherosclerotic stenosis have the highest risk of stroke in the 2 weeks after a TIA. Carotid Duplex ultrasonography is noninvasive and can effectively rule out significant atherosclerotic disease. If the ultrasound suggests greater than 50% stenosis, hospital admission and a confirmatory test with magnetic resonance or CT angiography is appropriate, with plans for early revascularization. Rapid cardiac testing with transthoracic echocardiography and cardiac rhythm evaluation also is advised within 24 hours for all patients with suspected TIA, as is vascular imaging of the extracranial carotid arteries.
CT angiography of the neck is inappropriate at this point because extracranial internal carotid artery stenosis can be excluded without exposing the patient to a highly invasive procedure with contrast and radiation.
Although an MRI of the brain can distinguish a TIA from an ischemic stroke and reveal infarcts in other arterial territories, it is inappropriate as the next diagnostic test in this patient because results are unlikely to affect immediate management. In addition, MRI may not be readily available and may be contraindicated in some patients.
Transesophageal echocardiography may be indicated to identify embolic sources of a TIA or stroke in patients in whom noninvasive diagnostic testing has been unrevealing. However, the yield of transesophageal echocardiography is low (approximately 1%) in patients who are in sinus rhythm, particularly among those older than age 45 years. Although MRI ultimately may be indicated for this patient, appropriate noninvasive testing should be performed first, including cardiac rhythm evaluation and vascular imaging of the carotid arteries.