Noninvasive Carotid Artery Testing

TO THE EDITOR:

We enjoyed the recent article by Blakeley and colleagues [1]. We were surprised, however, that they did not discuss functional nuclear noninvasive tests. In an era of cost-consciousness, functional imaging is becoming increasingly important for patient management, and general internists should be kept abreast of these available tests. In recent years, noninvasive functional perfusion imaging of the brain with carbon dioxide or acetazolamide challenge using single-photon emission computed tomography (SPECT) has been widely investigated for detecting substantial carotid disease and its functional effects on the brain [2-5]. These tests are similar to myocardial perfusion imaging with thallium-201, with which pharmacologic stress tests are used to diagnose coronary artery disease. In the stress brain perfusion study, the patient is given a radiotracer for measurement of cerebral perfusion at a baseline state. This procedure is followed by another injection of radiotracer after carbon dioxide or acetazolamide challenge. The change in perfusion between these two studies indicates the cerebral vasomotor reserve. Those who are at risk for stroke show decreased vasomotor reserve.

In patients who have had a transient ischemic attack, even baseline cerebral perfusion SPECT imaging is clinically helpful in predicting outcome. In a study of 12 patients who had transient ischemic attacks, 3 of 4 patients (75%) who had abnormal baseline cerebral SPECT imaging results after these attacks had a stroke within 3 to 7 days, whereas none of the 8 patients with normal brain SPECT results had a stroke as late as 1.5 to 8 months of follow-up [4]. It is expected that this noninvasive nuclear cerebral perfusion test, which has a cost similar to that of magnetic resonance angiography, will become more influential in the management decision for significant carotid disease. This nuclear cerebral perfusion test does not have the limitations of procedures mentioned in the review article [1]. The test has the additional advantage of directly visualizing the cerebral perfusion effects of substantial unilateral carotid stenosis, the relative importance of bilateral carotid disease, and intracranial vascular disease. Although the authors claimed that noninvasive tests cannot replace invasive angiography for surgical candidates, it should be noted that the nuclear stress brain SPECT study is the only comprehensive noninvasive test for carotid artery disease that can supplement angiography with important additional information on the status of cerebral perfusion to help in the decision-making process for revascularization [5].

• Copyright ©2004 by the American College of Physicians