September 9th, 2011
Asymptomatic Carotid Stenosis: Medical Management or Revascularization?
Every so often, one of my patients with no history of stroke or transient ischemic attack asks my opinion on what to do about a carotid ultrasound — not ordered by me — showing high-grade stenosis. I am a general internist, and I don’t obtain these studies in patients without a history of cerebrovascular symptoms. Guidelines don’t endorse carotid screening in such patients, yet they end up getting screened in various ways: Some cardiologists and vascular surgeons routinely get carotid studies in their patients with coronary disease; some clinicians order ultrasound for patients with asymptomatic carotid bruits; some clinicians include routine carotid ultrasound inappropriately in their “syncope workup”; and companies offer direct-to-consumer ultrasound screening. Because many of these patients are told “you need surgery” or “you need stenting” as if there’s no choice in the matter, a brief look at asymptomatic carotid stenosis is warranted.
Two large randomized trials compared carotid endarterectomy (CEA) and medical therapy in patients with asymptomatic carotid stenosis — a North American study published in 1995 (JAMA 1995; 273:1421) and a European trial published in 2004 (Lancet 2004; 363:1491). In both trials, the 5-year risk for stroke (including perioperative stroke or death) was significantly lower with CEA than with medical therapy, but the difference was only about 5 percentage points (5%–6% vs. 11%–12%), and no benefit was seen in women (Curr Opin Neurol 2007; 20:58). Given the 2% to 3% rate of perioperative stroke or death, it took several years for the benefit of CEA to clearly surpass that of medical therapy.
Because medical therapy has improved since these trials were conducted, researchers have examined whether stroke rates in patients with asymptomatic carotid stenosis have declined during the past decade. In fact, rates have fallen to around 1% annually in medically treated patients (Stroke 2010; 41:e11 and Stroke 2009; 40:e573). Thus, we must ask whether CEA has any role in patients with asymptomatic carotid stenosis. Recently, researchers have proposed several imaging findings that might identify high-risk subgroups — plaque echolucency, plaque ulceration, and embolic signals on transcranial Doppler ultrasound of the ipsilateral middle cerebral artery.
In one study of 435 patients with asymptomatic carotid stenosis (>70% stenosis by ultrasound), only 10 patients (2%) had strokes during an average follow-up of 2 years (Neurology 2011; 77:751). However, 4 of these strokes occurred among the 27 patients with both echolucent plaque and embolic signals (15% stroke rate). In contrast, only 1.5% of patients without these 2 findings had strokes.
In another study of 253 patients with asymptomatic carotid stenosis (>60% stenosis by ultrasound), only 6 patients (2.5%) had strokes during an average follow-up of 3 years (Neurology 2011; 77:744). Three of these strokes occurred in the 42 patients with at least 2 carotid ulcerations (7%); in contrast, the stroke rate was only 1.4% in the 211 patients with one or no ulcers. In addition, the stroke rate was 13% in patients with embolic signals (2 of 15 patients) but only 1.7% in those without embolic signals (4 of 238 patients).
The most striking aspect of these 2 studies is their confirmation of a very low overall incidence of stroke — about 1% per year. Thus, many asymptomatic patients who now undergo CEA (or carotid stenting, which is not safer than CEA) are likely risking harm without commensurate benefit. The use of embolic signals and plaque characteristics to identify candidates for CEA is promising but requires larger numbers and assurance that the techniques are reliable in community settings. Editorialists argue for “intensified medical management rather than revascularization procedures in patients with asymptomatic carotid stenosis,” until strategies to identify high-risk patients have been thoroughly investigated (Neurology 2011; 77:710). I find their position, which happens to reinforce my previous thinking on this topic, to be compelling. What’s your point of view?