The causes and risk of stroke in patients with asymptomatic internal-carotid-artery stenosis

Background: The causes of stroke in patients with asymptomatic carotid-arte ry stenosis have not been carefully studied. Information about causes might influence decisions about the use of carotid endarterectomy in such patien ts. Methods: We studied patients with unilateral symptomatic carotid-artery ste nosis and asymptomatic contralateral stenosis from 1988 to 1997. The causes , severity, risk, and predictors of stroke in the territory of the asymptom atic artery were examined and quantified. Results: The risk of stroke at five years after study entry in a total of 1 820 patients increased with the severity of stenosis. Among 1604 patients w ith stenosis of less than 60 percent of the luminal diameter, the risk of a first stroke was 8.0 percent (1.6 percent annually), as compared with 16.2 percent (3.2 percent annually) among 216 patients with 60 to 99 percent st enosis. In the group with 60 to 99 percent stenosis, the five-year risk of stroke in the territory of a large artery was 9.9 percent, that of lacunar stroke was 6.0 percent, and that of cardioembolic stroke 2.1 percent. Some patients had more than one stroke of more than one cause. In the territory of an asymptomatic occluded artery (as was identified in 86 patients), the annualized risk of stroke was 1.9 percent. Strokes with different causes ha d different risk factors. The risk factors for large-artery stroke were sil ent brain infarction, a history of diabetes, and a higher degree of stenosi s; for cardioembolic stroke, a history of myocardial infarction or angina a nd hypertension; and for lacunar stroke, age of 75 years or older, hyperten sion, diabetes, and a higher degree of stenosis. Conclusions: The risk of stroke among patients with asymptomatic carotid-ar tery stenosis is relatively low. Forty-five percent of strokes in patients with asymptomatic stenosis of 60 to 99 percent are attributable to lacunes or cardioembolism. These observations have implications for the use of enda rterectomy in asymptomatic patients. Without analysis of the risk of stroke according to cause, the absolute benefit associated with endarterectomy ma y be overestimated. (N Engl J Med 2000;342:1693-700.) (C) 2000, Massachuset ts Medical Society.