Low risk of ipsilateral stroke in patients with asymptomatic carotid stenosis on best medical treatment: a prospective, population-based study.

BACKGROUND AND PURPOSE: The annual risk of ischemic stroke distal to > or =50% asymptomatic carotid stenoses was approximately 2% to 3% in early cohort studies and subsequent randomized trials of endarterectomy. This risk might have fallen in recent years owing to improvements in medical treatment, but there are no published prognostic data from studies initiated within the last 10 years. METHODS: In a population-based study of all patients with transient ischemic attack (TIA) or stroke in the Oxford Vascular Study, we studied the risk of TIA and stroke in patients with > or =50% contralateral asymptomatic carotid stenoses recruited consecutively from 2002 to 2009 and given intensive contemporary medical treatment. RESULTS: Of 1153 consecutively imaged patients presenting with stroke or TIA, 101 (8.8%) had > or =50% asymptomatic carotid stenoses (mean age, 75 years; 39% women; 40% age > or =80 years). During 301 patient-years of follow-up (mean, 3 years), there were 6 ischemic events in the territory of an asymptomatic stenosis, 1 minor stroke (initially 50% to 69% stenosis), and 5 TIAs (2 initially 50% to 69% stenosis; 3 to 70% to 99% stenosis), 3 of which led to subsequent endarterectomy. The average annual event rates on medical treatment were 0.34% (95% CI, 0.01 to 1.87) for any ipsilateral ischemic stroke, 0% (95% CI, 0.00 to 0.99) for disabling ipsilateral stroke, and 1.78% (95% CI, 0.58 to 4.16) for ipsilateral TIA. CONCLUSIONS: In the first study of the prognosis of > or =50% asymptomatic carotid stenosis to be initiated in the last 10 years, the risk of stroke on intensive contemporary medical treatment was low. Larger studies are required to determine whether this apparent improvement in prognosis is generalizable.