In cohorts of younger patients (eg, age <45 years), vasculitis may account for 0% to 20% of stroke cases, depending on the depth of workup.705 In older population, the proportion of strokes caused by vas- culitis is smaller because of the increasing burden of aging-related risk factors. Vasculitis may cause stroke by directly causing brain arterial inflammation, which subsequently results in endothelial damage and pro- Alternatively, extracranial vascu- litis may cause stroke by promoting artery-to-artery embolism, flow obstruction attributable to endothelial thickening, or aneurysmatic wall damage.707 The over- all approach to treat vasculitis causing stroke is with immunosuppressants and antiplatelets, but the choice of immunosuppressant and regimens is specific to the type of vasculitis. Recommendation-Specific Supportive Text 1. Giant cell arteritis is a rare vasculitis (incidence rate, 9 16 per 100000 per year in individuals 50 years of age) that can cause stroke in 7% of confirmed cases.672 674 Patients with symptoms of giant cell arteritis should be treated urgently, and high-dose steroids should be initiated quickly within the first 24 hours after symptoms onset to reduce the risk of permanent blindness and to increase the chance of visual recovery.675 678 Practitioners should keep a high index of clini- cal suspicion to consider giant cell arteritis in the differential. Laboratory testing such as elevated sedimentation rate or C-reactive protein and a compatible semiology may be the only available elements to make a decision to initiate treat- If available, ultrasound finding of a halo sign surrounding a temporal artery may be helpful in diagnosis giant cell arteries.680,681 Biopsy con- firmation should not be imperative to initiate treat- ment in cases in which giant cell arteritis seems to be the most likely diagnosis. 2. 