Intracranial atherosclerotic disease (ICAD) is the most common proximate mechanism of ischemic stroke worldwide. Approximately half of those affected are Asians. For diagnosis of ICAD, intra-arterial angiography is the gold standard to identify extent of stenosis. However, noninvasive techniques including transcranial ultrasound and MRA are now emerging as reliable modalities to exclude moderate to severe (50%–99%) stenosis. Little is known about measures for primary prevention of the disease. In terms of secondary prevention of stroke due to intracranial atherosclerotic stenosis, aspirin continues to be the preferred antiplatelet agent although clopidogrel along with aspirin has shown promise in the acute phase. Among Asians, cilostazol has shown a favorable effect on symptomatic stenosis and is of benefit in terms of fewer bleeds. Moreover, aggressive risk factor management alone and in combination with dual antiplatelets been shown to be most effective in this group of patients. Interventional trials on intracranial atherosclerotic stenosis have so far only been carried out among Caucasians and have not yielded consistent results. Since the Asian population is known to be preferentially effected, focused trials need to be performed to establish treatment modalities that are most effective in this population. 1. Introduction 1.1. Epidemiology Intracranial atherosclerotic stenosis of the major arteries (intracranial internal carotid artery, middle cerebral artery, vertebral artery, and basilar artery) is the most common proximate mechanism of ischemic stroke worldwide [1]. It causes 30% to 50% of strokes in Asians [2] and 8% to 10% of strokes in North American Caucasians [3]. Intracranial atherosclerotic disease, ICAD, defined as atherosclerosis of the large arteries at the base of the brain, preferentially affects Asians, Hispanics, Far East Asians, and Blacks as compared to carotid bifurcation disease [3–6]. Also, about 20%–45% of non-Caucasians with large artery disease have combined extracranial and intracranial lesions [7–10]. The prevalence of atherosclerotic stenosis by subtype and race is further reported in Table 1. Table 1: Prevalence of intracranial atherosclerotic disease/extracranial atherosclerotic disease by race. 2. Predisposing Factors for ICAD in Susceptible Populations 2.1. Racial Associations Sacco et al. [3] found no difference between races in the proportion of patients with extracranial atherosclerotic stroke, while intracranial atherosclerosis was seen more frequently in African American and Hispanic subjects than in Caucasian
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