Biomarkers, Natural Course and Prognosis.

Increasing our knowledge about intracranial atherosclerosis (ICAS) natural history and prognostic factors is essential to improve its preventive therapy and thus reduce the dramatic clinical consequences caused by this entity. ICAS is characterized by a chronic and progressive course until it becomes symptomatic, mostly through complication of an unstable intracranial atherosclerotic plaque. Population-based studies in healthy subjects have shown that the prevalence of asymptomatic ICAS is higher in Asian than in Caucasian populations. In both settings, asymptomatic ICAS is associated with classical vascular risk factors and with the metabolic syndrome, and it is burdened with an increasing risk of having incident stroke and cognitive impairment. When it reaches its symptomatic stage, ICAS is a dynamic and aggressive condition, and affected patients are at high risk of having recurrent stroke and other major vascular events. The Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis (SAMMPRIS) trial has recently shown a robust impact of intensive medical therapy reducing the risk of clinical recurrence of symptomatic ICAS. However, even under best medical therapy and degree of risk factor control, symptomatic ICAS-related recurrence risk continues to be the highest among all stroke etiologic subtypes. The second part of the chapter reviews the current understanding of prognostic factors that may help discriminate the high-risk ICAS patients, divided into local factors (vulnerable ICAS plaque) and systemic factors (vulnerable ICAS patient). Regarding research on local factors, high-resolution magnetic resonance imaging (HRMRI) is an emerging technique that allows in vivo evaluation of intracranial arterial wall, which is displacing our research focus from intracranial stenosis degree towards intracranial atherosclerotic plaque composition and activity. Characterization of the vulnerable ICAS patient may be improved with biomarker research. The latest contributions in this field help support the hypothesis that inflammation determines the risk of progression and complication of this disease, as it occurs in atherosclerosis affecting extracranial arterial beds.