A systematic review of intracranial atherosclerosis epidemiology—the largest contributor to the global ischemic stroke burden?

Background Intracranial atherosclerosis (ICAD) is commonly stated to be the largest contributor to the ischemic stroke burden worldwide. However, there has been little systematic examination of the epidemiology literature. Methods PubMed, OVID-EMBASE and manual searches of references from retrieved literature were used to identify studies. Adult studies from 1990 onwards were included, with two reviewers independently reviewing titles and abstracts. Risk of bias was assessed using modified Newcastle-Ottawa Scale. Results There were 138 studies included in the systematic review. Due to risk of bias and inconsistent definitions, there was low certainty in the findings of this systematic review. Moderate and high-quality studies based in Asia found that 8.8%−41.1% of stroke was due to ICAD, compared to 2.2%−11.1% in Europe and 7.5%−25% in North America. Moderate and high-quality studies investigating stroke recurrence in ICAD found a rate of 8%−28.3%. Moderate and high-quality studies investigating ICAD prevalence in unselected populations found a prevalence of 2.6%−58.5%. Moderate and high-quality studies found an ICAD prevalence of 5.4%−64.7% amongst stroke patients, compared with 15.5% found by a high-quality study from Europe. Conclusions Epidemiological studies of ICAD demonstrate significant heterogeneity in design and risk of bias, leading to uncertainty regarding the true burden of this important disease. Nevertheless, current literature suggests that ICAD is at least as important as the other major etiologies in its contribution to the global ischemic stroke burden, highlighting the need for further research to inform therapeutic advances.