Understanding lacunar stroke: also an epidemiological challenge

Since lacunar stroke was first described by Miller Fisher 50 years ago [1], our understanding of the condition has not progressed a lot, although there is growing evidence that lacunar arteriopathy may be different from that of other ischaemic strokes. Currently, lacunar stroke is recognized as a cerebral small vessel disease related to arteriolosclerosis, including both the ischaemic (lacunar stroke and white matter lesions) and haemorrhagic (intracerebral haemorrhages and microbleeds) consequences [2]. However, many questions remain unsolved, and epidemiological studies could help to increase our knowledge about lacunar stroke. In this issue of the European Journal of Neurology, Fang et al. [3] aimed to describe the incidence, risk factors and prognosis of lacunar stroke in a community of Beijing, China. This study is informative with regard to several points. First, with one-fifth of the world s population living in China, the lengthening life expectancy and the influence of a westernized lifestyle, the burden of stroke is already a major health issue in this country that will undoubtedly grow over coming years. However, data about the true epidemiology in China are scarce and currently rely on studies that were limited by methodological weaknesses including retrospective design, non-exhaustive case ascertainment and lack of reliable diagnostic criteria [4]. In their study, Fang et al. [3] avoided these limitations by using a population-based stroke registry that fulfilled the criteria for conducting ideal incidence studies [5]. Secondly, our current knowledge about the distribution of ischaemic stroke subtypes among Chinese people comes from studies that were conducted in hospital-based settings [6], which unavoidably generates major biases linked to patients recruitment. In the present study, the use of a pertinent classification of stroke subtypes allowed the authors to provide reliable epidemiological information about lacunar stroke. As a result, they found that although the incidence of lacunar stroke was greater than that observed in western countries, it was lower than that previously reported in Asia [6,7]. Of note, intracerebral haemorrhage accounted for only 14.5% of overall strokes, which is much lower than the estimated 25– 65% for Asia [4]. These results seem to indicate that the incidence of lacunar stroke and intracerebral haemorrhage may vary in a similar manner. This suggests that these two entities could share common risk factors, whose distribution differs from one population to another. This therefore provides an epidemiological argument for the pathological concept of arteriolosclerosis [2]. One question remains: what are these factors that could influence the occurrence of lacunar stroke, and, in a wider context, small vessel disease due to arteriolosclerosis? It has been assumed that variations in the prevalence of vascular risk factors, especially hypertension, could be of importance. Indeed, hypertension was found to be more frequent in patients with lacunar than in those with non-lacunar stroke, both in the present as well as in previous studies. Nevertheless, although hypertension is an indisputable major contributor of intracerebral haemorrhage, its role in specifically increasing the risk of lacunar stroke compared to that of other ischaemic stroke subtypes is still a matter of debate, and this role is likely not as important as has long been believed [8]. Other contributors, such as genetic, environmental or sociocultural factors, remain to be identified. China is a large country with a heterogeneous population. Hence, multiplying other similar epidemiological studies with reliable methodology in different areas of the country could lead to better understanding of the mechanisms involved in lacunar stroke.