Differences in stroke subtypes between black and white patients with stroke: the South London Ethnicity and Stroke Study.

Background: Determining whether the distribution of stroke subtypes differs between ethnic groups is important in understanding the mechanisms of the increased stroke incidence in black patients.
Methods and Results: In this study, 600 black and 600 white patients with stroke were prospectively and consecutively recruited to determine differences in stroke subtypes. The pathophysiological Trial of Org 10172 (TOAST) classification was used and compared with a clinical (Oxfordshire Community Stroke Project) subtype classification. Stroke subtypes were determined by one investigator by review of original imaging. Black patients with stroke were significantly younger and had higher prevalences of hypertension, diabetes, and obesity. They were less likely to be smokers and had lower prevalences of myocardial infarction and atrial fibrillation. In the black patients, 33% of stroke was due to cerebral small vessel disease compared with 14% in the white stroke cohort (odds ratio, 2.94; 95% confidence interval, 1.97 to 4.39; P<0.001, controlling for age, gender, cardiovascular risk factors, and social class). The black stroke cohort had less large vessel atherosclerosis (odds ratio, 0.49; 95% confidence interval, 0.29 to 0.82; P=0.007) and cardioembolic disease (odds ratio, 0.54; 95% confidence interval, 0.37 to 0.80; P=0.002). Using a classification based on clinical syndrome alone gave a higher estimate of the frequency of small vessel disease stroke, particularly in white patients.
Conclusions: A relative excess of small vessel disease was observed in black patients with stroke compared with an excess of extracranial atherosclerosis and cardioembolic stroke in white patients with stroke that was independent of conventional risk factors and social class. Whether these excesses are due to differences in genetic susceptibility or as-yet undetermined differences in environmental risk remains to be determined.