Background: Stroke incidence is increased in Black individuals but the reasons for this are poorly understood. Exploring the differences in aetiological stroke subtypes, and the extent to which they are explained by conventional and novel risk factors is an important step in elucidating the underlying mechanisms for this increased stroke risk.

Methods: Between 1999- 2010, 1200 black and 1200 white stroke patients were prospectively recruited from a contiguous geographical area in South London in the UK. The Trial of Org 10172 (TOAST) classification was used to classify stroke subtype. Age and sex-adjusted comparisons of socio-demographics, traditional vascular risk factors and stroke subtypes were performed between black and white stroke patients and between Black Caribbean and Black African stroke patients using age, sex, and social deprivation adjusted univariable and multivariable logistic regression analyses.

Results: Black stroke patients were younger than white stroke patients (mean (SD) 65.1 (13.7) versus 74.8 (13.7) years). There were significant differences in the distribution of stroke subtypes. Small vessel disease stroke was increased in black patients versus white patients (27% versus 12%; OR 2.74 (95% CI 2.19-3.44)), whereas large vessel and cardioembolic stroke where less frequent in black patients (OR 0.59 (95% CI 0.45-0.78) and OR 0.61 (95% CI 0.50-0.74) respectively). These associations remained after controlling for traditional vascular risk factors and socio-demographics. Black Caribbean patients appeared to have an intermediate risk factor and stroke subtype profile between that found in Black African and white stroke patients. Cardioembolic stroke was more strongly associated with Black Caribbean ethnicity versus Black African ethnicity (OR 1.48 (95% CI 1.04-2.10)), whereas intracranial large vessel disease was less frequent in Black Caribbean patients versus Black African subjects (OR 0.44 (95% CI 0.24-0.83)).

Conclusions: Clear differences exist in stroke subtype distribution between black and white stroke patients with a marked increase in small vessel stroke. These could not be explained by differences in the assessed traditional risk factors. Possible explanations for these differences might include differences in genetic susceptibility, differing rates of control of vascular risk factors, or as yet undetermined environmental risk factors.