Cerebrovascular risk factors and stroke subtypes: differences between ethnic groups.

BACKGROUND AND PURPOSE The excess risk of stroke seen in the black population has not been explained by differences in age, sex, and social class, although differences in the frequency of cerebrovascular risk factors may be partly responsible. Data on risk factor profiles for the UK black stroke population are sparse. Previous studies have contrasted the association of cerebrovascular risk factors between hemorrhagic and ischemic stroke and between etiologic subtypes of infarct. The relationship of cerebrovascular risk factors to clinical classifications of stroke, however, has been little examined. The aim of this study was to establish the frequency of cerebrovascular risk factors in patients with first-ever strokes in the South London, UK, population and to examine the relationship of these risk factors to both ethnicity and Bamford stroke subtype. METHODS The study included 1254 first-ever stroke patients registered in the South London Community Stroke Register between 1995 and 1998; 995 patients (79.3%) were white, 203 (16.2%) were black, 52 (4.1%) were of other ethnic origin, and 4 (0. 3%) were of unknown ethnic origin. RESULTS In multivariate analysis, increasing age (P:<0.001) and previous cerebrovascular disease (P:=0.007) were independently associated with infarct rather than hemorrhage. Atrial fibrillation was associated with all nonlacunar (P:=0.02), total anterior circulation (P:=0.007), and partial anterior circulation infarcts (P:=0.02) compared with the lacunar group. All other risk factors were similar between infarct subtypes. Risk factors for hemorrhage subtypes were similar in multivariate analysis; increasing age was the only factor associated with primary intracerebral hemorrhage over subarachnoid hemorrhage (P:<0.001). The black stroke population suffered significantly less atrial fibrillation (P:=0.001) and engaged in less alcohol excess (P:<0. 001) and were less likely to have ever smoked (P:<0.001). Hypertension (P:<0.001) and diabetes mellitus (P:<0.001) were more prevalent in the black population. CONCLUSIONS Physiological cerebrovascular risk factors for the UK black population are similar to those of the US black population, but behavioral risk factors differ. Risk factors differ between ethnic groups in the United Kingdom, and future measures for secondary prevention should take this into consideration. Bamford clinical subtypes bear little association with cerebrovascular risk factors. Other classification systems, such as those that classify stroke by etiology, may be more useful in explaining the excess risk of stroke and the scope for its prevention.