Incidence rates of first-ever ischemic stroke subtypes among blacks - A population-based study

Background and Purpose-The aim of this study was to determine the incidence rates of ischemic stroke subtypes among blacks. Methods-Hospitalized and autopsied cases of stroke and transient ischemic a ttack among the 187 000 blacks in the 5-county region of greater Cincinnati /northern Kentucky From January 1, 1993, through June 30, 1993, were identi fied. Incidence rates were age- and sex-adjusted to the 1990 US population. Subtype classification was performed after extensive review of all availab le imaging, laboratory data, clinical information, and past medical history . Case-control comparisons of risk factors were made with age-, race-, and sex-matched control subjects. Results-Annual incidence rates per 100 000 for first-ever ischemic stroke s ubtypes among blacks were as follows: uncertain cause, 103 (95% confidence interval [CI], 80 to 126); cardioembolic, 56 (95% CI, 40 to 73); small-vess el infarct, 52 (95% CI, 36 to 68); large vessel, 17 (95% CI, 8 to 26); and other causes, 17 (95% CI, 9 to 26). Of the patients diagnosed with an infar ct of uncertain cause, 31% underwent echocardiography, 45% underwent caroti d ultrasound, and 48% had neither. Compared with age-, race-, and sex- (pro portionally) matched control subjects from the greater Cincinnati/northern Kentucky region, the attributable risk of hypertension for all causes of fi rst-ever ischemic stroke is 27% (95% CI, 7 to 43); for diabetes, 21% (95% C I, 11 to 29); and for coronary artery disease, 9% (95% CI, 2 to 16). For sm all-vessel ischemic stroke, the attributable risk of hypertension is 68% (9 5% CI, 31 to 85; odds ratio [OR], 5.0), and the attributable risk of diabet es is 30% (95% CI, 10 to 45; OR, 4.4). For cardioembolic stroke, the attrib utable risk of diabetes is 25% (95% CI, 4 to 41; OR, 3.1). Conclusions-Stroke of uncertain cause is the most common subtype of ischemi c stroke among blacks. Cardioembolic stroke and small-vessel stroke are the most important, identifiable causes of first-ever ischemic stroke among bl acks. The incidence rates of cardioembolic and large-vessel stroke are like ly underestimated because noninvasive testing of the carotid arteries and e chocardiography were not consistently obtained in stroke patients at the 18 regional hospitals. Most small-vessel strokes in blacks can be attributed to hypertension and diabetes.