Differences in Vascular Risk Factors Between Etiological Subtypes of Ischemic Stroke: Importance of Population-Based Studies

Background— To understand the mechanisms of stroke and to target prevention, we need to know how risk factors differ between etiological subtypes. Hospital-based studies may be biased because not all stroke patients are admitted. If risk factors differ between patients who are admitted and those who are not, then case-control studies will be biased. If the likelihood of admission also depends on stroke subtype, then case-case comparisons may also be biased. Methods— We compared risk factors and ischemic stroke subtypes (TOAST classification) in hospitalized and nonhospitalized patients in 2 population-based stroke incidence studies: the Oxford Vascular Study (OXVASC) and Oxfordshire Community Stroke Project (OCSP). We also performed a meta-analysis of risk factor–stroke subtype associations with other published population-based studies. Results— In OXVASC and OCSP, stroke subtypes differed between hospitalized (293 of 647) and nonhospitalized patients (P <0.0001), with more cardioembolic strokes (odds ratio [OR], 1.8; 95% CI, 1.3 to 2.6) and fewer lacunar strokes (OR, 0.4; 95% CI, 0.3 to 0.7). Premorbid blood pressure and cholesterol were higher in hospitalized patients (both P <0.0001). Risk factor–stroke subtype associations in hospitalized patients were consequently biased (P =0.001). Meta-analysis of data from all patients in OXVASC, OCSP, and 2 other studies demonstrated consistent risk factor–stroke subtype associations. However, contrary to previous hospital-based studies, there was only a weak (OR, 1.4; 95% CI, 1.1 to 1.8) and inconsistent (Pheterogeneity=0.01) association between small-vessel stroke and hypertension and no association with diabetes (OR, 1.0; 95% CI, 0.7 to 1.3). Conclusions— Prevalences of risk factors and stroke subtypes differ between hospitalized and nonhospitalized patients with ischemic stroke, which may bias hospital-based risk factor studies. Meta-analysis of population-based studies suggests that vascular risk factors differ between stroke subtypes.

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