title: Differences in vascular risk factors between etiological subtypes of ischemic stroke: importance of population-based studies.
abstract: 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 (P(heterogeneity)=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.
authors.affiliation: Stroke Prevention Research Unit, Department of Clinical Neurology, University of Oxford, Oxford OX2 6HE UK.
authors.forename: U G R
authors.initials: UG
authors.lastname: Schulz
authors.forename: P M
authors.initials: PM
authors.lastname: Rothwell
mesh_terms: D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D002545:Brain Ischemia / Q000145:classification* / Q000453:epidemiology*; D015984:Causality; D015331:Cohort Studies; D015897:Comorbidity; D005260:Female; D006801:Humans; D015994:Incidence; D007297:Inpatients / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010045:Outpatients / Q000706:statistics & numerical data; D015995:Prevalence; D012307:Risk Factors; D017678:Sex Distribution; D020521:Stroke / Q000145:classification* / Q000453:epidemiology*; D006113:United Kingdom / Q000453:epidemiology