Medicine & USMLE

Von Willebrand Disease

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Platelet Disorders
  1. Platelet Plug Formation
  2. Von Willebrand Disease
  3. Bernard-Soulier Syndrome
  4. Glanzmann Thrombasthenia
  5. Immune Thrombocytopenic Purpura (ITP)
  6. Thrombotic Thrombocytopenic Purpura (TTP)
  7. Hemolytic Uremic Syndrome (HUS)
  8. Disseminated Intravascular Coagulation (DIC)

Summary

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Key Points

  • Von Willebrand Disease (vWD)
    • Pathogenesis
      • Deficient von Willebrand Factor (vWF)
        • Impairs platelet adherence to blood vessels (primary hemostasis)
          • Since platelets bind to vWF released by endothelial cells to form the platelet plug
        • Decreases Factor VIII
          • vWF carries and protects factor VIII in the bloodstream
          • Causes bleeding due to defective intrinsic coagulation cascade
      • Note that vWF comes from Weibel-Palade bodies of endothelial cells and alpha-granules of platelets
    • Genetics
      • Autosomal dominant inheritance
      • More frequent in Caucasians
    • Presentation
      • Mucosal bleeding (oral, GI, uterine)
        • Epistaxis
        • Gingival bleeding
        • Petechiae
        • Easy bruising
        • Menorrhagia
    • Diagnosis
      • Ristocetin cofactor assay
        • Reduced ability of platelets to bind to ristocetin (artificial endothelial surface) is seen; no platelet aggregation
        • Corrects with addition of normal plasma containing vWF (contrast vs. Bernard-Soulier)
      • Normal or ↑ PTT
        • Due to decrease in active Factor VIII
      • Normal PT
        • Extrinsic coagulation pathway is unaffected
      • ↑ bleeding time
        • Unlike hemophilia, since platelet plug formation is impaired due to low vWF
      • CBC shows normal RBC and platelet count and appearance
        • Defect in quality of platelets, not quantity
    • Treatment
      • DDAVP (desmopressin)
        • Releases vWF stored in endothelial cells