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Discussion Starter · #1 ·
An 8-year-old boy presents to his pediatrician with recent onset of daily nosebleeds that have been occurring over the past 2 weeks. He has
bruises on his legs and arms that appeared after playing on the playground at school. The patient has a history of easy bruising since early childhood. He denies painful, tender, or swollen joints. The boy’s mother reports that she has a history of von Willebrand’s disease. A workup for von Willebrand’s disease would most likely reveal which of the following?
(A) Increased bleeding time
(B) Normal coagulation factor concentrations
(C) Prolonged prothrombin time
(D) Shortened partial thromboplastin time
(E) Thrombocytopenia
 

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Discussion Starter · #5 ·
Correct Answer

The correct answer is A. Von Willebrand's factor forms a bridge between platelets and vessel endothelium and acts as a carrier protein for factor VIII of the coagulation pathway. Patients with von Willebrand's disease (qualitative or quantitative defects in von Willebrand's factor) therefore have defective platelet function and abnormalities in the coagulation pathway. Because bleeding time correlates with platelet function, von Willebrand's disease is associated with decreased platelet interaction with the vessel endothelium and subsequent increased bleeding time.

Answer B is incorrect. Von Willebrand's factor normally stabilizes factor VIII in the circulation. Therefore, deficiency of von Willebrand's factor may lead to factor VIII proteolysis with reduced levels of factor VIII in the circulation.

Answer C is incorrect. Because von Willebrand's factor stabilizes factor VIII of the coagulation pathway, increased partial thromboplastin time (PTT) (due to decreased factor VIII concentration) may occur in a patient with abnormal von Willebrand's factor. Factor VIII is part of the intrinsic coagulation pathway, which corresponds to PTT, not prothrombin time (PT). Therefore, decreased levels of factor VIIII will not lead to prolonged PT, only prolonged PTT.

Answer D is incorrect. Von Willebrand's factor normally stabilizes factor VIII in the circulation. Abnormalities of von Willebrand's factor, such as those seen in von Willebrand's disease, are associated with a prolonged (not shortened) partial thromboplastin time due to increased proteolysis of factor VIII and decreased factor VIII concentrations.

Answer E is incorrect. Patients with von Willebrand's disease (vWD) have normal platelet counts, but abnormal platelet function, resulting in abnormal interactions between platelets and the vessel endothelium. Because there is no indication of decreased platelet formation or increased platelet destruction in a patient with von Willebrand's disease, the patient would not have disease related thrombocytopenia, except in the 2N variant. The 2N variant is very rare, and patients will present with hematuria, joint and soft tissue bleeding, unlike the other variants of vWD that present mostly with mucocutaneous bleeds.
 
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