A 5-year-old boy is brought to the emergency department due to an hour of epistaxis after he was elbowed in the face during a basketball game. He has a history of prolonged bleeding from the gums after brushing his teeth. Vital signs are normal. The patient has scattered bruises along his arms and legs. He receives desmopressin, which stops the bleeding. This treatment most likely improved the patient's condition through which of the following therapeutic mechanisms?

Question

A 5-year-old boy is brought to the emergency department due to an hour of epistaxis after he was elbowed in the face during a basketball game.  He has a history of prolonged bleeding from the gums after brushing his teeth.  Vital signs are normal.  The patient has scattered bruises along his arms and legs.  He receives desmopressin, which stops the bleeding.  This treatment most likely improved the patient's condition through which of the following therapeutic mechanisms?

Quizplus · Accepted Answer

11ec160b_3bec_f8fa_9249_6d30340ff864_MD0001_00 This patient's history of prolonged mucosal bleeding (eg, oropharyngeal, nasal), easy bruising, and responsiveness to desmopressin (DDAVP) likely indicate von Willebrand disease (vWD), the most common inherited bleeding disorder. VWD is caused by qualitative or quantitative defect in von Willebrand factor (vWF), a multimeric glycoprotein synthesized by endothelial cells and platelets. VWF contributes to hemostasis by forming a bridge between platelets and exposed subendothelial components at sites of injury and by serving as a carrier protein for factor VIII (whose half-life is tremendously shortened when not bound to vWF). Treatment of minor bleeding episodes in patients with vWD often involves desmopressin (DDAVP), a synthetic analogue of antidiuretic hormone that does not induce vasoconstriction. DDAVP induces a rapid and transient increase in vWF and factor VIII by indirectly releasing these compounds from endothelial storage sites. DDAVP is most useful in the acute setting, as repeated doses have limited effectiveness due to tachyphylaxis (endothelial stores become depleted). (Choices A and F) Antidiuretic hormone binds to the vasopressin 2 receptor on renal tubular cells, which leads to increased aquaporin channels, increased water reabsorption, and decreased urine output. It also binds to the vasopressin 1 (V1) receptor on vascular smooth muscle, which results in vasoconstriction. In contrast, DDAVP has antidiuretic effects but little or no vasoactive (vasoconstrictive) effects because it only binds to the V2 receptor. (Choice B) Factor IX, a vitamin K-dependent clotting factor produced in the liver, is deficient in hemophilia B. DDAVP has no effect on factor IX levels. Hemophilia B must be treated with factor IX replacement. (Choice D) Platelets form the initial hemostatic plug when bleeding occurs. DDAVP has no effect on platelet number. (Choice E) Patients with vitamin K deficiency are prone to bleeding due to decreased vitamin K-dependent coagulation factors (factors II, VII, IX, and X). Vitamin K deficiency is typically seen in patients with fat malabsorption (eg, pancreatic insufficiency) or those on warfarin, a vitamin K antagonist. Educational objective: Patients with symptomatic von Willebrand disease can be treated with desmopressin (DDAVP), a synthetic antidiuretic hormone analogue that has no vasoconstrictive effects. DDAVP transiently increases von Willebrand factor and factor VIII release from endothelial cell storage through indirect mechanisms; it can be used prophylactically prior to procedures or to treat minor bleeding. __________ References: Desmopressin (DDAVP) in the treatment of bleeding disorders: the first 20 years. (http://www.ncbi.nlm.nih.gov/pubmed/9326215)

A 5-Year-Old Boy Is Brought to the Emergency Department Due