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Zorluk: KolayHemodynamic and Coagulation Processes

A 29-year-old woman presents to the outpatient clinic for evaluation of heavy menstrual bleeding. She reports soaking through a pad every 1 to 2 hours during the first three days of her menstrual cycle. She also mentions a lifelong history of easy bruising and frequent nosebleeds that often require prolonged pressure to stop. She has no significant past medical history and takes no medications. Her vital signs are within normal limits. Laboratory evaluation reveals the following:

Hemoglobin: 11.2 g/dL11.2 \text{ g/dL}
Platelet count: 250,000/mm3250,000/\text{mm}^3
Prothrombin time (PT): 12 seconds12 \text{ seconds} (normal: 11−15 seconds11-15 \text{ seconds})
Activated partial thromboplastin time (aPTT): 45 seconds45 \text{ seconds} (normal: 25−40 seconds25-40 \text{ seconds})
Bleeding time: 12 minutes12 \text{ minutes} (normal: 2−7 minutes2-7 \text{ minutes})

Which of the following is the most likely underlying pathophysiologic mechanism for this patient's bleeding diathesis?

  1. Impaired synthesis or function of a carrier protein for factor VIIICevap
  2. B
    Immune-mediated destruction of circulating platelets
  3. C
    Congenital deficiency of coagulation factor IX
  4. D
    Decreased activity of a specific metalloproteinase that cleaves large multimers
  5. E
    Systemic activation of coagulation with consumption of clotting factors

Cevap

The correct underlying mechanism is the impaired synthesis or function of a carrier protein for factor VIII, which describes the pathophysiology of von Willebrand disease.
The correct answer identifies the mechanism of von Willebrand disease (vWD). Von Willebrand factor (vWF) has two critical roles in hemostasis. First, it cross-links platelet glycoproteins to exposed subendothelial collagen, thereby mediating primary hemostasis. Second, it serves as a carrier protein for factor VIII, protecting it from rapid proteolytic degradation in the circulation. A deficiency in vWF leads to impaired platelet adhesion (which prolongs the bleeding time) and a secondary decrease in circulating factor VIII (which prolongs the aPTT). The clinical presentation of mucocutaneous bleeding, such as epistaxis and menorrhagia, in a young woman with this specific laboratory profile is the classic presentation for vWD.

Adım Adım Çözüm

1
Analyze the patient's clinical presentation.
The patient has a history of easy bruising, heavy menstrual bleeding, and epistaxis, which indicates a defect in primary hemostasis (mucocutaneous bleeding).
Identifying the pattern of bleeding helps distinguish between primary hemostasis disorders (involving platelets and von Willebrand factor) and secondary hemostasis disorders (involving coagulation factors).
2
Evaluate the laboratory findings in the context of the bleeding pattern.
The patient has a normal platelet count, normal PT, prolonged aPTT, and prolonged bleeding time.
Correlating laboratory findings with the coagulation cascade points to a specific etiology.
3
Synthesize the clinical and laboratory data to identify the specific disease and its mechanism.
A prolonged bleeding time with a normal platelet count indicates a functional defect in platelet adhesion, pointing to von Willebrand disease (vWD). The accompanying prolonged aPTT confirms vWD, because von Willebrand factor acts as a carrier protein that protects factor VIII from degradation in the bloodstream.
Matching the classic laboratory profile to the underlying pathophysiology is required to select the correct mechanism.

Anahtar Kavram

von Willebrand disease (vWD) typically presents with mucocutaneous bleeding, a prolonged bleeding time (due to impaired platelet adhesion), and a prolonged aPTT (because von Willebrand factor normally protects factor VIII from rapid degradation).
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Hemodynamic and Coagulation Processes

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