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Zorluk: ZorPediatric Hematology and Oncology

A pediatric patient with a known history of severe hemophilia A is evaluated for acute-onset right knee pain and swelling. The child's caregivers administered the prescribed on-demand recombinant factor VIII concentrate twice over the preceding 24 hours; however, the joint effusion and pain have continued to worsen. He currently refuses to bear weight on the affected limb. Vital signs show a temperature of 37.1°C (98.8°F), heart rate of 110/min, and blood pressure of 100/65 mm Hg. Physical examination reveals a tense, warm, and highly tender right knee with a restricted range of motion. Laboratory evaluation demonstrates a normal prothrombin time (PT) and a significantly prolonged activated partial thromboplastin time (aPTT). An incubation mixing study is performed; the aPTT fails to correct upon the addition of normal plasma. Which of the following is the most appropriate next step in management?

  1. Intravenous recombinant factor VIIaCevap
  2. B
    Continuous infusion of high-dose factor VIII
  3. C
    Intravenous desmopressin
  4. D
    Diagnostic arthrocentesis of the right knee
  5. E
    Transfusion of fresh frozen plasma

Cevap

Intravenous recombinant factor VIIa
The correct intervention involves utilizing a bypassing agent. This patient has severe hemophilia A and presents with an acute hemarthrosis that is refractory to his usual factor VIII therapy. The critical diagnostic clue is the mixing study: the failure of the prolonged aPTT to correct when mixed with normal plasma confirms the presence of a circulating inhibitor (alloantibodies against factor VIII). In patients with functionally significant inhibitors, administering more factor VIII is ineffective because the antibodies neutralize the replacement factor. Instead, hemostasis must be achieved using bypassing agents, such as recombinant factor VIIa or activated prothrombin complex concentrate (aPCC). These agents bypass the factor VIII-dependent step in the intrinsic coagulation cascade to directly promote factor X activation and subsequent thrombin generation.

Adım Adım Çözüm

1
Interpret the clinical presentation and response to prior therapy.
The patient has an acute hemarthrosis that is refractory to his standard recombinant factor VIII therapy.
Lack of clinical improvement after two appropriate on-demand doses suggests decreased efficacy of the administered factor.
2
Analyze the coagulation laboratory results, specifically the mixing study.
The aPTT does not correct after incubating with normal plasma.
Normal plasma contains factor VIII. If the patient had a simple factor deficiency, the normal plasma would correct the aPTT. Failure to correct indicates the presence of a circulating alloantibody (inhibitor) neutralizing factor VIII.
3
Determine the appropriate management for an acute bleed in the setting of a factor VIII inhibitor.
Bypass agents are required to achieve hemostasis.
Because factor VIII is neutralized by antibodies, hemostasis must be achieved by bypassing the intrinsic pathway. Recombinant factor VIIa (or activated prothrombin complex concentrate) directly activates factor X, promoting clot formation.

Anahtar Kavram

Management of hemophilia A complicated by the development of factor VIII inhibitors (alloantibodies) using bypassing agents.
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Konular

Pediatric Hematology and Oncology

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