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Difficulty: HardImmunologic and Inflammatory Processes

Emergency medical services bring a 23-year-old woman to the resuscitation bay for rapid-onset throat swelling, voice changes, and difficulty swallowing that began two hours after a routine tooth extraction. She denies any new medications, food exposures, or known allergies. Her medical history is notable for three emergency department visits over the last four years for severe, colicky abdominal pain that was evaluated with computed tomography; each time, she was diagnosed with non-specific enteritis and symptoms resolved spontaneously within 48 hours. Her family history reveals that her father died suddenly of respiratory failure at age 35. On presentation, her blood pressure is 115/75 mm Hg, pulse is 102/min, and respirations are 24/min. Physical examination demonstrates massive non-pitting edema of the lips, tongue, and oropharynx. Urticaria and pruritus are completely absent. Stridor is audible. Intramuscular epinephrine, intravenous diphenhydramine, and intravenous methylprednisolone are administered immediately. Re-evaluation 30 minutes later reveals no improvement in her airway swelling. Which of the following is the primary molecular target of the most appropriate directed pharmacotherapy for this patient's current condition?

  1. A
    Angiotensin-converting enzyme
  2. B
    Beta-2 adrenergic receptor
  3. Bradykinin B2 receptorAnswer
  4. D
    Complement component C5
  5. E
    Histamine H1 receptor

Answer

Bradykinin B2 receptor
The correct answer is the Bradykinin B2 receptor. This patient's presentation of trauma-induced angioedema without urticaria, history of recurrent abdominal pain, family history of sudden airway compromise, and lack of response to standard anaphylaxis therapy is classic for Hereditary Angioedema (HAE). HAE is caused by a deficiency in C1 esterase inhibitor, leading to unregulated activation of plasma kallikrein and massive overproduction of bradykinin. Bradykinin acts primarily on the B2 receptor to cause profound vasodilation and increased vascular permeability. Acute, life-threatening attacks require directed therapy to halt this cascade, commonly achieved with icatibant (a highly specific bradykinin B2 receptor antagonist), ecallantide (a kallikrein inhibitor), or C1-INH replacement. Therefore, the bradykinin B2 receptor is the precise molecular target among the choices provided.

Step-by-Step Solution

1
Analyze the clinical presentation to establish a diagnosis.
The combination of isolated angioedema triggered by minor trauma (tooth extraction), absence of urticaria/pruritus, recurrent unexplained abdominal pain (intestinal edema), positive family history of asphyxiation, and failure to respond to epinephrine and antihistamines strongly points to Hereditary Angioedema (HAE).
Differentiating bradykinin-mediated angioedema from histamine-mediated (allergic) anaphylaxis is critical, as their pathophysiologic mechanisms and acute treatments are entirely different.
2
Determine the pathophysiologic mechanism of the disease.
HAE is an autosomal dominant disorder caused by a deficiency or dysfunction of C1 esterase inhibitor (C1-INH).
Understanding the underlying defect allows for targeted pharmacologic intervention.
3
Trace the biochemical pathway resulting from the defect.
C1-INH normally inhibits both the classical complement pathway (C1r/C1s) and the contact-kinin system (Factor XIIa and plasma kallikrein). Uninhibited plasma kallikrein cleaves high-molecular-weight kininogen into bradykinin.
Excess bradykinin is the direct molecular culprit causing the severe vasodilation and vascular permeability seen in HAE.
4
Identify the target of the required acute pharmacotherapy.
Acute airway-threatening HAE attacks must be treated by interrupting the kinin cascade. This is achieved using a bradykinin B2 receptor antagonist (icatibant), a plasma kallikrein inhibitor (ecallantide), or purified C1-INH concentrate.
The question asks for the primary molecular target of the most appropriate directed pharmacotherapy, making the bradykinin B2 receptor the correct choice.

Key Concept

Hereditary angioedema is a bradykinin-mediated process unresponsive to epinephrine, antihistamines, and glucocorticoids; acute airway attacks require targeted therapies such as bradykinin B2 receptor antagonists (icatibant), kallikrein inhibitors (ecallantide), or C1 inhibitor concentrate.
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Topics

Immunologic and Inflammatory Processes

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