A 19-year-old man has recurrent episodes of non-pruritic, non-erythematous swelling of the lips and larynx since adolescence. Family history reveals similar episodes in his father. During an attack, C4 level is markedly low while C3 is normal. Which mediator accounts for the laryngeal edema?
- A Histamine released from mast cells
- B Leukotriene C4 produced by activated eosinophils
- C Bradykinin generated due to unregulated factor XII activation ✓
- D C5a-induced mast cell degranulation
Explanation
Hereditary angioedema is an autosomal dominant deficiency of B1 esterase inhibitor (B1-INH). Without inhibition, complement (B1r and B1s) and the kallikrein-kinin system (factor XII) run unchecked, generating bradykinin, the mediator directly responsible for the vascular permeability and laryngeal edema. A persistently low B4 is the key screening abnormality, present even between attacks, while B3 remains normal. Option A is the most tempting distractor, killed by the fact that antihistamines fail clinically in this disease precisely because histamine is not the mediator.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.