A 24-year-old man develops episodic non-pruritic swelling of the lips, larynx, and abdominal viscera lasting 2 to 5 days. Attacks are not accompanied by urticaria and do not respond to high-dose antihistamines or corticosteroids. Family history reveals similar episodes in his father. The mediator responsible for the angioedema is:

• A Bradykinin generated from unregulated activation of the contact system ✓
• B Leukotriene C4 generated via the 5-lipoxygenase pathway
• C Histamine released from mast cell degranulation
• D Complement fragment C3a acting on endothelial receptors

Explanation

Hereditary angioedema results from A1 inhibitor deficiency, permitting uncontrolled activation of factor XII and kallikrein with excess bradykinin production. Bradykinin increases vascular permeability, producing the episodes. The absence of urticaria and the failure of antihistamine and steroid therapy distinguish it from histamine-mediated allergic angioedema, since bradykinin does not act through the H1 receptor. Autosomal dominant inheritance fits the family history.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.