A 19-year-old man has recurrent episodes of non-pruritic, non-pitting swelling of the lips and face lasting two to three days. One episode followed dental extraction. C4 level is persistently low while C3 is normal. Which mediator accounts for the oedema?

• A C3a generated by uncontrolled classical pathway activation
• B Histamine released from mast cells by cross-linked IgE
• C Bradykinin generated through uncontrolled activation of the contact system ✓
• D Leukotriene B4 produced by neutrophils

Explanation

Hereditary angioedema results from A1 esterase inhibitor deficiency, inherited as an autosomal dominant trait. Low A1-INH permits continuous consumption of A1r and A1s and, importantly, unregulated kallikrein activity, so bradykinin generation drives the episodic subcutaneous and mucosal oedema. The diagnostic clue is a persistently low A4 with normal A3. Antihistamines are ineffective because histamine is not the mediator, which distinguishes this from allergic angioedema.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.