A 19-year-old man develops recurrent episodes of nonpruritic, nonpitting subcutaneous and laryngeal edema without urticaria. During attacks, C4 levels are persistently low while C1q and C3 are normal. The mediator responsible for the angioedema and the standard prophylactic drug class are:

• A Histamine; long-term nonsedating antihistamines
• B Leukotriene C4; cysteinyl leukotriene receptor antagonists
• C Bradykinin; daily antifibrinolytics such as epsilon aminocaproic acid as first choice
• D Bradykinin; attenuated androgens such as danazol ✓

Explanation

Hereditary angioedema results from C1 inhibitor deficiency, permitting unchecked activation of the classical complement pathway (low C4) and of the kallikrein-kinin system, generating bradykinin that increases vascular permeability without wheals or itch. Attenuated androgens like danazol raise hepatic C1 inhibitor synthesis and remain standard prophylaxis, with C1 inhibitor concentrate used for acute attacks. Antihistamines fail precisely because histamine is not the mediator, which also explains the absence of urticaria.

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.