A 19-year-old man has recurrent episodes of non-pruritic, non-urticarial swelling of the face, larynx and abdominal wall without accompanying wheals. Complement studies show low C4 with normal C3. The mediator responsible for the edema in this condition is:

• A Histamine released from mast cells
• B Bradykinin generated from high molecular weight kininogen ✓
• C Leukotriene C4 from eosinophils
• D Complement fragment C3a

Explanation

Hereditary angioedema results from C1 inhibitor deficiency (or dysfunction), which permits uncontrolled activation of factor XII and the kallikrein-kinin system, generating excess bradykinin that increases vascular permeability. The absence of urticaria and pruritus distinguishes it from histamine-mediated allergic angioedema, killing option A. Low C4 reflects ongoing classical pathway consumption while C3 remains normal because C1 inhibitor blocks amplification before the C3 convertase stage.

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.