A 19-year-old woman presents with recurrent episodes of non-pruritic, non-erythematous swelling of the lips and larynx following minor dental trauma. Complement studies show low C4 during attacks, normal C3, and normal C1q. The mediator responsible for the edema is:

• A Histamine released from mast cells
• B Bradykinin generated from high-molecular-weight kininogen ✓
• C C3a produced by uncontrolled classical pathway activation
• D Leukotriene B4 from neutrophils

Explanation

Hereditary angioedema is caused by C1 esterase inhibitor deficiency (autosomal dominant), which permits uncontrolled activation of the kallikrein-kinin system and generation of bradykinin, the mediator of the angioedema. The absence of urticaria and pruritus distinguishes it from histamine-mediated allergic angioedema. Low C4 during attacks is a useful screening marker, but C3 remains normal because the classical pathway amplification loop is not sustained.

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.