A 19-year-old man presents with recurrent episodes of non-pruritic swelling of the lips and larynx without urticaria. His father has similar episodes. C4 level is persistently low during attacks. Which mediator accounts for the angioedema?

• A Histamine released from mast cells
• B Bradykinin generated from kininogen ✓
• C Leukotriene B4 from neutrophils
• D Complement fragment C3a

Explanation

Hereditary angioedema results from deficiency of C1 esterase inhibitor (C1-INH), inherited as an autosomal dominant trait. Unchecked activation of the classical complement pathway consumes C4, and unopposed factor XII activity generates excess bradykinin, which increases vascular permeability and produces the angioedema. The absence of urticaria and pruritus distinguishes it from histamine-mediated allergic angioedema, making antihistamines ineffective while C1-INH concentrate or icatibant works.

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.