A 40-year-old woman develops angioedema without urticaria, recurring for 3 years, triggered by ACE inhibitor therapy. She is switched to an ARB but still develops angioedema. What is the most likely mechanism of drug-independent angioedema in this patient?

• A IgE-mediated mast cell degranulation
• B C1-esterase inhibitor (C1-INH) deficiency — hereditary angioedema type I or II ✓
• C Acquired C1-INH deficiency secondary to lymphoproliferative disease
• D Complement C4 deficiency from congenital absence

Explanation

Recurrent non-urticarial angioedema persisting after ACE inhibitor and ARB discontinuation suggests hereditary angioedema (HAE) due to C1-esterase inhibitor deficiency. HAE type I has low C1-INH levels and function; HAE type II has normal or elevated C1-INH antigen but dysfunctional protein. Both show low C4 (during and between attacks). HAE is bradykinin-mediated, not histamine-mediated — hence antihistamines and corticosteroids are ineffective. Treatment: C1-INH concentrate, icatibant (bradykinin B2 antagonist), or tranexamic acid for prophylaxis.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.