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Diabetic Ketoacidosis (DKA) — UKMLA MCQ

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HardEndocrinologyDiabetic Ketoacidosis (DKA)UKMLAMRCP Part 1MRCEM SBAPARAPSA

A 28-year-old has recurrent abdominal pain and non-pruritic swelling without urticaria. His father is similarly affected. C4 is low, C1-inhibitor antigen is normal and no culprit medicine is identified. Which additional result most strongly establishes hereditary angioedema type 2?

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Correct answer: A — Reduced C1-inhibitor functional activity

The best answer is “Reduced C1-inhibitor functional activity”. Type 2 hereditary angioedema results from a dysfunctional C1 inhibitor: antigenic concentration may be normal or raised, but functional activity is reduced and C4 is usually low. Low C1q instead points towards acquired C1-inhibitor deficiency, especially with late onset and lymphoproliferative disease. C3 is generally normal. Tryptase supports mast-cell activation, which would more often cause urticaria, pruritus and a response to antihistamines.

Reference: WAO/EAACI international guideline for hereditary angioedema, 2021 revision: https://pmc.ncbi.nlm.nih.gov/articles/PMC9023902/