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NBME 21 Answers

nbme21/Block 1/Question#19

A 22-year-old man has had frequent episodes of ...

C1 esterase inhibitor (binds activated C1r, C1s)

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 +6  upvote downvote
submitted by mcl(202),

Patient may have hereditary angioedema, which is associated with "recurrent attacks of intense, massive, localized subcutaneous edema involving the extremities, genitalia, face, or trunk, or submucosal edema of upper airway or bowels". The article goes on to say "C1-esterase inhibitor works directly on the complement and contact plasma cascades to reduce bradykinin release" which is also probably good to know.


notadoctor  Thought this was a trick question as C1 esterase deficiency also results in a decrease in C4. However, the second answer choice was not referring to C4 but to C4 binding protein, which I now know is different. I also didn't realize C1 esterase was technically a complement protein. +3  
youssefa  Based on many sources hereditary angioedema does NOT cause a rash (urticaria) which is a main differentiating point between angioedema and allergy. This mislead me in this question. Any clarification? +3  
ergogenic22  +1 on the above because uptodate states that c1 esterase inhibitor deficiency, both acquired and nonhereditary, are both non-urticarial, non-pruritic, and that is confirmed by the above linked article +1  
sahusema  Question writer probably didn't know the difference between cutaneous urticaria and subcutaneous edema. +  

 +0  upvote downvote
submitted by kolivera(1),

This is what I came across putting the two (angioedema + laryngospasm) together. Take into account that this info is regarding ACEIs but, I guess with a certain severity, angioedema can be associated with other sx. "However, angioedema has occurred suddenly after months to years of therapy, and about 20% of known cases of angioedema occurring in this context may involve severe symptoms (e.g., dyspnea, stridor, laryngospasm)."