WBR0679

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Immunology, MainCategory::Pathology
Sub Category	SubCategory::Hematology
Prompt	[[Prompt::A 68-year-old man with no past medical history presents to the physician's office for swelling in his tongue, palate, and the submandibular region. His symptoms started acutely earlier the same day. The patient is unable to speak properly, but can still breathe normally. Upon further questioning, he denies the use of any drugs and denies any known tumors. He explains that he has had a similar condition recently that resolved within 2 days. Which of the following lab findings is most likely present in this patient?]]
Answer A	AnswerA::Low serum complement C1 esterase inhibitor concentration
Answer A Explanation	AnswerAExp::The patient is presenting with acquired C1 esterase inhibitor deficiency that manifests with symptoms similar to hereditary angioedema.
Answer B	AnswerB::Low serum complement C3 concentration
Answer B Explanation	AnswerBExp::C3 deficiency is characterized by recurrent pyogenic infections of the respiratory tract with increased susceptibility to type III hypersensitivity reactions.
Answer C	AnswerC::Low serum decay-accelerating factor (DAF) concentration
Answer C Explanation	AnswerCExp::DAF deficiency is characteristic of paroxysmal nocturnal hemoglobinuria (PNH).
Answer D	AnswerD::Low serum complement C5 concentration
Answer D Explanation	AnswerDExp::C5-C9 deficiencies are characterized by recurrent ''Neisseria'' bacteremia.
Answer E	AnswerE::Low serum complement C9 concentration
Answer E Explanation	AnswerEExp::C5-C9 deficiencies are characterized by recurrent ''Neisseria'' bacteremia.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient is presenting with acquired C1 esterase inhibitor deficiency, which is a condition that resembles hereditary C1 esterase inhibitor deficiency but involves older age groups. Similar to the hereditary form, acquired C1 esterase inhibitor deficiency manifests with recurrent painless angioedema that involves the head and neck region, with or without respiratory symptoms, that often resolves within 24-48 hours. When patients present with acquired forms of the disease, they must be worked-up extensively for concomitant lymphoproliferative and autoimmune disorders to rule out any secondary etiology for the deficiency, such as a B-cell neoplasm. Similarly, the use of ACE-inhibitors is contraindicated among these patients and medication-induced angioedema must also be ruled out. Educational Objective: C1 esterase inhibitor deficiency may be either acquired or hereditary. Both forms manifest similarly with painless angioedema of the head and neck region. The diagnosis is made by demonstration of low serum C1 esterase inhibitor concentration and when secondary causes (due to medications or systemic disorders) are ruled out. References: Sinclair D, Smith A, Cranfield T, et al. Acquired C1 esterase inhibitor deficiency or serendipity? The chance finding of a paraprotein after an apparently low C1 esterase inhibitor concentration. J Clin Pathol. 2004; 57(4):445-447. First Aid 2015 page 206]]
Approved	Approved::Yes
Keyword	WBRKeyword::C1, WBRKeyword::Complement, WBRKeyword::C1 esterase inhibitor deficiency, WBRKeyword::Hereditary angioedema, WBRKeyword::Angioedema, WBRKeyword::Immunology
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