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Retired NBME 18 Answers

nbme18/Block 3/Question#27 (reveal difficulty score)
A 39-year-old man comes to the physician ...
Type III (Immune complex-mediated) ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—mariame(16)
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I believe the diagnosis is Cryoglobulinemia. However you do not need to know this to answer the question.

Type III hypersenstivity is associated with vasculitis and systemic manifestations, while Type II usually has a specific target (an organ, hemolysis). Type I is anaphylactic and Type IV is delayed type hypersensitivity.

Cryoglobulinemia is often due to viral infxn especially HCV; inmunoglobulins precipitate in the cold and cause the pathology. It's characterized by: palpable purpura, weakness, arthralgias, peripheral neuropathy and renal involvement (FA 2019, 311).

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ih8payingfordis  Literally saw that C4 (complement component) is down in the serum and picked Type III and never looked back at this mess of a question. +5
cmeacham  Wait, can you explain this? +
plaguedbyspleen  @cmeacham Type III hypersensitivity reactions are due to antigen-antibody complexes that activate the complement cascade. So complement is consumed and levels are found to be low. This question shows a low C4 level. +2



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