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NBME 21 Answers

nbme21/Block 4/Question#10

A 64-year-old man is evaluated for cough, dyspnea, ...

Hyponatremia

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What threw me off in this question is the phrase "cells with little cytoplasm that are twice the size of lymphocytes." I though "small cell carcinoma" cannot be that big.

nala_ula  Omg literally the same thought process I had, that phrase through me off! +  
nala_ula  threw* +  




Small cell lung cancer causes SIADH. Location + exclusionary clues.

mcl  To expand, SIADH may also result in euvolemic hyponatremia. This is because, as we know, ADH increases absorption of water and therefore initially results in an increased circulating volume. However, this results in increased stretch of the atria and subsequent secretion of ANP. ANP (atrial natriuretic peptide) then results in loss of sodium and water. +2  




why is hyperlipidemia secondary to cushing syndrome not a possibility?

hello  SIADH = MC paraneoplastic syndrome of small oat cell lung cancer. Also, Cushing syndrome would cause would weight gain, skin hyperpigmentation, and hypokalemia. Not, lyperlipidemia. +  
charmrooftops  You do get hyperlipidemia in cushing though? https://www.amboss.com/us/knowledge/Cushing_syndrome So still unsure why this is not a possibility. Is it just a "more common" thing for SIADH? +  




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submitted by hello(66),

The patient has "cells arranged in infiltrating sheets" --> indicates malignant cancer cells.

The cells are neither glandular nor squamous --> the cancer is neither adenocarcinoma nor squamous cell lung cancer, respectively.

This leaves small oat cell lung cancer. SIADH is the most common paraneoplastic syndrome for small oat cell lung cancer --> leads to hyponatremia.