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Retired NBME Step 2 CK Form 7 Answers

step2ck_form7/Block 2/Question#39 (reveal difficulty score)
A 12-month-old boy is brought to the ...
Neutrophil ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: Immuno

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submitted by โˆ—russnels(20)
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This is likely Chronic Granulomatous Disease, which is characterized by a deficiency in NADPH Oxidase - which produces H2O2, a precursor to hypochlorite (bleach) for the respiratory burst.

Pts with CGD are especially susceptible to catalase + organisms, because the bacterial catalase neutralizes the bacterial H2O2 (which allows CGD patients to provide some resistance to certain catalase negative bacteria).

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submitted by โˆ—step_prep5(246)
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  • Young boy with persistent Staph aureus skin abscesses and lung empyema (which is commonly caused by Staph aureus), most consistent with chronic granulomatous disease (X-linked disease most commonly)
  • Key idea: Patients with chronic granulomatous disease are preferentially infected by catalase positive organisms, which can be remembered with the mnemonic BELCH SPANS (Burkholderia cepacia, E. coli, Listeria, Candida, H. pylori, Staph aureus, Pseudomonas aeruginosa, Aspergillus, Nocardia, Serratia)

https://step-prep.org/tutoring/

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submitted by โˆ—azibird(279)
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Yes, this is CGD. But which cell? According to UTD: "These genetic defects result in the inability of phagocytes (neutrophils, monocytes, and macrophages) to destroy certain microbes." https://www.uptodate.com/contents/chronic-granulomatous-disease-pathogenesis-clinical-manifestations-and-diagnosis

FA2020: "Involves the activation of the phagocyte NADPH oxidase complex (eg, in neutrophils, monocytes)."

Seems like NADPH oxidase deficiency would involve macrophages too... So is neutrophil just the most important/well known?

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