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NBME Step 2 CK Form 7 Answers

step2ck_form7/Block 2/Question#38 (reveal difficulty score)
A 12-month-old boy is brought to the ...
B lymphocyte ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: Immuno

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submitted by โˆ—carolebaskin(109)
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Male (XY) + Encapsulated organisms = X linked (Bruton) agammaglobulinemia

  • First: S pneumoniae
  • Then: H influenza type B
  • And now... S pneumoniae again!

Remember: S pneumoniae is a gram positive lancet-shaped diplococcus and is the #1 cause of MOPS (meningitis, otitis media, pneumonia, sinusitis)

N meningitidis is a gram negative diploccocus

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creamy  Thanks Carole. +3

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submitted by โˆ—russnels(20)
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Would this be x-linked agammaglobulinemia? With a BTK gene mutaiton?

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misscorona  I would agree. X-linked agammaglobulinemia is associated with recurrent sinopulmonary infections with encapsulated organisms which are all the organisms mentioned in the question stem. +1
jaypat  Agreed. You need Ab to opsonize encapsulated bacteria. +

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submitted by โˆ—step_prep5(246)
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  • Young boy who has been infected with Strep pneumo, H. influenzae, and now is infected N. meningitidis, all of which are the classic encapsulated bacteria, most consistent with X-linked Brutonโ€™s agammaglobulinemia
  • Key idea: Encapsulated bacteria (SHiN: Strep pneumo, H. Influenzae and Neisseria) are harder for our bodies to destroy and are therefore more dependent upon opsonization, which requires IgG (which will be absent in patients with defects in B lymphocytes because they canโ€™t produce plasma cells and therefore canโ€™t produce immunoglobulins)

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azibird  No Neisseria here, just strep pneumo again +

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submitted by โˆ—jj375(31)
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Nobody has mentioned this but I think another thing that helps with this answer is that the boy was infected with all these that he was immunized for. A 12 month old should've had immunizations for H. flu, and Strep pneumo, yet he was still getting sick. This makes me think he isnt making proper antibodies --> therefore a B cell issue

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