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NBME 21 Answers

nbme21/Block 3/Question#18 (33.9 difficulty score)
An 83-year-old man comes to the physician ...
Bullous pemphigoid antigenπŸ”

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submitted by castlblack(50),
  • Pemphigus vulgaris is vulgar in that the blisters rupture and it's gross. + Nikolsky sign. (Its also more vulgar to use your mouth which is why only vulgaris has oral blisters.) Desmosomes are shot.
  • bullous pemphigus is therefore not vulgar and doesn't pop = - Nikolsky sign. Hemidesmosomes are shot.

  • lets rule everything else out for completeness

  • Collagen type VII (i know wtf) = basement membrane btwn epidermis & dermis. NBME language synonyms = Basal Lamina, Reticular Lamina, Extracellular Matrix. Hemidesmosomes, which are made of integrin, fibronectin/laminin, bind to this collagen so it is close to correct but still wrong.

  • cytokeratin is that intracellular intermediate filament in epithelial cells used in stains to distinguish cancers.

  • Desmoplakin is apparently a part of desmosomes, which makes etymological sense. They are going for paraneoplastic pemphigus here. Sucks for them cuz we never learned that one haha. Gottem.

  • Aside here--FA 2020 just mentions desmosomes are made from desmoglein I and III. Antibodies against desmoglein I and III are seen in pemphigus vulgaris and against I is seen in scalded skin syndrome from Staph aureus via exfoliative toxin AKA exfolitoxin. That is why both diseases are + Nikolsky. Good old nikolsky

  • plakoglobin? nobody cares.

submitted by haliburton(208),
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Bsuolul hgpdiioepm tanengi stmu eb hd.mesemosieom AF: lbual ear ow""blul het rdisme adlmprbei(use .elsb)irt BP alos dlyie en"s"te .lualb

seagull  I love how this cant be straight forward. All the other proteins are either subunits of desmosomes or cytoskeletal components. Because I know molecular biology that well on top of the majority of medicine....FML +8  
cienfuegos  @seagull: excellent comment, literally loling right now +  
cienfuegos  or sobbing and threatening to hold my breath if they don't make it stop +1  

submitted by nicnac20(18),
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nI ulsoulb moiehdp,igp ediabisnouaott rae aedm tgaasni ABg1P nad PBgA2 fuodn on oseemsd.ismohme

submitted by drdre(21),
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suBolul i"p lilBgoepdmuh Ho"sue slblu rea ohtug P(B do otn uetpurr iyael)s an d hseuo nsiemdr us fo smdoieemsehoms

pmePhuisg "Dgsulev r"pmauihigs ofr seosemomds