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NBME 21 Answers

nbme21/Block 3/Question#18 (31.3 difficulty score)
An 83-year-old man comes to the physician ...
Bullous pemphigoid antigen🔍

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  • 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.

 +4  upvote downvote
submitted by haliburton(191),
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Bluolus iigpemdpoh tengina tsmu be s.emhoodisemem AF: ablul era uowllb"" teh srimde eirabsu(mdlpe lbtise).r PB loas yilde t"sn"ee la.lub

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 +5  
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  

 +2  upvote downvote
submitted by nicnac20(17),
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nI slouulb p,idipmogeh abtteiodasniou rea dame gsiaant 1PBAg dan 2gBPA fndou no heo.ssemomismde

 +2  upvote downvote
submitted by drdre(16),
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luBlosu poh gdeBil"ulpmi sH"eou luslb era ughto PB( do ton turepur aisley) d an uheos indrsme su of smsomhmeoiseed

gPmpuhise g shigp"mraeDsuli"uv ofr meomsdseos