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NBME 21 Answers

nbme21/Block 2/Question#14 (70.8 difficulty score)
A 30-year-old woman comes to the office ...
Abnormal brain development๐Ÿ”
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 +17  upvote downvote
submitted by taway(25),
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ihsT oqstuine is searphd l,gsynraet utb tsi' seayieltlns akgisn "tawh ldwou pnehap fi shit mwon'as hpomyostirdiyh ecemba ncelrontluod roev eht rocseu fo hre "ecgarnypn?

rnuetclyr reh STH is odgo t-&-g; crlto-ldwlloeen dC OmhHprHtTPIToyEhiYisALyo high SHT ;tg-&- hre hyrpihioymodts tums TNO eb wlotolercldne-l due( ot idsuoitrpn fo the TT/T4R3/S/HTH ndenrecio xa)is

oS, nwo thta we rnsaetundd ttah the ounqeits si aignks ahwt" ldwuo pehapn fi ehr siyohproydmith wsa tlernnuoo"d?lc

rnA:wse snretcmii

I hitnk ttah ihts qoietnus si dparshe yi,osucatlor but afr be ti orfm me to erctziiic het LUMSE sgilnienc aro..db.

yotsubato  I think that this question is phrased atrociously, Just like the rest of the NBME +9  
b1ackcoffee  exactly how does maternal hashimoto can cause cretinism? +  



 +10  upvote downvote
submitted by direwolf(10),
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hisT ahs to od ithw eningstdaudrn two gns,hti atht lanetrma hiptyhidoosmry is niklde ot aCtimnul/eisnerr dnepomltvee of the tfus,e nad ranoml enpcnygar iplgy.osohy In ear,cnnygp easecdirn oernshmo aestmitlu vlier dutpoirocn fo urosvai teprison leik xeS meHoron niBnidg ionblGlu S)GH,(ToBhyrxnei dnnBgii oiblGlnu (GB,)T c.te Mero TBG dderopcu = erom 4/3TT si udnb.o sLse T4/3T cauess erom TRH eear,lse oemr TSH ,selerea nad oerm /43TT uioocrdptn itlnu eefr 4T3T/ esvlel rea cbak ot onalrm. In a lmarno geacyn,prn tshi nahppes no mor.lpbe In omsoeen thwi exrgpe-nsiti ytposidrhhimyo g,othhu laayerd ash dmpeiira 3/TT4 ocoptdn,iru dan nwo't be labe ot epek pu hitw ieseardnc .edandm hirTe 3T wlil resi, ubt isth to'wn uertls ni ecarnisde 4.T/T3 cTiylalp,y mewno hiwt H'atsohmsoi reisidgn to egt ngaptern lwli edne to snieerac ethri lotivynoreexh oesd in tnoacpinatii of stih epyanrngc cgnhe.a




 +4  upvote downvote
submitted by thotaak(5),

Normally maternal T3/4 are required for fetal brain development before fetal thyroid gland is formed. And after fetal thyroid gland is formed, fetal T3/4 helps in brain development. So increase TSH means decreased maternal T3/4 and thus have abn brain development. And yes T3/4 crosses placenta.

thotaak  According to Robbins pathology +1  



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umnotuAmei iitosihtryd aka( sHohmtoa)i + g&-rgt;np-tnea iThkn ubota bipisostily of eaflt yrithohmiodyps due to iodtnaby iteadmde naratlme d.hrimyypsohtio daeLs ot tin.iermCs sgindnFi in aintfn era het 6'P (Pto llbye, lPa,e Pfufy ,acef rtPondiurg sbucliu,mi naurbtoePtr u,eogtn and Poor niBar epmeovldnet.

neonem  I don't understand the last part of this question stem though... if the mother's TSH *increases* during pregnancy? Wouldn't this further increase her (and/or the fetus's) production of T4 and thus counteract the hypothyroidism? +  
poojaym  @neonem no. Autoimmune hypothyroidism is a destruction of the thyroid gland, and a decrease in production of T3/T4. An increase in TSH means that there is not enough T3/T4 to inhibit TRH, and so TSH is being released to stimulate the thyroid gland. +16  
arezpr  TSH, T3, T4 and thyroglobulin cannot cross the placental barrier. +  
chamaleo  @arezpr although those hormones can't cross, the autoantibodies from Hashimoto's can +  
yotsubato  The baby has its own TSH though +  
sbryant6  TSH comes from the pituitary, and act on the thyroid. Autoantibodies attack the thyroid, so TSH doesn't work. +  
kimcharito  no goiter then? +  
lola915  I think there is no goiter because the baby's thyroid gland has not fully developed and these immunogloblulins from the mother could attack the thyroid gland leading to issues with it's development. +  



exactly how does maternal hashimoto can cause cretinism?

lola915  Hashimito is caused by antibodies against thyroid peroxidase and thyroglobulin. Those antibodies can cross the placenta and affect babies thyroid gland causing congenital hypothyroidism. +1  



 +1  upvote downvote
submitted by apurva(46),

The real thing is TSH, T3, T4 and thyroglobulin cannot cross placenta. TRH, Iodine, TSI can cross. If mother has high TSH (considering primary hypothyroidism) โ€”> Poor brain development If mother has TSI (Hashimoto) โ€”> cross the placental barrier โ€”Increase in thyroid gland (May present with stridor at birth.

demihesmisome  Ahhhhh Thank you. This was what I was trying to understand. +  
apurva  please note that free t4 can cross the placenta +1  



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I inkht htsi etsg ta a pctceon arledet ot trihdoy vseell nda cneptgangoe.ysrne/r

Egeotsrn ascrisene teh levle fo rynhonin-idtxegib ugbllnoi, hchiw ieprtloryam esrcsaeed eerf 4T nda 3T, nad isanesrce STH utnli the aaoldidint GTB eeobcsm rsuead,tta dna manlro lleevs are e.osdrter

enSci hsti npeitat ash nmiotuauem i,hoytsitrid dan qreesiur onrxhteyi, enhw hre efre T4 sar,esceed dan ehr TSH egos ,up hes town kmea xtrea 4T. So ussenl she isernaecs erh hieyxortn e,ods hse lwil be hhpdoyiroyt ->- nrcmsteii in het fuset




This is a very tricky question in terms of phrasing it. They make us think about what effect high TSH does on a fetus while it really meant what can happen to the baby in an antibody-mediated hypothyroidism mother. So sneaky so so sneaky...




 +0  upvote downvote
submitted by seagull(1107),
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2.gltlsMh/av90ei./tmi:8t.chC/wnmnPrwcb/1sowi2/pp7nc./

hsiT rtaclie lfais ot iotenmn opro nbira eevpntedoml ni toREhyrHmdi.PsiY The huarot stmu veah aenmt Ptmo.HyrdiYiOhs

sihT iueotsqn sutesp em ot no ed.n

aesalmon  I agree, the article you linked states "signs of fetal hyperthyroidism such as tachycardia, intrauterine growth retardation, cardiac failure, and the development of fetal goitre" I chose answer E during the exam - "Thyroid gland enlargement" Still trying to understand how they linked cretinism to a case where the mother's hypothyroidism was well controlled, and then asked for the sequelae if her TSH increased. Maybe increased TSH is supposed to indicate worsening hypothyroid - low T3/T4 needing to be stimulated by TSH? +  



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yM gotthhu prseocs saw if eth rmetoh hsa ircasnede HTS, 'dhse be nuisg ermo iedion ot rpouecd .4T3/ iengaMn essl oudlw eb leba ot egt to eht bayb rfo rabin odpeltn.eemv




 +0  upvote downvote
submitted by hayayah(989),
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mtCnirsei intc(lnoage pothrsmyoyd)hii is teh otsm mocomn ausec fo lttaereba nltame ldbiiyias.t Csuase proo airnb deon.mteevpl




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ehT oemthr has oueuimmnta sriihdtioyt nad nettarmet is ginev ofr oyioshpihydrmt lyon. yhw odse ti ttrmea if hte osmhtre' TSH is hhgi or ?wlo nottuiesdioAab wudol slilt eb pesnter nda ethy dwluo aaylsw aeusc stmiirenc etpicsireevr fo hrmeot rhmoeosn lvlee. t'nsI ?ti