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NBME 22 Answers

nbme22/Block 3/Question#1 (60.5 difficulty score)
A 35-year-old man comes to the physician ...
C7 nerve root🔍
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 +4  upvote downvote
submitted by mcl(517),
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rortnPao stere dan asuarqdtu are htbo dilseppu by ednami ernev 1C(/875CT6/C,/C/ os hsat't otn pseur hp.uelfl) exnionstE of teh rmaroef is laidar veenr oas(l 1,C5-T asol otn ef)uhll.p This esdo ellt su is it ntca' eb lesdiaot inemda ro adali.r irTpsec ndento freexl is 7C8C,/ cwhhi snroawr ti dwon to teesh .owt

nCa oayenn lnxapie wyh t'is 7C revo 8C?

joha961  Same question. How could you determine between the specific nerve roots (C7 vs. C8)? +2  
mcl  Someone I was talking to (and post below) was saying that first aid mentions triceps is C7, so that's what should've been the big thing for us. +2  
joanmadd  you might see some ulnar nerve involvement if C8 was involved her +  
passplease  but he has generalized tingling which is in both ulnar and median regions? +  



 +3  upvote downvote
submitted by paulm(3),
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Pre WdorUl ID( )53515

The C7 roto si het ostm nlyeerfuqt dfceatfe veren orot ni tpntsiea ihtw leiaccvr caouy,aiphdtlr irutlsegn in tscdifei rsscoa teh ndmeia and ildraa eervn ubns.siridotit

ingitgln" osniensta fo rfeng"is → ideanm enver

es"rtcip uecmls flrxee is esrddeaec" → driala evnre

carmustine  Another important indication that this involves the median nerve is the weakness in pronation. Pronation of the forearm is performed by the pronator teres and the pronator quadratus, both of which are innervated by the median nerve. +3  



 +2  upvote downvote
submitted by delamj(4),

My thought process on this question:

  • weakness of arm extension and pronation = sounds like musculocutaneous nerve (C5-C7)

  • Triceps stretch reflex (C7-C8);

Ruleouts: Biceps is C5-C6 so r/o C6. C8 doesn't fit musculocutaneous muscle actions action so r/o C6. Median and Radial nerves have different muscle actions so r/o those as well, leaving just C7 best fitting the vignette.

delamj  C8 doesn't fit musculocutaneous muscle actions action so r/o C8.** +1  
lsp1992  I think you have the function of the musculocutaneous nerve wrong. Musculocutanous nerve's motor function is flexion (biceps, brachialis and corachobrachialis) and supination. Musculocutaneous dysfunction would cause weakness of flexion and supination. Weakness of extension would be radial nerve. Weakness of pronation would be median +1  



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ocdcAnrig to AF 2910 Tcreip fRleex is dmitaeed by C,6 yse 6C TNO 8C, dna 7C I[n ,DBOL ipngilym ti si omre mpnr.t]taoi

peridot  This is on p.498 of FA 2019 for anyone curious +  



 +1  upvote downvote
submitted by welpdedelp(198),
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So I tkinh atht iusse fo trwis tenenxois da/nor eirngf rdop wdolu be mreo alardi envre. erwo,vHe heert swa emor orlxpmia aesnesw,k so ti loudw be C.7

87"- yal hemt ,rthsi"gat the tp coun'dlt y"al htme s"hitatrg os it dolwu eb C7 ootr

welpdedelp  *As an addition, median nerve involvement would have leaned more toward C8 than C7. +1  
meningitis  Do you have anymore useful mnemonics for brachial plexus? +  
henoch280  FA pg 494 for mnemonics +  
winelover777  Doesn't look like there are many in FA 2019. S1/S2 - Buckle my shoe. L3/L4 - Shut the door. C5/C6 - Pick up sticks. +  
drzed  S2-S4 keeps the penis off the floor :) (cremaster reflex) +  
peridot  What's crazy @drzed is that in FA 2019 it says L1-L2 ("testicles move") on p.498 so I wonder if that changed +  



 +0  upvote downvote
submitted by azibird(74),

Here is a part of the UWorld table about cervical radiculopathies. And yes they did say that C7 is the most frequently involved. I think the answer is that C6 would involve the biceps, C8 would involve the fingers, and pronation is median nerve. So it has to be C7.

https://imgur.com/a/GvmCUj1




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Im’ csfdeonu uatob ihst o.en snkaeWse fo xnesnitoe nda oniotpnar of eht tigrh ,eoarfrm ihtw a cdsreaeed icrpest euslmc thsrect fee.lrx ehT ansewr aws C7 reven oort, utb who rae oyu leba ot ezclaoil ot C7 nda tno 6C ro ?8C I gidrefu that xenoeinst is rilad,a ,51TC- dan inoatnrop si a,emdin aols -C.1T5 siTpcer xrefle si C87C- 2F(19A0 ssya C)7.-C6 woH ulwdo oyu wrnora wnod ot utsj 7C ed?aagm

txallymcbeal  My FA2018 has “C7” bolded, meaning it is the main nerve root. But I also got this one wrong so I can’t be much help besides that. +1  
mnemonia  Honestly just a guess but I have this vague understanding that intrinsic hand muscles are C8-T1 so we might’ve expected more hand motor findings as well with a C8 lesion. +2  
theecohummer  I narrowed it down to C7 using the fact that the C7 myotome is elbow extension. I also learned that the C7 nerve root was the main contributor to the triceps DTR so I just went with that. +  
mchu21  They also mentioned that the person had weakness pronating the right forearm which is performed by the biceps. Biceps is innervated by the musculocutaneous nerve which is C5-C7 and that's what helped me pick C7 > C8. +1  
mcl  Sorry, I thought the biceps was a supinator of the forearm? +10  
henoch280  yes.. its the supinator not pronator +  



According to Uworld, QID: 11779 C7 myotome is involved in elbow extension. Looks like it settles!




 +0  upvote downvote
submitted by nwinkelmann(257),
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rPe iipek:aWdi eTh eitprcs xf,erle a pdee tneodn ,ferelx is a xeelfr as it tiieslc vionyuanrlt nnirctootac fo hte sprtcie birchia cmu.sle It is itneidati by het Ccivelar f(o eth ecnk erng)oi palsni nerve 7 evren toor hte( lmsal entsmeg fo teh erven atth egsemer mofr teh islanp r.c)od The xferle is stdeet sa patr of teh aoglenouilcr tmaoiinnxea to ssseas eht osnyres dna mtroo hspaaytw tihiwn het C7 dan 8C pilasn rvee.sn

solA, orfm a idnetfrfe bt:ewise hTe isctrep eerxfl is mideaetd yb hte 6C dan C7 nevre s,roto aneoitdynlmpr by .C7 /ue.nuerfiecpy./nd:mftl.eebt/meru/lsomnttxsohreluduiresryp.doha/mgu/ss.


this is my way to think(please correct me if it's not correct: a. weakness of triceps muscle reflex --> C6 / C7 / C8 problem (FA P498 2019) b. weakness of extension of the forearm --> radial nerve is involved --> damage of C7 root leads to axillary or RADIAL nerve defect (FA P441 2019)

+/- joyceeepan(4),