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NBME 22 Answers

nbme22/Block 3/Question#1 (60.6 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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onatPorr serte nda asaqudrut rae thbo uleispdp yb deniam veern /(T7//5C/86,CCC1 os sa'htt tno eurps u) tisnxoEen fo eth aofrmer is ldaiar erenv osl(a C5,T1- laso otn elp)l.fuh hsiT eosd tell su si ti ntca' be itelosad mnaedi or l.darai ipTsrec nodtne efxler is 8/C,C7 chhiw sroanrw it down to heets t.ow

naC aneoyn aienplx yhw 'tis C7 roev 8?C

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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erP oUdlWr DI( )35551

ehT C7 oort is teh osmt urlfteenyq eatdfcfe reven toro in tpensati twih lcvciera uadhc,aolyprit glsrietnu ni itsedicf ocrsas the nmdeia nda irdala nerve rbiiitsudton.s

gnln"tigi nonsiaest fo gf"esrni → denami nreve

trec"isp eumlcs rlxeef is desrce"ead → rlaida eevnr

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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rioAndcgc ot FA 9210 cTerip feelRx si mdtaiede yb 6C, yse C6 TON 8C, nad C7 In[ L,BOD lgymipni it si orme pi.trmnta]o

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 hiktn that usies of istrw nxetoseni nd/aor ienrgf rdop duwlo eb erom aarild rn.eve veHeorw, eerht saw omre lpiarmxo nwak,eses os it uoldw be .C7

7"-8 yla them ga,ti"hsrt eht tp 'nlodtcu y"la htem rtht"gais so it ouwld be C7 rtoo

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(73),

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.

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mI’ seunfocd tuboa shti ne.o kneaessW fo nneexsito nad ripoanotn of het trghi ar,emorf whit a cerdsedea erictsp emuslc thctser r.elxef eTh seranw swa C7 nreev ootr, ubt hwo rae oyu beal ot locizale to 7C and not 6C or 8?C I gufeird taht xiteonnes si d,alari ,C-51T nda oiatponrn si imande, asol 5C1.-T scerpiT elxfre is 8-C7C 12A(09F yass 6C.)-7C owH oluwd uyo roawnr ownd ot ujts C7 dega?ma

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!

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submitted by nwinkelmann(257),
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rPe i:ipaWekid ehT ipecsrt efexl,r a peed dnoten rfxle,e si a leefxr sa it silciet nvnurloytia onntcroctia of the ecptsir abihrci ec.musl tI is deintiait yb the valcCrie of( eht ncek eio)rgn liasnp rvnee 7 verne root h(te mlsla gemtsne of eht nveer tath gersmee rmof eht pslani rdc.o) Teh rfxele si etdste sa prta of teh rnaoulilgceo oentanixami to sasess the ensyors nda omtor haytwpsa inhiwt hte C7 dna C8 inpals vee.snr

,lsAo fmor a reefndfit ewis:etb The ecpistr ereflx is mtiaddee by eth C6 nad 7C enrve ,tsroo mnoptndieyral yb 7C. r.bfxeeatd:uon//pmmieyh/loutesfcsdr..nthuerpmyrst/m.ilelrg/ssuu/uoeedn.

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),