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NERVE CONDUCTION STUDIESBasic PrinciplesBasharKatirji,M.D.
Professor and Director, Neuromuscular Center and EMG Laboratory
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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Repetitivestimulation Slow Rapid Postexercise
SinglefiberEMG Quantitativestudies
MUPanalysis Turnsandamplitudes MacroEMG Motorunitnumber
estimate(MUNE)
Nerveconductionstudies Sensory,motor,mixed
NeedleEMG Concentric Monopolar
Lateresponses Fwaves Hreflexes Blinkreflexes
SpectrumofElectrodiagnosticstudies
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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Bellytendonrecording Anactivelead(G1)
placedonthebellyofthemuscle
Anindifferentlead(G2)onthetendon
Musclerecordinghasamagnifyingeffect. Eachmotoraxon
innervatesuptoseveralhundredsmusclefibers
CMAPislarge(inmV)
Motorconductionstudies
Adopted from Neal & Katirji, NCS, 2011
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Motorconductionstudies
Adopted from Katirji, in Daroff et al 2012
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Antidromic studiesareperformedbyrecordingpotentialsdirectedtowardthesensoryreceptors
Orthodromic studiesareobtainedbyrecordingpotentialsdirectedawayfromthesereceptors.
Sensorylatenciesandconductionvelocitiesareidenticalwitheithermethod,butamplitudesarehigherinantidromicstudies.
Sensoryconductionstudies
Adopted from Neal & Katirji, NCS, 207
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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Onsetlatency isoftendifficulttodetermineandsubjecttodebate.
Peaklatency isveryaccurateandhasreplacedonsetlatencyinmostlaboratories
Tomeasureconductionvelocity,onsetlatencyisrequiredtoreflectthelargestconductingfibers
Sensoryconductionstudies
Orthodromic median (s)
Antidromic median (s)
Adopted from Katirji, in Daroff et al 2012
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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Sensorynerveactionpotential(SNAP)
Adopted from Neal & Katirji, NCS, 2011
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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SNAPisreducedorabsent: Plexopathies Mixedmononeuropathies Ganglionopathies
SNAPisnormal: Radiculopathies
Caudaequina Rootavulsions
Spinalcorddisorders Conusmedullaris Syringomyelia Myelitis
SNAPdistinguishesbetweenlesionsproximalvs.distaltoDorsalRoot
Ganglion(DRG)
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SegmentalrepresentationofSNAPs
Root SNAP
C6 Lateral antebrachial& Median/ thumb
C7 Median/index & Middle finger
C8 Ulnar/little finger
T1 Medial antebrachial
Root SNAP
S1 Sural
L5 Superficial peroneal
L4 Saphenous
NoSNAPrepresentationforC5oraboveandL3orabove
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Demyelination Focalslowing Conductionblock
Axonloss Mixed
Pathophysiologicalchangesinfocalneuropathies
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Conductionslowingduetoslowingofnervedepolarizationacrossthesegment
ItisbestexplainedbywideningofoneormorenodesofRanvier(Paranodaldemyelination)
Focaldemyelinativeslowingofmyelinatedaxon
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Mostcommonlyseenwithchronicentrapments Carpaltunnelsyndrome Ulnarneuropathyatelbow
Isduetoparanodaldemyelination(wideningofthenodesofRanvier)thataffectallthelargemyelinatedfibersequally
Doesnotcausesymptomsunlessassociatedwithotherpathologies
Focal(synchronized)slowing
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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InternalcomparisontestsinCTS
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FocalslowinginCTS(Internalcomparisonstudies)
Median
Ulnar
Median/ulnar comparison recording 2nd lumbrical/Interosseous
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Conductionblockoccurswhenactionpotentialscannotcrossademyelinatednervesegment
Itisbestexplainedbyinternodaldemyelination(demyelinationofoneormoresegments)andlackofsufficientNachannelsinthedemyelinatedsegment
DemyelinativeConductionblockofamyelinatedaxon
Normal Myelin Normal Myelin
Demyelinated Segment
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Thesensorynerveactionpotential(SNAP)andthecompoundmuscleactionpotential(CMAP)arethesummatedresponseduetodepolarizationofthousandsofaxons
TemporaldispersionCMAPandSNAP
Large myelinatedfibers
Small myelinatedfibers
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Temporaldispersion&phasecancellation CMAP
Short distance
Long distance
Withshortdistance,actionpotentialssummatewellwithlittleortemporaldispersionandphasecancellation
Withlongdistance,thereissignificanttemporaldispersionandphasecancellation
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Temporaldispersion&phasecancellation SNAP
Short Distance
Long Distance
Temporaldispersion&phasecancellationismoreprominentwithSNAPthanCMAPfor2reasons: TheCMAPdurationismuchlongerthantheSNAP Therangeoffiberconductionvelocityislessspreadinmotorthan
sensoryfibers(12m/secvs.25m/sec).
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Areadropgreaterthan50%betweenstimulationsites,regardlessoflengthofdistance
Overshorterdistances(e.g.10cm)20%isacceptable
Areadropisimportantinassessingconductionblock
Rhee RK, England JD, Sumner AJ. Ann Neurol 1990;28:146-159.
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PROBABLE 2050%dropinCMAP
amplitudewith50%dropinCMAP
amplitudewith50%dropinCMAPamplitudeandarea,or
>20%dropinCMAPamplitudeandareaoverashortnervesegment(10cm)
Conductionblock
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Mostcommonwithacutenervelesions Peronealatfibularneck Radialatspiralgroove Ulnaratelbow
Isduetosegmentalinternodaldemyelination
Istheelectrophysiologicalcorrelateofneurapraxia(firstdegreenerveinjury)
Conductionblock
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Radialnerveconductionblockatthespiralgroove(Saturdaynightpalsy)
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Ulnar&medianconductionblocksintheforearminmultifocalmotorneuropathy
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Identification of conduction block
>50% loss of distal amplitudeAbnormal amplitude reduction
>15% of distal durationCMAP duration increased
No Yes Yes
Area loss >50%
Pure conduction block (CB)
Area loss 50%
CB/TD
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Conductionblockvs.temporaldispersion
Ulnar neuropathies at the elbow
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Differentialslowingnotconductionblock
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Isduetoconductionslowingalongavariablenumberofthemediumorsmallnervefibers(averageorslowerconductingaxons)
Oftenitisassociatedwithfocalslowing
Differential(desynchronized)slowing
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Themostcommonmononeuropathiesseeninclinicalpractice
ResultsinlowCMAPfromallstimulationsites
Maymanifestwithconductionblockearly(beforeWalleriandegeneration)
Axonloss
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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0
2040
60
80
100
% Amplitude
1 2 3 4 5 6 7 8 9 10 11 12
Days from acute axonal injury
CMAP amplitudeSNAP amplitude
DistalSNAPandCMAPamplitudesduringWalleriandegeneration
Fibrillations with proximal /distal gradient
2 weeks
3 weeks
Adopted from Katirji, EMG in clinical practice , 2007
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Earlystudyinaxonlossmononeuropathyisveryusefulinlocalization,whileasecondstudyisnecessarytodetermine
pathophysiology
Ulnar nerve lesion in distal arm
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Considertheraredistaldemyelinatingconductionblockwhichmaymimicaxonalloss
e.g.acutemedianneuropathyatthewrist
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Demyelination Focalslowing Conductionblock
Axonloss Conductionblock
Early(beforeWalleriandegeneration) Conductionfailure(loworabsentCMAPs)
Late(afterWalleriandegeneration) Mixed
Electrophysiologicalfindingsinfocalneuropathies
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65yearoldwithrightfemoralneuropathyfollowinganabdominalhysterectomy
FemoralCMAPsrecordingrectusfemorisisconsistentwithapartialaxonlosslesion(50%ofaxonsarelost)
CMAPamplitudeandareaarethebestindicatorofextentofmotoraxonloss
Left
Right
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Axonlossandconductionslowing
Normal Nerve Axon Loss
Largest fibersLargest fibers
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Multiplepathologies
Below elbow
Above elbow
A 45 year man with progressive ulnar neuropathy
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Occursinapproximately1520%ofpopulation Fiberscrossfromthemediantotheulnarnerveinthe
forearm. Thecommunicatingbranch(es)usuallyconsistsofmotoraxons
thatsupplytheulnarinnervatedintrinsichandmuscles, thefirstdorsalinterosseousmuscle thehypothenarmuscles theulnarthenarmuscles Acombinationofthesemuscles
Anomalies.MartinGruberanastomosis
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MartinGruberanastomosistoADMandFDI(UlnarNCS)
Recording ADM Recording FDI
Wrist
Bel elbow
Ab elbow
Medwrist
Med elbow
From Katirji, EMG in clinical practice , 2007
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MartinGruberanastomosistoulnarthenarwithCTS
(medianNCS)
Adopted from Katirji, EMG in clinical practice , 2007
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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EDXmeansoflocalizationinperipheralnervelesions
Nerveconductionstudies Sensoryconductionstudies Motorconductionstudies Lateresponses(Hreflex,Fwaveandblinkreflex)
NeedleEMG Fibrillationpotentials Motorunitactionpotentials
Recruitment Morphology
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Fwaves.Values
Testtheintegrityofthemostproximalmotoraxons(includingroots)thatarenotaccessiblewithroutineNCS.
IsperformedduringNCS.
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Fwaves.Limitations
OnlyminimalFwavelatenciesarereproducible. Partialaxonallosslesionsareoftenassociatedwithnormallatenciesduetonormalconductioninintactaxons.
Slowingattherootlevelcanbeobscured(diluted)bythenormalconductionalongthelongaxon.
Sincemostmusclesareinnervatedbytwoormoreroots,normalconductionthroughintactroot(s)inpatientswithsingleradiculopathiesresultsinnormalminimalFwavelatencies.
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Hreflex.Values
Theonlytestthatevaluatethepreganglionicsensoryfibers
TibialHreflexmaybethesolemanifestationofmildS1radiculopathy
TibialHreflexamplitudecorrelatewellwiththeanklejerk
Adopted from Neal & Katirji, NCS, 2011
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Hreflex.Limitations
IsonlyreproduciblefromtheS1rootthroughthetibialnerve
Iscommonlyabsentbilaterallyinelderlypatientsorfollowingspinalsurgery
IsnotalwaysabnormalinS1radiculopathy
DoesnotaccuratelylocalizethelesiontotheS1root,buttotheS1reflex
Adopted from Neal & Katirji, NCS, 2011
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Blinkreflexes
Adopted from Neal & Katirji, NCS, 2011
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Blinkreflexes
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Facialpalsy:AbsentorprolongedR1andR2ipsilateraltothelesionwhilethecontralateralR2recordingswillbenormal.
Trigeminalneuropathy:R1andR2+contralateralR2areabsentordelayedwithipsilateralstimulation.Allresponsesarenormalwithcontralateralstimulation.
Lowerbrainstemlesion:Inapontinelesion,theaffectedsidewillhaveanabsentorprolongedR1butanormalipsilateralandcontralateralR2.Stimulatingthecontralateralsidewillresultinnormalresponses.AmedullarylesionwillrevealanormalR1andcontralateralR2whentheaffectedsideisstimulated;however,theipsilateralR2willbeabsentorprolonged.
DemyelinatingperipheralneuropathiessuchasGBSorCMT1:MarkedlyprolongedlatenciesinR1andR2dueslowingofthesensoryand/ormotorfibers.
Blinkreflexes
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EDXmeansoflocalizationinperipheralnervelesions
Nerveconductionstudies Sensoryconductionstudies Motorconductionstudies Lateresponses(Hreflex,Fwaveandblinkreflex)
NeedleEMG Fibrillationpotentials Motorunitactionpotentials
Recruitment Morphology
Advancing the Vision of the Neurological InstituteAdvancing the Vision of the Neurological InstituteMay 2013May 2013
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TheconceptoflocalizationbyneedleEMGissimilartoclinicallocalizationusingmanualmusclestrengthtestingthatispartoftheneurologicalexamination.
Mostoften,musclesinnervatedbybranchesarisingfromthenervedistaltothelesionareweak,whilethoseinnervatedbybranchesproximaltothelesionarenormal.
LocalizationbyneedleEMGinaxonlosslesions
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1.Nervelesionsalongsegmentswithnomotorbranches.
Theanatomyoftheinjurednerveplaysanimportantroleinthepreciselocalizationofnervelesions.
Manynervestravelsubstantialdistanceswithoutgivingoutanymotorbranches.
PitfallsofLocalizationbyneedleEMG
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2.Fascicularnervelesions. Occasionally,peripheral
nervelesionsspareoneortwonervefasciclesresultinginmusclesthatescapedenervationdespitebeinglocateddistaltothelesionsite.
Thisusuallyresultsinanerroneouslocalizationthatismoredistaltotheactualsiteofthelesion.
PitfallsofLocalizationbyneedleEMG
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3.Chronicnervelesions. Withmildormodestpartial
axonlosslesions,regenerationandreinnervationcanbeefficientinproximallylocatedmusclesresultinginremodelingofthemotorunits.
Hence,aneedleEMGdoneseveralyearsaftersuchlesionsmayonlydetecttheneurogenicchangesinthemoredistalmuscles
PitfallsofLocalizationbyneedleEMG