NERVE CONDUCTION STUDIESBasic PrinciplesBasharKatirji,M.D.

Professor and Director, Neuromuscular Center and EMG Laboratory

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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

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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

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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

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Sensorynerveactionpotential(SNAP)

Adopted from Neal & Katirji, NCS, 2011

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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

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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

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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

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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

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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