EMG 指南

Studiesof10PatientswithDifferentClinicalProblems

RachelDiTrapani,

KEYWORDS

󰀁Electromyography󰀁Nerveconductionstudies󰀁Algorithm󰀁Neuromusculardisorders

MD,

DevonI.Rubin,MD*

Otherarticlesinthisissuehavereviewedbasicconceptsofnerveconductionstudies(NCSs)andneedleelectromyography(EMG),andhavedetailedtheelectrodiagnosticfeaturesandapproachesthatareusedtoevaluatedifferenttypesofneuromusculardisorders.Thisarticlediscusses10representativecasevignettesthatmaybeencoun-teredduringadayintheEMGlaboratory,whichdemonstratetheapproachesusedinourEMGlaboratorytoevaluatepatientspresentingwithspecificsymptomsandavarietyofsuspectedneuromuscularconditions.Eachcasepresentsabriefdescrip-tionofthepatient’ssymptomsandclinicalfindings,suggeststhesuspectedlocaliza-tionordiagnosisthatwasconsideredbasedontheclinicalfeaturesbeforetheperformanceoftheelectrodiagnosticstudy,andthenpresentstheNCSandneedleEMGdatathatwereactuallygatheredfromthatpatient.Commentsandinstructiveelectrodiagnosticconsiderationsastheyrelatetoeachcasearediscussedattheendofthecase.AlthoughitwouldbeuncommontoencounterallofthesepatientsinasingledayintheEMGlaboratory,itwouldsurelybeaninterestingandeducationalworkday.

CASE1.AHOSPITALVOLUNTEERWITHHANDNUMBNESSClinicalHistory

A79-year-oldwoman,whoworkedasavolunteerattheinformationdeskofourhospital,complainedofnumbnessandparesthesiasinherrightthumbandindexfinger.Hersymptomswereconstant,butworsewhenshewoulddrivetoworkinthemorningandduringthenightwhenshewastryingtosleep.Shenotedthatrubbing

DepartmentofNeurology,MayoClinic,4500SanPabloRoad,Jacksonville,FL32224,USA*Correspondingauthor.

E-mailaddress:rubin.devon@mayo.edu

NeurolClin30(2012)731–755doi:10.1016/j.ncl.2011.12.010neurologic.theclinics.com0733-8619/12/$–seefrontmatterÓ2012ElsevierInc.Allrightsreserved.

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orshakingherhandimprovedthesymptomsslightly.Shedeniedweakness;however,shereporteddroppingobjectsthatshewasholdinginherhandonoccasion.Shealsoreportedsomeachinessofhershoulderandentirearm,andoccasionalmildneckstiff-ness.Shedidnotexperienceanysimilarsymptomsinherlefthand.

PhysicalExamination

Thepertinentneurologicexaminationfindingsweredecreasedsensationtopinprickontheflexorsurfaceofthethumb,index,andmiddlefingers.Therewasnoweaknessoratrophynotedintherightthenarorotherarmmuscles.Reflexeswerenormalandsymmetricinherupperextremities.

DifferentialDiagnosis

Theclinicalfeaturesweremostsuspiciousforarightmedianneuropathyatthewrist(carpaltunnelsyndrome[CTS]).However,otherlocalizationsthatmaypresentwithsimilarfeaturesandshouldbeconsideredincludeaC6-C7radiculopathy(especiallygivensomeneckandarmdiscomfort),aproximalmedianneuropathy,or,lesslikely,abrachialplexopathy.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables1and2.TheNCSsdemonstratedprolongedrightmedianmotorandsensorydistallatenciesandalowmediansensoryamplitudewithamildlyslowedconductionvelocity.NeedleEMGwasnormal.Thefindingsindicateamoderatelysevererightmedianneuropathyatthewrist(CTS).

CaseComment

Thiscasedemonstratestypicalfeaturesofamedianneuropathyatthewrist,suchasoccursinCTS,withconductionslowingidentifiedinmotorandsensoryfibersinthedistalmediannerveacrossthewrist.Inthiscase,motorNCSswereperformedfirstandbecausethemedianmotorfibersdemonstratedaprolongeddistallatency,theantidromicsensorytechniqueswereselectedforthesensorystudies.HadthemedianmotorNCSsbeencompletelynormal,theorthodromic(palmar)sensorystudiesorothercomparisonstudies(median–radialtothumbormedian–ulnartoringfinger)wouldhavebeenperformedtoincreasethesensitivityofidentifyingaverymilddistalmedianneuropathy.TheneedleexaminationconsistedofevaluationofmusclessuppliedbythemediannerveaswellasthoseinnervatedbytheC5throughT1rootstoexcludeasuperimposedcervicalradiculopathy(althoughacervicalradiculopathyatanylevelwouldnotaffectthemediansensoryNCSs).Giventhenormalmedian

Table1Case1:nerveconductionstudiesAmplitude(mVormV)Stimulate(Record)Ulnar,m(hypothenar)Ulnar,santi(fifth)Median,m(thenar)Median,santi(index)R12.7337.710820LNL>6>10>4>15R556051515866Velocity(m/s)LNL>51>54>48>56DistalLatency(ms)R3.03.05.14.63.43.0LNL<3.6<3.1<4.5<3.627.328.028.6F-WaveLatency(ms)R27LEst24.8Abbreviations:Est,estimate;NL,normalvalues.

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Table2Case1:needleexaminationoftherightupperextremityMuscleDeltoidBicepsTricepsPronatorteresAbductorpollicisbrevisFlexorpollicislongusFirstdorsalinterosseousInsertionalActivityNLNLNLNLNLNLNLFibrillationPotentials0000000MUPNLNLNLNLNLNLNLAbbreviations:MUP,motorunitpotential;NL,normal.

compoundmuscleactionpotential(CMAP)amplitude,theyieldofidentifyingsignifi-cantabnormalitiesintheabductorpollicisbreviswasrelativelylow;however,becausethemedianmotorNCSwasnotentirelynormal,themusclewasexaminedinthiscase.1Thestudywasinterpretedasshowingamoderatelyseveremedianneuropathy.Differentgradingscalesareusedtogradetheseverityofmedianneuropathiesatthewrist:mildcasestypicallydemonstrateonlysensoryNCSabnormalities,whereasmoderatelyseverecasesarethoseinwhichthereisslowingofconductioninmedianmotorfibersacrossthewristwithoutalossofamplitude,andseverecaseshavereductioninthemotoramplitude.DocumentinganelectrophysiologicgradeofthedegreeofthemedianneuropathyatthewristisusefulintheEMGreport,becauseitmayguidethereferringphysician’sdecisionontreatment.However,thedegreeofelectrodiagnosticabnormalitiesandtheclinicalsymptomsmaynotalwayscorrelatewell.Althoughthispatientdidnothaveanysymptomsinherlefthand,sensoryNCSswereperformedtoassessforsubclinicalinvolvementofherlefthandbecauseCTSisfrequentlybilateral.Thispatientdidnothaveamedianneuropathyontheleft.

CASE2.ACOMPUTERPROGRAMMERWITHANUMBPINKYANDWEAKHANDClinicalHistory

A31-year-oldmanwhoworksasacomputerprogrammerpresentedwithnumbnessofhisleftfifth(pinky)digit.Henotedthathefrequentlywouldresthiselbowonapadathisdeskinanefforttokeephiswristsinlinewhiletyping,toavoiddevelopingCTS.Bytheendofhisworkday,henoticedatinglingradiatingdownthemedialaspectofhisforearmintohisleftringandpinkyfinger.Thisprogressedtopersistentnumbnessinvolvinghisleftfifthdigitspecifically.Healsocomplainedofoccasionalelbowdiscomfort.Hedeniedanyweaknessinhishandorarm.

PhysicalExamination

Thepertinentfindingsincludeddecreasedsensationtopinprickoverthemedialaspectofthefourthandfifthdigitsofthelefthand.Therewasequivocalweaknessbutnoatrophyinhishypothenarandinterosseousmuscles.Reflexeswerenormalandsymmetric.

DifferentialDiagnosis

Theclinicalhistorysuggestsaleftulnarneuropathy,probablylocalizedattheelbowgivenhishistoryofrestinghiselbowonapadwhileatwork.Additionalconsiderations

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includeadistalulnarneuropathyatthewrist,aC8orT1radiculopathy,orabrachialplexuslesioninvolvingthelowertrunkormedialcord.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables3and4.NCSsdemonstratedlowleftulnarsensory(antidromic)nerveamplitude.Withelbowstimulation,noreliableresponsewasrecordedand,therefore,conductionvelocitycouldnotbedetermined.Shortsegmentalincrementalstimulation(inching)alongtheleftulnarnerveshowedapartialmotorconductionblockof28%inampli-tudeand30%inthearealocalizedadjacenttothemedialepicondyle(Fig.1).Needleexaminationdemonstratedonlyreducedrecruitmentinthefirstdorsalinterosseousandabductordigitiminimi.Nofibrillationpotentialsorothermotorunitpotential(MUP)morphologicchangeswereseen.Thereiselectrodiagnosticevidenceofamildleftulnarneuropathyintheregionoftheelbowthatislocalizedtothemedialepicondyle,characterizedprimarilybyfocaldemyelination.

CaseComment

Thiscasedemonstratestypicalfeaturesofanulnarneuropathyattheelbow.InthispatientthesensoryNCSsdemonstratedlowulnarsensoryamplitudes,whichsupportsaxonaldegenerationoftheulnarsensoryfibers.However,inisolationthisfindingcouldbeseenwithanulnarneuropathylocalizedproximaltothewrist,butcouldalsobeseenwithalowertrunkormedialcordplexopathy.Inthiscase,palmarstudieswerealsoperformedtoassessforslowingacrossthewrist,asmaybeseeninadistalulnarneuropathyattheGuyoncanal.Iftherewasahighindexofsuspicionforalesionatthewrist,thedorsalulnarcutaneoussensorystudywouldhavebeenusefulbecauseitwouldbenormalinanulnarnervelesionatthewristandabnormal(lowamplitude)inalesionattheelbow.

ThestandardulnarmotorNCS,withstimulationatthewristandabovetheelbow,wasnormal,includingtheconductionvelocityacrosstheelbow,makingitdifficulttopreciselylocalizetheprocesstotheulnarnerveattheelbow.However,thiscasedemonstratesthevalueofinchingalongtheulnarnervein2-cmsegmentsacrosstheelbowtoassistinmorepreciselocalizationofamildulnarneuropathycharacterizedbyveryfocaldemyelination.Theinchingstudydemonstratedasegment

Table3Case2:nerveconductionstudiesoftheleftupperextremityStimulate(Record)Ulnar,m(hypothenar)Ulnar,santi(fifth)Ulnar,spalmar(fifth)Median,m(thenar)Median,spalmar(wrist)Amplitude(mVormV)(Normal)8.8(>6)7(>10)13(>15)7.7(>4)197(50)Velocity(m/s)(Normal)53(>51)NR(>54)NR(>54)58(>48)66(>55)DistalLatency(ms)(Normal)2.5(<3.6)2.7(<3.1)1.9(<2.3)3.4(<4.5)1.9(<2.3)28(28.6)F-WaveLatency(ms)(Estimate)30(30)Abbreviation:NR,noresponseobtained.

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Table4Case2:needleexaminationoftheleftupperextremityMuscleDeltoidBicepsTricepsPronatorteresExtensorindicisFlexordigitorumprofundusIIIandIVFirstdorsalinterosseousFlexorcarpiulnarisAbductordigitiminimiInsertionalActivityNLNLNLNLNLNLNLNLNLFibrillationPotentials000000000MUPNLNLNLNLNLNLNLDurationNLDurationNLDuration1111Recruitment(Reduced)Abbreviation:NL,normalfindings.

whereadefiniteconductionblock(>10%overa2-cmsegment)andafocalshiftinlatency(1.4millisecondsinthiscase)wereidentifiedbetweentwositesofstimulation(seeFig.1).Thisfinding,whenpresent,provideslocalizingvalueinidentifyingtheprecisesiteofcompressionorinjurytotheulnarnerve.

Inthiscase,theneedleexaminationonlydemonstratedsubtleabnormalities(reducedrecruitment)inulnarinnervatedhandmuscles.Astheonlyfinding,thereducedrecruitmentwouldbecompatiblewithunderlyingpathophysiologyof

Fig.1.Ulnarmotorinchingstudyincase2,demonstratingapartialfocalconductionblockatthemedialepicondyle.Theresponsesateachstimulationsitearesuperimposed.Thefirstresponseontheleftisstimulationatthewrist.Theremainingresponsesoccurfromstimulationaroundtheelbowin2-cmincrements.

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focaldemyelinationandpartialconductionblockwithoutevidenceofaxonalloss(inwhichfibrillationpotentialsorlong-durationMUPswouldbeexpected).Other,nonul-narC8-T1muscles,suchastheabductorpollicisbrevisandextensorindicisproprius,werenormalandhelpedtoexcludethoselocalizations.Inthiscase,andinsomeulnarneuropathiesattheelbow,theproximalulnarmuscles(flexorcarpiulnarisandflexordigitorumprofundus)werenormal.Thesemusclesmayhavebeensparedbecausethebranchestothosemusclesoftenexittheulnarnerveproximaltotheelbow(andthusproximaltothelesion)orbecausethenervefasciclestothosemusclesmayhavebeenpreferentiallyspared.Incasessuchasthiswherethepathologicchangessuggestfocaldemyelination,theprognosisisgenerallyfavorableiftheoffendingcauseoftheulnarneuropathyiseliminated.

CASE3.ACANCERPATIENTWITHTINGLINGTOESClinicalHistory

An18-year-oldwomanwithahistoryofcancerpresentedwithdecreasedsensationinherfeet.Hersymptomsbeganshortlyafterthecompletionofacourseofchemo-therapy,whichincludedvincristineandcyclophosphamide.Shereporteddecreasedsensationinbothfeetanddescribedafeelingof“walkingonstaples.”Shefeltgenerallyweakerinherarmsandlegs.Shedeniedanypaininherextremities.

PhysicalExamination

Thepertinentneurologicexaminationabnormalitiesincludeddecreasedsensationtopinprick,temperature,vibration,andjointpositioninbothfeetuptotheleveloftheanklesbilaterally.Reflexeswerediminishedinherupperlimbsandabsentinherquadricepsandanklesbilaterally.Strengthtestingrevealedbilateralweaknessoffootdorsiflexion,eversion,inversion,andplantarflexion(MedicalResearchCouncil[MRC]grade4/5).HerRombergsignwaspresentandhergaitexaminationwasnotableforasensoryataxia.

DifferentialDiagnosis

Giventhetemporalrelationshipbetweenthepatient’schemotherapyanddevelop-mentofsymptoms,themostlikelydiagnosisisachemotherapy-associated,length-dependent,peripheralneuropathyinvolvingsensoryandmotorfibers.Anotherpossibilityisapolyradiculoneuropathyorsensoryganglionopathy(whichwouldbelesslikelywithtrueweakness).Inaddition,otherunlikelyconsiderationsarebilaterallumbosacralradiculopathiesorlumbosacralplexopathies.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables5and6.NCSsdemonstratedabsentsensoryresponsesdiffusely,anabsentperonealmotorresponse,lowtibialmotoramplitudewithaslowedconductionvelocity,andaslowedmedianmotorconductionvelocitywithaprolongeddistallatency.Needleexaminationdemonstratedmildlong-durationMUPsintheanteriortibialis.Thefind-ingsarethoseofasevere,length-dependent,large-fiber,peripheralneuropathyinvolvingmainlysensoryfibers,withmilderinvolvementofmotorfibers.

CaseComment

Inthiscaseaperipheralneuropathywassuspected,basedontheclinicalhistoryofhavingreceivedchemotherapeuticagentsknowntobeassociatedwithaperipheralneuropathy,andthetypicalclinicalexaminationfindingsofdistalsensoryloss,hypo-reflexia,milddistalweakness,andsensoryataxia.NCSsandEMGwereperformedto

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Table5Case3:nerveconductionstudiesAmplitude(mVormV)(Normal)7.2(>6)NRNR8.7(>4)NRNRNR3.1(>4)NR32(>40)48(>48)NRNRVelocity(m/s)(Normal)53(>51)NRDistalLatency(ms)(Normal)2.8(<3.6)NRNR5.2(<4.5)NRNRNR4.7(<6.1)NR66.8(73.2)28(28.6)F-WaveLatency(ms)(Estimate)31.4(23.8)Stimulate(Record)Ulnar,m(hypothenar)Ulnar,santi(fifth)Radial,s(wrist)Median,m(thenar)Median,santi(index)Peroneal,m(extensordigitorumbrevis)Sup.Peroneal,s(ankle)Tibial,m(abductorhallucis)Plantar,medial,s(ankle)Abbreviation:NR,noresponse.

characterizethedistributionofinvolvement,differentiatebetweensensoryandmotorcomponents,differentiatebetweenaxonaldegenerationordemyelinationastheprimarypathologicchanges,excludemultipleradiculopathiesoraplexopathy,andassessseverity.

ThemostprominentfindingonNCSswasthediffuselyabsentsensoryresponses.Thisfindingcanbeseeninadiffuseseveresensoryneuropathyorsensoryganglion-opathy,whichisdifficulttodistinguishonanelectrophysiologicbasis.Theperfor-manceofblinkreflexesmayhelp,althoughabsentblinkreflexresponsescanbeseenineitherprocess.Somehaveadvocatedusingthemasseter(jaw-jerk)responseinsituationsinwhichallsensoryresponses,includingblinkreflexes,areabsent(seethearticleonCranialNeuropathiesbyLacomiselsewhereinthisissue).Becausethejaw-jerkreflexisamonosynapticreflexwiththemesencephalicganglionlocatedwithinthebrainstemratherthanextramedullary,theresponseshouldbepreservedinganglionopathiesbutbeabnormalinsensoryneuropathies.However,thisreflexistechnicallydifficulttoelicitinsomenormalpeople,sointerpretationshouldbemadewithcaution.

Table6Case3:needleexaminationMuscleFirstdorsalinterosseousTensorfascialataVastusmedialisGluteusmaximusTibialisanteriorMedialgastrocnemiusInsertionalActivityNLNLNLNLNLNLFibrillationPotentials000000NLNLÆÆMUPNLNLÆÆDuration(Long)Amplitude(High)Abbreviation:NL,normal.

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Inthiscasethemotorconductionstudiesweremildlyabnormal,indicatingthattheneuropathyinvolvedmotorfiberstosomedegreeinadditiontothemoreseverelyaffectedsensoryfibers.Thetibialandmedianmotorconductionvelocitiesweremildlyslowedbutnotintherangeofdefinitedemyelination.Tobeconfidentthattheneurop-athyisprimarilyduetodemyelinationinthecaseofalowtibialmotoramplitude,theconductionvelocityshouldbelessthan50%ofthelowerlimitofnormal,whichinthiscasewasnot.Inaddition,themedianmotordistallatencywasprolongedwithanormalamplitude,suggestingthattheremaybeapossiblesuperimposedmedianneuropathyatthewrist.

TheNCSfindingscouldalsobeseeninadiffuse,patchypolyradiculoneuropathy.Theneedleexaminationdemonstratedonlymildabnormalitiesinthedistallegmuscles,andtheproximallegmuscleswerenormal.Examinationofproximalmusclesisimportanttoexcludeapolyradiculopathy,inwhichdistalandproximalmusclessuppliedbythesamerootswouldbeexpectedtobeabnormal.Inthiscase,thediscrepancybetweenthemoderatelyseverelowerextremitymotorNCSabnormalitiesandtheverymildneedleexaminationabnormalitiesinthedistallegmusclesmayreflectthepossibilitythatonlytheverydistalmotorfiberstothedistalfootmuscleswerepredominantlyaffected.Needleexaminationwasnotperformedinfootmuscles,suchastheabductorhallucisorfirstdorsalinterosseouspedisinthiscase;hadthosemusclesbeenexamined,theymayhaveshownmoresignificantabnormalitiesthanthelegmuscles.Thefeaturesofthiscasearetypicalforchemotherapy-inducedperipheralneuropathy.

CASE4.AWOMANWITHPAINLESS,PROXIMALWEAKNESSClinicalHistory

A48-year-oldwomanpresentedwitha1-yearhistoryofprogressive,painless,prox-imalmuscleweakness.Shedescribeddifficultywalkingaroundherblock,whichshehaddoneregularlyforyears.Shenotedweaknesswithclimbingstairs,anddifficultyraisingherarmsoverherheadwhileblow-dryingherhair.Shereportednospeechorswallowingimpairmentanddidnotexperiencedoublevisionordroopingofhereyelids.Shedeniedmuscletendernessorpainandhadnosystemicsymptoms,suchasskinabnormalitiesorpulmonarycomplaints.Bowelandbladderfunctionwasalsonormal.

PhysicalExamination

Thefindingswerenotableforsymmetric,moderatelysevereweaknessofproximalshouldermuscles,hipflexorsandabductors,andfootdorsiflexorsbilaterally.Sensoryexaminationwasnormal.Reflexeswerenormaldiffusely.

DifferentialDiagnosis

Theclinicalpossibilitiesinthiscaseincludeamyopathy,adisorderofneuromuscularjunctiontransmission,suchasmyastheniagravisorLambert-Eatonmyasthenicsyndrome(LEMS),orpolyradiculopathy(suchaschronicinflammatorydemyelinatingpolyradiculopathy).

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables7and8.NCSsoftheleftupperandlowerextremitieswerenormal.Needleexaminationdemonstratedfibrillationpotentialsandshort-durationMUPswithrapidrecruitmentinseveralproximalmuscles.Therewasdecreasedinsertionalactivityandmarkedly

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Table7Case4:nerveconductionstudiesoftheleftsideAmplitude(mVormV)(Normal)8(>6)16(>15)3.6(>2)5.2(>4)4(>0)Velocity(m/s)(Normal)77(>51)63(>56)46(>41)51(>40)47(>40)DistalLatency(ms)(Normal)2.6(<3.6)3(<3.6)4(<6.6)4.3(<6.1)3.9(<4.5)51.6(49.6)55.6(45.4)F-WaveLatency(ms)(Estimate)26.2(20.2)Stimulate(Record)Ulnar,m(hypothenar)aMedian,santi(index)Peroneal,m(extensordigitorumbrevis)Tibial,m(abductorhallucis)Sural,s(malleolus)aRepetitivestimulationat2Hz(nodecrement).

reducedrecruitmentofshort-durationMUPsintheanteriortibialis.Thefindingswereconsistentwithapatchymyopathy,mainlyinvolvinglowerextremitymuscles.

CaseComment

Theelectrodiagnosticapproachtothispatientbeganwithstandardmotorandsensoryconductionstudiesinthelegs,whichweremostclinicallyaffected,aswellasscreeningconductionstudiesinanarm.ThenormalfindingsontheNCSswouldmakeapolyradiculopathylesslikely,butcouldbeseeninmyopathiesandneuromus-cularjunctiondisorders.Repetitivestimulationstudieswereperformedontheulnarnerve,using2-Hzstimulationatrest,toscreenforaneuromuscularjunctiondisorder.HadtheindexofsuspicionforaneuromuscularjunctiondisorderbeenhighorhadtheroutineneedleexaminationdemonstratedmarkedMUPvariation,repetitivestimula-tionofadditionalproximalnerves,suchasthespinalaccessorynerve,wouldhavebeenperformed.

Herneedleexaminationconsistedofexaminationofmoderatelyweakmusclesanddemonstratedchangestypicalformyopathy,includingshort-duration,low-amplitude,polyphasicMUPswithrapidrecruitmentinproximalmuscles.Thefindingsofreducedrecruitment(alongwithshort-durationMUPs)intheanteriortibialiswereconsistentwithend-stagemyopathicchanges.Thepresenceoffibrillationpotentialssuggestsunderlyingpathologicchangesofmusclefibernecrosisorsplitting,orvacuolar

Table8Case4:needleexaminationoftheleftsideMuscleDeltoidBicepsFirstdorsalinterosseousVastusmedialisTibialisanteriorT10paraspinalInsertionalFibrillationActivityPotentialsMUPRecruitmentDurationAmplitudePhasesIncreasedNLNLIncreased11002111NL011NLNLRapid11Rapid11Rapid1121short21low11short11low11short11low25%50%NL11short11lowÆ25%TensorfascialataIncreasedIncreasedDecreased0Reduced2131short31lowAbbreviation:NL,normal.

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damagetomusclefibers.Thesefindingswouldraisethepossibilityofaninflammatorymyopathy,suchaspolymyositis,althoughmanyothertypesofmyopathiescanproducesimilarfindingsonEMG(seethearticleonMyopathieselsewhereinthisissue).Althoughneuromuscularjunctiondisorderscanoccasionallybeassociatedwithfibrillationpotentialsandmildshort-durationMUPsinsomemuscles,thefindingsinthispatientaremuchmorepronouncedthanwhatwouldbeexpectedinmyastheniagravisorLEMS,andtherapidrecruitmentismorecompatiblewithamyopathy.

Thispatientunderwentamusclebiopsyofherdeltoid,thefindingsofwhichwereconsistentwithpolymyositis.

CASE5.AGOLFERWITHNECKPAINClinicalHistory

A74-year-oldmanpresentedwitha6-weekhistoryofneckpainandintermittentsharppainthatradiateddownhisleftarmintothemiddlefinger.Hissymptomsbeganapproximately6weekspreviously,afterplayinginagolftournament.Hehadaprevioushistoryofoccasionalneckpainthatwouldlastforseveralweeksatatimebutneverradiateddownhisarm.Hereportedavaguesenseofheavinessinhisarmanddescribedsomenumbnessinhishand.

PhysicalExamination

Thepertinentfindingsincludedmildweaknessofelbowandwristextension,andadepressedlefttricepsmuscledeeptendonreflex.Neckmovementtotheleftcausedpaintoradiatefromtheneck,downthearm,andintothemiddlefinger(positiveSpurl-ingsign).Placingtheleftarmovertheheadrelievedhissymptomstemporarily.Sensoryexaminationwasnormal.

DifferentialDiagnosis

Inthiscasethedistributionofthepatient’ssubjectivesymptomsandfindingsonhisneurologicexamination,aswellasthereproducibilityofhissymptomswithneckmovement,suggestedthatthemostlikelydiagnosiswasaleftC7radiculopathy.Otherlesslikelypossibilitiesincludedaposteriorcordormiddletrunkbrachialplexuslesionoraradialneuropathy.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables9and10.TheNCSsoftheleftupperextremitywerenormal.NeedleexaminationdemonstratedamilddegreeofincreasedinsertionalactivityandfibrillationsinleftC7innervatedmuscles.Therewasincreasedpolyphasiaandmildlong-duration,

Table9Case5:nerveconductionstudiesAmplitude(mVormV)(Normal)7.6(>6)13(>10)10.0(>4)33(>15)Velocity(m/s)(Normal)55(>51)56(>54)50(>48)60(>56)DistalLatency(ms)(Normal)3.2(<3.6)2.8(<3.1)3.6(<4.5)3(<3.6)28.1(30.2)F-WaveLatency(ms)(Estimate)31.9(27.7)Stimulate(Record)Ulnar,m(hypothenar)Ulnar,santi(fifth)Median,m(thenar)Median,santi(index)ADayintheEMGLaboratory741

Table10Case5:needleexaminationMuscleDeltoidBicepsTricepsInsertionalFibrillationRecruitmentDurationAmplitudeActivityPotentialsMUP(Reduced)(Long)(High)PhasesNLNLIncreased00110ÆÆ011NL1175%NL1111ÆÆÆÆ50%50%NLNL11ÆÆ75%ExtensorindicisNLpropriusPronatorteresExtensorcarpiradialisFirstdorsalinterosseousC7paraspinalIncreasedIncreasedNLIncreasedAbbreviation:NL,normal.

high-amplitudeMUPsintheC7distribution.Thefindingswereconsistentwithasubacute,active,leftC7radiculopathy.

CaseComment

Inthiscase,theclinicalfeatureswereverytypicalofacervicalradiculopathy.BecausethemostfrequentlyaffectedrootinacervicalradiculopathyistheC7rootandalsobecausetheclinicalfindingsfitwithinthisrootdistribution,itmightbearguedthattheperformanceofelectrodiagnostictestingprovideslittleadditionalinformationandthatanEMGcouldbebypassedinplaceofimagingstudies.Althoughincertaincasesthisapproachwouldnotbeincorrect,EMGdoeshaveutilityandmayprovidecomplementaryinformationtoimagingstudiesregardingtheproblem.Thegoalofelectrodiagnosticstudiesintheevaluationofasuspectedcervicalradiculopathyisnotonlytoconfirmthattheprocessisattherootlevelandtolocalizewhichroot(s)is(are)involved,butalsotoassessseverityandactivity(ie,whetherthereisdenerva-tionofthemusclesinnervatedbytheroot).

InthiscaseroutinemotorNCSs(medianandulnar)wereperformedandwerenormal,whichwouldbeexpectedinallcervicalradiculopathiesoutsideoftheC8orT1distribution.InpatientswithsuspectedC7(orC6)radiculopathies,othermoreproximalmotorNCSs,suchastheradial(extensordigitorumcommunisrecording)inC7radiculopathiesormusculocutaneous(bicepsrecording)inC6radiculopathies,couldbeperformed.However,themoreproximalNCSsaremoretechnicallychal-lengingandwouldtypicallystillbenormalunlesstherewassignificantaxonalloss.Therefore,theseconductionstudiesarenotroutinelyperformedandtheC5toC7rootsaremostlyassessedbyneedleEMG.TheF-wavelatenciesmayoccasionallybeprolongedinrootdisorders(orplexuslesions),althoughthemedianandulnarFwavesagainonlyassessconductionthroughtheC8andT1roots.

ThesensoryNCSsmayperhapsbemoreusefulthanmotorNCSswhenevaluatingpatientswithsuspectedcervicalradiculopathies.Thesensoryresponsesshouldalwaysbenormalincervicalradiculopathies,becausetherootsaretypicallyinjuredproximaltothedorsalrootganglia,therebysparingthedistalaxonsinthearm.Inthiscase,themediansensory(antidromic)studyassessedthesensorypathwaythroughthemediannerve,lateralcordandupper/middletrunkoftheplexus,and

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throughtheC6/7root,whereastheulnarantidromicsensorystudyassessedthepathwaythroughtheulnarnerve,lowertrunk,medialcord,andC8root.Hadeitherofthesebeenabnormal,alesioninvolvingthedistalnerveorbrachialplexuswouldhavebeenconsidered.Inthiscase,noradialNCSswereperformed.Althoughradialneuropathywasinthedifferentialdiagnosisgiventhedistributionofweakness,itwasnotstronglysuspectedbecausethepatienthadsignificantneckpain.Hadtheindexofsuspicionforaradialneuropathybeenhigh,radialmotorandsensoryNCSswouldhavebeenperformed.

NeedleEMGistypicallythemostsensitiveandusefulcomponentoftheevaluationincervicalradiculopathies.InthiscasethefocuswasonthemusclessuppliedbytheC7root(triceps,pronatorteres,extensorcarpiradialis,andC7cervicalparaspinals),butmusclesinnervatedbyotherrootswerealsoexaminedtohelpdefinethelocaliza-tion.TheC7innervatedmusclesdemonstratedfibrillationpotentials,whichindicateddenervatedmusclefibers,andoftenimpliesanactiveradiculopathy(inwhichthereiseitherdenervationfromanongoingprocessoraprocessthatisresolvingbutinwhichreinnervationhasnotyetoccurred).TheMUPabnormalitiesweremainlyanincreasedpercentageofpolyphasicMUPswithonlyminimallyincreasedduration.ThispatternofMUPchangesoccursearlyinreinnervation,usuallyafteraboutamonth,andishelp-fulindefiningthetemporalprofileoftheprocess,whichwassubacuteinthiscase.Althoughthefindingsinthelimbmusclescouldalsohavebeenseenwithamiddle-trunkbrachialplexopathy,thepresenceofabnormalitiesinthecervicalparaspinalsandtheabsenceofanabnormalmediansensoryNCSconfirmtheprocessattherootlevel.

CASE6.ATRAVELINGBUSINESSMANWITHLEGPAINClinicalHistory

A48-year-oldbusinessexecutivewhotraveledoverseaseachmonthpresentedwitha4-monthhistoryoflowerbackandlegpain.Hedidnotrecallanyprecipitatingsingleeventbutwouldexperiencemorepaintheweekafterhistrips.Thepainwasdescribedasadeepacheinhislowlumbarregionwithadeep,achypainthatradiatedintohisrighthipandoccasionallydownhisbuttockandposteriorthightotheknee.Hedeniedexperiencinganyweaknessbuthadnotedthathenearlytrippedafewtimeswhilewalkingquicklythroughtheairport.Thesymptomswouldimprovebutdidnotresolvecompletelyafteraweekofminimalactivity.

PhysicalExamination

Hisneurologicexaminationdemonstratedmildweaknessoftherightfootdorsiflexionandfooteversion,andequivocalweaknessofrighthipabduction.Sensorytestingrevealsdecreasedpinpricksensationoftherightlateralleganddorsumofthefoot.Reflexeswerenormalandsymmetricinhislowerextremities.

DifferentialDiagnosis

Theclinicalhistoryandphysicalexaminationfindingsweremostconcerningforarightlumbosacralradiculopathy,localizedtotheL5orS1nerveroots.However,alumbosa-cralplexopathy,sciaticneuropathy,orperonealneuropathywasalsoaconsideration.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables11and12.TheNCSsdemonstratedalowrightperonealCMAPamplitudewithamildlyslowedconductionvelocity.TheperonealFwavewasabsent.Thesuperficialpero-nealsensoryresponsewaspresentbuttheamplitudewasapproximately50%of

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Table11Case6:nerveconductionstudiesAmplitude(mVormV)Stimulate(Record)Peroneal,m(extensordigitorumbrevis)Superficialperoneal,s(ankle)Tibial,m(abductorhallucis)Sural,s(malleolus)R1.755.911L4.213NL>2>0>4>64345>40>40R39Velocity(m/s)L42NL>41DistalLatency(ms)R5.53.84.53.9L5.33.7NL<6.6<4.1<6.1<4.5RNRF-WaveLatency(ms)LEstAbbreviations:Est,F-waveestimate;NL,normalvalues.

theamplitudeontheleft.NeedleEMGdemonstratedfibrillationpotentialsandlong-durationMUPsinrightL5innervatedmuscles.Thesefindingswereinterpretedasconsistentwithasubacutetochronic,activerightL5radiculopathy.

CaseComment

Thiscasebringsupseveralimportantpointsrelatedtotheelectrodiagnosticfeaturesofalumbosacral(particularlyL5)radiculopathy.ThelowerextremitymotorNCSsdemonstratedalowperonealCMAPamplitude,whichwasconsistentwith,butnotspecificfor,anL5radiculopathy.AlowperonealCMAPcanalsobeseeninasacralplexus,sciaticnerve,oraperonealnervelesion.Giventhisfindingandbecausethepatienthadsensorylossonthedorsumofhisfoot,thesuperficialperonealsensorynervewasperformedinadditiontothesuralsensoryNCSs.Inthiscase,thesuperficialsensoryresponsewaspresentbuttheamplitudewaspossiblylow(slightlylessthan50%oftheunaffectedside).Althoughalowsensorynerveactionpotential(SNAP)amplitudetypicallyindicatesapostganglionicprocess,suchasalumbosacralplexop-athy,sciaticneuropathy,orperonealneuropathy,insomeindividualsthedorsalrootganglionattheL5levelissituatedmoreproximalinthespinalcanal,andalateraldiskmaydirectlycompresstheganglionratherthantheproximalrootlet.2Therefore,alowsuperficialperonealSNAPcanoccurwithanL5radiculopathy,complicatingtheinterpretationandlocalizationoftheprocessbasedonNCSsaloneinthiscase.Thefactthatthetibialmotorandsuralresponseswerenormal(althoughwerenot

Table12Case6:needleexaminationMuscleVastusmedialisTensorfascialataMedialgastrocnemiusTibialisanteriorTibialisposteriorPeroneuslongusGluteusmaximusL5paraspinalAbbreviation:NL,normal.

InsertionalActivityNLIncreasedNLIncreasedIncreasedIncreasedIncreasedIncreasedFibrillationPotentials0110Æ2121011NLÆLong1111NLÆ2121Æ2121MUPNL1111Recruitment(Reduced)Duration(Long)Amplitude(High)744DiTrapani&Rubin

comparedwiththeotherside,socouldpotentiallybeoflowamplitude)wouldmakeasciaticneuropathyorsacralplexopathylesslikely.Inthispatient,theperonealFwaveswereabsent.AbsentperonealFwavesmayoccurinnormalindividualsandthereforedonotnecessarilyindicateaproximalnerveorrootlesion.

TheneedleexaminationincludedassessmentofmusclesintheL5,aswellastheL4andS1,distribution.BecausetheNCSfindingsraisedthepossibilityofaperonealneuropathyversusanL5root,theneedleEMGincorporatedL5musclesthatwerenotsuppliedthroughtheperonealnerve(suchastheposteriortibialisandtensorfascialata).Theneedleexaminationdemonstratedfibrillationpotentialsandlong-duration,polyphasicMUPsinL5innervatedmuscles.However,eachmusclewithL5innervationwasnotaffectedtoasimilardegree.Inparticular,theanteriortibialis,whichisaverycommonlyexaminedmusclewhenscreeningforanL5orlumbosacralradiculopathy,wasmuchlessabnormalthantheposteriortibialisorperoneuslongusbecausethelattermusclesoftenhavemoreL5innervationthantheanteriortibialis,whichusuallyhasmoreL4innervation.Therefore,inpatientsinwhomthereisastrongsuspicionofanL5radiculopathy,distalandproximalmusclesthatarepredominantlysuppliedbytheL5root(posteriortibialisorperoneuslongusandtensorfascialataorgluteusmedius)shouldbeexamined.

Thepatternoffindingsontheneedleexamination,withlong-durationMUPsandfibrillationpotentials,indicatedarelativelylong-standingprocess,whichhaslikelybeenpresentfororrecurrentformonths(becausethereisevidenceofsubstantialrein-nervation).ThepresenceoffibrillationpotentialsindistalandproximalL5musclessuggestsanactiveprocesswithongoingdenervation.HadfibrillationpotentialsonlybeenpresentinthedistalL5muscles,withoutproximalfibrillations,itwouldhavesug-gestedthattheprocessmaybeoldorresolving,withadequatereinnervationproximally.

CASE7.AWOMANWITHWRISTDROPClinicalHistory

A54-year-oldwomanunderwentanuneventfulminorsurgicalprocedureonherrightwrist.Aboutaweekafterthesurgery,sheawokeonemorningandnotedthatshewasunabletoextendherfingersorwristontheright.Shehadsomepossiblymildnumb-nessinherhand,butdeniedexperiencinganypaininherarmorneck.Shehadnosymptomsinthelefthand.

PhysicalExamination

Theabnormalfindingsincludedsevereweaknessinthefingerextensors,wristexten-sors,andsupinatorontheright.Theremainingmuscles,includingelbowextensors,werenormal.Shewasabletofeelpinprickthroughoutherrighthandbutthoughtthatthesensationwasslightlydiminishedonthedorsumofherhandcomparedwiththeleft.Reflexeswerenormal.

DifferentialDiagnosis

Theclinicalhistoryandexaminationfindingssuggestedaradialneuropathyasthecauseofthepatient’ssymptoms.Thedistributionofdeficitsfitsmostlyintotheradialnervedistribution,althoughthetricepsseemedtobespared.However,otherlesslikelypossibilitiesincludedaposteriorcordbrachialplexopathyorC7toC8radiculopathy.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables13and14.Theelectrodiagnosticstudywasperformedabout3weeksaftertheonsetof

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Table13Case7:nerveconductionstudiesAmplitude(mVormV)Stimulate(Record)Median,m(APB)Ulnar,m(ADM)Median,s(index)Ulnar,s(5th)Radial,m(EDC)Superficialradial,sR8.414.134211.2266.228>20LNL>4>6>15>10R5153585755Velocity(m/s)LNL>48>51>56>54DistalLatency(ms)R4.23.13.42.82.01.72.12.0<2.9LNL<4.5<3.6<3.6<3.1R26.726.1F-WaveLatency(ms)LEst27.723.2Abbreviations:ADM,abductordigitiminimi;APB,abductorpollicisbrevis;EDC,extensordigitorumcommunis;NL,normalvalues.

thepatient’ssymptoms.NCSsdemonstratednormalmedianandulnarmotorandsensoryresponses.Therightradialmotoramplitudewaslowcomparedwiththeleft.Inchingalongtheradialnervearoundthespiralgroovedemonstratedan80%dropinamplitudeovera2-cmsegmentattheproximalspiralgroove(Fig.2).Theradialsensoryamplitudewasnormalandsimilartothatoftheleft.NeedleexaminationdemonstratedfibrillationpotentialsandnovoluntaryMUPactivationinradialinner-vatedmuscles,apartfromthetricepsandanconeus.Thefindingswereconsistentwitharightradialneuropathylocatedattheproximalspiralgroove,characterizedbyfocaldemyelinationwithsomedegreeofaxonalloss.

CaseComment

Thiscasedemonstratedfindingsofanuncommonupperextremitymononeuropathy:aradialneuropathyatthespiralgroove.Thegoaloftheelectrodiagnosticstudyinthispatientwastoconfirmlocalizationtotheradialnerveandexcludeotherpossibilities,suchasaposteriorcordplexopathyoraC7toC8radiculopathy.Inaddition,theelec-trodiagnosticstudieswerehelpfulindeterminingtheprecisesiteofthenervelesion.In

Table14Case7:needleexaminationMuscleFirstdorsalinterosseousPronatorteresTricepsAnconeusBrachioradialisSupinatorExtensordigitorumcommunisExtensorindicispropriusBicepsDeltoidInsertionalActivityNLNLNLNLIncreasedIncreasedIncreasedIncreasedNLNLFibrillationPotentials00002121212100NLNLMUPNLNLNLNLNoactivationNoactivationNoactivationNoactivationRecruitmentAbbreviation:NL,normalfindings.

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Fig.2.Radialmotor(inching)nerveconductionstudyincase7,demonstratingafocalconductionblockatthespiralgroove.

thiscasestandard,nonradialmotorandsensoryconductionstudieswereperformedtoensurethattherewasnoevidenceofamorediffuseprocessorlocalizationoutsideoftheradialnervedistribution.TheradialmotorNCSsdemonstratedanormalampli-tudeatthedistalstimulationsite(attheelbow),andevendemonstratedanormalresponsewhenstimulationwasperformedatthedistalportionofthespiralgroove.Hadstimulationnotbeenperformedattheproximalspiralgroove,asoccurredduringtheinchingstudy,theseverefocalconductionblockwouldnothavebeenidentifiedonNCSs.Thisfindingdemonstratestheinstructivepointthatifapatienthassignificantweaknessbelievedtobecausedbyaperipheralnerveprocessandthemotorconduc-tionstudytotheweakmuscleisnormal,stimulationmoreproximallyalongthenerve(orevenattheplexusorroot)toassessforproximalconductionblockshouldbeconsidered.

Theneedleexaminationdemonstratedabnormalitiesintheradialmusclesdistaltotheanconeus.Thetricepsandtheanconeusaretheonlytworadialinnervatedmuscleswhosenervebranchesemanatefromtheradialnerveproximaltothespiralgroove.Thepresenceoffibrillationpotentialsindicatessomedegreeofaxonalloss(inadditiontothefocaldemyelinationnotedbytheconductionblock).Thistemporalprogressionfromconductionblocktoaxonallossiscommonwithmanynervecompressionlesions.

Itisalsonotablethattheradialsensoryamplitudewasspared,likelybecausethemajorpathophysiologicchangewasconductionblockandbecausethetypicalradialsensorystudyisperformedwithstimulationdistaltothesiteofblock(atthewrist).IdentifyingproximalconductionblockinsensoryfibersisverydifficultbecauseofthenormaldispersionoftheSNAPsoverlongdistances.Thispatientwasthoughttohavea“Saturdaynightpalsy.”

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CASE8.AMANWITHARMPAINANDWEAKNESSAFTERYARDWORKClinicalHistory

A54-year-oldmanpresentedwithrightupperextremityweaknessandpain.Themorningafteradayofyardwork,heexperiencedseverepaininhisrightshoulderthatworsenedwithmovementofhisarm.Thepaincontinuedoverthenextweek,duringwhichhenotedweaknessofhisrightarm.Overthenext2weekshispainreducedandwaspresentonlyintermittently;however,hecontinuedtonoteweaknessofhisarm.Hedescribedweaknessinraisinghisrightarmandsomeweaknessongrippingobjects.Hehadsomemildnumbnessinhisrightshoulder.Hedidnotcomplainofanysymptomsinhisleftarm.

PhysicalExamination

Theonlyabnormalfindingswereseeninthepatient’srightarm.Musclestrengthtestingintherightarmwasasfollows(gradedontheMRCscale):deltoid4,biceps4,infraspinatus2,supraspinatus2,triceps5,pronation4,supination4,wristextension5,wristflexion5,flexordigitorumprofundus(indexandmiddledigits)2,flexordigito-rumprofundus(fourthandfifthdigits)5,flexorpollicislongus2,extensordigitorumcommunis5,interossei5,andabductorpollicisbrevis5.Therewasprominentatrophyofhisrightsupraspinatusandinfraspinatus.Reflexeswerenormal.Therewasmilddecreasedpinpricksensationoverhisrightshoulder.

DifferentialDiagnosis

Inthispatient,theonsetofpaininthearmafteradayofyardworkwouldfirstraisetheconcernforacervicalradiculopathy.Thepatternofweaknessonhisneurologicexam-inationiscomplicatedanddifficulttolocalizeintoaspecificrootdistribution.OnepossibilitywasthatofaC5toC6rootlesion,althoughtheweaknessinsomeofhismoredistalarmmuscleswouldsuggestapossibleC8toT1lesion.Otherpossibilitieswouldincludemultiplemononeuropathies(axillary,musculocutaneous,andpartialmedian),abrachialplexopathy,oracentralcordlesion(althoughhedidnothavefeaturesofamyelopathy).

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables15and16.NCSsdemonstratedareducedrightsuprascapularCMAPamplituderelativetotheleft(Fig.3).Therightlateralantebrachialandradialsensoryamplitudeswere

Table15Case8:nerveconductionstudiesAmplitude(mVormV)Stimulate(Record)Median,m(APB)Ulnar,m(ADM)Median,s(index)Ulnar,s(5th)Lateralantebrachial,sSuprascapular,mSuperficialradial,sR6.812.24439195.920399.842>20LNL>4>6>15>10R52605861Velocity(m/s)LNL>48>51>56>54DistalLatency(ms)R4.43.53.33.22.02.02.42.02.22.2<2.9LNL<4.5<3.6<3.6<3.1F-WaveLatency(ms)R2929LEst3025748DiTrapani&Rubin

Table16Case8:needleexaminationMuscleRhomboidmajorInfraspinatusDeltoidBicepsbrachiiSupraspinatusTricepsbrachiiInsertionalFibrillationRecruitmentDurationAmplitudeActivityPotentialsMUP(Reduced)(Long)(High)PhasesNLIncIncIncIncNL0211111Æ0002121000NLNLNLNLNLNL212111111121NL212111Æ2121100%11100%ExtensordigitorumNLcommunisPronatorteresFlexorpollicislongusPronatorquadratusAbductorpollicisbrevisFirstdorsalinterosseousC6paraspinalNLIncIncNLNLNLAbbreviations:Inc,increased;NL,normal.

Fig.3.Suprascapularnerveconductionstudiesincase8,demonstratinganapproximately50%amplitudereductionintheaffected(right)sidecomparedwiththeunaffectedside.

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mildlylowrelativetotheleft.ConcentricneedleEMGdemonstratedfibrillationpoten-tialsandlong-duration,polyphasicMUPswithmarkedlyreducedrecruitmentintherightsupraspinatus,infraspinatus,flexorpollicis,andpronatorquadratus,andsimilar,butmuchmilder,findingsinthedeltoidandbiceps.Theremainingmuscleswerenormal.Thestudywasinterpretedasacomplexstudywithevidenceofapatchyprocess,mostlikelyinvolvingtheuppertrunkofthebrachialplexus(andmainlythefiberstothesuprascapularnerve)andtheanteriorinterosseousbranchofthemediannerve.Thepatternoffindings,primarilyinvolving2individualnerves,wouldbecompatiblewithapatchyinflammatoryprocessinvolvingthenerve,suchasseeninneuralgicamyotrophy.

CaseComments

Thisisacomplicatedcase,inwhichthepatternofabnormalitiesisdifficulttopreciselylocalizeintoasinglesitewithintheperipheralnervoussystem.Theinitialconcernbasedonthehistoryandclinicalexaminationwasformultiplecervicalradiculopathies,abrachialplexopathy,ormultiplemononeuropathies.ThestudybeganwithstandardmotorandsensoryNCSs(medianandulnar).Despitethepatient’sweaknessinsomemedian-innervatedmuscles,thenormalresponsesobtainedonmedianmotor(abductorpollicisbrevis)andsensory(recordedfromtheindexfinger)arguedagainstaprocessinvolvingtheproximalmediannerve.However,routinemedianNCSsdonotreliablyassesstheanteriorinterosseousbranchofthemediannerve(AION)(inwhichlesscommonlyperformedNCSs,suchasrecordingfromthepronatorquadratus,wouldneedtobeperformed).Inaddition,becausemostofhisweaknessoutsideoftheAIONwasintheshouldergirdlemuscles(especiallythespinati),theroutineNCSsdonotthoroughlyassessforaC5toC6rootlesionoranuppertrunkplexop-athy.Becausetheselocalizationswerestronglyconsidered,additionalsensoryNCSsoffibersthatcoursethroughtheuppertrunk(lateralantebrachialcutaneousandsuperficialradial)wereperformed.Thereductioninamplitudesinbothoftheseindicatedalesionthatwasdistaltothedorsalrootganglionandsupportedabrachialplexopathy(ormultiplemononeuropathies).ThesuprascapularmotorNCSwasalsoperformedtoprovideanobjectivemeasureofthedegreeofnervedysfunction,althoughassessmentofthisnervecouldhavealsobeenmadesolelyontheneedleexaminationofthesupraspinatusandinfraspinatus.

Theneedleexaminationdemonstratedfindingsofaneurogenicprocessthatagainwasdifficulttopreciselylocalizeintoasinglelesion.ThemostsevereabnormalitieswerepresentinmusclessuppliedbythesuprascapularandAION,buttherewerealsomildabnormalitiesinothermusclessuppliedbytheuppertrunkofthebrachialplexus.

Thepatternofelectrodiagnosticfindings,inthecontextofthepatient’shistory,wastypicalofneuralgicamyotrophy(Parsonage-Turnersyndrome).Thisentityiscatego-rizedasaninflammatoryorimmune-mediatedbrachialplexopathy;however,prefer-entialinvolvementofasingleormultipleindividualnervesinadditiontootherportionsofthebrachialplexusisverycommon.3Thisentitymayhaveapredilectiontocertainnerves,suchasthelongthoracic,suprascapular,andAION.Asaresultofthepatchynatureofinvolvement,neuralgicamyotrophymaybeoneofthemostdiffi-cultentitiestostudyfromanelectrodiagnosticstandpoint.Maintainingahighindexofsuspicion,performingaverythoroughclinicalneuromuscularexaminationbeforeper-forminganyelectrodiagnosticstudies,andliberalizingthenumberofNCSs(oftenwithside-to-sidecomparisons)andmusclesexaminedwithneedleEMGareimportantstepsinanappropriateassessmentofthesepatients.

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CASE9.AMANWITHPOSTOPERATIVEDIPLOPIA,DYSARTHRIA,ANDFATIGUEClinicalHistory

A67-year-oldmanunderwentanuncomplicatedarthroscopicsurgicalprocedureonhisleftshoulderforshoulderpain.Inthenext1to2weekshebegantoexperiencefluctuatingdysarthria,ptosis,andintermittentdiplopia.Henotedblurringofhisvisionwhenreadingordriving,withoccasionaldoublevision.Healsonotedthateitherorbothofhiseyelidswoulddroopwhenhewastired.Hehadsomedifficultyswallowingliquids.Thesymptomswerepresentthroughouttheday,buttendedtofluctuateinnatureandweretypicallyworsetowardtheafternoonandevening.Healsoreportedfeelinggeneralizedfatigueandsomeweaknessinhisarmsandlegs.Hehadnosensorycomplaintsorpain.

PhysicalExamination

Thepatient’sneurologicexaminationdemonstratedmildbilateralptosisthatseemedtoworsenslightlywithsustainedupgaze.Therewerenodefiniteextraocularmove-mentabnormalities.Strengthwasnormalexceptformildweaknessinhisorbicularisoculiandorismuscles,andintheproximalshouldermusclesbilaterally.Deeptendonreflexes,gait,sensory,andcoordinationwerenormal.

DifferentialDiagnosis

Thispatientseemedtohaveageneralizedprocess,primarilycausingweaknessinacranial-cervicaldistribution.Inthispatientwithfatigableweakness,doublevision,andbulbarsymptoms,theprimaryconcernwasaneuromuscularjunctiondisordersuchasmyastheniagravis.Othergeneralizedneuromuscularconditions,suchasamyopathy,polyradiculopathy,ormotorneurondisorder,werealsoconsidered,andcanbeassociatedwithfatigueoranincreasedsenseofweaknessafteractivityorlaterintheday.Inthiscase,itisunclearwhetherorhowthepatient’santecedentsurgerycontributedtohissymptoms,butthestressofthesurgerycouldhavebeenatriggerforunmaskingcertainconditions,includingmyastheniagravis,aninflamma-torypolyradiculopathy,orasubclinicalmyopathy.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables17and18.Themediansensoryandulnarmotorconductionstudieswerenormal.Repet-itivestimulationstudieswereperformedat2Hzbeforeandafter1minuteofexerciseintheleftspinalaccessoryandfacialnerves.NoabnormaldecrementintheCMAPamplitudeorareawasseeninthespinalaccessorynerve(maximumdecrement

Table17Case9:nerveconductionstudiesStimulate(Record)Median(index),sUlnar(hypothenar),mFacial(nasalis),maSpinalaccessory,m(trapezius)aaAmplitude(mVormV)(Normal)23(>15)7.2(>6.0)1.5(>1.8)4.5Velocity(m/s)(Normal)57(>56)52(>51)DistalLatency(ms)(Normal)3.2(<3.6)3.4(<3.6)2.0(<4.1)2.5F-WaveLatency(ms)(Estimate)28(27)2-Hzrepetitivestimulationperformed.

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Table18Case9:needleexaminationMuscleDeltoidFirstdorsalinterosseousFrontalisOrbicularisoculiInsertionalActivityNLNLNLNLFibrillationPotentials0000MUPNLNLVaryingVaryingAbbreviation:NL,normalfindings.

betweenthefirstandfourthstimuluswas8%),butamilddegreeofabnormaldecre-ment(maximumof12%)wasseeninthefacialnerve.After1minuteofexercise,themaximumdegreeofdecrementwas9%inthespinalaccessorynerveand20%inthefacialnerve(Fig.4).Theneedleexaminationdemonstratedvarying(unstable)MUPsintheorbicularisoculiandfrontalis,butnotinlimbmuscles.Themildabnormalitiesonrepetitivestimulationstudiesandneedleexaminationofcranialmusclesweresugges-tiveofamilddefectofneuromusculartransmission,consistentwithaneuromuscularjunctiondisordersuchasmyastheniagravis.

CaseComment

Thistypeofcase,apatientwithmildweaknessincranialandproximalmuscles,canbechallengingfromanelectrodiagnosticstandpoint.Inthesepatients,themaindiffer-entialdiagnosisisaneuromuscularjunctiondisorder,unusualdistributionmyopathy(eg,mitochondrial,facioscapulohumeralmusculardystrophy,andsoforth),motorneurondisorder,orpolyradiculopathy.ThestudybeganwithoneroutinemotorandsensoryNCSinthearm,bothofwhichwerenormalaswasexpected.Eventhoughthepatienthadnosensorysymptomsandnodistalweakness,theperformanceofatleastafewroutinestudiescanhelptoidentifyorexcludeaprocesssuchasapoly-radiculoneuropathy(inwhichtheremaybeabnormalsensoryresponses,orconduc-tionvelocityslowingorincreasedtemporaldispersiononthemotorstudies)aswellasamotorneurondisorder(inwhichtheCMAPamplitudesmaybelow).Inaddition,lowCMAPamplitudesmayalsoincreasethesuspicionforthelesscommontypesof

Fig.4.Facialnerverepetitivestimulationat2Hzat3minutesafterexerciseincase9.Thereisa20%decrementinamplitudebetweenthefirstandthefourthstimulus.

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neuromuscularjunctiondisorders,suchasLEMS.WhenthisdisorderissuspectedandlowCMAPamplitudesareseen,assessmentforfacilitationbysupramaximallystimulatingthemotornerveimmediatelyafter10secondsofexerciseshouldbeperformed.

InadditiontoroutinemotorandsensoryNCSs,repetitivestimulationisimportantandnecessarytoevaluateforaneuromuscularjunctiondisorder,suchasmyastheniagravis.Choosingthenerveonwhichtoperformrepetitivestimulationstudiesdependsonthedistributionandextentofclinicalinvolvement.Inpatientswithgeneralizedsymptoms,distalnerve-musclecombinations,suchastheulnarorperoneal,aretech-nicallytheeasiestandmostreliablenervestotest.However,thispatienthadonlybulbarandproximalweaknessand,therefore,repetitivestimulationwasperformedonthespinalaccessoryandfacialnerves.Therepetitivenervestimulationstudieswereessentiallynormalinthespinalaccessory,becausemanyconsideranabnormaldecrementasgreaterthan10%reductioninamplitudeandareabetweenthefirstandfourthorfifthstimulus.However,anydegreeoftruedecrementistechnicallyabnormal;sointhispatientthe8%decrementthatwasconsistentlypresentinthreetrialsatrestmayhavebeenacluetoadefectinneuromusculartransmission.Cautionshouldalwaysbeusedwheninterpretingabnormaldecrementtoensurethatthestudyistechnicallyreliableandthatthepatternofdecrement(largestdropbetweenthefirstandsecondstimuluswithataperingpattern)isphysiologic.Thispatientdemonstratedmoresignificant(>10%)decrementinthemostaffectedmuscles,withrepetitivestim-ulationofthefacialnerve.Becausethedecrementwasonlymildorborderlineatrest,repetitivestimulationstudieswereperformedalsoafter1minuteofexercise,whichmayincreasethedegreeofdecrementinsomepatients.

Theneedleexaminationfocusedonnotonlymusclesthatwereclinicallyweakbutalsosampledmuscles(suchasthefirstdorsalinterosseous)thatwereclinicallyspared,toassessformorewidespreadsubclinicalinvolvement.Theabsenceoffibril-lationpotentialsormarkedlyshort-durationorlong-durationMUPsessentiallyexcludedaseveremyopathyormotorneurondisorder.However,somemildmyopa-thiesmaynotdemonstrateprominentneedleexaminationabnormalities,buttheseconditionswouldalsonotbeexpectedtoproducedecrementonrepetitivestimulationeither.TheonlyfindingontheneedleexaminationintheclinicallyweakmuscleswasabnormalMUPvariation(unstableorvaryingMUPs),whichisthetypicalfindinginneuromuscularjunctiondisorders.UnstableMUPscanalsobeseeninmyopathiesandneurogenicdisorders,butthoseconditionswouldalsobeassociatedwithotherconfigurationalchangesintheMUPs.TheunstableMUPsinconjunctionwiththeabnormalrepetitivestimulationwereconsistentwithaneuromuscularjunctiondisorder.

Inthispatient,hadtheroutineneedleexaminationbeennormal,single-fiberEMGwouldhavebeenperformedasthemostsensitivetestforadefectofneuromusculartransmission.Single-fiberEMGshouldbeperformedifthereisahighclinicalindexofsuspicionorifptosisand/ordiplopiaaretheonlyclinicalsymptoms,andtheroutinestudiesarenormal.

Asafinalnote,patientswhoarebeingstudiedforaneuromuscularjunctiondisordershouldnottakepyridostigmine(Mestinon)foratleast4to8hoursbeforeelectrodiag-nostictesting,becausethemedicationmayimproveandmaskabnormaldecrement,producingafalse-negativestudy.Thispatientwasbeingtreatedforpresumedmyas-theniagraviswithpyridostigminebeforeconfirmationwiththeEMGstudy.Whenhearrivedatthelaboratoryonthemorningofthetest,hehadindicatedthathehadtakenhispyridostigmine1hourbefore.Thetestwasdelayeduntillaterintheafternoontoavoidfalse-negativeresults.

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CASE10.AVETERINARIANWITHPROGRESSIVEWEAKNESSClinicalHistory

A35-year-oldleft-handedveterinarianpresentedwitha3-yearhistoryofslowlyprogressiveweakness.Theweaknessinitiallybeganinherrighthandandgraduallyworsenedtoinvolvebothupperandlowerextremities.Sherequiredtheuseofawalkertoassistwithambulation.Shereportedmilddysphagia,butnoptosis,diplopia,dysar-thria,orrespiratorysymptoms.Shedescribednopainorsensorycomplaints.

PhysicalExamination

Herneurologicexaminationdemonstratedgeneralizedweaknessofmoderateseverityinherarmsandlegs,rightsideworsethanleft,withincreasedtoneintherightlowerextremity,briskdeeptendonreflexes,andbilateralBabinskisigns.Shehadatrophyofherintrinsichandmusclesbilaterallyandfasciculationsinmanymuscles.Herspeechwasnotableforasubtlespasticdysarthria,andtonguestrengthwasmildlyweak.Sensoryexaminationwasnormal.

DifferentialDiagnosis

Theprimaryconcerninthiscase,giventhecombinationofupperandlowermotorneuronexaminationfindings,isprogressivemotorneurondiseasesuchasamyotro-phiclateralsclerosis(ALS).Otherpossibilitiesincludemultiplecervical,thoracic,andlumbosacralradiculopathies,apolyradiculopathy,orasevereneuromuscularjunctiondisorderormyopathy.However,theuppermotorneuronsignswouldnotbetypicaloftheseotherpossibilities,unlessshehadtwoprocesses.

ElectrodiagnosticSummaryandInterpretation

Theelectrodiagnosticstudies(NCSsandneedleexamination)areshowninTables19and20.TheNCSsoftherightupperandlowerlimbsrevealedanabsentmedianmotorresponseandlowulnarandtibialmotorCMAPamplitudes.Noconductionvelocityslowing,conductionblocks,orabnormaltemporaldispersionwereseen.Needleexaminationdemonstratedfibrillationpotentialsinmostmusclesstudiedwithfascic-ulationpotentialsinmanymuscles.Inaddition,therewasreducedrecruitmentoflong-duration,high-amplitude,andfrequentlypolyphasicandvaryingMUPsinmostmuscles.Thefindingswerethoseofadiffuseneurogenicdisorderaffectinganterior

Table19Case10:nerveconductionstudiesStimulate(Record)Ulnar,m(hypothenar)Ulnar,santi(fifth)Median,m(thenar)Median,santi(index)Peroneal,m(extensordigitorumbrevis)Tibial,m(abductorhallucis)Abbreviation:NR,noresponse.

Amplitude(mVormV)VelocityDistalLatencyF-WaveLatency(Normal)(m/s)(Normal)(ms)(Normal)(ms)(Estimate)3.8(>6)66(>10)NR64(>15)4.8(>2)65(>51)64(54)NR57(>56)48(>41)3.0(<3.6)2.8(<3.1)NR2.7(<3.6)5.4(6.6)3.7(<6.1)41(>40)5.2(<6.1)52(49)45(43)24(28)Superficialperoneal,s(ankle)17(>0)1.9(4)754DiTrapani&Rubin

Table20Case10:needleexaminationMuscleBicepsaTricepsaInsertionalFibrillationFasciculationRecruitmentDurationAmplitudeActivityPotentialsPotentialsMUP(Reduced)(Long)(High)PhasesIncIncIncIncInc21312121111111110011011021212111211111212121212121Æ212121212111Æ25%25%FirstdorsalinterosseousVastuslateralisaTibialisanterioraLateralIncgastrocnemiusT7paraspinalIncAbbreviation:Inc,increased.aVaryingMUP.

horncellsortheiraxonsaffectingthecervical,thoracic,andlumbosacralsegments,consistentwithaprogressivemotorneurondiseasesuchasALS.

CaseComment

Thiscasedemonstrateselectrodiagnosticfeaturesthatareseenwithprogressivemotorneurondisease(eg,ALS).ThemotorNCSsintheupperandlowerextremitiesdemonstratedlowCMAPamplitudes,indicatingaxonalloss.Carefulobservationofthewaveformswasimportanttoassessforabnormaltemporaldispersionorconduc-tionblock(whichwerenotseeninthiscase),whichwouldbeseeninsomeinflamma-tory/demyelinatingpolyradiculopathies,suchaschronicinflammatorydemyelinatingpolyradiculopathyormultifocalmotorneuropathywithconductionblock,bothofwhichcanhavesomeclinicalsimilaritiestoALS.ThesensoryNCSswerenormal,whichwouldbeexpectedinmotorneurondiseaseunlesstherewasaconcomitantperipheralneuropathyormononeuropathy.

Theneedleexaminationapproachwasbasedonclinicalfindings.Theneedleexam-inationincludedexaminationof2to3musclesinthecervical,thoracic,andlumbarregionthatwerenotinnervatedbythesamerootornerve,toassessforadiffuseprocess.Thefindingsoffibrillationpotentialsandlong-durationMUPswithreducedrecruitmentinawidespreaddistributionwereconsistentwithasevere,diffuseneuro-genicprocess.VaryingorunstableMUPsarecommoninprogressiveneurogenicdisorders,suchasALS,butareoftenoverlookedwhentheexaminerisfocusingmoreontheMUPsizeandrecruitmentpattern.Musclesselectedwerethoselikelytobeabnormal.Thoracicparaspinalmuscleswereexaminedtodemonstrateinvolve-mentofthediseaseprocessinthissegment,andthepresenceofabnormalitiesinthesemuscleshelpstoexcludemultiplechroniccervicalandlumbosacralradiculopa-thies.Ofnote,fasciculationpotentialswerealsopresentinseveralmusclessampled,afindingwhichisnonspecificbutconsistentwithmotorneurondisease.

Thecombinationoffindingsfitwithprogressivemotorneurondisease.However,takeninisolationtheEMGfindingscouldalsobeseenwithasevereaxonalpolyradi-culopathyandthereforemustbeinterpretedinthecontextoftheclinicalfeatures.Inseverepolyradiculopathies,deeptendonreflexesaretypicallyreducedorabsentratherthanhyperactive,asinthiscaseofALS.Inaddition,thereisoftensomedegree

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ofsubjectiveorobjectivesensorylossinpolyradiculopathies,despitethenormalsensoryNCSs.

SUMMARY

These10casesdemonstratetheapproachestakenintheEMGlaboratorytocertaincommonanduncommonclinicalproblems.Althoughtheapproachtoanyonepatientmayvarytosomeextentbydifferentlaboratoriesorelectromyographersandneedstobeindividualizedtowardtheclinicalproblemandfindingsontheexamination,thegeneralguidelinesashavebeendescribedinthesecasesandelsewherecanassistinidentifyingtheappropriatelocalizationanddiagnosisofeachtypeofclinicalproblem.4REFERENCES

1.VennixMJ,HirshDD,Chiou-TanFY,etal.Predictingacutedenervationincarpaltunnelsyndrome.ArchPhysMedRehabil1998;79:306–12.

2.LevinKH.L5radiculopathywithreducedsuperficialperonealsensoryresponses:intraspinalandextraspinalcauses.MuscleNerve1998;21:3–7.

3.RubinDI.Neuralgicamyotrophy:clinicalmanifestationsandevaluation.Neurolo-gist2001;7:350–6.

4.RubinDI,DaubeJR.Applicationofclinicalneurophysiology:assessingperipheralneuromuscularsymptomcomplexes.In:DaubeJR,RubinDI,editors.Clinicalneurophysiology.3rdedition.NewYork:OxfordUniversityPress;2009.p.801–37.