Clinical Features of Ulnar Tunnel Syndrome and the ...

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Key Words:abductordigitiminimi;firstdorsalinterosseous;nerveconductionmeasurement;ulnarnervelesion;ulnartunnelsyndrome

INTRODUCTION

Ulnar tunnel syndrome (UTS) is anuncommon formofulnarentrapmentneuropathyatthewristthatcanbecausedbyseveralintrinsicorextrinsicfactors.1–4)Areviewoftheliterature indicated the following possible causes of UTS:ganglions,5–16) traumaticneuropathies,8) anomalousmuscleor fibrous bands,10,17,18) ulnar artery thromboses or aber-rancy,7,10)wristfracture,5)carpalosteoarthritis,8)pisohamatearch,11) and idiopathic.3) Most previous reports have dealtwith a small number of cases,5–7,11–18) and we previously

reportedfivecasesofUTScausedbyganglion.16) In1861,Guyon19)reportedtheanatomyoftheulnarareaandpredict-ed thatproblemscouldoccurwithentrapmentof theulnarnerve,andin1908Hunt20)describedthreepatientswithoc-cupationalneuritis.Seddon5)andRichmond6)reportedulnarnerve palsy caused by a carpal ganglion. In 1965,Dupontet al.7) used the term ulnar tunnel syndrome and reportedfourcases.AnexactclinicaldiagnosisofUTSanddetectionofthelocationofthecausativelesionaredifficult,andelec-trophysiologicaldiagnosismayhelptoconfirmthediagno-sis.2–4,11,13–16,21–25)Thepurposesofthisstudyweretoassess

Received:October16,2020,Accepted:January27,2021,Publishedonline:February13,2021aDepartmentofOrthopaedicSurgery,TohokuRosaiHospital,Sendai,JapanbDepartmentofOrthopaedicSurgery,TohokuUniversitySchoolofMedicine,Sendai,JapanCorrespondence:ShingoNobuta,MD,PhD,DepartmentofOrthopaedicSurgery,TohokuRosaiHospital,4-3-21Dainohara,Aoba-ku,Sendai,Miyagi981-8563,Japan,E-mail:[email protected]©2021TheJapaneseAssociationofRehabilitationMedicine

Thisisanopen-accessarticledistributedunderthetermsoftheCreativeCommonsAttributionNon-CommercialNoDerivatives(CCBY-NC-ND)4.0License.http://creativecommons.org/licenses/by-nc-nd/4.0/

Progress in Rehabilitation Medicine 2021; Vol. 6, 20210010doi: 10.2490/prm.20210010

Objectives: The purposes of this study were to assess the clinical features of ulnar tunnelsyndrome(UTS)andtoinvestigatethediagnosticvalueofnerveconductionmeasurementsforUTS.Methods:EighteenpatientswithUTSwerereviewedretrospectively.Fifteenpatientshadintrinsicmuscleatrophyandmotorweakness,and15hadnumbnesswithhypesthesia.Thecom-poundmuscle action potentials (CMAPs) from thefirst dorsal interosseous (FDI)muscle andtheabductordigitiminimi(ADM)muscleandthesensorynerveactionpotential(SNAP)fromthelittlefingerwererecordedandanalyzed.Allpatientsunderwentulnartunnelreleasesurgeryand neurolysis. Static two-point discrimination test results and pinch strengthswere assessedbeforeandaftersurgery.Results:Beforesurgery,FDI-CMAPwasrecordedin17patients,andADM-CMAPin16,andallshoweddelayedlatencyand/orlowamplitude.SNAPwasrecordedineightpatientsandtwoshoweddelayedlatency.Thecausesofulnarnervelesionswereganglioninfivepatients,traumaticadhesioninfour,ulnararteryaberrancyinfour,pisohamatearchinthree,anomalousmuscleinone,andulnarveinvarixinone.Thesitesofthelesionswereinzone1oftheulnartunnelanatomyin12patients,inzone2in2,andinzones1and2in4.Aftersurgery,allpatientsobtainedrecoveryofmotorfunctionandsensation;however,postoperativeFDI-CMAPandADM-CMAPdidnotimprovetothenormalrange.Conclusions:ThecausesofUTSwereganglion,traumaticadhesion,ulnararteryaberrancy,andpisohamatearch.BothFDI-CMAPandADM-CMAPwerevaluableforelectrophysiologicaldiagnosisofUTS.

ORIGINAL ARTICLEClinical Features of Ulnar Tunnel Syndrome and the

Diagnostic Value of Nerve Conduction MeasurementsShingo Nobuta, MD, PhD a Hiroshi Okuno, MD, PhD a Taku Hatta, MD, PhD a Ryo Sato, MD, PhD a

and Eiji Itoi, MD, PhD b

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theclinicalfeaturesofUTSandtoinvestigatethediagnosticvalueofnerveconductionmeasurementsforUTS.

PATIENTS AND METHODS

Eighteenhandsfrom18patientswithUTStreatedbetweenMay2008andJuly2016werereviewedafterameanfollow-upof11months(range,5–54months).Detailsofthe18casesareshowninTable 1.Theagesofthepatients(8menand10women)atsurgeryrangedfrom33to80years,withameanageof53years.Therightsidewasaffected in14patients,and the dominant extremity was involved in 12 patients.Themeandurationofsymptomswas9months(range,1–84months).UTSwasdiagnosedbasedonclinical symptoms,electrophysiological evaluations, and magnetic resonanceimaging (MRI) findings. Written informed consent wasobtained from each patient. All patients except for three(cases12,13, and17)hadmotorweakness andatrophyofthe intrinsicmuscleswith a positive Froment’s sign and aclawfingerdeformityofthelittlefinger.Fifteenpatientshadnumbness and hypesthesia in the ulnar nerve distribution;hypesthesiawasseenonlyonthepalmarsideinsixpatients

andonboth thepalmaranddorsalsides innine(Table 1).ATinel-likesignattheulnartunnelwasnotseeninanyofthesepatients.Theintrinsicmusclesincludedthefirstdorsalinterosseous(FDI)and theabductordigitiminimi(ADM).Theresultsofthestatictwo-pointdiscrimination(TPD)testonthelittlefingerrangedfrom5to45mm,withameanof19.6mm.Thepulppinchstrengthrangedfrom0to4.2kg,with amean of 2.1kg (Table 2). T1-weightedMRI of thewrist in 17 patients demonstrated a soft tissue mass in 5patients16) (cases12,14–16,and18),ahigh-signalarea in8(cases1–4,6,8,9,and17),andnormalfindingsin4(cases5,7,10,and13).Nerve conductionmeasurements were performed before

and after surgery.The compoundmuscle action potentials(CMAPs) from the FDI and ADM and the sensory nerveactionpotential(SNAP)fromthelittlefingerwererecordedandanalyzed.WeusedaNicoletVikingelectromyographysystem(NicoletInstruments,Madison,WI,USA)anda10-mmsilverdisc.Thepalmarskintemperaturewasnotallowedto fall below 32°C. FDI-CMAP and ADM-CMAP wererecordedbysupramaximalstimulationoftheulnarnerveatthewrist.Thestimulusdurationwas0.2–0.5ms.SNAPwas

2 Nobuta S, et al: Clinical Features of Ulnar Tunnel Syndrome

Table 1. DetailsandtestresultsforeighteenulnartunnelsyndromepatientsFollowup

Case Age Sex Side Durationofsymptoms

Hypesthesia TPD(mm)

Pinch (kg)

m TPD(mm)

Pinch(kg)

1. 34 F L 7m p,d 40 0 6 35 0.32. 38 M R 1 m p,d 15 0 6 5 2.03. 36 M R 2 m p,d 20 2.8 6 5 4.54. 41 F R 84 m none 5 2.5 13 5 3.35. 80 F R 5 m p,d 45 1.8 17 10 3.26. 33 F R 8 m p,d 15 2.6 9 7 3.47. 76 F R 2 m p,d 30 0.8 6 10 3.48. 68 M L 5 m p,d 30 1.5 8 7 3.59. 57 M R 5 m p,d 10 2.4 54 7 4.210. 44 F R 24 m p 15 2.3 7 7 3.511. 58 M R 1 m p 40 2.8 10 15 4.512. 54 F R 1 m p 10 4.2 12 5 4.513. 61 M R 5 m p,d 25 4.2 48 10 4.514. 45 F R 5 m p 10 2.0 5 5 4.015. 56 F L 3 m p 5 0.5 7 5 3.616. 66 F L 2 m none 7 1.3 10 5 4.217. 64 M R 3 m p 25 4.0 7 20 7.018. 56 M R 1 m none 5 2.1 6 5 7.4

F,female;M,male;L,left;R,right;m,months;p,palmarside;d,dorsalside;TPD,two-pointdiscrimination;Pinch,pulppinchstrength.

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recordedwithringelectrodesbyminimalstimulationoftheulnarnerveatthewrist.Accordingtothemeasurementsfor20healthysubjectsatourinstitute,themean±2SDindicatedthe normal values of latency and amplitude. The normalvalueswere:FDI-CMAPlatency<4.2mswithanamplitude>6.6mV,ADM-CMAPlatency<2.9mswithanamplitude>5.3mV,andSNAPpeaklatency<3.5mswithanamplitude>3.4μV.Wediagnoseddelayed latencyand lowamplitudeforCMAPsandSNAPbasedonthesecriteria.Furthermore,toruleoutcubitaltunnelsyndrome,FDI-CMAPandADM-CMAPwererecordedbystimulatingtheulnarnerveattheelbowtoconfirmnoconductiondelayatthecubitaltunnel.Surgerywasindicatedwhenmotorweaknessandatrophy

of the intrinsic muscles were present or there was severenumbnessorpainintheulnarnervedistribution(cases12,13,and17).Allpatientsunderwentulnartunnelreleasebysurgicaldivisionofthevolarcarpalligamentandulnarnerveneurolysis with release of the pisohamate arch (tendinousarch).Atsurgery,weconfirmedthesiteofthelesionwithintheulnartunnelandclassifiedtheminto3zones.12)Zone1istheareaproximaltothebifurcationoftheulnarnerve,zone2encompassesthemotorbranchofthenerveafterbifurcation,andzone3surroundsthesuperficialorsensorybranchoftheulnarnerve.Aspartoftheoutpatientrehabilitationprogram,after surgery,patientswere instructed toperform thepulppinch motion exercise under the supervision of a physio-therapisttwiceaweekfor4weeks.StaticTPDtestresultsonthelittlefinger,thepinchstrength,andFroment’ssignwereevaluatedaftersurgery.Thepresenceofcomplicationssuchasinfection,hematoma,andnerveinjurywerealsoassessed.This research passed the Tohoku Rosai Hospital Ethics

Committee review (approval number Tohoku-Rin 20–20).ThedatawereanalyzedusingStudent’st-testandtheMann-Whitney U test. P values less than 0.05 were consideredstatisticallysignificant.

RESULTS

Before surgery, FDI-CMAPwas recorded in 17 patientsbutwasunrecordablein1,andADM-CMAPwasrecordedin16patientsbutwasunrecordable in1 (Tables 2 and 3).FDI-CMAP showed delayed latency in 14 patients (mean:6.7ms) and low amplitude in 16 (mean: 1.6mV), whereasADM-CMAPrevealeddelayedlatencyin14patients(mean:5.1ms)andlowamplitudein16(mean:1.3mV).SNAPwasrecordedineightpatientsandtwoshoweddelayedlatency.At surgery, the causes of ulnar nerve compression wereganglion infivepatients, traumaticadhesion in four,ulnararteryaberrancy(aberrantbranch)infour,pisohamatearchinthree,anomalousmuscleinone,andulnarveinvarixinone. A ganglion rising from the triquetrohamate joint infivepatientswastracedtoitsoriginandexcised.Histologicexaminationconfirmedthediagnosisofganglion.Traumaticadhesioninfourpatientswascausedbyblunt trauma.Thepisohamatearchwascut,andtheanomalousmusclelocatedatthevolarcarpalligamentasapalmarislongusmusclewasexcised.Theaberrantulnararterybranchandtheulnarveinvarixwereexcised.Thesiteofcompressionwasinzone1in12cases,zone2in2,andzones1and2in4,whereastherewasnocaseofcompressioninzone3(Table 3).Infection,hematoma, and nerve injury are possible complications ofsurgeryforUTS,buttherewerenocomplicationsinour18

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Table 2. OverallresultsbeforeandaftersurgeryforUTSPreoperative Finalfollow-up Pvalue

StaticTPDtestonlittlefinger(mm)(SD) 19.6 (13.0) 9.3 (7.6) <0.05Pinchstrength(kg)(SD) 2.1 (1.3) 3.9 (1.5) <0.001DetectionofFDI-CMAP(hands) 17 18 Latency(ms)(SD) 6.7 (3.6) 4.6 (0.9) <0.02 Amplitude(mV)(SD) 1.6 (2.6) 3.1 (3.5) NSDetectionofADM-CMAP(hands) 16 17 Latency(ms)(SD) 5.1 (3.1) 3.7 (0.8) NS Amplitude(mV)(SD) 1.3 (1.5) 2.8 (2.1) NSDetectionofSNAP(hands) 8 3 Latency(ms)(SD) 3.5 (2.3) 3.2 (1.7) NS Amplitude(μV)(SD) 9.1 (8.9) 21.0 (23.5) NSTPD,two-pointdiscrimination;SD,standarddeviation;FDI,firstdorsalinterosseousmuscle;CMAP,compoundmuscle

actionpotential;ADM,abductordigitiminimimuscle;SNAP,sensorynerveactionpotential;NS,notsignificant.

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patients.After surgery, all patients recoveredmotor function and

sensation.ThemeanTPDimprovedfrom19.6to9.3mm(P<0.05), and themeanpinch strength increased from2.1to3.9kgatfinalfollow-up(P<0.001,Table 3).Asaresultofrehabilitation, themean pinch strength increased to 3.1kg(SD1.4)at2monthsaftersurgery(P<0.05).Exceptforcases1and17,patients showedanegativeFroment’s signat thefinal follow-up. Evaluation of postoperative FDI-CMAPshowed a shortening of latency (mean: 4.6ms, P <0.02)andanincreaseinamplitude(mean:3.1mV).PostoperativeADM-CMAPalso revealedashorteningof latency (mean:3.7ms)andanincreaseofamplitude(mean:2.8mV).FDI-CMAPlatencyrecoveredtothenormalrangeinsixpatientsandtheamplituderecoveredinthree,whereasADM-CMAPlatencyimprovedtothenormalrangeinthreepatientsandtheamplituderecoveredintwo(Tables 2 and 3).Inalmostallcases, residualdelayed latencyand lowamplitudewereseenatthefinalfollow-up.

Case PresentationA 45-year-old right-hand-dominant woman (case 14)

presented with a 5-month history of onset and intrinsicweaknessofherrighthand.Therighthandshowedintrinsicmuscle atrophy and weakness with a positive Froment’ssign and clawing of the little finger. Mild numbness andhypesthesiawereevidentinthelittlefingerandringfinger.TPDwas10mm,andthepinchstrengthwas2.0kg.AxialT1-weightedMRIshowedacysticmass lesionat theulnartunnel (Fig. 1). FDI-CMAP exhibited markedly delayedlatency and low amplitude (Fig. 2A), and ADM-CMAPalso showeddelayed latency and lowamplitude (Fig. 3A).Incontrast,SNAPindicatednormal latencyandamplitude(Fig. 4).Intra-operatively,afterdivisionofthevolarcarpalligament, a22/14/10mmganglionwas found tobemainlycompressing themotorbranchof theulnarnerve in zones1 and 2 (Fig. 5A). The ganglion, which arose from thetriquetrohamatejoint(Fig. 5B),wasexcised,andhistologyconfirmedthediagnosis(Fig. 6).Fivemonthsaftersurgery,motorfunctionandsensationhadrecoveredandthepatienthad a pinch strength of 4.0kg and a TPD of 5mm; FDI-

4 Nobuta S, et al: Clinical Features of Ulnar Tunnel Syndrome

Table 3. Detailsofcauses,zone,andnerveconductionmeasurementsinUTSpatientsParametermeasurementsbefore/aftersurgery

FDI-CMAP ADM-CMAP SNAPCase Cause Zone Lat.(ms) Amp.(mV) Lat.(ms) Amp.(mV) Lat.(ms) Amp(μV)1. ua 1 3.4/2.6 0.9/1.7 2.4/2.6 1.5/2.3 nr2. am 1 3.8/4.7 1.0/1.5 3.9/4.6 0.3/5.0 4.2/nr 2.0/nr3. uv 1 6.0/3.9 1.3/2.1 6.6/4.5 0.2/2.3 8.9/nr 1/nr4. ta 2 3.9/4.0 4.4/2.9 3.0/2.4 3.8/6.2 nr5. ta 1 17.0/3.7 0.05/0.2 ur/3.6 ur/0.5 nr6. ua 1 4.5/4.4 3.5/6.5 nr 2.0/nr 5.0/nr7. ua 1 ur/6.3 ur/0.5 12.7/4.1 0.1/0.6 nr8. pa 1,2 6.5/5.1 0.1/1.3 3.1/3.2 0.6/0.4 nr9. pa 1,2 7.5/5.7 0.5/0.6 3.5/5.4 0.6/1.0 nr10. pa 1,2 5.1/4.2 0.7/0.7 4.9/3.7 0.3/1.2 nr11. ta 1 10.3/6.1 0.1/1.5 6.2/4.2 0.1/4.1 3.1/5.0 2.0/5.012. gl 1 5.6/5.0 10.7/10.3 6.0/4.1 2.1/1.8 2.5/1.7 25/4813. ta 1 5.2/4.7 0.8/0.9 3.8/3.1 5.0/3.3 nr14. gl 1,2 12.6/5.3 0.1/4.0 11.8/3.9 0.2/4.4 2.6/2.8 10/1015. gl 2 6.5/4.9 0.6/6.8 3.1/3.1 3.6/5.6 nr16. gl 1 4.4/3.7 0.1/0.8 3.5/2.9 0.5/0.4 2.0/nr 8.0/nr17. ua 1 4.8/3.7 1.3/1.1 4.5/4.5 0.7/1.7 nr18. gl 1 6.4/4.2 1.5/12.2 2.6/2.7 0.5/6.6 2.6/nr 20/nr

Underlineddataarewithinthenormalrange.ua,ulnararteryaberrancy;am,anomalousmuscle;uv,ulnarveinvarix;ta,traumaticadhesion;pa,pisohamatearch;gl,

ganglion;Lat.,latency;Amp.,amplitude;nr,notrecorded;ur,unrecordable.

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CMAPandADM-CMAPrevealedashortenedlatencyandanincreasedamplitude(Figs. 2B,3B).

DISCUSSION

The ulnar tunnel is anatomically classified into threezones12): zone 1 is the area proximal to the bifurcation ofthe ulnar nerve, zone 2 encompasses themotor branch oftheulnarnerve(exceptthebranchtotheADM)afterithas

bifurcated,andzone3surroundsthesuperficialorsensorybranchoftheulnarnerve.Dependingonthesiteofcompres-sion,clinically, thelesionmaybeinthemotor,sensory,ormixedbranch,15)whereas thesensorybranchon thedorsalulnarsideisnormalinUTS.4)However,ifparesthesiaisseenon the dorsal ulnar side of the hand, the likely lesion siteis the cubital tunnel.4) In our series, compression involvedzone1in16cases(89%;12casesinzone1onlyand4casesinzones1and2)andzone2in6cases(2casesinzone2onlyand4casesinzones1and2).Forthetwocaseswithcompressioninzone2only,case4showednosensorylossand case 15 showed palmar side hypesthesia.Hypesthesia

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Fig. 1. AxialT1-weightedMRIshowedacysticmasslesionattheulnartunnel(arrow)incase14.

Fig. 2. FDI data for case 14. (A) Preoperatively, FDI-CMAPlatencywas12.6mswithanamplitudeof0.1mV.(B)Fivemonthsaftersurgery,latencywas5.3mswithanamplitudeof4.0mV.

Fig. 3. ADMdata for case14. (A)Preoperatively,ADM-CMAP latencywas 11.8mswith an amplitude of 0.1mV.(B)Fivemonthsafter surgery, latencywas3.9mswithanamplitudeof4.4mV.

Fig. 4. SNAPdataforcase14showednormallatency(2.6ms)andamplitude(8μV).

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wasseenonlyon thepalmarside insixpatients,andbothonthepalmaranddorsalsides inninepatients.Thesehet-erogeneousfindingsunderlinethefactthatanexactclinicaldiagnosisofUTSanddetectionofthelocationofthelesionare often difficult.A possible explanation for the nine pa-tientswho had hypesthesia both on the palmar and dorsalsides is the presence of an aberrant dorsal sensory branchoftheulnarnervewhichdivergedwiththepalmarsensorybranchintheulnartunnel.Murataetal.3)reportedthat90%ofcaseswithUTSwereinzone1.Apreviousreportstated

thatulnarnervelesioninzones1and2arelikelycausedbyganglionsorfracturesofthehamate,andthatlesionsinzone3arecausedbyvascularlesionsresultingfromthrombosisor aneurysm.12)However, inour series, the causesof zone1lesionswereganglions,ulnararteryaberrancy,traumaticadhesion,anomalousmuscle,andulnarveinvarix.Murataetal.3)statedthatsurgicalexplorationistheonlyreliablewaytoclarifythesiteofcompression.Theexpectedtheoreticalsymptomsofcompressionsinthe

threeanatomicalzonesare:zone1lesions–delayedADMlatencyandFDI latencyanddiminishedSNAPamplitude;zone2compression–delayedFDIlatencyaccordingtothesiteofcompression,althoughADMlatencymaybenormal;and zone 3 lesions – diminished SNAP amplitude andnormalADM-CMAPandFDI-CMAP.4)Inourseriesof18cases,therewere16casesofzone1compression;ofthese,14showeddelayedFDIlatency,15showedlowFDIampli-tude, 14haddelayedADM latency, and14had lowADM

6 Nobuta S, et al: Clinical Features of Ulnar Tunnel Syndrome

Fig. 5. (A)Intraoperativephotographofaganglionwhichwasmainlycompressingthemotorbranchoftheulnarnerveatzones1and2(arrow)incase14.(B)Theganglionarosefromtriquetrohamatejoint.

Fig. 6. Photomicrograph(hematoxylin-eosinstain,originalmagnification×20)showingtheganglioncystwithathick-walled cystic space and focal myxoid change in the sur-roundingmatrixincase14.

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amplitude.OftheeightpatientswhounderwentSNAP,theresults were normal in six (Table 3). Consequently, bothFDI-CMAPandADM-CMAPwerevaluable foradefiniteelectrodiagnosisofUTS;however,SNAPwasnotusefulforconfirmingthediagnosis.Cases12,13,and17showedad-equatepinchstrengths(4.2,4.2,and4.0kg,respectively),butcases13and17hadlowFDI-CMAPamplitudes.Thesetwocasesoriginallyhadadequatepinchstrengthsonthenormalside(5.4and5.2kg,respectively);therefore,thedecreaseinpinchstrengthbeforesurgeryandrehabilitationwassmall.Surgerywasindicatedforthesecaseswithseverenumbnessandpainintheulnarnervedistribution.Lumbrical-interossei motor studies21) and short segment

incrementalstudies (SSIS, inchingmethod)ofFDI-CMAPhavebeenreportedandindicatedthatSSISwasvaluablefordiagnosisofthepreciselocalizationofUTS.22–25)Neverthe-less, SSIS is somewhat time-consuming and technicallydifficult,24)particularlystimulatingasiteonthepalmarside.Accordingly, we performed traditional nerve conductionmeasurementsofCMAPsandSNAP.Murataetal.3)reportednormalvaluesforADM-CMAPlatencyof<3.5mswithanamplitude>2.5mV,andaSNAPlatencyof<2.2mswithanamplitude>15μV.Inthecurrentseries,basedonourcrite-ria,we identifieddelayed latenciesand lowamplitudes forCMAPsandSNAPs.Nerve conductionmeasurements forUTS have been re-

ported,2,3,10,11,13–16)andtheyallindicateddelayedconductionat the wrist. However, few studies have examined nerveconduction before and after surgery.2,11,14) Uriburu et al.11) reported three cases of UTS and found that FDI-CMAPwas recordable in one case after surgery.Moreover, post-operatively, FDI latency was shortened from 7to 4ms inonepatientandfrom24to4msinanother.Ebelingetal.2) describedninecasesofUTSandfoundthatFDIlatencywasshortenedpostoperatively.Erkin et al.14) reported apatientwithaganglionandfoundthattheFDIlatencywasshortenedfrom3.5to3.2msandtheFDIamplitudeincreasedfrom2.1to5.4mVpostoperatively.Inaparthyetal.15)reportedthatthetimeforhypothenarmusclestorecovertothenormalrangewas12to14weeksintheirpatients.Inourseriesof18pa-tients,afterrehabilitation,themeanpinchstrengthincreasedfrom2.1 to3.1kgat2monthsaftersurgery. Inapreviousreport,wedescribedfivecasesofUTScausedbyganglionand found that both FDI-CMAP and ADM-CMAP werevaluableforelectrophysiologicaldiagnosis 16);however,thecurrentstudydescribes18casesofUTSwithvariouscauses,includingganglion,andtheresultswereincidentallysimilartothoseofthepastreport.Inourcurrentseries,FDI-CMAP

and ADM-CMAP did not improve to the normal range,and residual delayed latency and lowamplitudewere seendespite recoveryof the intrinsicmuscles (Tables 2 and 3).Inthesecases,fromtheviewpointofneurophysiology,my-elinizationandaxonalregenerationoffibersintheFDIandADM branches were insufficient, notwithstanding ameanfollow-upof11months.Therewereseverallimitationstothisstudy.First,wedid

not investigate the relationship betweenMRIfindings andthecausesofUTS.Second,wecouldnotclarifytherelation-shipbetweentheelectrophysiologicaldataandtherecoverytimeforintrinsicmuscles.Third,todetectfurtherimprove-mentofFDI-CMAPandADM-CMAP,longerfollow-upisneeded.

CONCLUSIONS

ThecausesofUTSinourserieswereganglion,traumaticadhesion,ulnararteryaberrancy,orpisohamatearch.BothFDI-CMAP and ADM-CMAP were valuable for electro-physiological diagnosis of UTS. Delayed latency and lowamplitudeswere seenat thefinal follow-updespite the re-coveryofintrinsicmuscles.

ACKNOWLEDGMENTS

TheauthorsaregratefultoMs.YumiWatabe,Ms.HiromiTakeda,Ms.YokoKusakari, PathologistNoriyuki Iwama,MD, Fumie Nakayama,MD, and Honorary Director Kat-sumiSato,MD,TohokuRosaiHospital,forassistinginthemanuscriptpreparation.

CONFLICTS OF INTEREST

Theauthorsdeclarethattherearenoconflictsofinterest.

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8 Nobuta S, et al: Clinical Features of Ulnar Tunnel Syndrome