www.bjorl.org
Brazilian
Journal
of
OTORHINOLARYNGOLOGY
ORIGINAL
ARTICLE
Galvanic
vestibular
evoked
myogenic
potentials:
normative
data
and
the
effect
of
age
夽
Nizamettin
Burak
Avci
a,∗,
Zahra
Polat
b,
Ahmet
Atas
¸
caHacettepeÜniversitesi,FacultyofHealthSciences,AudiologyDepartment,Ankara,Turkey
bSa˘glıkBilimleriÜniversitesi,FacultyofHamidiyeHealthSciences,AudiologyDepartment,Istanbul,Turkey
c˙IstanbulÜniversitesi-Cerrahpas¸a,CerrahpasaFacultyofMedicine,OtorhinolaryngologyDepartment,Istanbul,Turkey Received5May2020;accepted30July2020
KEYWORDS Vestibularevoked myogenicpotential; Galvanicstimulation; Normalization; P1andN1latency; Ageeffect Abstract
Introduction:Galvanic vestibular evoked myogenic potentials evaluate vestibular nerve responsesusingelectricstimulationbyrecordscollectedfromthesternocleidomastoid mus-cle.Anormalvestibularevokedmyogenicpotentialresponseconsistsofthefirstpositive,P1, andnegative,N1,peaks.Theresponsecanbeaffectedbyfactorssuchasageandgenderand isalsoconsequentialinthediagnosisofpathologies.
Objectives: Thepresentstudywasperformedtoobtainnormativedataonhealthyadults,to helpindiagnosisbyestablishingclinicalnormsaswellastoinvestigatechangingtestparameters withageingalvanicvestibularevokedmyogenicpotentials.
Methods:A totalof100healthyparticipantswereincludedinthestudy.Galvanicvestibular evoked myogenic potential (current3mA,duration 1ms) was performedrandomly onboth earsofeachparticipant.Theparticipantsbetweentheagesof18---65(meanage39.7±13.9) weredividedinto5groupsaccordingtotheirages.Normativedataofgalvanicvestibularevoked myogenicpotentialsparameterswerecalculatedingroupsandintotal,andage-relatedchanges wereexamined.
Results:The galvanicvestibular evoked myogenicpotentialwaveform was elicited fromall participants (200ears). The latency ofP1 and N1was 7.82±3.29ms and 22.06±3.95ms, respectively. The P1−N1 amplitude value was 66.64±24.5V. The percentage of vestibu-lar asymmetrywas16.29±11.99%.Thelatencies ofP1andN1andP1−N1amplitudevalues demonstratedsignificantdifferencesamongdifferentagegroups(p<0.01).
Conclusions: The results of this study show that as age increased, latencies were pro-longed, and amplitudes gradually decreased. The normative data aids in the diagnosis of
夽 Pleasecitethisarticleas:AvciNB,PolatZ,Atas¸A.Galvanicvestibularevokedmyogenicpotentials:normativedataandtheeffectof
age.BrazJOtorhinolaryngol.2020.https://doi.org/10.1016/j.bjorl.2020.07.016
∗Correspondingauthor.
E-mail:nizamettinburakavci@gmail.com(N.B.Avci).
PeerReviewundertheresponsibilityofAssociac¸ãoBrasileirade OtorrinolaringologiaeCirurgiaCérvico-Facial.
https://doi.org/10.1016/j.bjorl.2020.07.016
1808-8694/©2020Associac¸˜aoBrasileiradeOtorrinolaringologiaeCirurgiaC´ervico-Facial.PublishedbyElsevierEditoraLtda.Thisisanopen accessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).
retrolabyrinthine lesions andthe increase in the clinical useof galvanicvestibular evoked myogenicpotentials.
© 2020 Associac¸˜ao Brasileira de Otorrinolaringologia e Cirurgia C´ervico-Facial. Published by Elsevier Editora Ltda. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/). PALAVRAS-CHAVE Potencialmiogênico evocadovestibular; Estimulac¸ão galvânica; Normalizac¸ão; LatênciadeP1eN1; Efeitodaidade
Potenciaisevocadosmiogênicosvestibularesgalvânicos:dadosnormativoseoefeito
daidade
Resumo
Introduc¸ão:Os potenciaisevocados miogênicosvestibulares galvânicos avaliam asrespostas donervovestibularutilizandoestimulac¸ãoelétricaatravésderegistroscoletadosdomúsculo esternocleidomastoideo.Umarespostanormaldedepotenciaisevocadosmiogênicos vestibu-laresconsistenosprimeirospicospositivo,P1,enegativo,N1.Arespostapodeserafetadapor fatorescomoidadeesexoetambémtemimportâncianodiagnósticodedoenc¸as.
Objetivos: Opresenteestudotevecomoobjetivoobterdadosnormativosemadultossaudáveis, para ajudar no diagnóstico através do estabelecimento de normas clínicas e investigar a alterac¸ãodosparâmetrosdetestecomaidadeempotenciaisevocadosmiogênicosvestibulares galvânicos.
Método: Umtotalde100participantessaudáveisforamincluídosnoestudo.Opotencial evo-cado miogênico vestibular galvânico (corrente 3mA, durac¸ão 1ms) foi realizado de forma aleatórianasduasorelhas decadaparticipante.Osparticipantes comidadesentre18 e65 (idademédiade39,7±13,9) foramdivididos em5gruposdeacordocomaidade.Osdados normativosdosparâmetrosdospotenciaisevocadosmiogênicosvestibularesgalvânicosforam calculadosnosgruposenototal,easalterac¸õesrelacionadasàidadeforamexaminadas.
Resultados: Aformadeondadopotencialevocadomiogênicovestibulargalvânicofoiobtida de todos os participantes (200 orelhas). A latência de P1 e N1 foi de 7,82±3,29ms e 22,06±3,95ms,respectivamente.OvalordaamplitudeP1−N1foide66,64±24,5V.O per-centualdeassimetria vestibular foide 16,29±11,99%.Osvalores daslatênciasde P1eN1 edaamplitudeP1-N1 mostraramdiferenc¸as significantesentreos diferentesgrupos etários (p<0,01).
Conclusões:Osresultadosdesteestudomostramqueàmedidaqueaidadeaumentou,as latên-ciasforamprolongadaseasamplitudesdiminuíramgradualmente.Osdadosnormativosauxiliam nodiagnósticodelesõesretrolabirínticasenadisseminac¸ãodousoclínicodospotenciais evo-cadosmiogênicosvestibularesgalvânicos.
© 2020 Associac¸˜ao Brasileira de Otorrinolaringologia e Cirurgia C´ervico-Facial. Publicado por Elsevier Editora Ltda. Este ´e um artigo Open Access sob uma licenc¸a CC BY (http:// creativecommons.org/licenses/by/4.0/).
Introduction
Vestibular-evoked myogenic potential (VEMP) is a neuro-physiological assessment method used for the evaluation ofotolithorgansintheinnerear.VEMPsareshort-latency potentials and theinhibition responseof themuscle that occurs with the stimulus.1 VEMP is the only vestibular
testbatterythatevaluatesthevestibulocollicreflex(VCR); therefore,ithasanessentialpositionforvestibular assess-mentin clinics.When considering defining applicationsof VEMPprocedures,VEMPis usedasadiagnostictool disor-dersthatcausedizziness,suchassuperiorcanaldehiscence, Meniere’s disease, and vestibular schwannoma.2 Although
anacousticstimulusisoftenused,amechanicaland elec-tricalstimuluscanalsobeperformed.Differentstimulation andrecordingmodalitiescanbeused,anddifferentnames expressthem,suchasocularVEMP(oVEMP),cervicalVEMP
(cVEMP),acousticVEMP,etc.Galvanicvestibularstimulation (GVS)isusedintheevaluationwithelectricalstimulusand iscalledgalvanicVEMP(gVEMP).
Theeffectoftheacousticstimulusbeginsinthesaccular macula andendsinthesternocleidomastoid muscle(SCM) viatheinferiorvestibularnerve,lateralvestibularnucleus, andmedialvestibulospinaltractincVEMP.3GVS stimulates
irregular vestibular afferents.4 Since GVS is an electrical
stimulus,itcontainsanadolandcathodalcurrents.Cathodal currentincreasesthespontaneousfiringrate,whileanodal current decreases it.5 This change in the spontaneous
fir-ing rateresults in the stimulationof VCR. When GVS and acousticstimuliactivatethesamereflexpathwayfrom dif-ferentregions,theyaidindifferentiatingretrolabyrinthand labyrinthlesions.
VEMPresultsdonotonlyshowchangesindiseases. Age-relatedvestibulardegenerationsalsoaffectVCRandVEMP
results.Althoughithasshowninmanystudiesthat vestibu-lar degeneration is associated with age, it is difficult to determineusingtheresultsofvestibulartests.
Inthisstudy,weaimedtoestablishthegVEMPnormative dataforourcountryandclinicandtoinvestigatethe age-relatedeffectsoftheresponsesindifferentagegroups.
Materials
and
methods
Designofthestudy
ThestudywasconductedinintheHearingandSpeech Dis-orders Center of Cerrahpasa Medical Faculty at Istanbul University-Cerrahpasa. The study wascompletedbetween November 2018 and February 2019 after approval from the ethical committee of the institute with the number 83045809-604.01.02.Thisstudywasdesignedandconducted in accordance with the ethical standards of the Helsinki Declaration.
Theinclusioncriteriaforthestudywere:1)Normal oto-scopicand immitancemetricfindings2)pure toneaverage (500---2000Hz) in the range of 0---25dB HL3) 18---65 years old4)nohistoryofvertigoandfall5)noknown neurolog-icalandorthopedic disease.Adetailedexplanationof the procedures that they mayundergo was given tothe sub-jects, and a signed informed consent form was obtained from each participant. Immitansmetric examinations and puretoneaudiometrywereperformed.gVEMPwasrandomly appliedtobothearsoftheparticipantswhometthe inclu-sioncriteria.
Participants
Ahundredadultsagerange18---65(mean±standard devia-tion39.7±13.9)whohadnohistoryofhearingloss,vertigo, and ear problems participated. Participants were divided intofivegroupsaccordingtotheirages,andeachgrouphad 20participants.Theagegroupswere18---25,26---35,36---45, 46---55,and56---65years,andthegroupswerenamedGroup 1,Group2,Group3,Group4,andGroup5,respectively.The distributionofwomenandmenineachgroupwasequal.A totalof50femalesand50malesparticipatedinthestudy. Allparticipantswereevaluatedwithimmitancemetricand audiologicalevaluations.gVEMPtestwasappliedrandomly tobothears(200ears)oftheparticipants.
Immitancemetricandaudiologicevaluations
The‘‘GSITympstarMiddlEarAnalyzer(GrasonStadlerInc., USA)’’ was used for the immittancemetric measurement. Tympanometry tests evaluating middle ear pressure was applied,andtypeAtympanogramwasacceptedasnormal middleearstatus.Allhearingevaluationswereperformed withan ‘‘InteracousticsAC40 clinical audiometer (Intera-cousticsA/S,DK)’’.Hearingthresholdsof500,1000,2000, and 4000Hz were tested withpure tone audiometry, and pure tone averages(500, 1000, and 2000Hz) were calcu-lated. Hearing levelsof the participantswhose pure tone averagewasin therangeof0---25dB HLwereacceptedas normal.
GalvanicVEMP
GVSstimulatedover themastoidprocesscausesdischarge directlyintheprimaryafferentsofthevestibularnucleiand thedistalpartofthevestibularnerve.Whiletheafferents onthenegative(cathodal)sideareactivated,theafferents onthe positive (anodal) side are inhibited in the bipolar configuration.Inthisstudy,thestimulatingelectrodeswere placedaccordingtotheunilateralbipolar placement.The cathodalelectrode wasplaced on themastoid of the ear tobetested,andthe anodalelectrodewasplacedonthe forehead.GoldcupelectrodeswereusedforGVS.Inorder topreventskinburnscausedbythestimulatingelectrodes andtoprovidebetterconductivity,Signaelectrodegel(USA) wasused.The stimulating electrodes were placed onthe appropriateareawiththetransdermalpatch.Whenthe gal-vanic stimuluswassent tothe participants,it wasstated thattheywouldnotfeelpain,rathertheywouldonlyfeela slighttapping.
GVScanonlyproduceanelectromyography(EMG) record-inginthemusclesthatprovidebalance:EMGrecordsfrom the SCM, paraspinal, triceps, tibialis anterior and soleus musclesareavailable.Inthisstudy,sincetherecordingwas collectedfromSCM,therecordingelectrodeswereplaced onthe same electrode placement asthe acoustic cVEMP. The active electrode, the reference electrode, and the ground electrodewere placed onthe middle of SCM, the sternum, and the forehead, respectively. Disposable wet-gelelectrodeswereusedforrecording.Aftertherecording electrodeswereplaced,itwasensuredthattheimpedance valueswerein therangeof 0---5k.The groundelectrode waspositionedundertheanodalelectrode,oneofthe stim-uluselectrodes placedontheforeheadwithcaretakento notbeincontactwitheachother.Recordingelectrodesand stimuluselectrodeswereplacedipsilaterallyonthesideto betested.
ThegVEMPtestwasperformedusingNeuro-Audio (Neu-rosoft Inc.,Russia). NeuroMEP EScontrol unit (Neurosoft Inc., Russia) electrical stimulator was used for GVS. The stimulus rate was 5Hz, the stimulus duration was 1ms, thecurrent level was3mA, thestimulus waveformwasa click,andthestimuluspolaritywasminus.Foreachtrace, thenumberofstimuliwas100.Recordingparameterswere identicaltothoseofacousticcVEMP.EMGrecordingswere amplified for analysis. A 20---2000Hz bandpass filter, and notchfilterwereappliedoncollectedrecordings.The anal-ysistimewindowwas50ms.
FortheaccuracyofVEMPresponses,thedegreeofSCM musclecontractionshouldbestablewithinaspecificrange duringthetesting.Inthisstudy,thisrangewasacceptedas 30---70V,andthemusculartonusofSCMwasmeasuredby electromyographyduringtesting.The feedbackmethodof thesoftwareincludedinthedevicewasusedtoenablethe participanttomaintainhis/herSCMcontraction.
The gVEMP test wasperformed withthe participantin a sitting position in two stages. In the first stage, when theSCMwasnotcontracted(headin anupright position), thefirsttrace(without SCM contraction)wasobtained by sendingthegalvanicstimulusoverthemastoidoftheside beingtested.Inthesecondstage,whentheSCMwas con-tracted(theheadinrotationtotheoppositedirectionofthe
Table1 Mean±standarddeviationsofnormativedataindifferentagegroupsandtotal.
P1latency(ms) N1latency(ms) P1---N1Amplitude(V) PercentageofVA(%)
Group1 6.63±2.88 20.57±3.16 73.39±23.72 16.85±14.03 Group2 5.27±1.94 20.03±3.46 77.04±23.55 17.91±13.37 Group3 9.04±2.79 22.61±3.05 68.01±25.85 15.1±9.32 Group4 8.49±3.46 22.61±3.65 63.97±19.44 11.67±9.55 Group5 9.67±3.15 24.5±4.68 50.77±21.76 19.9±12.41 Total 7.82±3.29 22.06±3.95 66.64±24.5 16.29±11.99
eartobetested),thesecondtrace(withSCMcontraction) wasobtainedbysendingthegalvanicstimulus.Therewere artefacts fromthegalvanic stimulusin both traces. Since thesewaveformsincludedveryhighartefacts,the subtrac-tionmethodwasusedtoeliminateartefacts.6Thefirsttrace
(withoutcontractionofSCM)wassubtractedfromthe sec-ondtrace(withcontractionofSCM),andfinally,thegVEMP waveformwasobtained.Thesamestages wereconducted forboththerightandleftsides.
ThegVEMPwaveformlooksthesameastheacousticVEMP waveform.Thewaveformhasapositiveandanegativepeak, whicharenamedP1andN1,respectively. gVEMP parame-ters includeP1 andN1 latencies, P1−N1 amplitudes, and thepercentageofVEMPAsymmetry(VA).P1andN1 laten-ciesand P1−N1 amplitude valueswererecorded for each participant’sright andleftear.The percentageof VA was calculated usingthe formula |Ar-Al|/(Ar+Al)×100. Ar is theP1---N1amplitudevalueoftherightear,AlistheP1---N1 amplitudevalueoftheleftear,and|Ar-Al|istheabsolute valueofthedifferencebetweenrightandleftearamplitude values.
Statistics
Themeanandstandard deviationforlatencies and ampli-tudeofgVEMP andthepercentageofVAwerecalculated. Normality tests were used to check whether or not data arenormallydistributed.If theskewness-kurtosisvalue is intherangeof±2, thedata areaccepted tobenormally distributed.7Therefore,ourdatawasacceptedtobe
nor-mally distributed and parametric tests were used for all statisticalanalysis.Independentsamplest-testwasusedfor thecomparisonofright/leftearandfemale/male.One-way analysisofvariance(ANOVA)testwasusedforthe compar-isonbetween fivedifferentage groups. Post-hocanalysis was conducted to determine which group or groups had significant differences. The relationship between age and gVEMP parameters was calculated by Pearson correlation analysis.The data were analysed withIBM SPSS Statistics 20.0.
Results
Thisstudywascarriedoutwith100participants,50females and50males,andatotalof200earsweretested.Galvanic VEMPresponsewasobtainedinallparticipants.P1andN1 latenciesandP1−N1amplitudevaluesweremeasured,and thepercentageofVAwascalculatedinthestudy.These
val-0 5 10 15 20 25 30 35 40
Group 1 Group 2 Group 3 Group 4 Group 5
Lat e n c y ( m s) P1 latency N1 latency
Figure1 P1andN1latencymeanvaluesingroups.
ueswerecomparedaccordingtogender,earside,andage groups.
Nostatisticalsignificancewasobservedinthecomparison oftheright-leftearandmale-female(p>0.05).Therefore, we calculated the mean values for total and age groups. MeanvaluesofP1andN1latencies,P1−N1amplitude,and percentagesofVAareshowninTable1.
P1 and N1 latency values and P1−N1 amplitude val-ueswerestatisticallysignificantinthecomparisonbetween age groups.Group 1[mean:6.6ms(P1) and20.5ms(N1)] hadshorterP1andN1latenciesthanGroup3[mean:9ms (P1)and22.6ms(N1)]andGroup5[mean:9.6ms(P1)and 24.5ms (N1)], alsoGroup 2 [mean: 5.2ms(P1) and 20ms (N1)]hadshorterP1andN1latenciesthanGroup3[mean: 9ms(P1)and22.6ms(N1)],Group4[mean:8.4ms(P1)and 22.6ms(N1)] andGroup5[mean:9.6ms(P1) and24.5ms (N1);(p<0.05)](Fig.1).Group5(mean:50.7V)hadlower amplitudevaluethanGroup1,Group2andGroup3(means: 73.3,77and68Vrespectively;p<0.001)(Fig.2). Statisti-calresultsofthecomparisonbetweengroupsareshownin Table2.
ThecorrelationbetweenageandgVEMPparameterswas examined.Therewasaweakpositivecorrelation between age and P1and N1latencies (p< 0.001, r = 0.416 for P1 latency and r = 0.378 for N1 latency) and a weak nega-tivecorrelationwithP1-N1amplitudevalues(p< 0.001,r= −0.319).Nocorrelationwasfoundbetweenthepercentage ofVAandage(p= 0.873,r=−0,016).
Table2 Comparisonofbetween-groupsforP1andN1latenciesandP1---N1amplitude.
Comparisonofbetween-groups p-valueforP1latencies p-valueforN1latencies p-valueforP1−N1amplitudes
Group1−Group2 0.109 0.948 0.954 Group1−Group3 0.003b 0.035a 0.833 Group1−Group4 0.081 0.070 0.358 Group1−Group5 0.000b 0.000b 0.000b Group2−Group3 0.000b 0.006b 0.401 Group2−Group4 0.000b 0.015a 0.085 Group2−Group5 0.000b 0.000b 0.000b Group3−Group4 0.933 1.000 0.934 Group3−Group5 0.876 0.214 0.008b Group4−Group5 0.501 0.265 0.080
One-wayANOVAforcomparisonofbetween-groups. PostHocs/TukeyHSDforcomparisonofamplitudes.
PostHocs/Games-HowellforcomparisonofP1andN1latencies.
a p<0.05. b p<0.01. 0 10 20 30 40 50 60 70 80 90
Group 1 Group 2 Group 3 Group 4 Group 5
A m plit ud e ( µ V ) P1-N1 amplitude
Figure2 P1−N1amplitudevaluesindifferentagegroups.
Discussion
Clinical research withVEMPs mostly focuses onthe diag-nosisofperipheralvestibulardiseases.Thewidespreaduse ofVEMPincreasesinterestinthedistinctionbetween cen-tralandperipheralvestibulardiseases.Therefore,different VEMPmodalitiesshouldalsobeusedtoevaluatedifferent regions of the vestibular apparatus. For instance, cervi-calVEMP (cVEMP)evaluates VCRandsaccular functionby recordingonSCM,ocularVEMP(oVEMP)evaluatesVORand utricularfunctionbyrecordingonocularmuscles.Although abnormalcVEMPandoVEMPresponsessuggestaproblemin thesystem,thesetestsfailtodifferentiatebetween retro-labyrinthine andlabyrinthine lesions.8 GalvanicVEMP can
behelpfulinthedifferentiationofthelesionwhenusedin combinationwithcVEMPoroVEMPbecauseitprovides stim-ulationbypassingthemechanical partoftheinnerear.9---11
Therefore, the normative data obtained in our study can beusedfrequentlyinthediagnosisofthedifferentiationof retrolabyrinthineandlabyrinthinelesions.
In our study, we applied gVEMP (3mA, 1ms duration) to100healthy individuals(200 healthyears)between the age ages of 18---65. The P1 and N1 latencies mean val-ueswere 7.82±3.29msand22.06±3.95ms,respectively.
TheP1−N1amplitudemeanvaluewas66.64±24.5V.The meanpercentageofVAwas16.29±11.99%.Therearefew studiesassessingthenormativedataofgVEMPinthe liter-ature.InastudyconductedbyChengetal.(2018),12 they
appliedgVEMP(3mA/1msduration)to16 healthy individ-uals(31healthyears)betweentheagesof20and60.The P1meanlatencywas11.7±3ms,theN1meanlatencywas 17.8±3.4ms,theP1−N1meanamplitudewas147±69V, and the mean percentage of VA was 16±1%. In another study conducted by Welgampola and Colebatch (2001),13
they obtained normative data by applying galvanic VEMP (4mA/2msduration) on70healthy adult individuals aged 25---85years.ThemeanvalueofP1latencywas12.1±1ms, N1latency was20.2±1.7ms,P1−N1amplitudevalue was 60±35.1V,andthepercentageofVAwas22%.Thenumber ofparticipantsinthesestudiesislessthaninourstudy.The smalldifferenceswerethoughttobeduetomethodological differencessuchasrecordinginstruments,electrode place-ment,andfeaturesofthestimulusand/orthedifferences inpopulation.
The changesin thevestibularsystem occurnotonly in thepresenceofpathologicalconditionsbutalsowithaging. Age-related changes create effects such as a decreased number of hair cells, nerve fibers, ganglion cells, and vestibularnucleusneuronsinthevestibularsystem.14---17 In
additionto the saccular macula and vestibularafferents, theaccessorynerveandSCMmusclearealsoincludedinthe VEMP reflexarch. The decrease in accessory nerve fibers ordecreasedneurogenicmuscleresponsesshouldconsider withaging.18
P1andN1 latencieswere prolonged fromGroup 3and onwardinourstudy.Theprolongationofthelatencieswas quite significant, especiallyin Group 5, comparedto the youngergroupsinthisstudy.Althoughtherewasno statis-ticalsignificancebetween Group1 andGroup 4inP1and N1 latencies, considering the mean values, we observed that group 1 had more shorter latencies than Group 4. This statistical significance was due to the difference in the standard deviations of both groups. The prolongation ofP1andN1latencieswasrelatedtoage-relatedchanges such as the decrease in vestibular neurons, Scarpa
gan-glion cells, the function of myelinated nerve fibers, and theaccumulation of amyloid onthe vestibularnerve. We observed significantlylower amplitude valuesin Group 5. Theloweramplitudewasrelatedtothelossofneuronsdue tovestibulardegeneration19andthedegenerationofSCM.18
Theresultsofthisstudy showedthatwhilelatencieswere prolongedafter35years,theamplitudewasdecreasedafter 55years.
The literature does not show a strong correlation between vestibular function tests and age.20 P1 and N1
latenciesandP1−N1amplitudevalueswerealsoweakly cor-relatedwithageinourstudy.Thecorrelationmirroredthe resultsobtainedintheliterature.Thissuggeststhatcentral compensatorymechanismshaveasubstantialeffectonthe vestibularsystem.21
Limitations
of
the
study
Ourstudyhasafewlimitations. Firstly,narrowingtheage rangesinordertodeterminethebreakingpointofthe age-relatedchangecanprovidemorespecificinformationabout vestibular degeneration. Secondly, normative data were obtained over a single current value in this study. Estab-lishingnormativedatabelongingtodifferentagegroupsat differentcurrentvalueswillbefavorablefordifferentiating pathologicalconditions.
Conclusion
Itshouldbenotedthatdifferencesinnormalizationstudies maybeaffectedbyconditionssuchaspopulation,stimulus type,and different test parameters.The most important contribution of this study is that it is thegVEMP normal-izationstudywiththemostparticipantsuptopresentand istheonlystudyinwhichnormativedataarecollectedfor differentagegroups. gVEMP,which isnot yetwidely used inclinics,canbeusedasanadjunctivediagnostictoolwith acousticVEMPinthedifferentiationofretrolabyrinthineand labyrinthinepathologies.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
Acknowledgments
Theauthorsthankalltheaudiologistswhohelpedmakethis studypossibleintheHearing andSpeechDisorders Center atIstanbulUniversity-Cerrahpasa.
References
1.Rosengren SM,ColebatchJG. Thecontributionsofvestibular evokedmyogenicpotentialsandacousticvestibularstimulation toourunderstandingofthevestibularsystem. FrontNeurol. 2018;9:1---17.
2.StoodyTM,InversoY.Developmentofvestibularevoked myo-genicpotentials.In:AtchersonSR,StoodyTM,editors.Auditory electrophysiology:a clinicalguide. 1sted NewYork:Thieme MedicalPublisher;2012.
3.Uchino Y, Sato H, Sasaki M, Imagawa M, Ikegami H, Isu N, et al. Sacculocollic Reflex Arcs in Cats. J Neurophysiol. 1997;77:3003---12.
4.GoldbergJM,Smith CE, FernandezC.Relation between dis-chargeregularityandresponsestoexternallyappliedgalvanic currentsinvestibularnerveafferentsofthesquirrelmonkey.J Neurophysiol.1984;51:1236---56.
5.GoldbergJM,FernandezC,SmithCE.Responsesof vestibular-nerveafferents inthesquirrelmonkey to externallyapplied galvaniccurrents.BrainRes.1982;252:156---60.
6.Watson SRD, Colebatch JG. Vestibulocollic reflexes evoked by short-duration galvanic stimulation in man. J Physiol. 1998;513:587---97.
7.GeorgeD,MalleryP.SPSSforwindowsstepbystep:asimple guideand reference,17.0 update.10th edBoston: Pearson; 2010.
8.ChangCM,YoungYH,JawFS,TeWC,ChengPW.Degeneration ofthevestibularnerve inunilateralMeniere’sdisease evalu-atedbygalvanicvestibular-evoked myogenicpotentials.Clin Neurophysiol.2017;128:1617---24.
9.ChengPW,ChenCC,WangSJ,YoungYH.Acoustic,mechanical andgalvanicstimulationmodeselicitocularvestibular-evoked myogenicpotentials.ClinNeurophysiol.2009;120:1841---4. 10.IwasakiS,TakaiY,OzekiH,ItoK,KarinoS,MurofushiT.Extent
oflesionsinidiopathicsuddenhearinglosswithvertigo:study usingclickandgalvanicvestibularevokedmyogenicpotentials. ArchOtolaryngolneckSurg.2005;131:857---62.
11.MurofushiT, Takegoshi H, Ohki M,Ozeki H. Galvanic-evoked myogenicresponsesinpatientswithanabsenceofclick-evoked vestibulo-collicreflexes.ClinNeurophysiol.2002;113:305---9. 12.ChengY,KimuraY,KagaK.Astudyonvestibular-evoked
myo-genicpotentialsviagalvanicvestibularstimulation innormal people.JOtol.2018;13:16---9.
13.WelgampolaMS, Colebatch JG. Vestibulocollicreflexes: nor-mal values and the effect of age. Clin Neurophysiol. 2001;112:1971---9.
14.Engstrom H, Bergstrom B, Rosenhall U. Vestibular sensory epithelia.ArchOtolaryngolneckSurg.1974;100:411---8. 15.BergstromB.Morphologyofthevestibularnerve:II.Thenumber
ofmyelinatedvestibularnervefibersinmanatvariousages. ActaOtolaryngol.1973;76:173---9.
16.ParkJJ,TangY,LopezI,IshiyamaA.Age-relatedchangeinthe numberofneuronsinthehumanvestibularganglion.JComp Neurol.2001;431:437---43.
17.Velazquez-VillasenorL,MerchantSN,TsujiK,GlynnRJ,WallC 3rd,RauchSD.Temporalbonestudiesofthehumanperipheral vestibularsystem:2.NormativeScarpa’sganglioncelldata.Ann OtolRhinolLaryngolSuppl.2000;181:14---9.
18.Wolfson LI, Whipple R, Amerman P, Kaplan J, Kleinberg A. Gait and balance in the elderly. Two functional capacities thatlinksensoryandmotorabilitytofalls.ClinGeriatrMed. 1985;1:649---59.
19.Richter E. Quantitative study of human Scarpa’s gan-glion and vestibular sensory epithelia. Acta Otolaryngol. 1980;90:199---208.
20.LordSR,DelbaereKIM,SturnieksDL.Aging.In:DayBL,LordSR, editors.Handbookofclinicalneurology,Vol159,3rded.2018. p.157---71.
21.ZalewskiCK.Agingofthehumanvestibularsystem.SeminHear. 2015;36:175---96.
