an intro on the vestibular investigations

Someimportantissuesrelatedtotheclinicalrelevanceofthehighlysophisticatedandcostlyneurotologicalinvestigations:Themostimportantaspectinallneurotologicalinvestigationsisneitherthesophisticationofinstrumentsthatarebeingusednortheexcellenceoftheinfrastructure.Itisthededication,commitment,honesty,expertise,clinicalinsightandknowledgeofthemanbehindthemachinei.e.,thepersonoperatingtheinstrumentwhichshouldideallybeamedicalpersonandnotaglorifiedswitchpresser/technicianwhichismostoftenthecasenotonlyinourcountrybuteveninthemostdevelopedcountries.Theclinicianwhohasorderedthetestshouldalsohavesufficientknowledgetogaugetheauthenticityofthetestandinterpretthefindingsinthelightoftheclinicalhistoryandthesignsandsymptomsofthepatient.Itisonlywheneachoftheseisperfectlyinorderthatthesesophisticatedneurotologicalinvestigationshaveanyrelevanceandclinicalsignificance.Otherwisethesearejustpiecesofnicelyprintedpaperwithsomemeaninglessgraphsonfancyletterheadsthatcanconfuseandcompletelymisleadthemostastuteclinician.Justorderingsomeneurotologicalinvestigationsandthentakingclinicalmanagementdecisionsonthebasisoftheprintoutsdoledoutfromaclinicwithoutverifyingitsauthenticityandreliabilityandwithoutmatchingitwiththeclinicalfindingsisridiculousifnotdangeroustosaytheleast.Mostneurotologicalinvestigationscanbeextremelymisleadingifithasnotbeendonebythecorrectperson.Unfortunately,gettingthe'correctperson'isnoteasyanditremainstheweakestlinkinthechain.Notuncommonlymostoftheneurotologicalinvestigationsaredonebyparamedicsandsometimesevenbyuntrainedstaffnoneofwhomhavetherequisiteclinicalknowledgeandinsightwhichisessentialforcarryingoutthetestethically.Thesetestsarenotjustpressingsomecomputerswitchesandthencollectingaprintoutfromtheprinter.Mostoftheneurotologicalinvestigationsrequireextremelysophisticatedevokedpotentialrecordingsystems,veryadvancedimageprocessingtechnologiesandadvancedcomputingmethodsallofwhicharepronetoalotofartifactsthatcanmimicandmaynotbedistinguishablefromtheactualresponse.Theactivecooperationofthepatientisalsoveryveryimportantforaproperrecordingfreefromartifacts.

Theinsightandclinicalknowledgeoftheoperatorandinterpreteraswellasthatoftheclinicianisofparamountimportanceindistinguishingartifactsfromactualgraphs.ThisisamajorlimitationofallneurotologicalinvestigationsbeitanENGoraVNGtest,anECochGoraBERAtestandthisistheprimaryreasonwhyneurotologicalinvestigationsarenotaspopularastheyshouldbeamongstpractitioners.Themajorityofdoctorsdenouncetheneurotologicalinvestigationsandhaveafeelingthattheyactuallydonotserveanymedicalpurpose.Thisisnotwithoutreasonbecausethesetestsaremostlydonebythewrongpeoplewhodonothavetherequisiteinsight,ethicsandhonestyanddoleoutsomenonsenseinthenameofneurotologicalreports.Unfortunatelyinmanycases,suchreportsareacceptedbyclinicianswithoutverifyingitsauthenticity.Thisissometimesbecausetheclinicianisnotsufficientlytrainedinjudgingtheauthenticityoftheinvestigationsorsometimesduetoreasonsthatarebestnotdiscussedinpublicforums.Properlydoneandproperlyinterpretedneurotologicalinvestigationsdonebythemodernmachinesbytheproperpersonsdopresentatremendousamountofclinicallyrelevantmaterialwithoutwhichascientificneurotologicaldiagnosisisnotpossibleandwithoutadefinitediagnosisadefinitivecurativetreatmentisnotpossible.Onlyamedicaldoctorwithsufficientclinicalknowledgecandojusticetotheneurotologicalinvestigationsanditisnotsomethingthatparamedicscanbereliedupon.Anotherissuethatneedstobestressedinregardtotheinvestigationsofthevestibularsystemisthenecessityofatestbatteryapproachi.e.,combiningtheresultsofmanyteststoarriveatadiagnosis.Itistotallydifferentfromjustcarryingoutabloodtestandfindingmalariaparasitesinthebloodandthendiagnosingitasmalaria.Maintenanceofbalanceinvolvesdifferentsystemslikethevestibularsystem,theneurologicalsystem,themusculoskeletalsystem,thevisualsystemandeventhecognitiveandpsychologicalsystems.Nosingletestcandiagnosethewidevarietyoflesionsthatcanbemanifestedasvertigoorimbalance.Justthevestibularlabyrinthswhicharetheorgansforsensinghead/bodymovementshavefivedifferentpartswhichneedtobetestedseparatelybydifferenttests.WhiletheENG/VNGtestscanpickupsomeofthelabyrinthinelesionsinvolvingthevestibuloocularreflex(VOR),yettheydonottestthewhole

vestibularlabyrinth.Theybasicallytestonlythelateralsemicircularcanalandthesuperiorvestibularnerve,nothingmuchmore.Totesttheothersemicircularcanalsinthevestibularlabyrinth,namelytheanteriorandposteriorcanals,othertestslikethevideoaheadimpulsetest(VHIT)isnecessary.Totesttheotolithorgansinvestigationslikethesubjectivevisualvertical(SVV)andthevestibularevokedmyogenicpotential(VEMP)testsarerequired.ThissacculeandtheinferiorvestibularnerveisspecificallytestedbythecervicalVEMPtest.Thevestibulospinalreflexsystemcanbetestedbycraniocorpographyandthedifferentformsofposturographylikestabilometryandcomputeriseddynamicposturography.Totesttheconductivityofthenervesthattransmitthebalancesensationfromtheproprioceptorsindifferentpartsofthebodytothebrainaswellasthatofthenervesthatconductthemotoroutputfromthebraintothedifferentmusclesofthebody,testslikenerveconductionvelocity(NCV)studyandthesomatosensoryevokedpotential(SSEP)studiesarenecessary.Notonlythesevestibularinvestigationsbutalsootherrelatedinvestigationslikepsychometricstudies,audiologicaltestsandophthalmologicalstudiesarealsoimportantinalotofpatientsthatpresentwithbalancedisorders.Thebalancesystemisoneofthemostcomplexsystemsofthehumanbodyanditsstructural/functionalintegritycanonlybeassessedbyacombinationofmanytests.Nosingletestisastandalonetestinevaluatingthefunctioningofthebalancesystem.Nodoubtthatthesearecostly,cumbersomeandtimeconsuming(butdefinitelynoninvasiveandpainless)tests,buttofathomthecomplexfunctioningofthebalancesystemaverythoroughevaluationofthedifferentconstituentsofthesystemismandatory.