MedicineLakex

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Update on cVEMP and oVEMP testing in Superior Canal Dehiscence Erin Piker, AuD PhD Doug Garrison, AuD

• VEMP Background • Recording a VEMP • Clinical Utility of VEMP • Superior Canal Dehiscence • Case Studies

Peripheral Vestibular System • 3 semicircular canals (SCC) – Angular acceleration and deceleration • Utricle and saccule – Linear acceleration and deceleration

Vestibular Evoked Myogenic Potentials • In addition to movement, vestibular afferents may be activated – Sounds of high intensity – vibration and – electrical stimulation applied over the mastoid process • Then a series of reflexes are triggered that include short latency activations and inhibitions of electromyographic (EMG) activity • EMG: measures the modulation of muscle activity • When mediated through the vestibular end organs referred to as vestibular evoked myogenic potentials (VEMP) • We are using sound only as a pressure stimulus • i.e. sound pressure is being used as a hydro- mechanical force to move the endolymphatic fluid and, as a consequence, to translate otoliths to create transduction Slide courtesy of Gary Jacobson Vestibular Evoked Myogenic Potentials • A VEMP recorded from the • A VEMP recorded from the SCM = cervical VEMP EOM = ocular VEMP adapted from Curthoys 2010 • Afferent pathway – Inferior vestibular nerve • Central connections – vestibular nucleus • Efferent pathway – Medial or lateral vestibulospinal tract to the spinal accessory nucleus of cranial nerve XI – Cranial nerve XI innervates the motor neurons of the adapted from Iwasaki et al, 2008 • Afferent pathway: – superior vestibular nerve • Central connections: – vestibular nucleus • Efferent pathway – medial longitudinal fasciculus (MLF) routes to cranial nerve III – CN III innervates four of the six extraocular muscles – Contralateral inferior Recording a VEMP • Air conduction (e.g. click or tone burst) • Bone conduction (e.g. B-71) • Mechanical taps (tendon/reflex hammer) • Galvanic stimulation • AC tone bursts are most common in use clinically – AC is feasible and accessible – Low frequency tone burst - large amplitude response Stimulus Characteristics (both cVEMP and oVEMP) Stimulus Type
500 Hz tone burst, 2-0-2 cycle, Blackman gated; 100 usec click Transducer
ER3a insert earphone Intensity
Recording Characteristics Sweeps per average Artifact Rejection Patient set-up and Electrode montage Supine, head turned away from Supine/sitting, gazing upward stimulus and lifted Non-Inverting/Active cVEMP: ipsi SCM oVEMP: contra IO Inverting/Reference cVEMP: sternum, chin, hand oVEMP: below non-inv. cVEMP versus oVEMP • cVEMP waveform is positive/negative • oVEMP waveform is negative/positive • Peak-to-peak amplitude • Peak latency • Threshold • Interaural amplitude, latency, and threshold VEMP Parameters: Threshold • cVEMP, 500 Hz TB • oVEMP, 500 Hz TB – 15 – 350 uV • IAA: > 44% • IAA: > 33% – Mean Range: 11.81 – – Mean Range: 8.77 – – Cut-off: >20.47 – Cut-off: >14.4 • ILD: >3.39 • ILD: > 2.47 Zapala & Brey 2004; Piker et al. 2011; Li et al. 2014 Subject Variables that can affect the VEMP • Conductive hearing loss – Stimulus can't reach the inner ear at an – Must use bone conduction or taps Yang & Young (2003) • Patient with right • Tone-burst VEMP present in left ear, absent in right • Tapping produced VEMPs bilaterally Subject Variables that can affect the • Patient's ability to – cVEMP – Voluntary tonic EMG influences the cVEMP No EMG – Linear relationship between cVEMP amplitude and degree Akin et al. 2004 of SCM contraction Subject Variables that can affect the • Gaze direction (oVEMP) – oVEMP amplitude is greatly effected by gaze Govender, Rosengren, & Colebatch (2009) Subject Variables that can affect the – VEMPs can be recorded across the lifespan, from neonates to elderly – Neonates show increased latencies and smaller amplitudes (e.g. Chen et al. 2007) – Older adults show smaller amplitudes, increased latencies (maybe?), increased thresholds, and reduced response rate (i.e. not all older adults will produce a VEMP in response to air conduction stimulus) Piker et al. 2012 Clinical Utility of VEMP Clinical use of VEMPs Curthoys & Manzari, 2013 Vestibular Neuritis • Using both cVEMP and oVEMP can localize superior vs inferior nerve involvement – oVEMP measuring utricle and superior vestibular nerve – cVEMP measuring saccule and inferior vestibular nerve • If patient has superior vestibular neuritis, should have impaired oVEMP on that side but cVEMP should be normal • If patient has inferior vestibular neuritis, patient should have preserved oVEMPs bilaterally and the cVEMP should be absent on side of neuritis Example of Inferior Vestibular Neuritis • Prior to our ability to assess the inferior cVEMP: Abnormal, 50% asymmetry nerve and localize the impairment, many patients with IVN were mistaken for central vestibular disorders (Kim & Kim, 2012) Jacobson, McCaslin, & Piker (2011) Clinical use of VEMPs • cVEMP and oVEMP also used in evaluation of many other pathologies when function of the vestibular system is questioned – e.g. vestibular neuritis, Meniere's Disease, migraine- associated vertigo, multiple sclerosis, superior canal dehiscence (SCD) • One of the clinical limitations of VEMP tests is that, as with most vestibular tests, VEMPs assess site of lesion…not necessarily the presence or absence of disease Clinical use of VEMPs • cVEMPs abnormal in cases of IVN, while oVEMPs and caloric testing are usually – However, the diagnosis of inferior neuritis is ultimately based on case history • cVEMPs are hypothesized to be useful in Meniere's Disease because the saccule is believed to be the second most involved structure in endolymphatic hydrops – However, the sensitivity and specificity of cVEMPs are reportedly only 50% and 48.9%, respectively, in patients with unilateral definite Meniere's Disease • VEMPs are not essential for the diagnosis of migraine – but it may be important to quantify vestibular involvement • Patients with utricle and saccule impairments, as measured using cVEMP and oVEMP tests, may be more susceptible to BPPV since the otoconia responsible for canalithiasis originate in the otolith end organs Hong et al., 2011; Kim & Kim, 2012; Egami et al., 2013 Clinical use of VEMPs • Research still working towards defining the value of the VEMP in most of these pathologies – e.g. Should we expect otolith or nerve impairment in this disease? How sensitive are the tests to such an impairment? • But….VEMPs have proven to be VERY EFFECTIVE at measuring the presence of disease in cases of superior canal dehiscence (SCD) Superior Canal Dehiscence Superior Canal Dehiscence • History • Etiology • Pathophysiology • Symptoms • Audiogram • Vestibular Testing • CT Scan • Treatment Superior Canal Dehiscence Minor et al, 1998 • 8 cases identified over 2 year period • Chief complaint: vertigo, oscillopsia, dysequilibrium related to sound, changes in middle ear pressure, changes in intracranial pressure • 7 of 8 showed vertical/torsional eye movements induced by sound and/or pressure • Dehiscence confirmed by CT scan • Two patients underwent surgical plugging Sound and pressure induced vertigo • Tullio Phenomenon – first identified in patients with congenital syphilis – later reported in cases of congenital deafness, perilymph fistula, head trauma, Lyme Disease and canal erosion associated with cholesteatoma • Hennebert Sign – First associated with congenital syphilis – Later reported in cases of Meniere's Disease due to adhesions between stapes and membranous labyrinth • Cawthorne, 1956, postulated these symptoms were due to disruption of the bony labyrinth causing a third ‘mobile window' of the vestibule Superior Canal Dehiscence • An abnormality of the temporal bone showing an absence of bone where the roof of the superior semicircular canal meets the floor of the middle cranial fossa – 5/1000 temporal bones with dehiscence – 14/1000 temporal bones with thinning (<0.1mm) – 1.9% prevalence was thought to be conservative SCD – How is it Diagnosed • History and Symptoms • Audiologic and vestibular testing • CT scan – Near sagittal fine cut CT through the plane of the – Fine cuts are 0.3 to 0.5mm thickness • Congenital Malformation – Half of individuals with thinning or dehiscence were – Dehiscence visually looked similar to INFANT temporal • Normal development shows thickening until 4 years of age • Trauma • Increased Intracranial Pressure SCD and Spontaneous CSF Leak • Retrospective chart review of patients undergoing surgical repair of spontaneous CSF leak – Excluded for history of trauma, cholesteatoma, neoplasm – 5 of 31, 16%, with spontaneous CSF leak had visually confirmed dehiscence • Incidence of CSF leak is greater in patients with intracranial hypertension as higher pressure causes erosion of temporal bone • Cases of spontaneous CSF leak present to audiology clinics as superior canal dehiscence SCD and Chiari Malformation • Prevalence of Chiari Type I: 0.6% – 1.0% – The cerebellar tonsils are displaced downward into the foramen magnum and this results in overcrowding of the posterior cranial fossa • Retrospectice chart review over 8 years of patient diagnosed with SCD – 7 of 30 patients (23%) diagnosed with canal dehiscence also had radiographically identified Chairi Type I • Most dehiscence located at posterior canal • Chiari results in obstruction of CSF flow which may lead to slow erosive process at posterior cranial fossa Normal Physiology-Air Conduction • As the stapes pushes INWARD at the oval window, pressure is exerted upon the perilymph within the • Because fluids are essentially incompressible AND the round window offers an outlet via OUTWARD movement, this pressure wave moves into the cochlea via the scala vestibuli and out via the scala • The basilar membrane is conveniently positioned in the scala media to take advantage of the impedance inequality between the two windows Normal Physiology-Air Conduction Merchant and Rosowski, 2008 Abnormal Physiology-Air Conduction Merchant and Rosowski, 2008 Abnormal Physiology-Air Conduction • When a ‘third window' is introduced, the impedance relationship changes such that the round window is no longer the only outlet. • The dehiscence permits the fluid pressure to divert into the vestibular portion of the membranous labyrinth and the result is less fluid pressure moving into the scala vestibuli • One result is decreased sensitivity to AC stimuli Normal Physiology-Bone Conduction • When the temporal bone is vibrated, there is an impedance inequality between the scala vestibuli and scala tympani. – Again, this is due to an impedance inequality between the oval and round windows • Normal hearing is predicated on appropriate impedance of the inner ear and across those two windows Normal Physiology-Bone Conduction Merchant and Rosowski, 2008 Abnormal Physiology-Bone Conduction Merchant and Rosowski, 2008 Abnormal Physiology-Bone Conduction • When the temporal bone is vibrated and those vibrations are able to escape via a ‘third window', it disrupts the normal impedance relationship between the oval and round windows. • This occurs by decreasing impedance on the scala vestibuli side and the result is enhanced movement of the cochlear partition. • One result is increased sensitivity to BC stimuli Questions on Pathophysiology? Vestibular Signs and Symptoms • First description of this pathology included solely the vestibular symptoms – Oscillopsia – Tullio Phenomenon and vertical/torsional nystagmus to sound or possibly own voice – Hennebert Sign and vertical/torsional nystagmus to • Chronic Dysequilibrium • Positional Vertigo • Head tilt in response to sound Audiologic Signs and Symptoms • Aural fullness • Autophony – Own voice echoes, excessively loud • Amplified body noises – Pulsatile tinnitus, eye movements, feet striking ground • Hearing loss – Low frequency air-bone gaps with normal immittance – ‘Inner ear conductive' Other "Inner Ear Conductive" Hearing Loss - Enlarged Vestibular Aqueduct • Prospective study – 8 ears from 5 individuals identified in routine clinical practice – CT scan confirmed EVAS • vestibular aqueduct greater than 1.5 mm on CT scan • Seven of 8 showed low frequency air-bone gaps • Six of 8 showed normal tympanogram • Acoustic reflexes present in 3 of 4 ears tested • One middle ear surgical exploration normal • Agrees with pathophysiology of third mobile window proposed by Merchant and Rosowski – Raises interesting questions about hearing loss type in EVA Dehiscence Size and Symptoms • Size of Dehiscence correlated with symptoms • 27 patients identified prospectively – Dehiscence at least 2.5mm showed cochlear AND vestibular signs and symptoms – Dehiscence less than 2.5mm showed either cochlear OR vestibular signs and symptoms • Larger the dehiscence, the greater the symptoms Size of Dehiscence and ABG • Size of air-bone gap correlated with size of • Retrospective case review of 23 patients – Air-bone gap with every dehiscence over 3mm • Average size of ABG correlated with average size SCD is great otologic mimicker • Otosclerosis – Stapedectomy, ossiculoplasty doesn't help – Likely diagnosed if symptoms center around hearing • Perilymphatic Fistula – Packing middle ear doesn't help – Likely diagnosed if symptoms center around dizziness • Meniere's Disease – Low salt diet, diuretic doesn't help • Eustachian Tube Dysfunction – Nasal Steroids don't help SCD – Not Otosclerosis • Eight patients, 10 ears found via retrospective • All 10 ears had conductive hearing loss • No patient presented with vestibular complaints • 6 individuals had surgical exploration for assumed • All middle ear surgeries unsuccessful SCD – Not Otosclerosis SCD – Not Otosclerosis SCD – Key Audiometrics • Air-bone gap – This may be BC thresholds below zero and AC thresholds • Normal immittance – Normal tympanogram – Present acoustic reflexes • Subjective dizziness with tympanogram, ‘fistula test' • Bone oscillator to ankle localizes to affected ear • VEMPs!! • Surgical Intervention • Surgery takes 3 hours • Patient spends 3 nights in hospital • If successful, vestibular dysfunction guaranteed • "repair of SCD reduce the function of the operated canal but typically preserve function of the other semicircular canals" • Apparently more difficult, results variable – Knowledge is Power – Expectations drive satisfaction Treatment in Literature 3/27 middle fossa approach with canal plugging – One patient ‘fixed' – Two patients closed ABG, but now unsteady 10/27 middle fossa approach with canal plugging – Five showed no change in post-op ABG – Two recurrent 18/19 middle fossa approach with canal plugging, 1 resurfaced – Two showed complete vestibular loss – Six showed various degrees of vestibular dysfunction of other semicircular canals based on head – Resurface showed dysfunction of posterior canal 10/11 middle fossa approach with canal plugging, 1 resurfaced – Four showed high frequency hearing loss – Two showed non-operated ear symptomatic – Two showed transient BPPV – Resurfaced showed no improvement Possible Complications from Treatment • Prolonged Hospital Stay • Possible Hearing loss – Persistent low frequency conductive – High frequency sensorineural – Profound sensorineural • Possible Vestibular Dysfunction – Plugged canal non-functioning – Horizontal or posterior canal deficit – BPPV • If bilateral, non-operated side becomes symptomatic • VEMP tests can be used to detect whether a dehiscence is causing pathological pressure transmission in the vestibular labyrinth • In healthy ear, sound stimuli activate the otolith organs leading to inhibition of SCM and excitation of extraocular muscles cVEMP and oVEMP • In SCD, the dehiscence acts as a "third mobile window" – effectively creating a path of lower impedance for the transmission of sound pressure to • VEMPs are larger in amplitude • Threshold to elicit VEMP is reduced Old Criteria: cVEMP Threshold • cVEMP amplitudes tend to be larger in SCD ears….but the intra-ear variability in cVEMP amplitude precludes it from separating SCD ears from healthy ears – In other words, there is a great deal of overlap in cVEMP amplitude between healthy individuals and – Sensitivity 74% • cVEMP parameter of most interest for the identification of SCD has been the cVEMP Janky et al. 2014 • Average cVEMP threshold using an air conduction tone burst of 500 Hz in a normal ear is around 85 - • Average cVEMP threshold in an SCD ear is between Watson et al. 2000; Streubel et al. 2001; Zhou et al. 2007; Brandtberg et al. 2009; – Sensitivity ranges from 80 – 91%, specificity 80 – 95% – Non-invasive • Disadvantages – Takes time and multiple test runs – Patient can fatigue – Variable cut-offs • i.e. definition of "normal" and "pathological" threshold differ by site and study cVEMP Threshold
Sensitivity
Specificity
• 20 dB nHL range between recommended cut-off values??? Zhou et al. 2007; Crane et al. 2008; Zuniga et al. 2013 New Criteria: oVEMP Amplitude • oVEMP thresholds tend to be 10 dB nHL lower in SCD patients….but oVEMP amplitudes are often ten times larger in an SCD ear! • Mean amplitudes: • Normal = 2.9 uV (3.0) • SCD = 29.0 uV (16.6) Janky et al. 2014 • 29 patients with surgically confirmed SCD, 25 age-matched • Looked at whether oVEMP amplitudes were more sensitive and specific than cVEMP thresholds for the diagnosis of SCD Zuniga et al. (2013) • Mean SCD cVEMP threshold = 75 dB nHL • Mean Control cVEMP threshold = 95 dB nHL Zuniga et al. (2013) Zuniga et al. (2013) • Mean SCD amplitude = 48.9 uV • Mean Control amplitude = 3.8 uV Zuniga et al. (2013) Zuniga et al. (2013) oVEMP amplitude: best cut-off differs by age, sensitivity 90 – 100% and specificity 94 – 100% cVEMP threshold: best cut-off differs by age, sensitivity 45 – 100% and specificity 46 – 100% Other single-step oVEMP tests? • 22 CT-verified SCD subjects, 22 healthy controls • Purpose was to find a single-step screener that separated SCD from healthy ears • Ran oVEMPs at multiple frequencies • 100% of SCD subjects generated oVEMPs at 4000 Hz, no healthy controls did oVEMP, 4000 Hz, 95dBnHL • 500 Hz oVEMP: Left = 71.2 uV, Right = 6.69 uV • 4000 Hz oVEMP: Left = 37.33 uV, Right = absent 4.98 ms/div, 10 uV/div 4.98 ms/div, 10 uV/div Thank you, Gary Jacobson • Clinical gold-standard is still a CT scan • But VEMP testing plays a key role in determining whether the apparent dehiscence is actually causing pathologic pressure transmission in the inner ear • Why is that important? CT scan of pt with complete dehiscence in left ear CT scan of pt WITH0UT complete dehiscence • "CT imaging alone can be misleading in the diagnosis of SCD. It can overestimate the size of the dehiscence, and can falsely detect dehiscences." • "CT cannot be used in isolation for the diagnosis of SCD." • Clinical symptoms and signs and test results must be clearly indicative before definitive diagnosis, and definitely before surgery • Diagnosis needs to be based on combination of patient symptoms, CT findings, and VEMPs • 66 y/o female • Reports constant disequilibrium for 13 years, getting worse • "She reports Tullio Phenomenon, dizziness with cough, sneeze, strain, exertion, bending. She also reports left autophony, aural fullness, left pulsatile tinnitus that is essentially constant" • Reports a previous vestibular work-up at outside facility that showed normal VNG • Audio from 2000 showed a mild conductive hearing loss in left • 2001 exploratory left ear surgery looking for a fistula (none was CASE 1: Vestibular Testing • VNG exam: normal • Rotary chair exam: normal • VEMP: "Cervical and ocular VEMPs are present on the left, absent on the right. Ocular VEMP shows absolute amplitude of 24uV which is abnormal. Subthreshold cVEMPs are absent. Presence of any VEMP measure on the left, given large ABG in the left, is abnormal and indicates superior canal dehiscence." Case 1: Vestibular Testing • Left oVEMP amplitude = 24 uV • Right oVEMP absent Case 1: Vestibular Testing • Left cVEMP present at 90dBnHL despite 60 dB • Right cVEMP absent CASE 1: Treatment • CT scan confirmed left SCD • Patient decided to proceed with a left middle fossa craniotomy to repair the dehiscence via canal plugging CASE 1: Post-Op Audio • Patient reports sudden hearing loss one day after surgery • Pulsatile tinnitus has • Autophony resolved • Imbalance improved initially, able to drive • 1 month later stated she felt persistent CASE 1: Follow-up • Underwent PT for balance • Referred for single sided deafness workup to discuss options (e.g. CROS vs BAHA) – Opted to get a BiCros hearing aid Case 1: Discussion • History of previous middle ear surgery looking for a cause of symptoms and ABG – No cause found, probably resulted in ME CHL • Audio shows 65 dB ABG, some of it ME CHL, some of it enhanced BC due to SCD – Normal tymps, reflexes not completed • Present VEMPs with large ABG • "Classic" SCD symptoms, very bothersome, chose surgical • Outcome of surgery was poor (total loss of hearing in left ear, chronic imbalance) • 53 y.o. male • Complains of chronic dizziness for 10 years, began after • Increase in tinnitus • Double vision • Surgical procedure to repair perilymphatic fistula, • No help with vestibular rehabilitation therapy • Patient reports prior CT ruled out SCD • Medical history significant for variety of other health • "Mild conductive hearing loss in both ears in the low • Normal tympanograms, bilaterally • Acoustic reflexes not performed • Second CT scan showed ‘rather large' dehiscence of right superior canal involving entire dome of the canal and probable thinning of left superior canal • Spinal tap showed increased CSF pressure Case 2: Vestibular Testing • Right cervical VEMP threshold = 65dBnHL • Left cervical VEMP 70dB screening negative Case 2: Vestibular Testing • Ocular VEMP amplitude = 22.5 uV Case 2: Follow-up • Air-bone gap closed • Cervical VEMP threshold increased • Still some dysequilibrium at 9 months post-op • Spinal tap showed increased intracranial pressure – CSF drainage offered no relief • Dysequilibrium improving at one year with VRT, but still present Case 2: Follow-up Testing threshold 95dBnHL • No change on Case 2: Discussion • History of previous middle ear surgery looking for a • "Classic" SCD symptoms and history of previous work-up for SCD, negative • cVEMP threshold and oVEMP amplitude consistent with SCD in right ear • Chose surgical plugging • Outcome of surgery was good • cVEMP threshold back to WNL post-surgery • 61 y/o female • January 2013 – c/o of right pulsatile tinnitus and right aural fullness – NO VESTIBULAR COMPLAINTS – Audio: • "mild to moderate CHL right ear, NL hearing left ear". • Tympanometry: Type C tymps bilaterally (-148 R, -144 L) – Diagnosed with right Eustachian Tube Dysfunction – Treated with Flonase, f/u in month • February 2013 – Same complaints, no change in symptoms – PE tube placed in right TM – Still c/o of right tinnitus and fullness, now complains of right hearing loss – Prior to f/u had seen neurosurgery to follow-up on previous history of right cerebral AVM, neuro ordered CT – CT showed possible SCD in right ear – She is referred for vestibular testing Case 3: Vestibular Testing • VNG: not completed due to PE tube Case 3: Vestibular Testing – Left ear = absent – Right ear = 276.95 uV at 100 dB nHL and threshold at 85 dB nHL Case 3: Vestibular Testing – Left ear = absent – Right ear = 25.78 uV at 100 dB nHL Case 3: Vestibular Testing • "Results consistent with right SCD (i.e. any VEMP response in the presence of a 45 dB ABG is significant. Larger ocular VEMP response on the right provides further evidence of this. Absent response on left may be due to significant negative middle ear pressure." Case 3: Follow-up • Elected not to have surgery as her symptoms do not bother her very much and she has no vestibular symptoms Case 3: Discussion • Presumed to have ETD (fullness and CHL in ear) • No vestibular symptoms • History of PE tube due to ETD – not sure if ETD was truly present, but procedure did not resolve symptoms and resulted in ME CHL • SCD incidental finding on CT looking for evidence of • cVEMP threshold and oVEMP amplitude consistent with SCD – especially given the 45 dB ABG, some of which was most likely ME conductive • 58 female • Complained of: – spinning vertigo, lasting seconds, that occurred when – chronic disequilibrium – constant pressure in right ear that increased when • Had been evaluated by multiple ENTs over several years, told nothing wrong with her ear Case 4: Audiogram Case 4: Vestibular Testing • VNG: Normal • Rotational Testing: Normal • cVEMP: Normal • oVEMP Abnormal • Present and symmetrical • Screened at 75 dB nHL, response absent • Absent in left ear (patient age?) • Right ear amplitude = 93 uV Case 4: Temporal Bone CT The radiologist reported a "bony dehiscent of the superior semicircular canal bilaterally" Case 4: Follow-up • Though the CT scan identified bilateral SCD, based on symptoms and oVEMP results the patient was ultimately diagnosed with SCD in the right ear only • During follow-up with our otolaryngology colleague, she decided not to undergo surgical treatment….but expressed gratitude and relief in finally having a diagnosis and no longer feeling like she was "going crazy" Case 4: Discussion • The patient's symptoms did not include all the "classic" SCD symptoms that typically trigger the suspicion of SCD (i.e. she denied autophony or dizziness in response to loud sounds) – Her main complaint was aural fullness in the right ear • Based solely on her symptoms and normal cVEMP thresholds, a diagnosis of SCD would most likely not have been reached – would she have continued to search for an answer to her symptoms? • She may have a low frequency CHL – Though BC on audio not completed – should it be if hearing is normal but patient complains of fullness or other SCD-like symptoms? • Relying solely on her CT report may have resulted in a diagnosis of – may have caused an increase in health anxiety for the patient given her lack of symptoms on the left side • oVEMP amplitude is what raised suspicion of SCD, and combination of oVEMP and symptoms led to diagnosis of right-sided SCD only (even though CT scan interpreted as showing a bilateral dehiscence) • Cervical VEMP-saccule and inferior vestibular nerve • Ocular VEMP-utricle and superior vestibular nerve • VEMPs are sensitive and specific to SCD because provide an objective measure of abnormal pressure transmission in inner ear – cVEMP threshold decreases – oVEMP response amplitude increases (may be more sensitive than cVEMP threshold) – oVEMP response is recordable up to 4kHz • CT scan at risk for overdiagnosing SCD - difficulty differentiating between ‘thinning' and true dehiscence – and results need to be corroborated with symptoms • Audiogram will likely show – Air-bone gap with normal immittance – May see BC thresholds below 0 • SCD complaints may be cochlear, vestibular or both • Surgical treatments for SCD have the potential to improve some symptoms, possibly not all. • Surgical treatment may lead to other balance problems and/or hearing loss • Questions/comments?

Source: http://www.ncshla.org/sites/default/files/fallCon/2014/Session-27.pdf