M. Geraldine Zuniga

Ocular versus cervical VEMPs in the diagnosis of superior semicircular canal dehiscence syndrome

Objectives To determine whether cervical vestibular evoked myogenic potential (cVEMP) thresholds or ocular VEMP (oVEMP) amplitudes are more sensitive and specific in the diagnosis of superior semicircular canal dehiscence syndrome (SCDS). Study Design Prospective case-control study. Setting Tertiary referral center. Subjects and Methods Twenty-nine patients with SCDS (mean age 48 yr; range, 31–66 yr) and 25 age-matched controls (mean age 48 yr; range, 30–66 yr). Intervention(s) cVEMP and oVEMP in response to air-conducted sound. All patients underwent surgery for repair of SCDS. Main Outcome Measure(s) cVEMP thresholds; oVEMP n10 and peak-to-peak amplitudes. Results cVEMP threshold results showed sensitivity and specificity ranging from 80% to 100% for the diagnosis of SCDS. In contrast, oVEMP amplitudes demonstrated sensitivity and specificity greater than 90%. Conclusion oVEMP amplitudes are superior to cVEMP thresholds in the diagnosis of SCDS.

Air-conducted oVEMPs provide the best separation between intact and superior canal dehiscent labyrinths.

Objective First, to define the best single-step suprathreshold screening test for superior canal dehiscence syndrome (SCDS); second, to obtain further insight into the relative sensitivity of vestibular afferents to sound vibration in the presence of a superior canal dehiscence. Study Design Prospective study. Setting Tertiary referral center. Patients Eleven patients with surgically confirmed SCDS (mean, 50 yr; range, 32–66 yr) and 11 age-matched, healthy subjects (right ear only) with no hearing or vestibular deficits (mean, 50 yr; range, 33–66 yr). Intervention All subjects completed ocular and cervical vestibular evoked myogenic potential (o- and cVEMP) testing in response to air conduction (click and 500 Hz tone burst) and midline bone conduction (reflex hammer and Mini-shaker) stimulation. Main Outcome Measures OVEMP n10 amplitude and cVEMP corrected peak-to-peak amplitude. Results OVEMP n10 amplitudes were significantly higher in SCDS when compared with healthy controls in response to all stimuli with the exception of reflex hammer. Likewise, cVEMP-corrected peak-to-peak amplitudes were significantly higher in SCDS when compared with healthy controls for air conduction stimulation (click and 500 Hz toneburst). However, there were no significant differences between groups for midline taps (reflex hammer or mini-shaker). Receiver operating characteristic curves demonstrated that oVEMPs in response to air conduction stimulation provided the best separation between SCDS and healthy controls. Conclusion OVEMPs in response to air conduction stimulation (click and 500 Hz toneburst) provide the best separation between SCDS and healthy controls and are therefore the best single-step screening test for SCDS.

Multislice computed tomography in the diagnosis of superior canal dehiscence: how much error, and how to minimize it?

Hypothesis Multi-slice computed tomography (MSCT) overestimates the size of superior semicircular canal dehiscences (SSCDs) and also can misinterpret thin bone over the superior semicircular canal as dehiscent. A threshold of the radiodensity of the bone over the superior semicircular canal may exist that could optimize prediction of an actual SSCD. Background The gold standard for diagnosis of SSCD is MSCT, but there is a higher prevalence of SSCD based on MSCT compared with histologic studies. Overestimation of SSCD can lead to inappropriate diagnosis and treatment. Methods We correlated radiographic and surgical findings in SSCD to determine if MSCT overestimated the size of SSCD and if a threshold radiodensity could be defined, below which actual dehiscence could best be predicted. Participants were 34 humans with SSCD confirmed at surgery. MSCT scans were acquired axially with 0.5-mm collimation and a small field of view (24 cm). Dehiscence sizes measured from radial reconstructions were compared with measurements made during surgery. Results There were significant differences between radiographic and actual length and width, indicating that MSCT tends to overestimate the size of SSCD. Receiver operating characteristic analysis found a threshold in Hounsfield units that optimized the prediction of dehiscence. Conclusion Computed tomographic imaging alone can be misleading for diagnosis of SSCD. It can overestimate the size of the dehiscence, and it can falsely detect dehiscences. Clinical symptoms and other signs must be clearly indicative before surgery, and MSCT cannot be used exclusively for the diagnosis of SSCD.

Can Vestibular-Evoked Myogenic Potentials Help Differentiate Ménière Disease from Vestibular Migraine?

Objectives. To characterize both cervical and ocular vestibular-evoked myogenic potential (cVEMP, oVEMP) responses to air-conducted sound (ACS) and midline taps in Ménière disease (MD), vestibular migraine (VM), and controls, as well as to determine if cVEMP or oVEMP responses can differentiate MD from VM. Study Design. Prospective cohort study. Setting. Tertiary referral center. Subjects and Methods. Unilateral definite MD patients (n = 20), VM patients (n = 21) by modified Neuhauser criteria, and age-matched controls (n = 28). cVEMP testing used ACS (clicks), and oVEMP testing used ACS (clicks and 500-Hz tone bursts) and midline tap stimuli (reflex hammer and Mini-Shaker). Outcome parameters were cVEMP peak-to-peak amplitudes and oVEMP n10 amplitudes. Results. Relative to controls, MD and VM groups both showed reduced click-evoked cVEMP (P < .001) and oVEMP (P < .001) amplitudes. Only the MD group showed reduction in tone-evoked amplitudes for oVEMP. Tone-evoked oVEMPs differentiated MD from controls (P = .001) and from VM (P = .007). The oVEMPs in response to the reflex hammer and Mini-Shaker midline taps showed no differences between groups (P > .210). Conclusions. Using these techniques, VM and MD behaved similarly on most of the VEMP test battery. A link in their pathophysiology may be responsible for these responses. The data suggest a difference in 500-Hz tone burst–evoked oVEMP responses between MD and MV as a group. However, no VEMP test that was investigated segregated individuals with MD from those with VM.

Balance Dysfunction and Recovery after Surgery for Superior Canal Dehiscence Syndrome

OBJECTIVE To characterize (1) the impairment and recovery of functional balance and (2) the extent of vestibular dysfunction and physiological compensation following superior canal dehiscence syndrome (SCDS) surgical repair. DESIGN Prospective study. SETTING Tertiary referral center. PARTICIPANTS Thirty patients diagnosed as having SCDS. INTERVENTIONS Surgical plugging and resurfacing of SCDS. MAIN OUTCOME MEASURES Balance measures were assessed in 3 separate groups, each with 10 different patients: presurgery, postoperative short-term (<1 week), and postoperative long-term (≥6 weeks). Vestibular compensation and function, including qualitative head impulse tests (HITs) in all canal planes and audiometric measures, were assessed in a subgroup of 10 patients in both the postoperative short-term and long-term phases. RESULTS Balance measures were significantly impaired immediately but not 6 weeks after SCDS repair. All patients demonstrated deficient vestibulo-ocular reflexes for HITs in the plane of the superior canal following surgical repair. Unexpectedly, spontaneous or post-head-shaking nystagmus beat ipsilesionally in most patients, whereas contrabeating nystagmus was noted only in patients with complete canal paresis (ie, positive HITs in all canal planes). There were no significant deviations in subjective visual vertical following surgical repair (P = .37). The degree of audiometric air-bone gap normalized 6 weeks after surgery. CONCLUSIONS All patients undergoing SCDS repair should undergo a postoperative fall risk assessment. Nystagmus direction (spontaneous and post-head-shaking) seems to be a good indicator of the degree of peripheral vestibular system involvement and central compensation. These measures correlate well with the HIT.

Characterization of Vestibulopathy in Individuals with Type 2 Diabetes Mellitus

Objective Previous observational studies suggest higher rates of vestibular dysfunction among patients with type 2 diabetes mellitus (DM) compared with those without diabetes. This study aims to functionally localize vestibular dysfunction in adults with type 2 DM. Study Design Prospective cohort study. Setting Tertiary academic medical center. Subjects and Methods Adults 50 years of age and older with ≥10-year history of type 2 DM were recruited (December 2011–February 2013, n = 25). Vestibular function was assessed by cervical and ocular vestibular-evoked myogenic potentials (VEMPs), testing the saccule and utricle, respectively. Head thrust dynamic visual acuity testing assessed semicircular canal (SCC) function in all canal planes. Results were compared with nondiabetic age-matched controls (n = 25). Results Subjects were 64.7 ± 7.6 years old, were 40% female, and had a mean hemoglobin A1c of 8.3% ± 1.7%. SCC dysfunction was more common than otoconial organ dysfunction, with 70% of subjects with DM demonstrating impaired performance of at least 1 SCC (ΔlogMAR ≥0.18) and 50% demonstrating otoconial organ impairment (absent ocular VEMP and/or cervical VEMP). Adults with type 2 DM had poorer lateral and superior SCC performance (P < .05) but similar posterior SCC performance compared with controls (P = .16). Both cervical VEMP peak-to-peak amplitude and ocular VEMP n1 amplitude were also decreased with diabetes (P < .01). Conclusion Adults with type 2 DM have poorer performance on tests of vestibular function related to both SCC and otoconial organ function compared with nondiabetic age-matched adults. Future studies are needed to better understand the relationship between vestibular function and functional disability in persons with diabetes.

Tip Fold-over in Cochlear Implantation: Case Series.

OBJECTIVE To describe the incidence, clinical presentation, and performance of cochlear implant (CI) recipients with tip fold-over. STUDY DESIGN Retrospective case series. SETTING Tertiary referral center. PATIENTS CI recipients who underwent postoperative computed tomography (CT) scanning. INTERVENTION(S) Tip fold-over was identified tomographically using previously validated software that identifies the electrode array. Electrophysiologic testing including spread of excitation or electric field imaging (EFI) was measured on those with fold-over. MAIN OUTCOME MEASURE(S) Location of the fold-over; audiological performance pre and postselective deactivation of fold-over electrodes. RESULTS Three hundred three ears of 235 CI recipients had postoperative CTs available for review. Six (1.98%) had tip fold-over with 5/6 right-sided ears. Tip fold-over occurred predominantly at 270 degrees and was associated with precurved electrodes (5/6). Patients did not report audiological complaints during initial activation. In one patient, the electrode array remained within the scala tympani with preserved residual hearing despite the fold-over. Spread of excitation supported tip fold-over, but the predictive value was not clear. EFI predicted location of the fold-over with clear predictive value in one patient. At an average follow-up of 11 months, three subjects underwent deactivation of the overlapping electrodes with two of them showing marked audiological improvement. CONCLUSION In a large academic center with experienced surgeons, tip fold-over occurred at a rate of 1.98% but was not immediately identifiable clinically. CT imaging definitively showed tip fold-over. Deactivating involved electrodes may improve performance possibly avoiding revision surgery. EFI may be highly predictive of tip fold-over and can be run intraoperatively, potentially obviating the need for intraop fluoroscopy.

Automatic Cochlear Duct Length Estimation for Selection of Cochlear Implant Electrode Arrays.

HYPOTHESIS Cochlear duct length (CDL) can be automatically measured for custom selection of cochlear implant (CI) electrode arrays. BACKGROUND CI electrode array selection can be influenced by measuring the CDL, which is estimated based on the length of the line that connects the round window and the lateral wall of the cochlea when passing through the modiolus. CDL measurement remains time consuming and inter-observer variability has not been studied. METHODS We evaluate an automatic approach to directly measure the two-turn (2T) CDL using existing algorithms for localizing cochlear anatomy in computed tomography (CT). Pre-op CT images of 309 ears were evaluated. Two fellowship-trained neurotologists manually and independently measured CDL. Inter-observer variability between measurements across expert and automatic observers is assessed. Inter-observer differences for choice of electrode type are also investigated. RESULTS Manual measurement of CDL by experts tends to underestimate cochlea size and has high inter-observer variability, with mean absolute differences between expert CDL estimations of 1.15 mm. Our results show that this can lead to a large number of cochleae for which a different electrode array type would be selected by different observers, depending on the specific threshold value of CDL used to decide between array type. CONCLUSION Choosing the best CI electrode array is an important task for optimizing hearing outcomes. Manual cochleae length measurements are user-dependent, and errors impact upon the CI electrode array choice for certain patients. Measuring cochlea length automatically is less time consuming and generates more repeatable results. Our automatic approach could make use of CDL for patient-customized treatment more clinically adoptable.

Optimizing ocular vestibular evoked myogenic potential testing for superior semicircular canal dehiscence syndrome: Electrode placement

Objective: To compare the sensitivity and specificity of ocular vestibular evoked myogenic potentials (oVEMPs) using 2 electrode montages for the diagnosis of superior canal dehiscence syndrome (SCDS). Subjects: 16 SCDS patients (17 affected-SCDS ears, 15 contralateral-SCDS ears) and 12 controls (24 ears). Methods: oVEMPs were recorded in response to 500-Hz tone bursts using 2 electrode montages. For both montages the active electrode was placed approximately 5 mm below each eye and a ground electrode on the sternum. For montage 1 (standard), the reference electrode was centered 2 cm below each active electrode. For montage 2, the reference electrode was placed on the chin. Results: For either montage, the separation between oVEMP amplitudes in affected-SCDS ears and controls was significant (p < 0.001), with excellent sensitivity and specificity (>90%). Conclusion: oVEMP recordings with the standard montage remain a reliable method for evaluation of SCDS.

The effect of increased intracranial pressure on vestibular evoked myogenic potentials in superior canal dehiscence syndrome

OBJECTIVE To determine if vestibular evoked myogenic potential (VEMP) responses change during inversion in patients with superior canal dehiscence syndrome (SCDS) compared to controls. METHODS Sixteen subjects with SCDS (mean: 43, range 30-57 years) and 15 age-matched, healthy subjects (mean: 41, range 22-57 years) completed cervical VEMP (cVEMP) in response to air conduction click stimuli and ocular VEMP (oVEMP) in response to air conduction 500 Hz tone burst stimuli and midline tap stimulation. All VEMP testing was completed in semi-recumbent and inverted conditions. RESULTS SCDS ears demonstrated significantly larger oVEMP peak-to-peak amplitudes in comparison to normal ears in semi-recumbency. While corrected cVEMP peak-to-peak amplitudes were larger in SCDS ears; this did not reach significance in our sample. Overall, there was not a differential change in o- or cVEMP amplitude with inversion between SCDS and normal subjects. CONCLUSIONS Postural-induced changes in o- and cVEMP responses were measured in the steady state regardless of whether the labyrinth was intact or dehiscent. SIGNIFICANCE VEMP responses are blunted during inversion. Although steady-state measurements of VEMPs during inversion do not increase diagnostic accuracy for SCDS, the findings suggest that inversion may provide more general insights into the equilibration of pressures between intracranial and intralabyrinthine fluids.