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64. Cervical and Ocular Vestibular-Evoked Myogenic Potentials in Patients With Intracochlear Schwannomas

Author

Fröhlich, Laura, Curthoys, Ian S., Kösling, Sabrina, Obrist, Dominik, Rahne, Torsten, and Plontke, Stefan K.

Subjects
VEMP, intracochlear, third window, secondary hydrops, lcsh:RC346-429, Neurology, vestibular schwannoma, otorhinolaryngologic diseases, semicircular canal dehiscence, sense organs, intralabyrinthine, lcsh:Neurology. Diseases of the nervous system, asymmetry, Original Research
Abstract

Objective: To evaluate ocular and cervical vestibular evoked myogenic potentials (oVEMPs and cVEMPs) in patients with solely intracochlear localization of an intralabyrinthine schwannoma (ILS). Study Design: Retrospective analysis of a series of cases. Setting: Monocentric study at a tertiary referral center. Patients: Patients with intracochlear schwannoma (ICS) and VEMP measurements. Outcome Measures: Signed asymmetry ratio (AR) of cVEMPs and oVEMPs to air conducted sound with AR cut-offs considered to be asymmetrical when exceeding ±30% for cVEMPs and ±40% for oVEMPs with respect to the side affected by the tumor (reduced amplitudes on the affected side indicated by negative values, enhanced amplitudes by positive values); VEMP amplitudes and latencies; tumor localization in the cochlear turn and scala. Results: Nineteen patients with a solely intracochlear tumor (ICS patients) [10 males, 9 females, mean age 57.1 (SD: 13.4) years] were included in the study. On the affected side, cVEMPs were absent or reduced in 47% of the patients, normal in 32%, and enhanced in 21%. Ocular VEMPs on the affected side were absent or reduced in 53% of the patients, normal in 32% and enhanced in 15%. Latencies for cVEMPs and oVEMPs were not significantly different between the affected and non-affected side. In all patients with enhanced VEMPs, the tumor was located in the scala tympani and scala vestibuli. Conclusions: As a new and unexpected finding, VEMP amplitudes can be enhanced in patients with intracochlear schwannoma, mimicking the third window syndrome.

Published
2020
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65. Enhanced Eye Velocity in Head Impulse Testing—A Possible Indicator of Endolymphatic Hydrops

Author

Curthoys, Ian S, Manzari, Leonardo, Rey-Martinez, Jorge, Dlugaiczyk, Julia, Burgess, Ann M, Curthoys, Ian S, Manzari, Leonardo, Rey-Martinez, Jorge, Dlugaiczyk, Julia, and Burgess, Ann M

Abstract

Introduction: On video head impulse testing (vHIT) of semicircular canal function, some patients reliably show enhanced eye velocity and so VOR gains >1.0. Modeling and imaging indicate this could be due to endolymphatic hydrops. Oral glycerol reduces membranous labyrinth volume and reduces cochlear symptoms of hydrops, so we tested whether oral glycerol reduced the enhanced vHIT eye velocity.Study Design: Prospective clinical study and retrospective analysis of patient data.Methods: Patients with enhanced eye velocity during horizontal vHIT were enrolled (n = 9, 17 ears) and given orally 86% glycerol, 1.5 mL/kg of body weight, dissolved 1:1 in physiological saline. Horizontal vHIT testing was performed before glycerol intake (time 0), then at intervals of 1, 2, and 3 h after the oral glycerol intake. Control patients with enhanced eye velocity (n = 4, 6 ears) received water and were tested at the same intervals. To provide an objective index of enhanced eye velocity we used a measure of VOR gain which captures the enhanced eye velocity which is so clear on inspecting the eye velocity records. We call this measure the initial VOR gain and it is defined as: (the ratio of peak eye velocity to the value of head velocity at the time of peak eye velocity). The responses of other patients who showed enhanced eye velocity during routine clinical testing were analyzed to try to identify how the enhancement occurred.Results: We found that oral glycerol caused, on average, a significant reduction in the enhanced eye velocity response, whereas water caused no systematic change. The enhanced eye velocity during the head impulses is due in some patients to a compensatory saccade-like response during the increasing head velocity.Conclusion: The significant reduction in enhanced eye velocity during head impulse testing following oral glycerol is consistent with the hypothesis that the enhanced eye velocity in vHIT may be caused by endolymphatic hydrops.

Published
2021

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