Vestibular function and vertigo control after intratympanic gentamicin for Ménière's disease

Efficacy and preservation of hearing with low-dose gentamicin in unilateral meniere's disease: A clinical symptomatology-based study

PURPOSE

Meniere's disease (MD), a disorder of the inner ear, presents numerous therapeutic challenges, and intratympanic (IT) gentamicin has been proposed for intractable cases. However, controversy regarding dosage and method persists. The purpose of this study was to assess the efficacy and safety of low-dose IT gentamicin on vertigo attacks in MD using a clinical symptomatology-based method, wherein administration was repeated only if vertigo attacks recurred, with a 2-week interval between injections.

MATERIALS AND METHODS

This study included 88 patients with unilateral intractable MD. All patients received one to five IT injections with 0.5 ml of 10 mg of gentamicin (80 mg/2 ml) with an interval of 2 weeks between injections. Vertigo attacks were evaluated before and after therapy and categorized into classes A-F according to the 2015 Equilibrium Committee criteria. Audiovestibular assessments, including Pure Tone Audiometry and Vestibulo-Ocular Reflex evaluations, were performed.

RESULTS

Before treatment, patients had an average of 4.4 vertigo attacks/month; after treatment, this average decreased to 0.52. The majority of patients (57 %) reached Class A or B vertigo control with five or fewer gentamicin injections. VOR gain was slightly affected on the healthy side and significantly reduced on the affected side. No hearing deterioration was found in any of the treated patients.

CONCLUSIONS

Low-dose IT gentamicin administration based on clinical symptomatology can produce a satisfactory control of vertigo attacks after treatment. This protocol primarily affected the vestibular function, as demonstrated by the significant reduction in VOR gain on the affected side, while avoiding cochlear damage. The lack of adverse events and preservation of hearing underscore the safety and efficacy of this method. These findings have significant clinical implications, suggesting that a low-dose, clinical symptomatology-based gentamicin treatment regimen could be an effective and safe strategy for managing unilateral Meniere's disease in a larger population.

Low-Dose Intratympanic Gentamicin for Unilateral Ménière‘s Disease: Accuracy of Early Vestibulo-Ocular Reflex Gain Reduction in Predicting Long-Term Clinical Outcome

Background

The number of intratympanic gentamicin (ITG) injections needed to achieve vertigo control in patients with intractable Ménière's disease (MD) may vary from a single dose to several instillations. Changes in different vestibular test results have been used to define an endpoint of treatment, including the decrease of the vestibulo-ocular reflex (VOR) gain elicited by the head-impulse test.

Objective

To assess the accuracy of the VOR gain reduction after horizontal canal stimulation, as measured with the video head-impulse test (vHIT) 1 month after the first intratympanic injection, in predicting the need for one or more instillations to control vertigo spells in the long term.

Methods

The VOR gain reduction was calculated in 47 patients submitted to (ITG) therapy 1 month after the first instillation.

Results

Single intratympanic treatment with gentamicin has a 59.6% efficacy in vertigo control in the long term. Hearing change in the immediate period after treatment (1 month) is not significant to pre-treatment result and is similar for patients who needed multiple doses due to recurrence. Chronic disequilibrium and the need for vestibular rehabilitation were less frequent in patients with a good control of vertigo with just one single injection of gentamicin. A fair accuracy was obtained for the VOR gain reduction of the horizontal canal (area under the curve = 0.729 in the Receiver Operating Characteristic analysis) in predicting the need for one or more ITG.

Conclusions

Single intratympanic treatment with gentamicin is an effective treatment for patients with MD. That modality of treatment has very limited damaging effect in hearing. The degree of vestibular deficit induced by the treatment is significant as measured by the reduction in the gain of the VOR but not useful for prognostic purposes.

Characterizing the impact of advancing age on 500 Hz tone-burst evoked ocular-vestibular evoked myogenic potentials

PURPOSE

Ageing is process that brings about steady decline in most of the systems, and vestibular system is no different. Although the effects of advancing age on the functioning of the semicircular canals and saccule has been well explored, its impact on the utricle remains the least studied component. While some researchers have investigated the effect of advancing age on the utricular functioning by virtue of studying ocular-vestibular evoked myogenic potentials (oVEMP), the use of smaller sample sizes would hamper the generalization of their results. Therefore, the present study aimed at investigating the effect of advancing age on oVEMP using a substantially larger sample size than the predecessors.

METHODS

A total of 480 individuals in the age range of 10-70 years were used as participants and were divided into six age groups, each one defined as a decade. Contralateral oVEMPs were elicited by 500-Hz tone-bursts and averaged over 200 sweeps to obtain the final waveform.

RESULTS

There was a significant decline in the response rates, prolongation of latencies and reduction of peak-to-peak amplitude of oVEMP with increasing age after 50 years (p < 0.05). However, there was no significant difference among the age groups until 50 years of age on any of these parameters (p > 0.05). Further, there was no significant change in inter-aural amplitude difference ratio with increasing age (p > 0.05).

CONCLUSION

The results of the study confirm significant impact of the ageing process on oVEMP after the age of 50 years and, therefore, age appropriate norms should be considered when using oVEMP for investigating utricular functioning in an individual, especially after the age of 50 years.

VOR gain calculation methods in video head impulse recordings

BACKGROUND: International consensus on best practices for calculating and reporting vestibular function is lacking. Quantitative vestibulo-ocular reflex (VOR) gain using a video head impulse test (HIT) device can be calculated by various methods. OBJECTIVE: To compare different gain calculation methods and to analyze interactions between artifacts and calculation methods. METHODS: We analyzed 1300 horizontal HIT traces from 26 patients with acute vestibular syndrome and calculated the ratio between eye and head velocity at specific time points (40 ms, 60 ms) after HIT onset (‘velocity gain’), ratio of velocity slopes (‘regression gain’), and ratio of area under the curves after de-saccading (‘position gain’). RESULTS: There was no mean difference between gain at 60 ms and position gain, both showing a significant correlation (r2 = 0.77, p < 0.001) for artifact-free recordings. All artifacts reduced high, normal-range gains modestly (range –0.06 to –0.11). The impact on abnormal, low gains was variable (depending on the artifact type) compared to artifact-free recordings. CONCLUSIONS: There is no clear superiority of a single gain calculation method for video HIT testing. Artifacts cause small but significant reductions of measured VOR gains in HITs with higher, normal-range gains, regardless of calculation method. Artifacts in abnormal HITs with low gain increased measurement noise. A larger number of HITs should be performed to confirm abnormal results, regardless of calculation method.

Change of VOR gain and pure-tone threshold after single low-dose intratympanic gentamicin injection in Meniere's disease

Background: Intratympanic gentamicin injection (ITG) is a well-accepted means to treat intractable Meniere's disease (MD).Aims/Objectives: To investigate change of vestibule-ocular reflex (VOR) gain and pure-tone threshold after low-dose ITG for MD.Methods: Sixteen patients with definite MD who were treated by low-dose ITG were retrospectively reviewed. We defined VOR gain difference as an amount of decreased gain in video head impulse test one month after ITG. Patients were classified into two groups: single injection vs. multiple injections. Multiple injections group was composed of patients with poor vertigo control after initial ITG who required second or third ITG later in follow up period.Results: VOR gain differences of both horizontal and posterior canal plane were higher than those of anterior canal plane. Between two groups, mean VOR gain difference of horizontal canal plane in multiple injections group was lower than that in single injection group. Only two patients showed increased pure-tone threshold more than 10 dB.Conclusion and significance: Our results suggest that ITG appears to cause a differential loss of function across three semicircular canals. Furthermore, if VOR gain difference of horizontal canal is relatively low after initial ITG, patient might have poor vertigo control and be required another ITG.

On-Demand and Low Dose Intratympanic Gentamicin for Meniere's Disease: A Customized Approach

OBJECTIVE

To evaluate the efficacy of on demand and low dose intratympanic gentamicin (ITG) in patients with intractable Meniere's disease (MD).

STUDY DESIGN

Clinical chart review.

SETTING

Secondary care center.

PATIENTS

Subjects with MD who failed conventional treatment and underwent on demand ITG infiltration from June 2013 to December 2018.

INTERVENTION

0.4 to 0.5 ml of buffered gentamicin were administered through an intratympanic route. A total of 5 mg in case of low dose and 20 mg as a standard dose.

MAIN OUTCOME MEASURES

Vertigo control, Meniere's Disease Functional Level Scale (MDFLS), Dizziness Handicap Inventory (DHI), and pure tone audiometry pre and posttreatment.

RESULTS

Thirty-one patients, 16 women and 15 men with a mean age of 52.81 (22-79) years were included. The number of ITG injections ranged from 1 to 7, with a mean of 2.52 applications per patient. Mean interval between doses was 212.15 (21-1442) days. Average follow-up was 24.03 months. An improvement on MDFLS was seen on 77.4% (n = 24) patients. DHI score improved after gentamicin treatment (mean 55.23 versus 24.06, p ≤ 0.001). Thirty patients (96.8%) reached complete or substantial vertigo control. Only one patient did not achieve control. Hearing was preserved in 43.5% (n = 10) of analyzed audiograms, whereas 17.4% (n = 4) developed hearing loss greater than 20 dB, which was not statistically significant (p = 0.099).

CONCLUSIONS

In our study, on demand and low dose ITG was effective for vertigo control in patients with intractable MD. Individualized therapy is recommended in all patients to minimize vestibular and cochlear toxicity.

Low-dose intratympanic gentamicin administration for unilateral Meniere's disease using a method based on clinical symptomatology: Preliminary results

PURPOSE

There are many therapeutic options for Meniere's disease (MD); intratympanic (IT) gentamicin has been proposed for intractable cases although controversy about dosage and method exists. The purpose of this study was to assess the efficacy and safety of low-dose IT gentamicin on vertigo attacks in MD using a clinical symptomatology-based method in which administration was repeated only if vertigo attacks recurred, with a 2-week interval between injections.

MATERIALS AND METHODS

Forty-eight patients with unilateral intractable MD were included in the study. All patients received one to five IT injections with 0.5 ml of 10 mg of gentamicin (80 mg/2 ml) with an interval of 2 weeks between injections. Vertigo attacks were evaluated before and after therapy and categorized into classes A-F according to the 2015 Equilibrium Committee criteria. Audiovestibular assessment with pure tone audiometry, vestibular bed-side examination and video head impulse test was performed.

RESULTS

Before treatment patients had an average of 4.4 vertigo attacks/month; after treatment the average number decreased to 0.52. The majority of patients (77%) reached Class A vertigo control with 5 or less gentamicin injections. VOR gain was unaffected in the healthy side and significantly reduced in the affected side. No hearing deterioration was found in all treated patients.

CONCLUSIONS

Low-dose IT gentamicin administration based on clinical symptomatology can produce a satisfactory control of vertigo attacks after treatment; such protocol had an effect mainly on the vestibular function as demonstrated by the significant reduction in VOR gain in the affected side avoiding a cochlear damage.

Nonhuman primate vestibuloocular reflex responses to prosthetic vestibular stimulation are robust to pulse timing errors caused by temporal discretization

Electrical stimulation of vestibular afferent neurons to partially restore semicircular canal sensation of head rotation and the stabilizing reflexes that sensation supports has potential to effectively treat individuals disabled by bilateral vestibular hypofunction. Ideally, a vestibular implant system using this approach would be integrated with a cochlear implant, which would provide clinicians with a means to simultaneously treat loss of both vestibular and auditory sensation. Despite obvious similarities, merging these technologies poses several challenges, including stimulus pulse timing errors that arise when a system must implement a pulse frequency modulation-encoding scheme (as is used in vestibular implants to mimic normal vestibular nerve encoding of head movement) within fixed-rate continuous interleaved sampling (CIS) strategies used in cochlear implants. Pulse timing errors caused by temporal discretization inherent to CIS create stair step discontinuities of the vestibular implant's smooth mapping of head velocity to stimulus pulse frequency. In this study, we assayed electrically evoked vestibuloocular reflex responses in two rhesus macaques using both a smooth pulse frequency modulation map and a discretized map corrupted by temporal errors typical of those arising in a combined cochlear-vestibular implant. Responses were measured using three-dimensional scleral coil oculography for prosthetic electrical stimuli representing sinusoidal head velocity waveforms that varied over 50-400°/s and 0.1-5 Hz. Pulse timing errors produced negligible effects on responses across all canals in both animals, indicating that temporal discretization inherent to implementing a pulse frequency modulation-coding scheme within a cochlear implant's CIS fixed pulse timing framework need not sacrifice performance of the combined system's vestibular implant portion. NEW & NOTEWORTHY Merging a vestibular implant system with existing cochlear implant technology can provide clinicians with a means to restore both vestibular and auditory sensation. Pulse timing errors inherent to integration of pulse frequency modulation vestibular stimulation with fixed-rate, continuous interleaved sampling cochlear implant stimulation would discretize the smooth head velocity encoding of a combined device. In this study, we show these pulse timing errors produce negligible effects on electrically evoked vestibulo-ocular reflex responses in two rhesus macaques.

Long-term Vertigo Control and Vestibular Function After Low-dose On-demand Transtympanic Gentamicin for Refractory Menière's Disease

OBJECTIVE

To describe the long-term clinical vertigo control along with measured lateral canal vestibular function in patients with unilateral refractory Menière's disease (MD) treated with gentamicin transtympanic injections (TTI).

STUDY DESIGN

Retrospective analytic study.

SETTING

Tertiary referral center.

PATIENTS

Thirty-eight patients treated by TTI for medically refractory unilateral MD, defined by the 1995 AAO-HNS criteria, between May 2006 and December 2012.

INTERVENTION(S)

One-year course of treatment with gentamicin TTI following a low dose on-demand protocol. TTI were repeated in new courses of treatment when MD recurrence occurred.

MAIN OUTCOME MEASURE(S)

AAO-HNS class of control, caloric tests (CalT), recurrence rate.

RESULTS

After an average clinical follow-up of 71 months, all patients entered a class of control A (78%) or B (22%), with an average of 2.3 TTI received. The mean maximal obtained deficit was 88.5%, and the mean long-term deficit was 85.5%. Ten (26%) patients had disease recurrence requiring a new course of treatment. A value of the first CalT in the 3 months following the first TTI strictly higher than 78% was significantly associated with disease control and the absence of symptom recurrence (p≤0.01). In the "recurrence" group, four patients had a significantly lower mean value of all CalT performed after the first TTI when compared with other patients (p≤0.001), indicating gentamicin resistance CONCLUSION:: Achieving a sustainable vestibular deficit on caloric testing is key for MD symptom control after gentamicin TTI. Gentamicin resistance must be diagnosed early to adapt therapeutic strategies.

Intratympanic Therapies in Ménière Disease: Evaluation of Outcomes and Early Vertigo Control

OBJECTIVE

To evaluate outcomes of intratympanic (IT) dexamethasone and gentamicin in Ménière Disease (MD).

METHODS

Charts of adult patients with unilateral definite MD receiving IT gentamicin or dexamethasone from 2005 to 2017 were retrospectively reviewed. All patients had at least 6 months follow-up. Failure in each group was defined as the need for more aggressive therapy. Prior to 2011, all patient received IT gentamicin, administered as primary therapy after failure of conservative treatment measures. Gentamicin was administered every 2 weeks, up to three injections, until vertigo control was achieved. Beginning in 2011, the treatment protocol shifted to IT dexamethasone as initial treatment, with gentamicin used for dexamethasone failures. Dexamethasone was administered weekly for up to three injections. Treatments could be repeated if symptoms recurred.

RESULTS

Thirty-three patients received IT dexamethasone, and 70 patients received IT gentamicin. Dexamethasone patients received a mean of 3.3 injections compared to 2.7 in the gentamicin group (P = 0.011). There were 12 (38%) failures in the dexamethasone group and only seven (10%) gentamicin failures (P = 0.025). No patients failed both treatments. The mean time to failure in the dexamethasone group was 5 months, whereas in the gentamicin group it was 27 months. Change in pure tone audiometry from baseline was not different between treatment groups (P = 0.30).

CONCLUSION

Subjects receiving IT gentamicin required fewer injections and had a significantly longer time to failure than IT dexamethasone. Audiometric outcomes were similar between the groups. The use of IT gentamicin as initial therapy for early and long-term control of MD is safe and effective.

LEVEL OF EVIDENCE

3 Laryngoscope, 129:216-221, 2019.

Instrumental head impulse test changes after intratympanic gentamicin for unilateral definite Ménière's disease: A systematic review and meta-analysis

OBJECTIVE

To estimate how much could intratympanic gentamicin (ITG) interfere with the vestibular-ocular reflex (VOR) parameters on instrumental head impulse test (HIT), either with scleral search coil or video head impulse test and, eventually, foresee the control of vertigo crisis in unilateral intractable Ménière's disease (MD).

METHODS

A literature search was conducted in PubMed, Scopus, Web of Science and Cochrane search engines. The search terms used were "vestibular ocular reflex", "head impulse test", "gentamicin," and "Meniere's disease". Limitations included text availability to be full text, species to be humans and language to be English. All study types were included. 89 articles were screened identifying four eligible studies were identified. Studies were included after consensus of the authors. Meta-analysis was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Data was analysed using Review Manager software.

RESULTS

Instrumental HIT, after ITG for MD, demonstrated, in the treated ear, a decreased gain in the horizontal, posterior and superior semicircular canals (SCC), of 0.36 (0.26; 0.47; 95% CI), 0.35 (0.22; 0.48; 95% CI) and 0.28 (0.21; 0.35; 95% CI), respectively. Gain asymmetry increases between the treated and non-treated ear of 23.78 (7.22; 40.35; 95% CI), 32.01 (12.27; 51.76; 95% CI) and 17.49 (9.99; 24.99; 95% CI), were similarly detected in the horizontal, posterior and superior SCC, respectively. Significantly smaller gain values after the first treatment were observed for a single injection group versus multiple injection group in the horizontal (p=0.002) and superior SCCs (p=0.016).

CONCLUSIONS

Instrumental HIT is effective in evaluating the SCC function after ITG for intractable unilateral MD. VOR gain changes in the direction of the treated ear in the three SCC have been clearly registered. An increased reduction of the VOR gain in the horizontal and anterior SCC also seemed to foresee the control of vertigo crisis. Still, after meta-analysis, the small number of patients' data available did not allow to define a treatment end-point value. This review also indicated that further and better-designed studies are warranted.

Comparison of the video head impulse test with the caloric test in patients with sub-acute and chronic vestibular disorders

The aim of this prospective register-based study was to compare video Head Impulse Tests (vHIT) with caloric tests on 173 patients assessed by a tertiary Neurology referral centre who had been referred for investigation of dizziness or vertigo and whose symptom duration was one month or longer. Abnormal vHIT was defined as angular velocity gain (peak eye velocity/peak head velocity) less than 0.79 at 80 ms and 0.75 at 60 ms, which was two standard deviations below our institutions' lower limit of normal; together with refixation saccades. Abnormal bi-thermal caloric testing defined unilateral hypofunction as a 25% difference using Jongkee's formula and bilateral hypofunction was defined by the sum of the peak slow phase velocities over the four irrigations being <20°/s. Sixty patients had abnormal results on one or both tests, of whom 51 had unilateral and nine bilateral hypofunction. With caloric testing considered as the gold standard, the sensitivity (95% CI) of the vHIT was 18/52, 34.6% (22.0-49.1), and the specificity (95% CI) was 113/121, 93.4% (87.4-97.1). However vHIT was more sensitive in the nine patients with bilateral hypofunction with 100% abnormal vHIT results while only 4/9, 44% had abnormal caloric results. In conclusion these results support the continued use of both vHIT and caloric tests in patients with sub-acute and chronic vestibular symptoms, especially if the vHIT is normal.

Partial Aminoglycoside Lesions in Vestibular Epithelia Reveal Broad Sensory Dysfunction Associated with Modest Hair Cell Loss and Afferent Calyx Retraction

Although the effects of aminoglycoside antibiotics on hair cells have been investigated for decades, their influences on the dendrites of primary afferent neurons have not been widely studied. This is undoubtedly due to the difficulty in disassociating pathology to dendritic processes from that resulting from loss of the presynaptic hair cell. This was overcome in the present investigation through development of a preparation using Chinchilla laniger that enabled direct perilymphatic infusion. Through this strategy we unmasked gentamicin's potential effects on afferent calyces. The pathophysiology of the vestibular neuroepithelia after post-administration durations of 0.5 through 6 months was assessed using single-neuron electrophysiology, immunohistochemistry, and confocal microscopy. Hair cell densities within cristae central zones (0.5-, 1-, 2-, and 6-months) and utricle peri- and extrastriola (6-months) regions were determined, and damage to calretinin-immunoreactive calyces was quantified. Gentamicin-induced hair cell loss exhibited a profile that reflected elimination of a most-sensitive group by 0.5-months post-administration (18.2%), followed by loss of a second group (20.6%) over the subsequent 5.5 months. The total hair cell loss with this gentamicin dose (approximately 38.8%) was less than the estimated fraction of type I hair cells in the chinchilla's crista central zone (approximately 60%), indicating that viable type I hair cells remained. Extensive lesions to afferent calyces were observed at 0.5-months, though stimulus-evoked modulation was intact at this post-administration time. Widespread compromise to calyx morphology and severe attenuation of stimulus-evoked afferent discharge modulation was found at 1 month post-administration, a condition that persisted in preparations examined through the 6-month post-administration interval. Spontaneous discharge was robust at all post-administration intervals. All calretinin-positive calyces had retracted at 2 and 6 months post-administration. We found no evidence of morphologic or physiologic recovery. These results indicate that gentamicin-induced partial lesions to vestibular epithelia include hair cell loss (ostensibly reflecting an apoptotic effect) that is far less extensive than the compromise to stimulus-evoked afferent discharge modulation and retraction of afferent calyces (reflecting non-apoptotic effects). Additionally, calyx retraction cannot be completely accounted for by loss of type I hair cells, supporting the possibility for direct action of gentamicin on the afferent dendrite.

Intratympanal gentamicin in Meniere's disease: Effects on individual semicircular canals

OBJECTIVE

In this retrospective study the aim of the authors was to examine the effect of gentamicin on the individual semicircular canals after low dose, single injection intratympanal gentamicin therapy in Meniere's disease.

METHODS

Data of 32 patients treated between 2011 and 2015 were collected. The high frequency, high acceleration vestibuloocular reflex (VOR) gain was measured in the individual semicircular canals using video head impulse test immediately before the first intratympanal gentamicin instillation and approximately two months later.

RESULTS

In all cases 'AAO-HNS Class A' vertigo control could be attained at least for several months. In 13 cases only one instillation was necessary. In the other 19 cases the attacks returned after a few months. In 11 cases the injection had to be repeated a second time, in 4 cases 3 injections, in 2 cases 4, in 1 case 5 injections and in another 6 injections were necessary. The initial VOR gain was normal in all cases and two months after one injection it decreased in average by 40% in a highly significant manner. However, there were cases in which, although the patients became free of attacks, the gain values remained normal.

CONCLUSION

It was possible to demonstrate a significant correlation between the gain decrease of the individual canals. There was no prognostic correlation between the initial gain decrease after the first injection and the necessity of further injections. Gain values also decreased slightly but significantly in the lateral and posteriors canals on the contralateral, untreated side, possibly because of the missing disfacilitation from the treated side.

Perilymph pharmacokinetics of locally-applied gentamicin in the guinea pig

Intratympanic gentamicin therapy is widely used clinically to suppress the vestibular symptoms of Meniere's disease. Dosing in humans was empirically established and we still know remarkably little about where gentamicin enters the inner ear, where it reaches in the inner ear and what time course it follows after local applications. In this study, gentamicin was applied to the round window niche as a 20 μL bolus of 40 mg/ml solution. Ten 2 μL samples of perilymph were collected sequentially from the lateral semi-circular canal (LSCC) at times from 1 to 4 h after application. Gentamicin concentration was typically highest in samples originating from the vestibule and was lower in samples originating from scala tympani. To interpret these results, perilymph elimination kinetics for gentamicin was quantified by loading the entire perilymph space by injection at the LSCC with a 500 μg/ml gentamicin solution followed by sequential perilymph sampling from the LSCC after different delay times. This allowed concentration decline in perilymph to be followed with time. Gentamicin was retained well in scala vestibuli and the vestibule but declined rapidly at the base of scala tympani, dominated by interactions of perilymph with CSF, as reported for other substances. Quantitative analysis, taking into account perilymph kinetics for gentamicin, showed that more gentamicin entered at the round window membrane (57%) than at the stapes (35%) but the lower concentrations found in scala tympani were due to greater losses there. The gentamicin levels found in perilymph of the vestibule, which are higher than would be expected from round window entry alone, undoubtedly contribute to the vestibulotoxic effects of the drug. Furthermore, calculations of gentamicin distribution following targeted applications to the RW or stapes are more consistent with cochleotoxicity depending on the gentamicin concentration in scala vestibuli rather than that in scala tympani.

Surgery for vertigo: 10-year audit from a contemporary vertigo clinic

OBJECTIVE

To present the profile of patients undergoing surgical treatment for vertigo at a contemporary institutional vertigo clinic.

STUDY DESIGN

A retrospective analysis of clinical charts.

METHODS

The charts of 1060 patients, referred to an institutional vertigo clinic from January 2003 to December 2012, were studied. The clinical profile and long-term outcomes of patients who underwent surgery were analysed.

RESULTS

Of 1060 patients, 12 (1.13 per cent) were managed surgically. Of these, disease-modifying surgical procedures included perilymphatic fistula repair (n = 7) and microvascular decompression of the vestibular nerve (n = 1). Labyrinth destructive procedures included transmastoid labyrinthectomy (n = 2) and labyrinthectomy with vestibular nerve section (n = 1). One patient with vestibular schwannoma underwent both a disease-modifying and destructive procedure (translabyrinthine excision). All patients achieved excellent vertigo control, classified as per the American Academy of Otolaryngology - Head and Neck Surgery 1995 criteria.

CONCLUSION

With the advent of intratympanic treatments, surgical treatments for vertigo have become further limited. However, surgery with directed intent, in select patients, can give excellent results.

Histopathologic Changes of the Inner ear in Rhesus Monkeys After Intratympanic Gentamicin Injection and Vestibular Prosthesis Electrode Array Implantation

Bilateral vestibular deficiency (BVD) due to gentamicin ototoxicity can significantly impact quality of life and result in large socioeconomic burdens. Restoring sensation of head rotation using an implantable multichannel vestibular prosthesis (MVP) is a promising treatment approach that has been tested in animals and humans. However, uncertainty remains regarding the histopathologic effects of gentamicin ototoxicity alone or in combination with electrode implantation. Understanding these histological changes is important because selective MVP-driven stimulation of semicircular canals (SCCs) depends on persistence of primary afferent innervation in each SCC crista despite both the primary cause of BVD (e.g., ototoxic injury) and surgical trauma associated with MVP implantation. Retraction of primary afferents out of the cristae and back toward Scarpa's ganglion would render spatially selective stimulation difficult to achieve and could limit utility of an MVP that relies on electrodes implanted in the lumen of each ampulla. We investigated histopathologic changes of the inner ear associated with intratympanic gentamicin (ITG) injection and/or MVP electrode array implantation in 11 temporal bones from six rhesus macaque monkeys. Hematoxylin and eosin-stained 10-μm temporal bone sections were examined under light microscopy for four treatment groups: normal (three ears), ITG-only (two ears), MVP-only (two ears), and ITG + MVP (four ears). We estimated vestibular hair cell (HC) surface densities for each sensory neuroepithelium and compared findings across end organs and treatment groups. In ITG-only, MVP-only, and ITG + MVP ears, we observed decreased but persistent ampullary nerve fibers of SCC cristae despite ITG treatment and/or MVP electrode implantation. ITG-only and ITG + MVP ears exhibited neuroepithelial thinning and loss of type I HCs in the cristae but little effect on the maculae. MVP-only and ITG + MVP ears exhibited no signs of trauma to the cochlea or otolith end organs except in a single case of saccular injury due to over-insertion of the posterior SCC electrode. While implanted electrodes reached to within 50-760 μm of the target cristae and were usually ensheathed in a thin fibrotic capsule, dense fibrotic reaction and osteoneogenesis were each observed in only one of six electrode tracts examined. Consistent with physiologic studies that have demonstrated directionally appropriate vestibulo-ocular reflex responses to MVP electrical stimulation years after implantation in these animals, histologic findings in the present study indicate that although intralabyrinthine MVP implantation causes some inner ear trauma, it can be accomplished without destroying the distal afferent fibers an MVP is designed to excite.

Single intratympanic gentamicin injection in Ménière's disease: VOR change and prognostic usefulness

OBJECTIVE

Assess angular vestibular-ocular reflex (VOR) changes after treatment with intratympanic gentamicin (ITG) for Ménière's disease (MD) and impact on short-term follow-up.

DESIGN

Prospective study.

METHODS

Patients submitted to ITG for unilateral MD. The gain VOR and the presence of compensatory saccades elicited by rapid head impulses were measured using the video head impulse test (vHIT).

RESULTS

The study included 31 subjects (mean age: 59 years). Functional Level Scale (FLS) distributions were 35,5% (FLS3); 32,2% (FLS4); and 32,2% (FLS5). Mean follow-up was 21 ± 7 months. Multiple injections were needed in nine patients. VOR gain in the treated ear was significantly reduced in all subjects and for all the semicircular canals (paired samples t test; P < 0,05). Gain averages after treatment were 0,61 (superior); 0,69 (horizontal); and 0,47 (posterior). A horizontal canal VOR gain superior to 0,80 after treatment was associated with the need for a second gentamicin injection (Chi-square; P = 0,003). Gain asymmetry between the symptomatic and asymptomatic ear (GASM) was increased after treatment. The rate of vestibular function reduction was 47,9%; 26,0%; and 35,8% for the superior, horizontal, and posterior canals, respectively. According to the receiving operator characteristic curve, the amount of change in GASM must be greater than 7 in order to predict the avoidance of a second procedure (area under the curve [AUC] horizontal canal = 0,861) and the amount of vestibular function reduction in the pathologic ear in patients with a controlled disease must be greater than 17,8% (AUC horizontal canal = 0,843).

CONCLUSIONS

When evaluated with the vHIT, intratympanic gentamicin changes in VOR seem to foresee short-term control of vertigo attacks.

LEVEL OF EVIDENCE

4.

Outcomes after cochlear implantation for patients with single-sided deafness, including those with recalcitrant Ménière's disease

OBJECTIVE

Compare preoperative and postoperative performance in patients undergoing cochlear implantation (CI) for unilateral severe-to-profound sensorineural hearing loss (single-sided deafness, SSD).

STUDY DESIGN

IRB-approved, prospective

SETTING

Tertiary center

PATIENTS

Twenty-nine patients have undergone CI for SSD. SSD was due to Ménière's disease (MD) in 10 subjects; these also suffered from recalcitrant vertigo spells and in these 10 patients along with 2 others the CI was placed simultaneous with a labyrinthectomy.

INTERVENTION(S)

CI with or without labyrinthectomy.

MAIN OUTCOME MEASURE(S)

CNC word and AzBio sentences in quiet were administered to the implanted ear. A multiple-loudspeaker sound localization test was administered in the bilateral listening condition. All data were collected preoperatively and 3, 6, and 12 months postoperatively with postoperative data available for 19 subjects. Additionally, a tinnitus handicap questionnaire is administered pre- and 12-months post-operatively.

RESULTS

CNC word and AzBio sentence scores showed improvement in the implanted ear. Sound localization appeared to improve in an experience-dependent fashion in some patients. Most patients reported diminished tinnitus after cochlear implantation. All patients undergoing labyrinthectomy experienced resolution of vertigo attacks.

CONCLUSION

CI restores auditory function to the deafened ear. Additionally, the binaural input appears to improve sound localization for most patients. In patients with severe hearing loss and recalcitrant vertigo attacks because of MD, simultaneous labyrinthectomy and CI effectively relieves vertigo attacks and improves auditory function.

Horizontal VOR function shows frequency dynamics in vestibular schwannoma

The objective of this retrospective study was to investigate the horizontal vestibulo-ocular reflex (hVOR) pathway with caloric test (low-frequency hVOR) and video head impulse test (vHIT) (high-frequency hVOR) in patients with sporadic vestibular schwannoma (69 patients, 27-86 years, mean age 58.1 years) and to compare both test methods in terms of their sensitivity and specificity to detect a retrocochlear lesion. Test results with a unilateral weakness (UWCaloric) >25 % (caloric test) or a Mean-GainvHIT <0.79/asymmetry ratio of Gain (AR-GainvHIT) >8.5 % and accompanied refixation saccades (vHIT) were considered abnormal. The overall sensitivity of the caloric test was 72 %. The evaluation of AR-GainvHIT detected more abnormal cases than did Mean-GainvHIT (44 vs. 36 %). In up to 4 %, a normal caloric test result was related to an abnormal vHIT. There was only a moderate correlation of UWCaloric and AR-GainvHIT (r = 0.54, p < 0.05) with a linear regression line intercept/slope of 32.2/0.9 (p < 0.05). Receiver operating characteristics curve analysis exhibited at a UWCaloric of 50 % a vHIT sensitivity/specificity/positive predictive value/negative predictive value of 0.45/0.9/0.94/0.42. Vestibular testing at varying frequencies provides deeper insights into hVOR function and is helpful in detecting a cerebello-pontine lesion. Whereas caloric test yields a high sensitivity for nerve dysfunction, vHIT test reveals a remaining function of hVOR in the high-frequency range.

Intratympanic gentamicin for Meniere's disease: short- and long-term follow-up of two regimens of treatment

OBJECTIVES

(1) To compare the results of the 2 regimens of treatment at 2-year follow-up and (2) to evaluate the need and the efficacy of retreatment after the recurrence of vertigo attacks in a longer period of follow-up (using the Kaplan-Meier method of analysis).

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral center.

SUBJECTS AND METHODS

We analyzed 77 patients treated with intratympanic gentamicin (ITG). Thirty-five patients were treated with high-dose (HD) ITG (in total 6 injections, twice a day, repeated every 3 days) and 42 with low-dose (LD) ITG (1-2 injections). The results of treatment were evaluated in terms of functional level scale, control of vertigo, and hearing impairment.

RESULTS

At 2-year follow-up, a similar percentage of vertigo control was obtained in the 2 groups; the incidence of hearing loss and posttreatment disequilibrium was significantly higher in patients treated with HD-ITG. The long-term follow-up showed a control of vertigo attacks with a single round of treatment in 71.4% of patients treated with HD-ITG and in 55% of those treated with LD-ITG. With repeated rounds, an effective control of vertigo could be achieved in 88.5% using a HD-ITG protocol and 97.7% using a LD-ITG protocol.

CONCLUSIONS

LD-ITG allows obtaining good results in term of vertigo attacks associated with a limited occurrence of side effects. The long-term follow-up showed that LD-ITG needed repeated rounds more frequently than the HD-protocol. HD-ITG ran less risk of needing repeated rounds, but retreatment was ineffective in 40% of the cases requiring surgical therapy.

Developments in delivery of medications for inner ear disease

INTRODUCTION

Hearing loss, tinnitus and balance disturbance represent common diseases that have tremendous impact on quality of life. Despite the high incidence of inner ear disease in the general population, there are currently no dedicated pharmacologic interventions available to treat these problems.

AREAS COVERED

This review will focus on how treatment of inner ear disease is moving toward local delivery at the end organ level. The authors will discuss current practice, ongoing clinical trials and potential areas of development such as hair cell regeneration and neurotrophin therapy.

EXPERT OPINION

The inner ear is accessible through the middle ear via the oval and round windows allowing diffusion of drugs into the perilymph. With a better understanding of the physiology of the inner ear and the underlying molecular causes of inner ear disease there is great potential for the development of novel therapeutics that can be locally administered. At present, there is a rapid development of drugs to target diverse inner ear diseases that cause sensorineural hearing loss and balance dysfunction.

Dynamic Change of VOR and Otolith Function in Intratympanic Gentamicin Treatment for Ménière's Disease: Case Report and Review of the Literature

Intratympanic gentamicin treatment (IGT) is an evidence-based therapeutic option for recurrent vertigo attacks in Ménière's disease (MD). Today, in MD it is possible to monitor changes of vestibular receptor function, induced by IGT, with objective test methods such as the video head impulse test (vHIT) and cervical and ocular vestibular evoked myogenic potentials (cVEMP, oVEMP) in a dynamic, time-and frequency-dependent manner. We report on a 65-year-old female patient with recurrent vertigo attacks in a right-sided MD, where receptor function was followed up before and up to 4 weeks after IGT (time dynamic). Quantitative changes of vestibular function (frequency dynamic) were detected with bithermal calorics and vHIT, with air-conducted sound (ACS) cVEMP and bone-conducted vibration (BCV) oVEMP at 500 Hz. The horizontal vestibuloocular reflex (hVOR) gain in vHIT decreased successively until the 4th week with the appearance of catch-up covert and catch-up overt refixation saccades, and side asymmetry increased in caloric testing. Saccular function was extinguished within 4 weeks, whereas utricular function was diminished after 4 weeks. Monitoring vestibular receptor function with objective test methods provides a quantitative insight into the dynamic activity of vestibular function and is therefore applicable in order to adjust IGT regimen at different therapeutic stages.

Multichannel vestibular prosthesis employing modulation of pulse rate and current with alignment precompensation elicits improved VOR performance in monkeys

An implantable prosthesis that stimulates vestibular nerve branches to restore the sensation of head rotation and the three-dimensional (3D) vestibular ocular reflex (VOR) could benefit individuals disabled by bilateral loss of vestibular sensation. Our group has developed a vestibular prosthesis that partly restores normal function in animals by delivering biphasic current pulses via electrodes implanted in semicircular canals. Despite otherwise promising results, this approach has been limited by insufficient velocity of VOR response to head movements that should inhibit the implanted labyrinth and by misalignment between direction of head motion and prosthetically elicited VOR. We report that significantly larger VOR eye velocities in the inhibitory direction can be elicited by adapting a monkey to elevated baseline stimulation rate and current prior to stimulus modulation and then concurrently modulating ("co-modulating") both rate and current below baseline levels to encode inhibitory angular head velocity. Co-modulation of pulse rate and current amplitude above baseline can also elicit larger VOR eye responses in the excitatory direction than do either pulse rate modulation or current modulation alone. Combining these stimulation strategies with a precompensatory 3D coordinate transformation improves alignment and magnitude of evoked VOR eye responses. By demonstrating that a combination of co-modulation and precompensatory transformation strategies achieves a robust VOR response in all directions with significantly improved alignment in an animal model that closely resembles humans with vestibular loss, these findings provide a solid preclinical foundation for application of vestibular stimulation in humans.

Perspectives in vestibular diagnostics and therapy

Vestibular diagnostics and therapy ist the mirror of technological, scientific and socio-economics trends as are other fields of clinical medicine. These trends have led to a substantial diversification of the field of neurotology.The improvements in diagnostics have been characterized by the introduction of new receptor testing tools (e.g., VEMPs), progress in imaging (e.g., the endolymphatic hydrops) and in the description of central-vestibular neuroplasticity. The etiopathology of vestibular disorders has been updated by geneticists (e.g., the description of the COCH gene mutations), the detection of structural abnormalities (e.g., dehiscence syndromes) and related disorders (e.g. migraine-associated vertigo). The therapeutic options were extended by re-evaluation of techniques known a long time ago (e.g., saccus exposure), the development of new approaches (e.g., dehiscence repair) and the introduction of new drug therapy concepts (e.g., local drug delivery). Implantable, neuroprosthetic solutions have not yet reached experimental safety and validity and are still far away. However, externally worn neuroprosthetic solution were introduced in the rehab of vestibular disorders (e.g., VertiGuard system).These and related trends point into a medical future which is characterized by presbyvertigo as classical sign of the demographic changes ahead, by shortage of financial resources and a medico-legally over-regulated, even hostile environment for physicians in clinical medicine.

Cochlear function in Ménière's disease

OBJECTIVE

The authors assessed the effectiveness of therapy, common features of pure-tone audiograms, and results of non-invasive electrocochleography before and after mild inhibition of peripheral vestibular function by infrequent administration of single intratympanic gentamicin injections (ITPG) in patients with Ménière's disease (MD).

STUDY SAMPLE

Sixty-two patients with Ménière's disease.

DESIGN

Retrospective study.

RESULTS

Out of 62 patients 65% received one injection, 24% two, 6% three, 3% five, and 2% six injections. Between injections, class A vertigo control was obtained after two weeks in all cases. Before ITPG, out of 62 pure-tone threshold audiograms 37 were 'flat'. Average hearing threshold at 2 kHz was significantly better than that of 250, 500, and 0.75 kHz on the affected side.

CONCLUSIONS

Hearing threshold in advanced MD is often flat with a characteristic small peak in the high frequency range, most frequently around 2-3 kHz. Should the complaints be intolerable, single injection ITPG-therapy may be safe and effective.

Physiologic effects on the vestibular system in Meniere's disease

Ménière syndrome is an inner ear disorder characterized by spontaneous attacks of vertigo, fluctuating low-frequency sensorineural hearing loss, aural fullness and tinnitus. When the syndrome is idiopathic and cannot be attributed to any other cause (eg, syphilis, immune-mediated inner ear disease, surgical trauma), it is referred to as Ménière disease. This article reviews the physiologic effects of Ménière disease on vestibular function, as measured by caloric, head impulse, and vestibular-evoked myogenic potential testing.

New methods for diagnosis and treatment of vestibular diseases

Dizziness and vertigo are common complaints, with a lifetime prevalence of over 30%. This review provides a brief summary of the recent diagnostic and therapeutic advances in the field of neuro-otology. A special focus is placed on the clinical usefulness of vestibular tests. While these have markedly improved over the years, treatment options for vestibular disorders still remain limited. Available therapies for selected vestibular diseases are discussed.