Intratympanic Gentamicin Research Articles

Pharmacological, surgical and diagnostic innovations in Meniere’s disease: a review

Meniere’s disease is an inner ear disorder characterized by the presence of endolymphatic hydrops in the inner ear and symptomatology of recurrent and debilitating vertigo attacks, tinnitus, aural fullness, and fluctuating sensorineural hearing loss. Although many therapeutic options for MD have been proposed during years, no consensus has been reached by the scientific community. In the last decade, many therapeutic options have been proposed, as intratympanic steroid, intratympanic gentamicin, and intravenous glycerol. Recently, the role of the antisecretory factor in the diet of MD patients have been investigated. Surgery is recommended for intractable MD; some authors proposed new approaches including transcanal endoscopic infracochlear vestibular neurectomy, new marsupiliazation technique in sac surgery, and tenotomy of the stapedius and tensor tympani muscles.

The instantaneous training demand drives vestibulo-ocular reflex adaptation.

The vestibulo-ocular reflex (VOR) maintains stable vision during rapid head rotations by rotating the eyes in the opposite direction to the head. The latency between onset of the head rotation and onset of the eye rotation is 5-8ms in healthy humans. However, VOR latency can be 3-4 times larger in patients treated with intra-tympanic gentamicin. A prior study showed that latency can be trained with head rotations at 0.2Hz. We sought to determine how the VOR is affected when a delay between vestibular and visual stimuli is added during adaptation training with high-frequency head rotations (impulses), where the VOR is the main vision-stabilizing system. Using a variant of the incremental VOR adaptation technique, the delay between head rotation onset and movement onset of a visual target was gradually increased. With this training, the instantaneous VOR gain demand (= target/head velocity) varied from less than unity to greater than unity during each head impulse, albeit in a consistent and repeatable way. We measured the active and passive VOR gain and latency before and after VOR adaptation training in healthy normal subjects. There was no significant change in VOR latency across subjects; however, there was a significant decrease in VOR gain of - 6.0 ± 4.5%. These data suggest that during high-frequency head rotations delay/latency is interpreted as a changing instantaneous VOR gain demand. Although the gain demand in this study had a complex trajectory, adaptation was evident with the VOR seeming to use an average of the instantaneous gain demand.

Pharmacologic and surgical therapies for patients with Meniere's disease: A systematic review and network meta-analysis.

BackgroundMeniere’s disease (MD) is a chronic condition of the inner ear consisting of symptoms that include vertigo attacks, fluctuating sensorineural hearing loss, tinnitus and aural fullness. Despite availability of various interventions, there is uncertainty surrounding their relative efficacy, thus making it difficult to select the appropriate treatments for MD. The objective of this systematic review was to assess the relative effects of the available pharmacologic and surgical interventions in patients with MD with regard to vertigo and other key patient outcomes based on data from randomized clinical trials (RCTs).MethodsOur published protocol registered with PROSPERO (CRD42019119129) provides details on eligibility criteria and methods. We searched various databases including MEDLINE, Embase and the Cochrane Library from inception to December 10th, 2018. Screening at citation and full-text levels and risk of bias assessment were performed by two independent reviewers in duplicate, with discrepancies resolved by consensus or third-party adjudication. Bayesian network meta-analyses (NMA) were performed for hearing change and vertigo control outcomes, along with pairwise meta-analyses for these and additional outcomes.ResultsWe identified 2,889 unique citations, that yielded 23 relevant publications describing 18 unique RCTs (n = 1,231 patients). Overall, risk-of bias appraisal suggested the evidence base to be at unclear or high risk of bias. Amongst pharmacologics, we constructed treatment networks of five intervention groups that included placebo, intratympanic (IT) gentamicin, oral high-dose betahistine, IT steroid and IT steroid plus high-dose betahistine for NMAs of hearing change (improvement or deterioration) and complete vertigo control. IT steroid plus high-dose betahistine was associated with the largest difference in hearing improvement compared to placebo, followed by high-dose betahistine and IT steroid (though 95% credible intervals failed to rule out the possibility of no difference), while IT gentamicin was worse than IT steroid. The NMA of complete vertigo control suggested IT gentamicin was associated with the highest probability of achieving better complete vertigo control compared to placebo, followed by IT steroid plus high-dose betahistine. Only two studies related to surgical interventions were found, and data suggested no statistically significant difference in hearing changes between endolymphatic duct blockage (EDB) versus endolymphatic sac decompression (ESD), and ESD with or without steroid injection. One trial reported that 96.5% of patients in EDB group compared to 37.5% of the patients in ESD group achieved complete vertigo control 24 months after surgery (p = 0.002).ConclusionTo achieve both hearing preservation and vertigo control, the best treatment option among the pharmacologic interventions compared may be IT steroid plus high-dose betahistine, considering that IT gentamicin may have good performance to control vertigo but may be detrimental to hearing preservation with high cumulative dosage and short interval between injections. However, IT steroid plus high-dose betahistine has not been compared in head-to-head trials against other interventions except for IT steroid alone in one trial, thus future trials that compare it with other interventions will help establish comparative effectiveness with direct evidence.

Low Dose Intratympanic Gentamicin in Ménière's Disease.

Intratympanic gentamicin has become an accepted standard of care for Ménière's disease. But there still exists controversies regarding the dosing protocol as well as the drug concentration for optimum control of vertigo and hearing preservation. To determine if 20mg of intratympanic gentamicin administered once a month for a maximum of 2months can alleviate intractable vertigo caused by definite Ménière's disease with hearing preservation. Once diagnosed with definite Ménière's disease as per AAO-HNS criteria, the patient was given 0.5ml of 40mg/ml intratympanic gentamicin. Follow-up was done at 1-month and 6-month post-treatment. If at 1-month review patient continued to have vertigo one more dose of intratympanic gentamicin was administered. Thirty-two patients were included in the study. Seventeen patients (53.1%) received one dose and 15 patients (46.9%) received two doses of intratympanic injection. We achieved an effective vertigo control of 59.4% and complete vertigo control rate of 53.1%. Worsening of symptoms was noted in 1 patient. Hearing was preserved in all patients except for one. Among the patients who attained effective vertigo control, 72.2% had dead labyrinth at 6-month cold caloric status. A single injection of 20mg intratympanic gentamicin can alleviate intractable vertigo caused by definite Ménière's disease with hearing preservation. Non-responders may be given a second dose after one month. Intratympanic gentamicin is a simple, cheap treatment that can be carried out in an out-patient setting.

Transmastoid Labyrinthectomy for Menière's Disease: Experience and Outcomes.

To characterize presurgical symptoms and treatment history and postoperative course in patients with medically recalcitrant Menière's disease undergoing transmastoid labyrinthectomy in the post-intratympanic gentamicin era. Retrospective case series. Tertiary academic medical center. All patients who underwent transmastoid labyrinthectomy for medically recalcitrant Menière's disease in 2003 to 2019 by the senior author. Review of patients' medical records for: preoperative history of drop attacks, gentamicin injections, endolymphatic sac decompression or vestibular neurectomy, preoperative audiograms, length of hospital stay, postoperative complications, and persistent symptoms or challenging recovery. Presurgical clinical history and proximal postoperative outcomes. Seventy-two patients with a mean age of 56.7 (standard deviation [SD] 10.7) were included. All cases were unilateral. Forty-three patients (59.7%) suffered from drop attacks. Sixty-two (86.1%) had failed sufficient symptom control with gentamicin injections. The mean preoperative word recognition score was 36.4% (SD 23.7) versus 95.1% (SD 8.5) in the contralateral ear. The mean pure-tone average (PTA) of the ipsilateral ear before surgery was 65.5 dB (SD 18.0) versus 16.2 (SD 13.5) for the contralateral ear. Mean hospital stay was 2.0 days (SD 0.87 days, range of 1-5 d). Three patients (4.2%) had prolonged postoperative vertigo. Transmastoid labyrinthectomy at our center is performed for unilateral Menière's disease, generally when intratympanic gentamicin has failed. A majority of surgical patients suffer from drop attacks preoperatively. Hospital stay is typically brief.

Effectiveness of Intratympanic Administration of Gentamicin in Unilateral MeniÈre's Disease.

To the Editor: In a recent issue published by Otology and Neurotology, Yaz et al. (1) presented an interesting work to analyze the effectiveness of an intratympanic (IT) injection of aminoglycosides compared to intratympanic corticosteroids to control vertigo and protect hearing in Menière's disease (MD) patients with persistent vertigo attacks despite medical treatment. MD is an idiopathic inner ear disorder characterized by recurrent attacks of vertigo, accompanied by fluctuating sensorineural hearing loss, aural fullness, and tinnitus; vertigo attacks in MD are often debilitating and may severely affect quality of life. Endolymphatic hydrops (EH) of the inner ear is currently considered the pathophysiological mechanism that underlies MD symptomatology. EH seems to follow an overproduction of endolymph and/or a decrease in the absorption of endolymph as shown by histopathological research. Several therapeutic options for MD have been proposed but none is considered fully effective by the scientific community. Evidence has confirmed the importance of dietary changes in the management of MD, such as the reduction of caffeine and alcohol intake and the restriction of sodium, also suggesting introducing monosodium glutamate in patients’ diet. The article from Yaz et al. (1) is very interesting and precise; however, we would like to share some brief considerations regarding dietary changes and possible treatment options. Concerning the current discussion on the optimal dietary management in patients with MD, we would like to underline the lack of mention about glucose intake. In a recent review from our group, we remarked the possible role played by hyperinsulinemia in subjects affected by MD (2). There is actually a strong evidence that the saccule, which is the main labyrinthine structure affected following EH, has a large number of insulin receptors. This observation was confirmed by postmortem histopathological findings and by in vivo analysis through cervical vestibular evoked myogenic potentials. When first-line treatment with dietary modifications is not able to offer a satisfactory symptom control, especially of vertigo, IT administrations of corticosteroids or gentamicin is recommended; corticosteroids have been shown to have a lower risk of hearing damage but less efficacy in vertigo attack control compared to gentamicin (3). In a previous study(4), we treated 48 patients with unilateral intractable MD with IT injections (1 to 5) of 10 mg gentamicin every 2 weeks; we evaluated vertigo attacks before and after therapy and performed pure-tone audiometry, vestibular bed-side examination, and video head impulse test. Before treatment, patients had an average of 4.4 vertigo attacks/mo; after treatment the average number decreased to 0.52. The majority of patient (77%) reached vertigo control with 5 or less gentamicin injections. Although there is no current consensus on clinical guidelines for the use of gentamicin in terms of dose and duration, evidence suggests preferring low-dose protocols to minimize hearing deterioration (5). In our study, we observed that low-dose IT gentamicin can produce a satisfactory control of vertigo attacks with limited risk of hearing loss.

What is the efficacy of gentamicin on the incidence of vertigo attacks and hearing in patients with Meniere's disease compared with steroids? A meta-analysis.

To compare the efficacy of gentamicin and steroids in patients with Meniere's disease (MD). The study protocol was structured in accordance with the Population, Intervention, Comparison and Outcome (PICO) framework. We used "Endnote" (Thomson ResearchSoft; Stanford, Connecticut, the United States) to retrieve database documents. A systematic literature search of Web of Science and PubMed Database through May 2020 was conducted using specific search terms. Inclusion criteria, exclusion criteria, vertigo improvement, and exact hearing changes were defined. Review Manager 5.3 (Cochrane) was used for data analysis. A total of 80 articles were searched from Web of Science and 23 articles were searched from PubMed database. After further reviewing the specific points of the inclusion criteria and exclusion criteria, 9 papers were finally selected. Intratympanic gentamicin (ITG) was superior to intratympanic steroid (ITS) in reducing the number of vertigo attacks (odds ratio (OR) 3.08, 95% confidence intervals (CI) [2.05-3.65]), probability (P) < 0.01). As for hearing improvement, we did the analysis twice. With all the studies included, the odds of hearing improvement (by "x") was 0.31 among patients receiving gentamicin compared to those treated by steroids (OR 0.31, 95% CI [0.16-0.61]). But after removing one study with outlying results from the analysis, this effect disappeared. Hearing loss of ITG and ITS was not statistically significant (P = 0.29). ITG is superior to ITS in reducing the number of vertigo attacks in the treatment of MD (P < 0.01); the impact on hearing is more heterogeneous in the studies. Overall, there was no clear difference between ITG and ITS on hearing improvement and on hearing loss.

Is Endolymphatic Sac Surgery Beneficial For Meniere's Disease?

Is Endolymphatic Sac Surgery Beneficial For Meniere's Disease?

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

To evaluate the efficacy of on demand and low dose intratympanic gentamicin (ITG) in patients with intractable Meniere's disease (MD). Clinical chart review. Secondary care center. Subjects with MD who failed conventional treatment and underwent on demand ITG infiltration from June 2013 to December 2018. 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. Vertigo control, Meniere's Disease Functional Level Scale (MDFLS), Dizziness Handicap Inventory (DHI), and pure tone audiometry pre and posttreatment. 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). 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.

A Case of Tumarkin Otolithic Crisis Treated with Intratympanic Gentamicin Injection

A Case of Tumarkin Otolithic Crisis Treated with Intratympanic Gentamicin Injection

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.

Long-term outcomes of triple semicircular canal plugging for the treatment of intractable Meniere's disease: A single center experience of 361 cases.

Meniere's disease is a common chronic inner ear disease. Because the definitive pathogenesis is still unknown, there is currently no cure for this disorder. Semicircular canal plugging (SCP), first used to treat patients with intractable benign paroxysmal positional vertigo, has since been applied to patients with intractable peripheral vertigo. This study was aimed to explore the long-term efficacy of triple semicircular canal plugging (TSCP) in the treatment of intractable Meniere's disease (MD) so as to provide a new method in the framework of treatment with MD. Three hundred and sixty-one unilateral MD patients, who were treated with TSCP in our hospital between Dec. 2010 and Sep. 2016, were recruited in this study for retrospective analysis. Vertigo control and auditory function were monitored during a period of two-year follow-up. Seventy three patients who were subjected to intratympanic gentamicin were selected as a control group. Pure tone audiometry, caloric test, vestibular evoked myogenic potential (VEMP) were performed in two-year follow-up. The total control rate of vertigo in TSCP group was 97.8% (353/361) in the two-year follow-up, with complete control rate of 80.3% (290/361) and substantial control rate of 17.5% (63/361). The rate of hearing loss was 26.3% (95/361). The total control rate of vertigo in intratympanic gentamicin group was 83.6% (61/73), with complete control rate of 63.0% (46/73) and substantial control rate of 20.5% (15/73). The rate of hearing loss was 24.7% (18/73). The vertigo control rate of TSCP was significantly higher than that of chemical labyrinthectomy(χ2 = 24.798, p < 0.05). There was no significant difference of hearing loss rate between two groups. (χ2 = 0.087, p > 0.05). Triple semicircular canal plugging (TSCP), which can reduce vertiginous symptoms in patients with intractable Meniere's disease (MD), represents an effective therapy for this disorder. It might become a new important method in the framework of treatment with MD.

Intratympanic Treatment in Menière's Disease, Efficacy of Aminoglycosides Versus Corticosteroids in Comparison Studies: A Systematic Review.

To compare the functional outcomes and complications of intratympanic gentamicin (ITG) versus intratympanic corticosteroids (ITC) in Menière's disease. An electronic search was conducted in the Cochrane Library, PubMed, and Embase databases on February 3, 2019. Articles written in English, Dutch, German, French, or Turkish language were included. Study inclusion criteria were: 1) patients diagnosed with definite Menière's disease according to the criteria of the American Academy of Otolaryngology-Head and Neck Surgery, 2) treated with ITG or ITC in a comparison study, and 3) reported subjective and objective outcomes concerning Menière's disease. The quality of eligible studies was assessed according to an adjusted version of the Cochrane Risk of Bias tool. The extracted data were study characteristics (study design, publication year, and number of relevant patients), patient's characteristics (sex and age), disease characteristics (uni or bilateral and duration of Menière's disease), treatment protocol, and different therapeutic outcomes (vertigo, tinnitus, aural fullness, and hearing loss). A total of eight articles were included for data extraction and analysis. For subjective outcomes, ITG was slightly favored compared to intratympanic corticosteroids. This was significant only in three studies (p < 0.05). For objective outcomes and complications, no significant differences were seen. The result of this systematic review shows some benefit of ITG over ITC for subjective outcomes and no difference regarding objective outcomes or complication rate. However, this superiority of ITG is rather weak. Both interventions can be effectively and safely used in controlling Menière's disease in acute situations.

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

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. 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. 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. 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.

Intratympanic gentamicin injection for Meniere's disease

Meniere's disease is characterized by idiopathic progressive fluctuating hearing loss, tinnitus, and episodic vertigo. Intratympanic gentamicin injection is the preferred therapeutic option for those who have failed conservative management including lifestyle modifications and oral medications. The procedure is simple and can be performed in the outpatient setting under local anesthesia with manageable recovery time. Patients may experience a disequilibrium sensation beginning approximately 3-5 days after injection, which peaks around 10-14 days after injection and fades over the course of several more weeks. The presence of this reaction is an indicator of treatment response. Intratympanic gentamicin injection achieves control of vertigo in 80%-90% of patients. Risks include prolonged imbalance from delayed vestibular compensation after treatment, as well as sensorineural hearing loss, both of which are generally preferable to disabling vertigo attacks.

Perioperative vestibular assessment and testing

Vestibular disorders can be difficult to accurately diagnose and manage. A careful history and focused physical examination are typically adequate to establish a diagnosis and initiate medical treatment. Vestibular testing is an important component of the work-up, but it is particularly essential for patients being considered for surgical intervention for a vestibular disorder, where the testing can be used to more definitively confirm a suspected diagnosis and to determine baseline vestibular organ function. In this article, we will first briefly review key components of the history and physical examination of patients with vestibular complaints. We will then discuss the most commonly used vestibular tests and their role in the preoperative assessment of patients undergoing vestibular surgery, including nystagmography, caloric testing, rotary chair testing, video head impulse testing, and vestibular evoked myogenic potential testing.

A Case of Binocular Vertical Diplopia after Intratympanic Gentamicin Therapy.

Intratympanic gentamicin therapy is a useful alternative treatment for refractory Meniere’s disease and is generally well tolerated. Visual disturbances as side effects of this treatment are rarely reported in the literature. In this report we describe the case of a 52-year-old woman with refractory Meniere’s disease who developed binocular vertical diplopia following intratympanic gentamicin therapy. Spontaneous resolution of diplopia occurred within 2 weeks. The development of diplopia should be discussed as a potential complication with patients undergoing intratympanic gentamicin therapy.LEARNING POINTSMeniere’s disease is an inner ear disorder which can cause vertigo and hearing loss.As medical treatment sometimes fails, other therapeutic options should be considered.Gentamycin chemical labyrinthectomy can be administered as an alternative treatment, but the development of diplopia should be discussed as a potential side effect.

Benefits of pre-labyrinthectomy intratympanic gentamicin: contralateral vestibular responses.

To determine the impact of pre-operative intratympanic gentamicin injection on the recovery of patients undergoing translabyrinthine resection of vestibular schwannomas. This prospective, case-control pilot study included eight patients undergoing surgical labyrinthectomy, divided into two groups: four patients who received pre-operative intratympanic gentamicin and four patients who did not. The post-operative six-canal video head impulse test responses and length of in-patient stay were assessed. The average length of stay was shorter for patients who received intratympanic gentamicin (6.75 days; range, 6-7 days) than for those who did not (9.5 days; range, 8-11 days) (p = 0.0073). Additionally, the gentamicin group had normal post-operative video head impulse test responses in the contralateral ear, while the non-gentamicin group did not. Pre-operative intratympanic gentamicin improves the recovery following vestibular schwannoma resection, eliminating, as per the video head impulse test, the impact of labyrinthectomy on the contralateral labyrinth.

Management of Ménière's Disease: How Does the Coexistence of Vestibular Migraine Affect Outcomes?

To report the incidence of vestibular migraine (VM) in patients with Ménière's disease (MD) and investigate whether management outcomes of MD differ by the association of VM. Retrospective cohort study. Tertiary care academic center. MD patients (n = 251) with/without VM who were managed for 5 years in a dizziness clinic. Influence of VM on management outcomes and hearing at the latest follow-up in stepwise management options. Incidence of VM was 35% in MD patients. VM was more common in women than men (40 vs. 22%) and in probable MD than definite MD (43 vs. 29%). Bilateral MD was more frequent with coexistence of VM than without VM in definite MD (14 vs. 0%) as well as probable MD (24 vs. 7%). At the latest follow-up, preventive medications were effective in controlling vertigo in most (80%) patients (74%/90% in definite/probable MD). Additional intratympanic steroids were required in 16% (20%/10% in definite/probable MD) and intratympanic gentamicin or surgeries in 9 (6%) patients with intractable MD. The percentage of intractable MD did not differ with coexistence of VM, though definite MD showed a significantly higher percentage of intractable MD than probable MD (6 vs. 0%, respectively, p = 0.002). Worsening hearing was more frequent in definite MD than probable MD (19 vs. 4%), and association of VM did not influence the incidence of worsening hearing. Coexistence of VM was about 30 to 40% in definite and probable MD, especially frequent in bilateral MD (77%) and women with probable MD (50%), requiring identification of coexisting VM while managing MD patients. Management outcomes and worsening hearing in MD patients are not dependent on the coexistence of VM, when both are managed.

Intratympanic Gentamicin Versus Labyrinthectomy: Inner Ear Sensitivity to Gentamicin and Impact on the Contralateral Labyrinth.

Objectives.To investigate the impact of labyrinthectomy and intratympanic (IT) gentamicin injections on the contralateral labyrinth, we also assessed the response of each individual semicircular canal to each IT gentamicin application.Methods.We performed a pilot observational study on tertiary, referral, academic settings. Thirteen patients with unilateral vestibular pathology were organized into two groups, group I (seven patients) receiving IT gentamicin and group II undergoing labyrinthectomy (six patients). All patients underwent six-canal video-head-impulse test in predetermined time intervals. Patients receiving gentamicin were additionally tested 3 to 5 days after every sequential injection, until all ipsilateral canals were ablated, to determine the order of response to gentamicin. We recorded the vestibular-ocular reflex gains and the presence of covert/overt saccades for each canal.Results.The posttreatment ipsilateral gains were abnormal. No patient from the gentamicin group developed abnormal contralateral responses, while patients undergoing labyrinthectomy had abnormal contralateral responses from at least one canal, even several months posttreatment. Finally, the lateral semicircular canal was the first one to be affected by IT gentamicin followed by the posterior canal: the superior canal was ablated last.Conclusion.In our study, labyrinthectomy had an impact on the responses recorded from the contralateral ear, while IT gentamicin ablated the ipsilateral labyrinthine function without affecting the contralateral responses, possibly because of a milder, more gradual impact. We also show for the first time the order that IT gentamicin application affects the semicircular canals, with the lateral being the first to be affected.