Transtympanic Electrocochleography Research Articles

Clinical, oculographic and vestibular test characteristics of Ménière's disease.

Seventy Ménière's disease (MD) patients with spontaneous vertigo (100%), unilateral aural fullness (57.1%), tinnitus (78.6%), and subjective hearing loss (75.7%) self-recorded nystagmus during their episodes of vertigo using portable video oculography goggles. All demonstrated ictal spontaneous nystagmus, horizontal in 94.3% (n = 66) and vertical in 5.7% (n = 4), with a mean slow-phase velocity (SPV) of 42.8 ± 31.1°/s (range 5.3-160.1). Direction reversal of spontaneous horizontal nystagmus was captured in 58.6%, within the same episode in 34.3%, and over different days in 24.3%. In 18.6%, we observed ipsiversive then contraversive nystagmus, and in 12.9% contraversive to ipsiversive direction reversal. Ictal nystagmus SPV (42.8 ± 31.1°/s) was significantly faster than interictal (1.4 ± 3.1°/s, p < 0.001, CI 34.277-48.776). Compared to age-matched healthy controls, interictal video head impulse test gains in MD ears were significantly lower, cumulative and first saccade (S1) amplitudes were significantly larger, and S1 peak velocities were significantly faster (p = 0.038/0.019/0.008/ < 0.001, CI 0.002-0.071/0.130-1.444/0.138-0.909/14.614-41.506). Audiometry showed asymmetrically increased thresholds in 100% of MD ears (n = 70). Significant caloric, air-conducted (AC) cervical vestibular-evoked myogenic potential (VEMP), and AC ocular VEMP asymmetries were found in 61.4, 37.9, and 44.4% of patients (MD ear reduced). Transtympanic electrocochleography tested in 36 ears (23 patients) showed 81.8% of MD ears had a positive result for hydrops (either a summating potential at 1/2kHz < - 6µV, or an SP/AP ratio > 40%). Using ictal nystagmus findings of SPV > 12°/s, and a caloric canal paresis > 25%, we correctly separated a diagnosis MD from Vestibular Migraine with a sensitivity and specificity of 95.7% and 85.1% (CI 0.89-0.97).

Cochlear Synaptopathy due to Mutations in OTOF Gene May Result in Stable Mild Hearing Loss and Severe Impairment of Speech Perception.

Congenital profound hearing loss with preserved cochlear outer hair cell activity (otoacoustic emissions and cochlear microphonic) is the most common phenotype associated with mutations in the OTOF gene. The aim of this study was to investigate the pathophysiological mechanisms behind the auditory dysfunction in five patients (2 adults and 3 children) carrying biallelic mutations in OTOF, who showed an uncommon phenotype of mild hearing impairment associated with severe difficulties in speech perception and delay of language development. Patients underwent audiometric assessment with pure-tone and speech perception evaluation, and otoacoustic emissions and auditory brainstem response recording. Cochlear potentials were recorded in all subjects through transtympanic electrocochleography in response to clicks delivered in the free field from 120 to 60 dB peak equivalent SPL and were compared to recordings obtained from 20 normally hearing controls and from eight children with profound deafness due to mutations in the OTOF gene. Three patients out of five underwent unilateral cochlear implantation. Speech perception measures and electrically evoked auditory nerve potentials were obtained within 1 year of cochlear implant use. Pathogenic mutations in the two alleles of OTOF were found in all five patients, and five novel mutations were identified. Hearing thresholds indicated mild hearing loss in four patients and moderate hearing loss in one. Distortion product otoacoustic emissions were recorded in all subjects, whereas auditory brainstem responses were absent in all but two patients, who showed a delayed wave V in one ear. In electrocochleography recordings, cochlear microphonics and summating potentials showed normal latency and peak amplitude, consistently with preservation of both outer and inner hair cell activity. In contrast, the neural compound action potential recorded in normally hearing controls was replaced by a prolonged, low-amplitude negative response. No differences in cochlear potentials were found between OTOF subjects showing mild or profound hearing loss. Electrical stimulation through the cochlear implant improved speech perception and restored synchronized auditory nerve responses in all cochlear implant recipients. These findings indicate that disordered synchrony in auditory fiber activity underlies the impairment of speech perception in patients carrying biallelic mutations in OTOF gene who show a stable phenotype of mild hearing loss. Abnormal nerve synchrony with preservation of hearing sensitivity is consistent with selective impairment of vesicle replenishment at the ribbon synapses with relative preservation of synaptic exocytosis. Cochlear implants are effective in restoring speech perception and synchronous activation of the auditory pathway by directly stimulating auditory fibers.

Detailed insight into transtympanic electrocochleography (TT-ECochG) and direct cochlear nerve action potential (CNAP) for intraoperative hearing monitoring in patients with vestibular schwannoma - methodology of measurements and interpretation of results.

&lt;b&gt;Background:&lt;/b&gt; The aim was to present the methodology and interpretation of intraoperative hearing monitoring with simultaneous Transtympanic Electrocochleography (TT-ECochG) and direct Cochlear Nerve Action Potential (CNAP) measurements during vestibular schwannoma removal. &lt;br&gt;&lt;b&gt;Materials and Methods:&lt;/b&gt; Detailed methodology of measurements and interpretation of results are presented in three exemplary patients who underwent tumor removal via middle fossa approach (MFA) with the use of intraoperative monitoring of hearing with TT-ECochG and direct CNAP performed in real time. In addition, all responses were automatically recorded and stored along with surgical information and subjected to detailed analyses and calculation after surgery. &lt;br&gt;&lt;b&gt;Results:&lt;/b&gt; The following changes in TT-ECochG and direct CNAP responses were observed: Patient #1 - TT-ECochG and CNAP responses with minor, but transient, morphology changes (hearing was preserved); Patient #2 - CNAP responses changed significantly but, temporarily, from triphasic into biphasic responses later, with marked but partially reversible desynchronization of CNAP; changes in TT-ECochG responses were also observed but, at the end, returned to baseline (surgery-related deterioration of hearing); Patient #3 - irreversible changes of TT-ECochG and direct CNAP (complete loss of hearing). &lt;br&gt;&lt;b&gt;Conclusions:&lt;/b&gt; A combination of TT-ECochG and direct CNAP allows for real-time monitoring of auditory function during vestibular schwannoma resection and surgical manipulation which contribute to the risk of hearing loss. Therefore, the surgeon can be instantly informed about changes which could increase the possibility of preserving the patient's hearing.

Hearing Dysfunction in a Large Family Affected by Dominant Optic Atrophy (OPA8-Related DOA): A Human Model of Hidden Auditory Neuropathy.

Hidden auditory neuropathy is characterized by reduced performances in challenging auditory tasks with the preservation of hearing thresholds, resulting from diffuse loss of cochlear inner hair cell (IHC) synapses following primary degeneration of unmyelinated terminals of auditory fibers. We report the audiological and electrophysiological findings collected from 10 members (4 males, 6 females) of a large Italian family affected by dominant optic atrophy, associated with the OPA8 locus, who complained of difficulties in understanding speech in the presence of noise. The patients were pooled into two groups, one consisting of 4 young adults (19–50 years) with normal hearing thresholds, and the other made up of 6 patients of an older age (55–72 years) showing mild hearing loss. Speech perception scores were normal in the first group and decreased in the second. Otoacoustic emissions (OAEs) and cochlear microphonics (CMs) recordings were consistent with preservation of outer hair cell (OHC) function in all patients, whereas auditory brainstem responses (ABRs) showed attenuated amplitudes in the first group and severe abnormalities in the second. Middle ear acoustic reflexes had delayed peak latencies in all patients in comparison with normally hearing individuals. Transtympanic electrocochleography (ECochG) recordings in response to 0.1 ms clicks at intensities from 120 to 60 dB peak equivalent SPL showed a reduction in amplitude of both summating potential (SP) and compound action potential (CAP) together with delayed CAP peak latencies and prolonged CAP duration in all patients in comparison with a control group of 20 normally hearing individuals. These findings indicate that underlying the hearing impairment in OPA8 patients is hidden AN resulting from diffuse loss of IHCs synapses. At an early stage the functional alterations only consist of abnormalities of ABR and ECochG potentials with increased latencies of acoustic reflexes, whereas reduction in speech perception scores become apparent with progression of the disease. Central mechanisms increasing the cortical gain are likely to compensate for the reduction of cochlear input.

Tone Burst Electrocochleography for the Diagnosis of Clinically Certain Meniere's Disease.

The technique of transtympanic electrocochleography was initially developed as an objective hearing threshold test by Eggermont. Gibson et al. (1977) claimed that an enlarged direct current component of the action potential (AP) called the summating potential (SP) is an indication of endolymphatic hydrops, later confirmed by Coates who proposed an SP/AP ratio measure. This led to numerous publications using diagnostic ratios of 0.33–0.35. The insensitivity led to an eventual disenchantment with the test as a reliable objective test for Meniere's disease. It was further confused by audiologists employing remote canal or ear drum electrodes which give a response about one-fourth of the magnitude obtained by an electrode in contact with the cochlea. Subsequently Gibson stated that an SP/AP ratio of <0.5 is not diagnostic for hydrops. He then showed that a tone burst stimulus gave the test a significantly higher sensitivity and specificity, which has been supported by others. On MRI inner ear imaging with gadolinium hydrops can be seen, but the quality of images and what is seen may vary according to brand of scanner, settings, mode of gadolinium administration, and the possibility that gadolinium entry may favor the vestibule. Transtympanic tone burst electrocochleography is to date the simplest, cheapest and most sensitive technique for detecting cochlear endolymphatic hydrops to confirm a diagnosis of Meniere's disease.

Elektrokochleografie mit Trommelfell-, Gehörgangs- und transtympanaler Elektrode bei V.a. Morbus Menière

Aim of this study was to explore the clinical value of non-invasive recordings of electrocochleography in comparison to the use of invasive electrodes for the diagnosis of endolymphatic hydrops in patients with suspicious Morbus Menière. 15 patients with clinical suspicion of Morbus Menière underwent electrocochleography with transtympanic needle-electrode as well as tympanic membrane electrode. 10 patients received electrocochleography with transtympanic needle-electrode and ear canal electrode. A control group of 12 healthy adults was evaluated using tympanic membrane electrode. The negative electrode was placed on the ipsilateral mastoid, the ground electrode in the middle of the forehead. For stimulation broadband click stimulus as well as long tone bursts of 1, 2 and 4 kHz were applied. In addition the impedance of the electrode was registered. While transtympanic electrocochleography gave reliable results in 100% of these cases, extratympanic recordings often manifested poor wave morphology. The electrocochleographic measures following stimulation with 1 and 2 kHz long tone bursts were the best measures to identify endolymphatic hydrops. This was the case with transtympanic as well as with tympanic membrane electrodes. There was no correlation between impedance and wave morphology. For the evaluation of Morbus Menière non-invasive electrocochleography showed good results using a tympanic canal electrode with 1 and 2 kHz tone bursts. Yet in unclear cases transtympanic electrocochleography should be preferred.

OPA1-related auditory neuropathy: site of lesion and outcome of cochlear implantation.

Hearing impairment is the second most prevalent clinical feature after optic atrophy in dominant optic atrophy associated with mutations in the OPA1 gene. In this study we characterized the hearing dysfunction in OPA1-linked disorders and provided effective rehabilitative options to improve speech perception. We studied two groups of OPA1 subjects, one comprising 11 patients (seven males; age range 13-79 years) carrying OPA1 mutations inducing haploinsufficiency, the other, 10 subjects (three males; age range 5-58 years) carrying OPA1 missense mutations. Both groups underwent audiometric assessment with pure tone and speech perception evaluation, and otoacoustic emissions and auditory brainstem response recording. Cochlear potentials were recorded through transtympanic electrocochleography from the group of patients harbouring OPA1 missense mutations and were compared to recordings obtained from 20 control subjects with normal hearing and from 19 subjects with cochlear hearing loss. Eight patients carrying OPA1 missense mutations underwent cochlear implantation. Speech perception measures and electrically-evoked auditory nerve and brainstem responses were obtained after 1 year of cochlear implant use. Nine of 11 patients carrying OPA1 mutations inducing haploinsufficiency had normal hearing function. In contrast, all but one subject harbouring OPA1 missense mutations displayed impaired speech perception, abnormal brainstem responses and presence of otoacoustic emissions consistent with auditory neuropathy. In electrocochleography recordings, cochlear microphonic had enhanced amplitudes while summating potential showed normal latency and peak amplitude consistent with preservation of both outer and inner hair cell activities. After cancelling the cochlear microphonic, the synchronized neural response seen in both normally-hearing controls and subjects with cochlear hearing loss was replaced by a prolonged, low-amplitude negative potential that decreased in both amplitude and duration during rapid stimulation consistent with neural generation. The use of cochlear implant improved speech perception in all but one patient. Brainstem potentials were recorded in response to electrical stimulation in five of six subjects, whereas no compound action potential was evoked from the auditory nerve through the cochlear implant. These findings indicate that underlying the hearing impairment in patients carrying OPA1 missense mutations is a disordered synchrony in auditory nerve fibre activity resulting from neural degeneration affecting the terminal dendrites. Cochlear implantation improves speech perception and synchronous activation of auditory pathways by bypassing the site of lesion.

Is Meniere Disease Caused by a Pathological Immune Response?

The etiology of Meniere disease (MD) is unknown. Among the several factors which can provoke the disease is a pathological immune response. Objective: To investigate whether MD is due to a pathological immune reaction. Materials and methods: Immunological assay (IA) was evaluated in a consecutive study on 159 patients with MD (mean age 47.8. years) and the results compared with those from 26 patients operated on because of vestibular schwannoma (VS, mean age 54.1 years), who served as a control group. In cases of MD, transtympanic electrocochleography (ECoG) and hearing threshold were measured. Results: The average hearing level (HL) in the affected ears of patients with MD was 30 dB. Evidence of abnormal plasma protein pattern was found in 127 MD patients (80%). Elevations were found in β1-globulin (54.5%), β2-globulin (26.5%), a2-globulin (34.3%), g-globulin (17.3%), complement (CH100, 36.4%) and antinuclear antibodies (ANA, 43.4%). The onset of the disease did not correlate with the level of the plasma protein neither with the level of IgG titers. Conclusion: Elevated certain plasma proteins in patients with Meniere’s disease could be a sign that Meniere’s disease is a consequence of pathological immune reaction.

Patterns of hearing loss following retrosigmoid excision of unilateral vestibular schwannoma.

Objectives To determine the pattern of auditory responses, time-course of hearing deterioration, and possible site of lesion following retrosigmoid excision of unilateral vestibular schwannomas. Design Prospective, nonrandomized, observational pilot study. Setting Tertiary referral medical center. Main outcome measures Preoperative and postoperative pure-tone and speech audiometry, auditory brainstem response testing, and distortion product otoacoustic emissions were performed in 20 patients. Testing was conducted every 24 hours for the duration of hospitalization. Transtympanic electrocochleography was performed if delayed deterioration of auditory responses was documented. Results Of the 20 patients, 7 had no discernible cochlear nerve at the end of the procedure. Of the 13 patients with an intact nerve, 6 retained hearing, 3 with evidence of reduced neural function. Of the 7 who lost hearing despite an intact nerve, 5 lost at least cochlear and possibly also neural function, and 1 had reduced neural function but retained cochlear function. There were two examples of delayed deterioration of cochlear nerve responses. Conclusions Hearing loss following retrosigmoid removal of vestibular schwannomas most often involves loss of at least cochlear function, possibly in addition to neural damage. In a smaller number of cases anacusis or hearing deterioration can be attributed to purely neural trauma.

Comparison of Transtympanic and Extratympanic Electrocochleography

Electrocochleography (ECoG) has been an important tool in the diagnosis of Meniere’s disease or endolymphatic hydrops. There are two methods employed, transtympanic and extratympanic. Many have regarded the results of these methods as being equally reliable. The purpose of this study is to determine any differences in sensitivity between the two methods. In this study patients with known endolymphatic hydrops or Meniere’s disease underwent ECoG testing with both the extratympanic method and the transtympanic method on the same day in the same ear. The results show a significant difference between the two methods, with the transtympanic wave values being smaller and therefore more sensitive than the extratympanic method. In addition, transtympanic ECoG resulted in better waveform morphology and better correlation with the audiometric findings in endolymphatic hydrops and Meniere’s disease. The results emphasize the superior role of transtympanic ECoG over extratympanic ECoG as a valuable component in the confirmation of Meniere’s disease or endolymphatic hydrops along with history and audiometric findings characteristic of the disease. Implications of the study promote the use of transtympanic ECoG rather than extratympanic ECoG in patients with symptoms suggestive of Meniere’s disease or endolymphatic hydrops.

Does ‘Cochlear Ménière’s Disease’ Exist? An Electrocochleographic and Audiometric Study

Introduction: According to current diagnostic criteria, patients exhibiting only cochlear symptoms without vertigo cannot be diagnosed with Ménière’s disease (MD). The recently reported Ménière’s Disease Index (MDI) combines audiometric and electrocochleographic parameters in a multidimensional measure correlating with the clinical degrees of MD. Materials and Methods: Twenty-one patients with hearing loss, tinnitus and aural fullness, but without vertigo, underwent transtympanic electrocochleography. Based on the previously reported formula, the MDI value for every patient was calculated. Results: Mean MDI value was 5.7 on a scale from 0 (mean value of non-MD patients) to 10 (mean value of definite MD patients). Conclusions: We can thus hypothesize that, based on audiometry and electrocochleography, ‘cochlear MD’ patients may represent a separate clinical entity with Ménière-like pathophysiology or underlying endolymphatic hydrops.

Differences and Supplemental use of Transtympanic Electrocochleography and Auditory Brainstem Response Audiometry for Intraoperative Neuromonitoring

Differences and Supplemental use of Transtympanic Electrocochleography and Auditory Brainstem Response Audiometry for Intraoperative Neuromonitoring

Transtympanic Electrocochleography for the Diagnosis of Ménière's Disease

This paper evaluated the diagnostic power of electrocochleography (ECochG) in detecting Ménière's disease (MD) as compared with two subjective assessment methods, including the clinical guidelines provided by the American Academy of Otolaryngology—Head and Neck Surgery Committee on Hearing Equilibrium and the Gibson score. A retrospective study of 250 suspected MD cases was conducted. The agreement between the three assessment methods was found to be relatively high, with a total reliability being higher than 70%. Participants who tested “positive” with ECochG exhibited a higher occurrence rate of asymmetric hearing threshold as well as the four MD symptoms, namely, vertigo, hearing loss, tinnitus, and aural fullness. The “positive” ECochG group also showed a high correlation between the ECochG measures in response to stimuli at adjacent frequency ranges, suggesting that the interfrequency ECochG correspondence may be sensitive to the presence of endolymphatic hydrops and thus may serve as a useful diagnostic marker for MD.

Magnetic resonance imaging for Ménière's disease: correlation with tone burst electrocochleography

The newly developed use of magnetic resonance imaging of the human inner ear, on a 3 Tesla scanner with intratympanically administered gadolinium, can now reliably distinguish perilymph from endolymph and visually confirm the presence or absence of endolymphatic hydrops. Transtympanic tone burst electrocochleography is an established, and under-utilised evoked response electrophysiological test for hydrops, but it relies on a symptom score to indicate the likelihood of hydrops being present. The current diagnostic criteria for Ménière's disease make no allowance for any in vivo test, making diagnostic errors likely. In this small pilot study of three patients undergoing tone burst electrocochleography, subsequent magnetic resonance imaging confirmed or excluded the hydrops that the electrocochleography predicted. Magnetic resonance imaging of the inner ear is a safe technique that can be performed in conjunction with imaging of the VIIIth cranial nerves. As this report comprised only three patients in a pilot study, rigorous clinical studies are required to define the possible role of magnetic resonance imaging in the diagnosis of Ménière's disease.

The Ménière's Disease Index

Diagnosis of Ménière's disease (MD) is made according to the diagnostic criteria proposed by the American Academy of Otolaryngology-Head and Neck Surgery. Value of transtympanic electrocochleography (TT-ECoG) in diagnosis of endolymphatic hydrops remains controversial. The aim of our study is to determine which combination of audiometric and electrocochleographic measures correlates best with the clinical diagnosis of endolymphatic hydrops. Retrospective analysis of 109 consecutive patients undergoing TT-ECoG. All 131 tested ears were divided in categories: definite MD, probable MD, possible MD, and non-MD, according to the criteria of the American Academy of Otolaryngology-Head and Neck Surgery. TT-ECoG was performed using clicks and tone burst stimuli. Audiometric and electrocochleographic data were collected and analyzed. TT-ECoG with tone burst stimuli correctly identified 91% of the definite MD group and 71% of the non-MD group. Using binary logistic regression followed by discriminant analysis, we found a linear combination of 3 variables (air-conduction threshold at 125 and 8,000 Hz, and TT-ECoG summating potential amplitude at 4,000 Hz) that showed a good correlation with the clinical diagnosis of definite MD. This combination was able to identify 98% of the non-MD cases and 94% of the definite MD cases. The Ménière's Disease Index was created to scale the degree of MD from 0 (non-MD) to 10 (definite MD). The Ménière's Disease Index is an objective measure that correlates with the clinical degrees of MD. Future validation is still needed to confirm the added diagnostic and clinical value of this method.

Does intratympanic gadolinium injection predict efficacy of gentamicin partial chemolabyrinthectomy in Menière’s disease patients?

Using actual diagnostic criteria, the diagnosis of certain Menière's disease remains impossible during life without histopathologic confirmation. Assessing the value of a diagnostic test is difficult due to the lack of a gold standard. Recent studies reported on the use of MRI after intratympanic gadolinium injection to demonstrate endolymphatic hydrops in vivo. We evaluate whether MRI after intratympanic gadolinium administration is useful for predicting the effect and outcome of intratympanic gentamicin therapy. The correlation between transtympanic electrocochleographic (TT-ECoG) results and hydrops grade on MRI images is also investigated. Twelve definite Menière's disease patients with incapacitating vertigo attacks, not responding to drug and behavioral treatment, were selected for partial chemolabyrinthectomy with intratympanic gentamicin. All patients underwent transtympanic electrocochleography followed by surgical middle ear inspection, partial chemolabyrinthectomy (gentamicin solution 40 mg/ml applied during 60 min) and intratympanic gadolinium injection with clear exposure of the round window membrane. The MR images were reviewed and a hydrops grade was assigned. Correlation between the hydrops grade and the electrocochleographic data was assessed. Only 5 of 12 patients showed gadolinium enhancement in the inner ear. However, 6 of the 7 patients that did not show postoperative intracochlear or intralabyrinthine gadolinium distribution did report the clinical improvement after intratympanic gentamicin therapy. Hydrops grade correlated with the result of transtympanic electrocochleography in four of five cases that showed gadolinium enhancement. We conclude that the use of intratympanic gadolinium has no added value in predicting the clinical outcome of intratympanic gentamicin application. However, based on these data, a correlation between the result of TT-ECoG and hydrops grading on MRI images can be suggested.

Presynaptic and postsynaptic mechanisms underlying auditory neuropathy in patients with mutations in theOTOForOPA1gene

AbstractObjective: Our objective was to compare acoustically- and electrically-evoked potentials of the auditory nerve in patients with postsynaptic or presynaptic auditory neuropathy with underlying mutations in the OPA1 or OTOF gene. Study design: Transtympanic electrocochleography (ECochG) was recorded from two adult patients carrying the R445H OPA1 mutation, and from five children with mutations in the OTOF gene. Cochlear potentials to clicks or tone-bursts were compared to recordings obtained from 16 normally hearing subjects. Electrically-evoked neural responses recorded through the cochlear implant were also obtained. Results: The cochlear microphonic (CM) was recorded from all subjects, with normal amplitudes. After cancelling the CM, cochlear potentials were of negative polarity with reduced amplitude and prolonged duration compared to controls in both groups of patients. Prolonged negative responses were recorded as low as 50–90dB below behavioural threshold in subjects with OTOF mutations where...

A comparison of three methods of using transtympanic electrocochleography for the diagnosis of Meniere's disease: Click summating potential measurements, tone burst summating potential amplitude measurements, and biasing of the summating potential using a low frequency tone

Conclusion: Stimulus biasing modulated the amplitude of the tone burst evoked summating potential (SP) in ears affected by Meniere's disease less than in normal ears. A reduced SP bias ratio added diagnostic accuracy for the diagnosis of Meniere's disease. Objectives: To evaluate the effect of stimulus biasing on the human tone burst SP, and to determine if stimulus biasing could contribute to the electrocochleography as a means of confirming the diagnosis of Meniere's disease. Patients and methods: Patients referred for transtympanic electrocochleography (TT ECochG) were assessed prospectively on clinical grounds according to the AAO-HNS criteria and a scale devised by one of the authors. A Meniere's group of ears and a non-Meniere's group of ears was determined. The ears opposite a Meniere's ear were not included in the analysis. The ratio of the click SP amplitude and the action potential (AP) amplitude (SP/AP ratio), the tone burst SP amplitude at 500 Hz,1 kHz, 2kHz and 8 kHz, and the effect of stimulus biasing on the tone burst SP were measured. Results: A unipolar stimulus biasing ratio established for the modulation of the 1 kHz tone burst SP separated the Meniere's ears from the non-Meniere's ears with a sensitivity of 85% at a specificity of 80.6% and the difference between groups reached statistical significance (p=0.016). The 1 kHz SP amplitude measurements and the stimulus biasing measurements were superior to the click SP/AP ratio for identifying the Meniere's group. A combination of 1 kHz SP amplitude measurements and SP bias ratio separated the Meniere's ears from the non-Meniere's ears with an accuracy of 85%.

Alterations in cochlear function during induced acute hyperinsulinemia in an animal model

Hyperinsulinism secondary to peripheral insulin resistance has been described as the most frequent etiologic factor in cochlear and vestibular syndromes. AIM: This experimental study recorded and analyzed evoked auditory potential changes using transtympanic electrocochleography (EcochG) during induced acute hyperinsulinism in an animal model. MATERIALS AND METHODS: Six adult male sheep were randomly divided into 2 groups. The animals were submitted to EcochG under general anesthesia, and a peripheral blood sample was collected to measure glycemia and insulinemia. Animals in the intervention group (n=3) received regular human insulin IV (0.1 U/kg). The control group (n=3) received saline solution. Glycemia and insulinemia were measured simultaneously with the recording of evoked potentials at 10-minute intervals during 90 minutes. RESULTS: The intervention group experienced a progressive suppression in action potential amplitude when compared to the control group (p=0.001). CONCLUSION: Data strongly suggest that acute induced hyperinsulinism suppresses cochlear function. Results may be attributed to loss of Na+K+ATPase activity in the stria vascularis, leading to loss of endocochlear potential and subsequent depolarization of cochlear hair cells as well as of neural cells in the auditory portion of cranial nerve VIII.

Mutation of OPA1 gene causes deafness by affecting function of auditory nerve terminals

Autosomal dominant optic atrophy (DOA) is a retinal neuronal degenerative disease characterized by a progressive bilateral visual loss. We report on two affected members of a family with dominantly inherited neuropathy of both optic and auditory nerves expressed by impaired visual acuity, moderate pure tone hearing loss, and marked loss of speech perception. We investigated cochlear abnormalities accompanying the hearing loss and the effects of cochlear implantation. We sequenced OPA1 gene and recorded cochlear receptor and neural potentials before cochlear implantation. Genetic analysis identified R445H mutation in OPA1 gene. Audiological studies showed preserved cochlear receptor outer hair cell activities (otoacoustic emissions) and absent or abnormally delayed auditory brainstem responses (ABRs). Trans-tympanic electrocochleography (ECochG) showed prolonged low amplitude negative potentials without auditory nerve compound action potentials. The latency of onset of the cochlear potentials was within the normal range found for inner hair cell summating receptor potentials. The duration of the negative potential was reduced to normal during rapid stimulation consistent with adaptation of neural sources generating prolonged cochlear potentials. Both subjects had cochlear implants placed with restoration of hearing thresholds, speech perception, and synchronous activity in auditory brainstem pathways. The results suggest that deafness accompanying this OPA1 mutation is due to altered function of terminal unmyelinated portions of auditory nerve. Electrical stimulation of the cochlea activated proximal myelinated portions of auditory nerve to restore hearing.