Early Loss of Spiral Ganglion Neurons in the Auditory System after Noise Trauma.

INTRODUCTION: Noise-induced hearing loss is one of the most frequent recognized occupational diseases. The time course of the involved pathologies is still under investigation. Several studies have demonstrated an acute damage of the sensory tissue, but only few experiments investigated the degeneration of (type I) spiral ganglion neurons (SGNs), representing the primary neurons in the auditory system. The aim of the present study was to investigate the time course of SGN degeneration within a 7-day period after traumatic noise exposure starting immediately after trauma. METHODS: Young adult normal hearing mice were noise exposed for 3 h with a broadband noise (5-20 kHz) at 115 dB SPL. Auditory threshold shift was measured by auditory brainstem recordings, and SGN densities were analyzed at different time points during the first week after acoustic trauma. RESULTS: Significant reduction of SGN densities was detected and is accompanied by a significant hearing loss. Degeneration starts within hours after the applied trauma, further progressing within days post-exposure. DISCUSSION: Early neurodegeneration in the auditory periphery seems to be induced by direct overstimulation of the auditory nerve fibers. SGN loss is supposed to be a result of inflammatory responses and neural deprivation, leading to permanent hearing loss and auditory processing deficits.

Intra-cochlear electrode position impacts the preservation of residual hearing in an animal model of cochlear implant surgery.

INTRODUCTION: Preservation of residual hearing after cochlear implantation remains challenging. There are several approaches to preserve residual hearing, but the configuration of the implant electrode array seems to play a major role. Lateral wall electrode arrays are seemingly more favorable in this context. To date, there are no experimental data available which correlate the spatial electrode position in the scala tympani with the extent of hearing preservation. METHODS: Based on µCT imaging data, this study analyses the exact position of a pure- silicone electrode array inserted into the cochlea of four guinea pigs. Array position data were correlated with the extent of hearing loss after implantation, measured using auditory brainstem measurements in the frequency range of the area occupied by the electrode array area as well as apical to the array. RESULTS: The use of pure-silicone arrays without electrodes resulted in artifact-free, high-resolution µCT images that allowed precise determination of the arrays' positions within the scala tympani. The electrode arrays' locations ranged from peri-modiolar to an anti-modiolar. These revealed a correlation of a lower postoperative hearing loss with a higher spatial proximity to the lateral wall. This correlation was found in the low-frequency range only. A significant correlation between the interindividual differences in the diameter of the scala tympani and the postoperative hearing loss could not be observed. CONCLUSION: This study demonstrates the importance of the intra-cochlear electrode array's position for the preservation of residual hearing. The advantage of such an electrode array's position approximated to the lateral wall suggests, at least for this type of electrode array applied in the guinea pig, would be advantageous in the preservation of residual hearing for the apical part of the cochlea, beyond the area occupied by the electrode array.

Neuroprotective Effect of Near-Infrared Light in an Animal Model of CI Surgery.

INTRODUCTION: The preservation of residual hearing has become an important consideration in cochlear implant (CI) recipients in recent years. It was the aim of the present animal experimental study to investigate the influence of a pretreatment with near-infrared (NIR) light on preservation of sensory hair cells and residual hearing after cochlear implantation. METHODS: NIR was applied unilaterally (15 min, 808 nm, 120 mW) to 8 guinea pigs, immediately before a bilateral scala tympani CI electrode insertion was performed. The nonirradiated (contralateral) side served as control. Twenty-eight days postoperatively, auditory brainstem responses (ABRs) were registered from both ears to screen for hearing loss. Thereafter, the animals were sacrificed and inner hair cells (IHCs) and outer hair cells (OHCs) were counted and compared between NIR-pretreated and control (contralateral) cochleae. RESULTS: There was no IHC loss upon cochlear implantation. OHC loss was most prominent on both sides at the apical part of the cochlea. NIR pretreatment led to a statistically significant reduction in OHC loss (by 39.8%). ABR recordings (across the frequencies 4-32 kHz) showed a statistically significant difference between the 2 groups and corresponds well with the apical structural damage. Hearing loss was reduced by about 20 dB on average for the NIR-pretreated group (p ≤ 0.05). DISCUSSION/CONCLUSION: A single NIR pretreatment in this animal model of CI surgery appears to be neuroprotective for residual hearing. This is in line with other studies where several NIR posttreatments have protected cochlear and other neural tissues. NIR pretreatment is an inexpensive, effective, and noninvasive approach that can complement other ways of preserving residual hearing and, hence, should deserve further clinical evaluation in CI patients.

Can hearing amplification improve presbyvestibulopathy and/or the risk-to-fall ?

PURPOSE: The decline of sensory systems during aging has been widely investigated and several papers have correlated the visual, hearing and vestibular systems and the consequences of their functional degeneration. Hearing loss and presbyvestibulopathy have been found to be positively correlated as is with the risk-to-fall. MATERIAL AND METHODS: The present study was therefore designed as systematic review (due to PRISMA criteria) which should correlate hearing amplification by hearing aids and/or cochlear implants with balance outcome. However, the literature review (Cochrane, PubMed) revealed ten paper (prospective, controlled trials and acute trials) with heterogenous patient popiulations and non-uniform outcome measures (i.e., gait analysis, questionnaires, postural stabilometry) so that no quantitative, statistical analysis could be performed. RESULTS: The qualitative analysis oft he identified studies showed that hearing amplification in the elderly improves spatio-temporal orientation (particularly with cochlear implants) and that the process of utilizing auditory information for balance control takes some time (i.e., the neuroplasticity-based, learning processes), usually some months in cochlear implantees. DISCUSSION: Hearing and balance function degenerate independently from each other and large interindividual differences require a separate neurotological examination of each patient. However, hearing amplification is most helpful to improve postural stability, particularly in the elderly. Future research should focus on controlled, prospective clinical trials where a standardized test battery covering the audiological and neurotological profile of each elderly patient pre/post prescription of hearing aids and/or cochlear implantation should be followed up (for at least 1 year) so that also the balance improvements and the risk-to-fall can be reliably assessed (e.g., by mobile posturography and standardized questionnaires, e.g., the DHI).

Constant severe imbalance following traumatic otoconial loss: a new explanation of residual dizziness.

Benign paroxysmal positional vertigo (BPPV) is the most common type of vertigo, caused by otoconia falling from the utricle into a semicircular canal (SCC). After successful repositioning maneuvers residual dizziness (RD) has been described and several reasons are used to explain RD. It can last for only a few days or weeks, but also much longer. We present a patient with a severe traumatic loss of otoconia from both maculae utriculi and a persistent imbalance more than 9 years. We think that the loss of otoconia from the utricular and probably also saccular macula induced a sudden reduction of her ability to sense gravity thus logically explaining her symptoms. We show the vestibular test results also supporting our hypothesis and we extrapolate this support to other forms of so far unexplained dizziness especially increasing imbalance with aging. We also discuss the normal c- and oVEMP indicating intact haircell function and supporting our hypothesis of isolated otoconial loss as the major cause for imbalance.

Correction to: Constant severe imbalance following traumatic otoconial loss: a new explanation of residual dizziness.

The original article was updated.

Apoptotic mechanisms after repeated noise trauma in the mouse medial geniculate body and primary auditory cortex.

A correlation between noise-induced apoptosis and cell loss has previously been shown after a single noise exposure in the cochlear nucleus, inferior colliculus, medial geniculate body (MGB) and primary auditory cortex (AI). However, repeated noise exposure is the most common situation in humans and a major risk factor for the induction of noise-induced hearing loss (NIHL). The present investigation measured cell death pathways using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) in the dorsal, medial and ventral MGB (dMGB, mMGB and vMGB) and six layers of the AI (AI-1 to AI-6) in mice (NMRI strain) after a second noise exposure (double-exposure group). Therefore, a single noise exposure group has been investigated 7 (7-day-group-single) or 14 days (14-day-group-single) after noise exposure (3 h, 5-20 kHz, 115 dB SPL peak-to-peak). The double-exposure group received the same noise trauma for a second time 7 days after the initial exposure and was either TUNEL-stained immediately (7-day-group-double) or 1 week later (14-day-group-double) and data were compared to the corresponding single-trauma group as well as to an unexposed control group. It was shown that TUNEL increased immediately after the second noise exposure in AI-3 and stayed upregulated in the 14-day-group-double. A significant increase in TUNEL was also seen in the 14-day-group-double in vMGB, mMGB and AI-1. The present results show for the first time the influence of a repeated noise trauma on cell death mechanisms in thalamic and cortical structures and might contribute to the understanding of pathophysiological findings and psychoacoustic phenomena accompanying NIHL.

Time course of cell death due to acoustic overstimulation in the mouse medial geniculate body and primary auditory cortex.

It has previously been shown that acoustic overstimulation induces cell death and extensive cell loss in key structures of the central auditory pathway. A correlation between noise-induced apoptosis and cell loss was hypothesized for the cochlear nucleus and colliculus inferior. To determine the role of cell death in noise-induced cell loss in thalamic and cortical structures, the present mouse study (NMRI strain) describes the time course following noise exposure of cell death mechanisms for the ventral medial geniculate body (vMGB), medial MGB (mMGB), and dorsal MGB (dMGB) and the six histological layers of the primary auditory cortex (AI 1-6). Therefore, a terminal deoxynucleotidyl transferase dioxyuridine triphosphate nick-end labeling assay (TUNEL) was performed in these structures 24 h, 7 days, and 14 days after noise exposure (3 h, 115 dB sound pressure level, 5-20 kHz), as well as in unexposed controls. In the dMGB, TUNEL was statistically significant elevated 24 h postexposure. AI-1 showed a decrease in TUNEL after 14 days. There was no statistically significant difference between groups for the other brain areas investigated. dMGB's widespread connection within the central auditory pathway and its nontonotopical organization might explain its prominent increase in TUNEL compared to the other MGB subdivisions and the AI. It is assumed that the onset and peak of noise-induced cell death is delayed in higher areas of the central auditory pathway and takes place between 24 h and 7 days postexposure in thalamic and cortical structures.

Sound and postural control during stance tasks in abnormal subjective haptic vertical.

BACKGROUND: Patients with vestibular impairment often suffer from postural instability. This could be compensated by other sensory systems such as the auditory system. OBJECTIVE: The aim of this study was to investigate whether auditory input improves postural stability in patients with abnormal subjective haptic vertical (SHV). METHODS: Participants (n = 13) with normal hearing and vision, but abnormal SHV participated. Participants performed standing on firm ground and foam support (eyes open/closed) and Tandem Romberg test (eyes closed) in quiet (reference), noise and with plugged ears. All tasks were conducted in a soundproofed and reverberant room. Postural stability was recorded close to the body's center of gravity. Reference conditions were compared with a control group. RESULTS: In only two tasks sway increased significantly when noise was presented during challenging tasks in the soundproofed room. Sway of the reference conditions did not differ significantly between control and study group. CONCLUSIONS: This study shows no influence of applied auditory stimulation on posture in participants with abnormal SHV in a reverberant room, but an adverse effect on balance during difficult tasks in the soundproofed room. Noise possibly masked auditory information that was helpful in improving posture in the quiet condition. Futhermore, noise might have distracted participants from maintaining balance.

Neurodegeneration after repeated noise trauma in the mouse lower auditory pathway.

High intensity noise exposure leads to a permanent shift in auditory thresholds (PTS), affecting both peripheral (cochlear) tissue and the central auditory system. Studies have shown that a noise-induced hearing loss results in significant cell loss in several auditory structures. Degeneration can be demonstrated within hours after noise exposure, particularly in the lower auditory pathway, and continues to progress over days and weeks following the trauma. However, there is limited knowledge about the effects of recurring acoustic trauma. Repeated noise exposure has been demonstrated to increase neuroplasticity and neural activity. Thus, the present study aimed to investigate the influence of a second noise exposure on the cytoarchitecture of key structures of the auditory pathway, including spiral ganglion neurons (SGN), the ventral and dorsal cochlear nucleus (VCN and DCN, respectively), and the inferior colliculus (IC). In the experiments, young adult normal hearing mice were exposed to noise once or twice (with the second trauma applied one week after the initial exposure) for 3 h, using broadband white noise (5 - 20 kHz) at 115 dB SPL. The cell densities in the investigated auditory structures significantly decreased in response to the initial noise exposure compared to unexposed control animals. These findings are consistent with earlier research, which demonstrated degeneration in the auditory pathway within the first week after acoustic trauma. Additionally, cell densities were significantly decreased after the second trauma, but this effect was only observed in the VCN, with no similar effects seen in the SGN, DCN, or IC. These results illustrate how repeated noise exposure influences the cytoarchitecture of the auditory system. It appears that an initial noise exposure primarily damages the lower auditory pathway, but surviving cellular structures may develop resistance to additional noise-induced injury.

Radiological control of the floating mass transducer attached to the round window.

The surgical rehabilitation of mixed hearing losses can be performed by coupling the floating mass transducer of the Vibrant Soundbridge to the round window. The quality of coupling the floating mass transducer to the round window is crucial for the audiological outcome. It was the aim of this study to further observe the different patterns of floating mass transducer position at the round window. We compared twenty patients with mixed hearing loss implanted with a floating mass transducer attached to the round window and 24 surgeries between 5/2007 and 6/2010. An evaluation of the chronological observation of the flat panel angiography-controlled position of the floating mass transducer at the round window with relation to the surgical report and the audiological outcome was done. We observed no changes in the mean pre- and postbone conduction thresholds. The floating mass transducer position was variable and could be radiologically classified and correlated with the audiologically outcome. A learning curve was observed from the earlier to later implantations. Postoperative, radiological evaluation of the location and angle of the floating mass transducer by means of flat panel tomography allowed us to classify the floating mass transducer position at the round window into 4 groups.

Influence of Auditory Information on Postural Control During Different Gait Tasks in the Elderly.

BACKGROUND: Hearing loss is frequently associated with reduced postural control. This is possibly not only related to simultaneous pathophysiological changes within the hearing and vestibular system. The auditory input itself could provide helpful information for maintaining postural control. Previous studies of our group already showed that continuous or interrupted white noise can significantly improve postural control during gait conditions in young healthy individuals. The present study aimed at investigating if those effects are also active in the elderly. METHODS: Elderly volunteers (mean age 67 years) without any history of disorders to influence gait performance successfully completed 5 walking tasks under 4 different acoustic conditions. Angular sway velocity was measured close to the center of gravity with the Vertiguard® system. RESULTS: Significant changes in body sway velocity were found in 4 of 5 investigated tasks. Only "walking with turning head in rhythm" was not associated with any change in the acoustic input. The sway increased by 8.9% during "walking with open eyes" in the pitch direction and by 11.5% during "tandem walking" in the roll direction if ear protection was applied. The sway was reduced by 9.1% during "walking over barriers" in the pitch direction and by 16.7% in the roll direction during "walking with closed eyes" if a stationary source of continuous white noise was presented. CONCLUSION: The data of the present study indicate that auditory information could significantly alter postural control during walking in the elderly. Continuous white noise seems to be helpful for maintaining balance in different walking tasks.

Short-term overstimulation affects peripheral but not central excitability in an animal model of cochlear implantation.

Objective: Upper current limits (C-levels) are sometimes extremely increased over time since this procedure can enhance speech perception. It should be clarified if a larger amount of electrical stimulation is tolerated by the remaining peripheral and central auditory pathway.Materials and Methods: An animal electrode array was inserted in mechanically deafened guinea pigs. C-levels were adjusted to a mean of approximately 10 CL ('LOS' group), 40 CL ('MOS' group) or 60 CL ('HOS' group) above the electrode specific electrically evoked compound action potential (eCAP) threshold. The stimulation was performed via a sound processor in standardized auditory environment. Implanted and not stimulated animals served as controls.Results: A significant eCAP threshold shift was observed in the 'HOS'-group aftereight hours of stimulation at basal electrodes. Electrically evoked auditory brainstem thresholds were stable over time in all stimulation groups. The ratio between eCAP- and eABR threshold shifts was significantly enhanced in the 'HOS'- group.Conclusion: Even short-time overstimulation reduces the excitability of peripheral but not central auditory structures. The changed relationship between the excitability of spiral ganglion neurons and inferior colliculus neurons seems to indicate an overstimulation. The results are of utmost importance for a safe CI-processor fitting especially in children or non-compliant patients.

Individualized Vibrotactile Neurofeedback Training in Patients with Chronic Bilateral Vestibulopathy.

Patients with bilateral vestibulopathy (BVP) suffer from postural imbalance during daily life conditions, which in turn leads to a high frequency of falls. Unfortunately, vestibular rehabilitation has only modest and somewhat inconsistent effects in this patient group. Approximately 50% of BVP patients show an improved postural control after conventional vestibular rehabilitation training. New and more promising approaches are required. The individualized vibrotactile neurofeedback training (IVNT) in stance and gait conditions has already been described as highly effective in patients with various vestibular disorders. The purpose of the present multicenter study was to determine the efficacy of the IVNT in improving balance, reducing self-perceived disability, and improving gait in patients with confirmed BVP. In total, 22 patients performed the IVNT with the Vertiguard® system for 10 daily sessions. The dizziness handicap inventory (DHI), the stance stability score of the sensory organization test (SOT) and the score for everyday life mobility in stance and gait tasks (SBDT) were obtained immediately before and after the rehabilitation training period, as well as 3 and 12 months later. All measures improved significantly after the IVNT. Between 77.3% and 94.4% of patients showed an individual benefit (depending on outcome measure). The effect was not significantly reduced within the follow-up period of 12 months. The results demonstrate a high efficacy of the IVNT for vestibular rehabilitation in BVP patients.

Advances to electrode pullback in cochlear implant surgery.

OBJECTIVE: To observe the intracochlear behavior of a cochlear implant electrode insertion technique (called "pullback") in temporal bones. Study Design. Experimental. Settings. Tertiary referral center. METHOD: The change of the intracochlear electrode position was investigated under various conditions of an electrode pullback (N = 54) in 9 radiologically, size-estimated temporal bones (TBs). Those TBs were prepared by removal of the cochlear scalar roof to apply digital video capture procedures to monitor the pullback procedures. The digitally captured pictures were analyzed with specific software. RESULTS: An optimal pullback of the electrode varied between 1.37 mm and 2.67 mm. While a limited pullback is without risk, an extended pullback bears the risk of removing the electrode tip out of its initial position or out of the cochlea. A correlation between cochlear size and the amount of pullback was not found. CONCLUSION: An initial insertion to the first or the second marker on the electrode followed by a limited pullback of about 1.37 mm to 1.5 mm can be recommended to achieve an optimized perimodiolar position. A pullback of up to two marker positions bears the risk of removing the electrode tip out of its initial position.

Cytomegalovirus Seropositivity as a Potential Risk Factor for Increased Noise Trauma Susceptibility.

Context: Cytomegalovirus (CMV) represents the leading congenital viral infection in humans. Although congenital CMV due to vertically transmitted infections is the main cause of CMV-related diseases, adult CMV infections might still be of clinical significance. It is still discussed how far CMV seropositivity, due to horizontal infection in immunocompetent adults, is able to induce significant dysfunction. The present study investigates in how far CMV seropositivity is an additional risk factor for an increasing susceptibility to sensorineural hearing loss induced by acoustic injury during adulthood in a guinea pig CMV (GPCMV) model of noise-induced hearing loss (NIHL). Methods: Two groups (GPCMV seropositive vs. seronegative) of normal hearing adult guinea pigs were exposed to a broadband noise (5-20 kHz) for 2 hours at 115 dB sound pressure level. Frequency-specific auditory brainstem response recordings for determination of auditory threshold shift were carried out and the number of missing outer hair cells was counted 2 weeks after the noise exposure. Results: The data show a slightly increased shift in auditory thresholds in seropositive animals compared to the seronegative control group in response to noise trauma. However, the observed difference was significant at least at high frequencies. The differences in threshold shift are not correlated with outer hair cell loss between the experimental groups. Conclusion: The results point to potential additional pathologies in a guinea pig NIHL model in correlation to GPCMV seropositivity, which should be taken into account when assessing risks of latent/reactivated CMV infection. Due to the relatively slight effect in the present data, the aim of future studies should be a more detailed consideration (e.g., larger sample size) and to localize possible target structures as well as the significance of the infection route.

The possible impact of noise-induced Ca2+-dependent activity in the central auditory pathway: a manganese-enhanced MRI study.

Noise exposure at high intensities leads to a temporary shift of hearing thresholds (TTS) and is followed by a permanent threshold shift (PTS). Permanent threshold shift is not only associated with cochlear damage as the primary site-of-lesion, but also with subsequent structural and functional changes within the central auditory pathway. The aim of the present study was to monitor neuronal activity within central auditory structures in mice after noise exposure at different time intervals using manganese-enhanced magnetic resonance imaging (MEMRI). The results demonstrate for the first time that calcium-dependent activity patterns are modified in several structures of the central auditory system as the result of a noise-induced hearing loss (NIHL). The MEMRI data demonstrate that temporary threshold shift is correlated with an activity increase in hierarchically lower structures of the auditory pathway. This seems to be indicative of a direct noise impact at the first stage of central auditory processing. However, noise-dependent changes of higher auditory structures were found as well in the phase of PTS. Repeated noise exposure was found to induce an additional elevation of calcium-dependent activity in all investigated auditory structures - without a significant shift in auditory thresholds. Sustained manganese accumulation was present in the auditory brainstem after moderate acoustic stimulation as well without PTS induction. The long-lasting enhancement of MEMRI signals suggests a noise-induced activity increase of various calcium-dependent processes of different origin (such as neuroprotective mechanisms). The present findings could be helpful to better understand the time-course of different symptoms in NIHL and the individual susceptibility to noise.

A static sound source can improve postural stability during walking.

BACKGROUND: During walking, postural stability is controlled by visual, vestibular and proprioceptive input. The auditory system uses acoustic input to localize sound sources. For some static balance conditions, the auditory influence on posture was already proven. Little is known about the impact of auditory inputs on balance in dynamic conditions. OBJECTIVE: This study is aimed at investigating postural stability of walking tasks in silence and sound on condition to better understand the impact of auditory input on balance in movement. METHODS: Thirty participants performed: walking (eyes open), tandem steps, walking with turning head and walking over barriers. During each task, acoustic condition changed between silence and presented noise through an earth-fixed loudspeaker located at the end of the walking distance. Body sway velocity was recorded close to the body's center of gravity. RESULTS: A decreased body sway velocity was significant for walking (eyes open), tandem steps and walking over barriers when noise was presented. Those auditory stimuli did not affect sway velocity while walking with turning head. The posture has probably improved due to the localization ability when walking with the head facing forward, while the localization ability was impaired when turning the head. CONCLUSIONS: The localization ability of a fixed sound source through the auditory system has a significant but limited impact on posture while walking.

Balance Training With Vibrotactile Neurofeedback and Ginkgo Biloba Extract in Age-Related Vertigo.

Background: Balance training with vibrotactile neurofeedback (VNF) can improve balance and subjective impairment in age-related vertigo and dizziness. Ginkgo biloba dry extract EGb 761 has been shown to improve subjective impairment in chronic vertigo and the efficacy of conventional balance training. The combination was expected to work synergistically in this difficult-to-treat population. Objectives: To demonstrate the efficacy of VNF added to EGb 761 for age-related vertigo and dizziness. Design: Multicenter, prospective, controlled, randomized, single-blind, two-arm trial (German Clinical Trials Register https://www.drks.de No. DRKS00007633). Setting: Specialist offices and tertiary care outpatient department. Participants: One hundred and twenty subjects aged 60+ years with chronic dizziness for over 3 months, a Dizziness Handicap Inventory (DHI) Sum Score >25 and fall risk in balance-related situations as measured by the geriatric Standard Balance Deficit Test Composite Score (gSBDT-CS)>40. Patients with other distinct vestibular pathology (e.g., Meniére's disease, stroke, BPPV) were excluded. Intervention: EGb 761 (80 mg twice daily for 12 weeks) plus 10 days of individually adapted balance training with VNF, randomized 1:1 to sensitive (active) or non-sensitive (sham) neurofeedback. Measurements: The change in gSBDT-CS after 6 weeks (primary), other gSBDT outcomes, DHI, cognition, hearing, and safety. Results: One hundred nine of 120 enrolled subjects received both treatments at least once. Over 12 weeks, the gSBDT-CS improved by 6.7 (active) vs. 4.5 (sham). There was a difference in favor of the active treatment of -2.4 (95% CI -5.4; 0.6) after 6 weeks. Under active treatment, more pronounced effects occurred in all secondary analyses and in nearly all secondary endpoints. The DHI sum score decreased from 44.1 to 31.1 in the total sample with a treatment group difference after 6 weeks of -3.1, 95% CI (-7.1; 0.9). No safety issues were reported. Conclusion: Over 12 weeks, the combination of balance training with VNF and Ginkgo biloba dry extract EGb 761 reached a clinically relevant improvement of age-related vertigo and dizziness with a good pharmacological safety profile.

Vestibular and taste disorders after bilateral cochlear implantation.

The objective of this study was to investigate the occurrence of vestibular receptor deficiency and taste disorders after bilateral cochlear implantation in postlingually deafened patients and to find out whether the risk for these complications is higher for the second implantation. In a retrospective cohort study, we examined 20 patients (11-58 years, mean age 41.5 years), implanted sequentially between 2000 and 2007 (mean period between cochlear implantation 32.9 ± 25 months). Pre- and postoperative vestibular testing was performed by subjective rating [Dizziness Handicap Inventory (DHI)], caloric irrigation [vestibuloocular reflex (VOR)] and by vestibular-evoked myogenic potential (VEMP) recordings for saccular function. The sense of taste was evaluated pre- and postoperatively by a questionnaire and testing (sour/sweet/bitter/salty bilaterally on the tongue). DHI evaluation showed a moderate not significant mean increase by 2.7 ± 7.7 SD points after the first and a significant increase by 9.4 ± 16.6 SD points after the second implantation. Ipsilateral VEMP responses disappeared in three ears (27.3%) after the first and in two ears (18.2%) after the second operation. VOR disappeared only once (5.9%) after the first implantation. One (5%) patient complained of a persisting disturbance of taste in the questionnaire after unilateral and 3 (15%) after bilateral implantation. Specific testing showed in one case (5%) a unilateral taste disorder after ipsilateral cochlear implantation. Our data show that there is a higher risk for subjective vertigo after the second implantation. The occurrence of unilateral and/or bilateral vestibular dysfunction and the potential risk of taste disorder should be included in the risk counseling before bilateral cochlear implantation to increase patients' and medicolegal safety in the decision-making process.