Auditory Neuropathy: Bridging the Gap Between Hearing Aids and Cochlear Implants

Cochlear Implantation in Charcot-Marie-Tooth Patients: Speech Perception and Quality of Life

OBJECTIVES

There is a limited understanding of the impact of cochlear implantation (CI) in patients with Charcot-Marie-Tooth disease (CMT), given the scarcity of reported cases. We aim to evaluate the audiological outcomes and quality of life (QoL) after CI in CMT.

METHODS

Multi-institutional, university-affiliated, tertiary-referral centers, retrospective chart review.Our cohort includes 5 patients with CMT. Patients' charts were reviewed for demographic characteristics, operation notes, and pre- and post-implantation audiology evaluation. Patients completed the Cochlear Implant Quality of Life-10 (CIQOL-10) Global questionnaire.

RESULTS

Pre-implantation, the mean pure tone average was 84.1 ± 7.2 dB, and the mean word recognition score was 2.4% in the implanted ear. AzBio sentence test was performed in quiet, revealing a mean of 4 ± 1.4% in the implanted ear. Post-implantation, PTA results were all within the mild hearing loss range (mean 33.0 ± 5.9 dB). Post-CI, AZ-Bio test results were 5%, 65%, and 74% (for 3 patients), and HINT scores were 55% and 58% (for 2 patients). The mean score of the CIQOL-10 questionnaire was 42.7 ± 10.47 (range 1-100). Patients were most satisfied with their ability to listen to the television or radio, have conversations in a quiet environment, and feel comfortable being themselves.

CONCLUSION

To the best of our knowledge, this is the most extensive series of CI in CMT-associated sensorineural hearing loss and auditory neuropathy. Our cohort suggests that CI is a safe and reliable method for hearing rehabilitation that can achieve good speech performance and improve QoL in CMT patients.

The Effects of Stimulus Repetition Rate on Electrically Evoked Auditory Brainstem Potentials in Postlingually Deafened Adult Cochlear Implant Recipients

Background: By using outcome prediction scores, it is possible to distinguish between good and poor performers with cochlear implants (CI) after CI implantation. The reasons for poor performance, despite good basic conditions, can be manifold. On the one hand, the postoperative fitting may be inadequate; on the other, neurophysiological disease processes may impair speech understanding with a CI. These disease processes are not yet fully understood. In acoustics, it is known that the auditory brainstem responses (ABR) and their latencies and amplitudes allow differential diagnosis based on reference values for normal-hearing individuals. The aim of this study was to provide reference values for electrically evoked brainstem responses (EABRs) in terms of rate-dependent latencies and amplitudes. Methods: 20 ears of 18 experienced adult CI recipients with a predicted and measured good postoperative word recognition score were recruited from the clinic's patient pool. In the same stimulation mode and intensity we measured latencies and interpeak-latencies of EABRs and electrically evoked compound action potentials (ECAPs). With a defined supra-threshold stimulation intensity above the individual ECAP threshold, we applied stimulation at several rates between 11 and 91 stimuli per second. Results: We found rate dependences for EABR latency t3 and t5 in the order of 0.19 ms and 0.37 ms, respectively, while ECAP was not affected by rate. Correspondingly, the interpeak intervals' rate dependences for t5-t1, t5-t3 and t3-t1 were of the order of 0.37 ms, 0.18 ms and 0.19 ms. Comparing the EABR amplitudes between the stimulation rates 11/s and 81/s, we found that at 81/s the amplitudes were significantly reduced down: to 73% for A3 and 81% for A5. These rate dependences of latency and amplitude in EABR have characteristics comparable to those of acoustic ABR. Conclusions: These data may serve to provide reference values for EABR and ECAP latencies, interpeak intervals and amplitudes with respect to stimulation rate. Altered response patterns of ECAPs and EABRs to normalised stimulation modes could be used in the future to describe and classify neuropathological processes in a better-differentiated way.

Expanding Understanding of Electrocochleography in Cochlear Implantation: Auditory Neuropathy Spectrum Disorder With Normal Pure Tone Average

Objective

Describe the preoperative decision-making, intraoperative electrocochleographic (ECoG) findings, and outcome of cochlear implantation (CI) in a patient with auditory neuropathy spectrum disorder (ANSD) and normal pure-tone thresholds.

Patients

A 19-year-old with a history of hypoxic ischemic encephalopathy and seizures was referred for hearing rehabilitation in the setting of typical hearing by pure tone audiometry but poor speech understanding. A diagnosis of ANSD was made based on acoustic brainstem response (ABR), distortion product otoacoustic emission, and acoustic reflex testing. Imaging revealed no central cause of hearing impairment.

Interventions

Right-sided CI.

Main Outcome Measures

Preoperative and postoperative audiometric data. Intraoperative ECoG.

Results

Preoperatively the patient underwent comprehensive audiologic testing with behavioral audiometry, ABR testing, and CI candidacy evaluation. In the right ear, the pure tone average (PTA) was 15 dB and word recognition score was 36%. ABR confirmed ANSD. Preoperative CNC and AzBio in quiet were 8% and 0%, respectively. Intraoperative ECoG amplitudes and audiometry showed responses in the 100 uV range and estimated PTA of 42 dB HL. Postoperative testing at 1-month post-initial activation revealed PTA of 45 dB HL and unchanged word and sentence scores. However, the patient cites an improved ability to communicate and increased confidence and averages over 14 hours of device use daily.

Conclusions

To our knowledge, this is the first reported case of CI in an ear with normal PTA. Given that nearly all presently available ECoG data comes from patients with greater degrees of hearing loss, this unique case adds to our understanding of hearing preservation in CI.

Cochlear Implantation Outcomes in Patients With OTOF Mutations

Auditory neuropathy is a special type of hearing loss caused by dysfunction of the synapse of the inner hair cells, the auditory nerve, and/or the auditory nerve itself. For patients with auditory neuropathy who have severe to profound hearing loss or failed auditory skills development with hearing-aids, cochlear implantation (CI) serves as the only possible effective treatment. It is accepted that the exact sites of lesion causing auditory neuropathy determine the CI performance. Mutations in the OTOF gene were the first identified and the most common cause of congenital auditory neuropathy. The site of lesion in patients with auditory neuropathy caused by biallelic OTOF mutations (OTOF-related auditory neuropathy) is presumed to be presynaptic, leaving auditory nerve function intact. Thus, OTOF-related auditory neuropathy is expected to have good CI performances. In this review, we describe the CI outcomes in patients with OTOF mutations. We will focus on whether biallelic OTOF mutations are ideal indications for CI in patients with auditory neuropathy. Also, the factors that may still influence the CI outcomes in patients with OTOF mutations are discussed.

Outcomes of audiometric testing in children with auditory neuropathy spectrum disorder

INTRODUCTION

Auditory Neuropathy Spectrum Disorder (ANSD) is characterized by hearing loss ranging from normal to profound. Additionally, results are confounded by commonly fluctuating hearing thresholds in ANSD. As such, we sought to evaluate results of audiometric testing on children with ANSD and the impact of age and time on testing results.

METHODS

Retrospective chart review on children <18 years of age diagnosed with ANSD at two tertiary care academic institutions. Data analyzed included initial audiogram with speech detection thresholds (SDT) and pure tone averages (PTA) as well as most recent unaided audiogram SDT and PTA.

RESULTS

75 ANSD patients were analyzed, of which 32 (42.7%) were female. Bilateral and unilateral ANSD was seen in 55 (73.3%) and 20 (26.7%), respectively. A total of 130 ears with ANSD were assessed with 80 (61.5%) meeting inclusion criteria. Of these patients, the median age in years at first audiogram and most recent audiogram were 1.94 (0.45-13.68) and 4.22 (0.97-14.61), respectively. The median ages at which an SDT and PTA could first be acquired on the audiogram in ANSD patients were 1.94 (0.50-13.68) and 2.86 (0.45-13.68), respectively. The average SDT/PTA at the initial and most recent audiogram were 47.5/45.7 and 49.4/53.0 dB, respectively. SDT to PTA within the same audiogram exhibited strong correlation (r = 0.82, p < 0.001). Similarly, comparison of initial SDT to SDT at a later time interval showed strong correlation (r = 0.73, p < 0.001). SDT and PTA at initial audiogram and PTA at later time demonstrated lower correlation but was still statistically significant (r = 0.49, p < 0.009 and r = 0.51, p < 0.044, respectively). Individual PTA was associated with age (r = -0.56, p < 0.001).

CONCLUSIONS

SDT and PTA within the same audiogram and initial SDT to SDT acquired at a later time correlate strongly in audiometric testing in children with ANSD. Although not as strong, initial SDT and PTA still correlate with PTA at a later time interval. These findings suggest that audiometric results yielding a reliable SDT and frequency specific information necessary to calculate the PTA is not typically obtained until 2-3 years old. However, once this information is obtained, the child's hearing is fairly stable but may fluctuate over time.