Auditory neuropathy: endocochlear lesion or temporal processing impairment? Implications for diagnosis and management

Evaluation of the Efficacy of Human Dental Pulp Stem Cell Transplantation in Sprague-Dawley Rats with Sensorial Neural Hearing Loss

OBJECTIVES

 The purpose of the present study was to evaluate the efficacy of spiral ganglion neuron (SGN) regeneration after dental pulp stem cell (DPSC) transplantation in a rat sensorineural hearing loss (HL) model.

MATERIALS AND METHODS

 Sham or experimental HL was induced in adult Sprague-Dawley rats by cochlear round window surgery. An HL rat model was established with a single 10 mM ouabain intratympanic injection. After 7 days, the rats received DPSCs, stem cells from human exfoliated deciduous teeth (SHED), or culture medium in the sutural area to establish four groups: sham, HL-DPSC, HL-SHED, and HL-medium. Histological analyses were performed at 4, 7, and 10 weeks after transplantation, and the number of SGNs, specific SGN protein expression, and the function of SGNs were evaluated.

STATISTICAL ANALYSIS

 Data were statistically by MS Excel and SPSS v.15.0. Intergroup level of significance was determined via a one-way analysis of variance and Duncan's multiple range test with 95% confidence intervals.

RESULTS

 New SGN formation was observed in the HL-DPSC and HL-SHED rat groups. The number of SGNs was significantly higher in the HL-DPSC and HL-SHED groups than in the HL-medium group over 4 to 10-week survival period. HL-DPSC rats exhibited higher SGN density compared with that in HL-SHED group, which was statistically significant at week 10. The regenerated SGNs expressed cochlear wiring regulator GATA-binding-protein 3. Moreover, the SGNs from the HL-DPSC group also exhibited a higher expression of synaptic vesicle protein and regulated action potential-dependent neurotransmitter release compared with SGNs from the HL-SHED group.

CONCLUSIONS

 Our findings suggest that DPSCs and SHED repair and regenerate SGNs in rat HL model. Dental pulp stem cells represent a promising treatment strategy for restoring damage to the sensory circuits associated with deafness.

Systematic Literature Review and Early Benefit of Cochlear Implantation in Two Pediatric Auditory Neuropathy Cases

Approximately 1 in 10 children with hearing loss is affected by auditory neuropathy spectrum disorder (ANSD). People who have ANSD usually have great difficulty understanding speech or communicating. However, it is possible for these patients to have audiograms that may indicate profound hearing loss up to normal hearing. This disorder is prognosed with positive, intact or present otoacoustic emissions (OAE) and/or cochlear microphonics (CM) as well as abnormal or absent auditory brainstem responses (ABR). Treatment methods include conventional hearing aids as well as cochlear implants. Cochlear implants (CI) usually promise better speech understanding for ANSD patients. We performed a systematic literature review aiming to show what improvements can effectively be achieved with cochlear implants in children with ANSD and compare this with our experience with two cases of ANSD implanted at our clinic. The retrospective review of two young CI patients diagnosed with ANSD during infancy demonstrated improvements over time in speech development communicated by their parents.

Animal-to-Human Translation Difficulties and Problems With Proposed Coding-in-Noise Deficits in Noise-Induced Synaptopathy and Hidden Hearing Loss

Noise induced synaptopathy (NIS) and hidden hearing loss (NIHHL) have been hot topic in hearing research since a massive synaptic loss was identified in CBA mice after a brief noise exposure that did not cause permanent threshold shift (PTS) in 2009. Based upon the amount of synaptic loss and the bias of it to synapses with a group of auditory nerve fibers (ANFs) with low spontaneous rate (LSR), coding-in-noise deficit (CIND) has been speculated as the major difficult of hearing in subjects with NIS and NIHHL. This speculation is based upon the idea that the coding of sound at high level against background noise relies mainly on the LSR ANFs. However, the translation from animal data to humans for NIS remains to be justified due to the difference in noise exposure between laboratory animals and human subjects in real life, the lack of morphological data and reliable functional methods to quantify or estimate the loss of the afferent synapses by noise. Moreover, there is no clear, robust data revealing the CIND even in animals with the synaptic loss but no PTS. In humans, both positive and negative reports are available. The difficulty in verifying CINDs has led a re-examination of the hypothesis that CIND is the major deficit associated with NIS and NIHHL, and the theoretical basis of this idea on the role of LSR ANFs. This review summarized the current status of research in NIS and NIHHL, with focus on the translational difficulty from animal data to human clinicals, the technical difficulties in quantifying NIS in humans, and the problems with the SR theory on signal coding. Temporal fluctuation profile model was discussed as a potential alternative for signal coding at high sound level against background noise, in association with the mechanisms of efferent control on the cochlea gain.

Prevalence, risk factors, and audiological characteristics of auditory neuropathy

OBJECTIVE

The objective of this study was to determine the prevalence, risk factors, and audiological characteristics of auditory neuropathy spectrum disorder (ANSD) in the pediatric population.

DESIGN

A retrospective review of medical charts was conducted for children visiting two hospitals in Saudi Arabia.

STUDY SAMPLE

Medical records of 1025 patients with sensorineural hearing loss (SNHL) were reviewed. We analyzed the databases for results of audiological examinations, risk factors, and outcomes of intervention including hearing aid (HA) and cochlear implantation (CI).

RESULTS

Out of 1025 children with SNHL, 101 patients (9.85%) were identified to have ANSD. Audiological characteristics of the ANSD group revealed a severe-to-profound degree of hearing loss, all showed type A tympanogram and absent reflexes, absent auditory brainstem response (ABR) findings with present cochlear microphonic while otoacoustic emissions were absent in 54.5% of patients. The most prevalent risk factors for ANSD in this group were family history of hearing loss, consanguinity, hyperbilirubinemia, and low birth weight. Pure tone and speech detection thresholds improved significantly with CI compared to HA use in this sample of patients with ANSD.

CONCLUSION

This study shows that ANSD is not extremely rare among Saudi children with severe to profound hearing loss, with a prevalence of 9.85%.

Cortical Auditory Event-Related Potentials and Categorical Perception of Voice Onset Time in Children With an Auditory Neuropathy Spectrum Disorder

Objective: This study evaluated cortical encoding of voice onset time (VOT) in quiet and noise, and their potential associations with the behavioral categorical perception of VOT in children with auditory neuropathy spectrum disorder (ANSD). Design: Subjects were 11 children with ANSD ranging in age between 6.4 and 16.2 years. The stimulus was an /aba/-/apa/ vowel-consonant-vowel continuum comprising eight tokens with VOTs ranging from 0 ms (voiced endpoint) to 88 ms (voiceless endpoint). For speech in noise, speech tokens were mixed with the speech-shaped noise from the Hearing In Noise Test at a signal-to-noise ratio (SNR) of +5 dB. Speech-evoked auditory event-related potentials (ERPs) and behavioral categorization perception of VOT were measured in quiet in all subjects, and at an SNR of +5 dB in seven subjects. The stimuli were presented at 35 dB SL (re: pure tone average) or 115 dB SPL if this limit was less than 35 dB SL. In addition to the onset response, the auditory change complex (ACC) elicited by VOT was recorded in eight subjects. Results: Speech evoked ERPs recorded in all subjects consisted of a vertex positive peak (i.e., P1), followed by a trough occurring approximately 100 ms later (i.e., N2). For results measured in quiet, there was no significant difference in categorical boundaries estimated using ERP measures and behavioral procedures. Categorical boundaries estimated in quiet using both ERP and behavioral measures closely correlated with the most-recently measured Phonetically Balanced Kindergarten (PBK) scores. Adding a competing background noise did not affect categorical boundaries estimated using either behavioral or ERP procedures in three subjects. For the other four subjects, categorical boundaries estimated in noise using behavioral measures were prolonged. However, adding background noise only increased categorical boundaries measured using ERPs in three out of these four subjects. Conclusions: VCV continuum can be used to evaluate behavioral identification and the neural encoding of VOT in children with ANSD. In quiet, categorical boundaries of VOT estimated using behavioral measures and ERP recordings are closely associated with speech recognition performance in children with ANSD. Underlying mechanisms for excessive speech perception deficits in noise may vary for individual patients with ANSD.

Neural representation of consonant-vowel transition in individuals with cochlear hearing loss and auditory neuropathy spectrum disorder

PURPOSE

Acoustic change complex (ACC) is an evoked potential recorded in response to subtle change(s) in the continuing stimuli. It is assumed that poor speech perception can be due to poor encoding of consonant-vowel (CV) transition in cochlear hearing loss (CHL) and auditory neuropathy spectrum disorder (ANSD). The present study aims to investigate the use of ACC as an objective tool to study neural representation of CV transition in individuals with ANSD, CHL, and normal hearing (NH).

METHODS

The study consisted of three groups of population (NH, ANSD, and CHL) in the age range of 18-40 years. ACC was recorded for naturally produced CV stimulus /sa/ of 380 ms in duration, which consists consonant (150 ms) and vowel (230 ms) using Biologic Navigator pro 7.2.1.

RESULTS

The result showed significantly prolonged latencies of ACC in individuals with ANSD compared to NH. The current study also showed significantly prolonged latency and significantly lower peak-to-peak amplitude in individuals with ANSD compared to CHL. The interesting finding of the present study was significantly better peak-to-peak amplitude for CHL compared to NH. Whereas, there was no significant difference between NH and CHL for latencies measures.

CONCLUSION

Poor neural synchronization in individuals with ANSD could be the reason of poor neural representation of CV transition in present study. The outcome of the present study showed poor neural representation of CV transition in individuals with ANSD compared to CHL and NH. Current study also showed better encoding of CV transition in individuals with CHL compared to ANSD.

Phrases in noise test (PINT) Brazil: effectiveness of the test in children with hearing loss

INTRODUCTION

One of the main implications of hearing impairment is the difficulty in perceiving speech sounds, especially in noisy environments. Thus, the frequency-modulated system is considered an important educational tool for children with hearing impairment because it improves speech perception in acoustically-unfavorable environments, such as in the classroom. The assessment of speech perception in noise is included in the verification protocol of this device.

OBJECTIVES

To verify the effectiveness of the phrases in noise test Brazil in children with hearing impairment using an frequency-modulated system.

METHODS

This was a cross-sectional cohort study. The sample included 40 children, aged 4 years to 11 years and 11 months old, divided into 4 groups: (1) 10 normal hearing children; (2) 13 children with hearing aids and frequency-modulated system; (3) 12 children using cochlear implant and fitted with the frequency-modulated system; and (4) 5 children diagnosed with auditory neuropathy spectrum disorder, fitted with hearing aids and/or cochlear implant and with the frequency-modulated system. The phrases in noise test Brazil was used to evaluate speech perception in noise under the conditions with and without the frequency-modulated system. For the statistical analysis of the data, a significance level of 5% (p < 0.05) was adopted.

RESULTS

There was a significant difference between the groups when they were evaluated with the frequency-modulated system. The test was also validated through concurrent and convergent validation measures. Phrases in noise test Brazil is a viable option for monitoring auditory performance in noise in different groups of children with hearing impairmen.

CONCLUSION

Phrases in noise test Brazil was effective in assessing speech perception in noise and may contribute to the improvement of the indication, fitting and follow-up protocols for the frequency-modulated system use.

Relationship research between auditory neuropathy spectrum disorder and exchange transfusion in neonates with severe hyperbilirubinemia

OBJECTIVE

To explore the effects of exchange transfusion on auditory neuropathy spectrum disorder (ANSD) in neonates with severe hyperbilirubinemia (SH).

METHODS

The clinical data of 2216 SH neonates who met the standard of exchange transfusion and 732 non severe-hyperbilirubinemia (NSH) neonates in the same period who did not require exchange transfusion in the neonatology department of Childrens' Hospital of Chongqing Medical University between January 2010 and December 2015 were retrospectively analyzed. In addition, the SH neonates were further divided into the exchange transfusion group and photography group. Hearing screening was conducted on all neonates using transiently evoked otoacoustic emission (TEOAE) and auto auditory brainstem response (AABR), and neonates who failed the above screening were performed diagnostic hearing test. And then neonates diagnosed with hearing disorder were followed up for 2-5 years.

RESULTS

The pass rates of hearing screening were 80.58%, 79.71% and 87.84% in the phototherapy group, exchange transfusion group and NSH group respectively, with a significant difference(P < 0.05). Hearing loss was diagnosed in 10.15%, 12.39% and 8.54% of neonates in the phototherapy group, exchange transfusion group and NSH group. After follow-up, ultimate incidence rates of ANSD were 11.96%, 11.57% and 2.4% respectively in the 3 groups, with a significant difference (P < 0.05).

CONCLUSIONS

SH is one of risk factors for ANSD. SH neonates have a lower incidence of ANSD in the exchange transfusion group than in the phototherapy group. Neonates who meet the standards of exchange transfusion adopt this therapy in early stage, which can quickly decrease bilirubin level and ultimately reduce incidence of ANSD.

Cochlear implantation in children with auditory neuropathy spectrum disorder: A multicenter study on auditory performance and speech production outcomes

OBJECTIVES

To evaluate the auditory performance and speech production outcome in children with auditory neuropathy spectrum disorder (ANSD). The effect of age on the outcomes of the surgery at the time of implantation was also evaluated.

METHODS

Cochlear implantation was performed in 136 children with bilateral severe-to- profound hearing loss due to ANSD, at four tertiary academic centers. The patients were divided into two groups based on the age at the time of implantation; Group I: Children ≤24 months, and Group II: subjects >24 months. The categories of auditory performance (CAP) and speech intelligibility rating (SIR) scores were evaluated after the first and second years of implantation. The differences between the CAP and SIR scores in the two groups were assessed.

RESULTS

The median CAP scores improved significantly after the cochlear implantation in all the patients (p value < 0.001). The improvement in the CAP scores during the first year in Group II was greater than Group I (p value: 0.007), but the improvement in CAP scores tended to be significantly higher in patients who were implanted at ≤24 months (p value < 0.001). There was no significant difference between two groups in SIR scores at first-year and second-year follow-ups. The evaluation of the SIR improvement revealed significantly higher values for Group I during the second-year follow-up (p value: 0.003).

CONCLUSION

The auditory performance and speech production skills of the children with ANSD improved significantly after cochlear implantation, and this improvement was affected by age at the time of implantation.

Children with Auditory Neuropathy Spectrum Disorder Fitted with Hearing Aids Applying the American Academy of Audiology Pediatric Amplification Guideline: Current Practice and Outcomes

BACKGROUND

Up to 15% of children with permanent hearing loss (HL) have auditory neuropathy spectrum disorder (ANSD), which involves normal outer hair cell function and disordered afferent neural activity in the auditory nerve or brainstem. Given the varying presentations of ANSD in children, there is a need for more evidence-based research on appropriate clinical interventions for this population.

PURPOSE

This study compared the speech production, speech perception, and language outcomes of children with ANSD, who are hard of hearing, to children with similar degrees of mild-to-moderately severe sensorineural hearing loss (SNHL), all of whom were fitted with bilateral hearing aids (HAs) based on the American Academy of Audiology pediatric amplification guidelines.

RESEARCH DESIGN

Speech perception and communication outcomes data were gathered in a prospective accelerated longitudinal design, with entry into the study between six mo and seven yr of age. Three sites were involved in participant recruitment: Boys Town National Research Hospital, the University of North Carolina at Chapel Hill, and the University of Iowa.

STUDY SAMPLE

The sample consisted of 12 children with ANSD and 22 children with SNHL. The groups were matched based on better-ear pure-tone average, better-ear aided speech intelligibility index, gender, maternal education level, and newborn hearing screening result (i.e., pass or refer).

DATA COLLECTION AND ANALYSIS

Children and their families participated in an initial baseline visit, followed by visits twice a year for children <2 yr of age and once a yr for children >2 yr of age. Paired-sample t-tests were used to compare children with ANSD to children with SNHL.

RESULTS

Paired t-tests indicated no significant differences between the ANSD and SNHL groups on language and articulation measures. Children with ANSD displayed functional speech perception skills in quiet. Although the number of participants was too small to conduct statistical analyses for speech perception testing, there appeared to be a trend in which the ANSD group performed more poorly in background noise with HAs, compared to the SNHL group.

CONCLUSIONS

The American Academy of Audiology Pediatric Amplification Guidelines recommend that children with ANSD receive an HA trial if their behavioral thresholds are sufficiently high enough to impede speech perception at conversational levels. For children with ANSD in the mild-to-severe HL range, the current results support this recommendation, as children with ANSD can achieve functional outcomes similar to peers with SNHL.

Recurrent variants in OTOF are significant contributors to prelingual nonsydromic hearing loss in Saudi patients

Purpose

Hearing loss is more prevalent in the Saudi Arabian population than in other populations; however, the full range of genetic etiologies in this population is unknown. We report the genetic findings from 33 Saudi hearing-loss probands of tribal ancestry, with predominantly prelingual severe to profound hearing loss.

Methods

Testing was performed over the course of 2012–2016, and involved initial GJB2 sequence and GJB6-D13S1830 deletion screening, with negative cases being reflexed to a next-generation sequencing panel with 70, 71, or 87 hearing-loss genes.

Results

A “positive” result was reached in 63% of probands, with two recurrent OTOF variants (p.Glu57* and p.Arg1792His) accountable for a third of all “positive” cases. The next most common cause was pathogenic variants in MYO7A and SLC26A4, each responsible for three “positive” cases. Interestingly, only one “positive” diagnosis had a DFNB1-related cause, due to a homozygous GJB6-D13S1830 deletion, and no sequence variants in GJB2 were detected.

Conclusion

Our findings implicate OTOF as a potential major contributor to hearing loss in the Saudi population, while highlighting the low contribution of GJB2, thus offering important considerations for clinical testing strategies for Saudi patients. Further screening of Saudi patients is needed to characterize the genetic spectrum in this population.

Auditory neuropathy in Brown-Vialetto-Van Laere syndrome due to riboflavin transporter RFVT2 deficiency

AIM

Mutations in the genes encoding the riboflavin transporters RFVT2 and RFVT3 have been identified in Brown-Vialetto-Van Laere syndrome, a neurodegenerative disorder characterized by hearing loss and pontobulbar palsy. Treatment with riboflavin has been shown to benefit individuals with the phenotype of RFVT2 deficiency. Understanding the characteristics of hearing loss in riboflavin transporter deficiency would enable early diagnosis and therapy.

METHOD

We performed hearing assessments in seven children (from four families) with RFVT2 deficiency and reviewed results from previous assessments. Assessments were repeated after 12 months and 24 months of riboflavin therapy and after cochlear implantation in one individual.

RESULTS

Hearing loss in these individuals was due to auditory neuropathy spectrum disorder (ANSD). Hearing loss was identified between 3 years and 8 years of age and progressed rapidly. Hearing aids were not beneficial. Riboflavin therapy resulted in improvement of hearing thresholds during the first year of treatment in those with recent-onset hearing loss. Cochlear implantation resulted in a significant improvement in speech perception in one individual.

INTERPRETATION

Riboflavin transporter deficiency should be considered in all children presenting with an auditory neuropathy. Speech perception in children with ANSD due to RFVT2 deficiency may be significantly improved by cochlear implantation.

Understanding auditory neuropathy spectrum disorder: a systematic review in transgenic mouse models

Auditory neuropathy spectrum disorder is a unique group of hearing dysfunctions characterized by preserved outer hair cell function and abnormal neural conduction of the auditory pathway. However, the pathogenic mechanism underlying this disorder is not clear. We therefore performed a systematic review of genetic mouse models with different gene mutations to provide a valuable tool for better understanding of the process and the possible molecular mechanisms. Of the 18 articles retrieved, nine met the required criteria. All biochemical, histological, and electrophysiological results were recorded for each of the mouse models, as was the transgenic technology. This review provides a summary of different mouse models that may play an important role in the diagnosis and management of auditory neuropathy spectrum disorder in the future.

Audiological findings in Infantile Refsum disease

Audiological manifestations in a four-year-old child with Infantile Refsum disease are reported. He was born to non-consanguineous parents and had normal birth history and mildly delayed milestones prior to presentation. Clinical features were characterized by neuroregression, retinitis pigmentosa, hearing loss, peripheral neuropathy and white matter signal changes on magnetic resonance imaging. Biochemical evaluation showed elevated serum levels of long chain fatty acid and phytanic acid confirming the diagnosis. The audiological profile was characterized by absent auditory brainstem responses with robust otocoustic emissions, which indicated auditory neuropathy as the possible cause of hearing loss.

Mutations in apoptosis-inducing factor cause X-linked recessive auditory neuropathy spectrum disorder

Background

Auditory neuropathy spectrum disorder (ANSD) is a form of hearing loss in which auditory signal transmission from the inner ear to the auditory nerve and brain stem is distorted, giving rise to speech perception difficulties beyond that expected for the observed degree of hearing loss. For many cases of ANSD, the underlying molecular pathology and the site of lesion remain unclear. The X-linked form of the condition, AUNX1, has been mapped to Xq23-q27.3, although the causative gene has yet to be identified.

Methods

We performed whole-exome sequencing on DNA samples from the AUNX1 family and another small phenotypically similar but unrelated ANSD family.

Results

We identified two missense mutations in AIFM1 in these families: c.1352G>A (p.R451Q) in the AUNX1 family and c.1030C>T (p.L344F) in the second ANSD family. Mutation screening in a large cohort of 3 additional unrelated families and 93 sporadic cases with ANSD identified 9 more missense mutations in AIFM1. Bioinformatics analysis and expression studies support this gene as being causative of ANSD.

Conclusions

Variants in AIFM1 gene are a common cause of familial and sporadic ANSD and provide insight into the expanded spectrum of AIFM1-associated diseases. The finding of cochlear nerve hypoplasia in some patients was AIFM1-related ANSD implies that MRI may be of value in localising the site of lesion and suggests that cochlea implantation in these patients may have limited success.

Societal impact of bilirubin-induced hearing impairment in resource-limited nations

Infants with bilirubin-induced neurologic dysfunction (BIND) are characterized by several developmental disabilities including auditory impairments. This paper explores the societal impact of bilirubin-induced auditory impairments, inclusive of hearing impairments and auditory neuropathy spectrum disorders, on these infants, their families, and on the community in resource-limited countries (per capita income of US$6,000 or less). Auditory impairments have substantial emotional, social, and economic impact on the affected infants, their families and communities. The burden is exacerbated by widespread poverty, unfavorable community attitudes towards disabilities, and lack of requisite health, educational, and social services. Curtailing the incidence of avoidable severe hyperbilirubinemia through proactive and effective management of infants at risk or with severe hyperbilirubinemia is necessary at all levels of healthcare delivery. Early detection and intervention for unavoidable auditory impairments should be widely promoted to provide improved developmental trajectories for the affected infants.

Relationship between electrically evoked auditory brainstem response and auditory performance after cochlear implant in patients with auditory neuropathy spectrum disorder

OBJECTIVE

To analyze the pattern of electrically evoked auditory brainstem response (EABR) in auditory neuropathy spectrum disorder (ANSD) patients and to compare their performances with controls.

STUDY DESIGN

Retrospective analysis.

SETTING

Tertiary referral center.

PATIENTS

Eleven patients with ANSD and 9 control subjects with sensorineural hearing loss who did not have neural pathology.

INTERVENTION

Diagnostic.

MAIN OUTCOME MEASURES

Patients and control subjects each received a cochlear implant (CI) and underwent EABR. EABR threshold, wave V latency, and amplitude were measured as EABR parameters. The results of EABR were categorized as good response, variable response, or no response. Speech perception ability was assessed by the categories of auditory performance (CAP) score.

RESULTS

All controls responded to EABR, whereas 6 of the 11 ANSD patients did not respond to EABR. The EABR threshold of the ANSD patients was measured almost within the value of disease controls. However, the Wave V latency displayed variable lengths, and the amplitude showed a wider distribution compared with the value of the disease control. The EABR response group among the ANSD patients showed relatively good performance after CI. In contrast, the nonresponse group demonstrated variable outcomes, although all of them still benefited from CI.

CONCLUSION

The data suggested that all ANSD patients require CI and that EABR results can help establish realistic expectations about future performance. Even if electrical stimulation fails to generate sufficiently synchronized signal for eliciting EABR, CI provides at least partial, measurable auditory benefit in ANSD.

Auditory dyssynchrony or auditory neuropathy: understanding the pathophysiology and exploring methods of treatment

OBJECTIVE

To review the literature on auditory dyssynchrony (AD) or neuropathy which is characterized by absent auditory brainstem responses, normal otoacoustic emissions, and word discrimination disproportional to the pure tone audiogram.

RESULTS

Several papers attempt to estimate the prevalence of AD that seems to range between 0.23 and 2% in infants "at risk" for hearing impairment and it is considered to be responsible for approximately 8% of newly diagnosed cases of hearing loss in children per year. The prevalence gets even higher, reaching 10% in children with permanent hearing loss. It seems that AD is not a single disease but a spectrum of pathologies that affect the auditory pathway at the level of the inner hair cells, the synapses, or the auditory nerve. Many predisposing or contribution factors have been reported, including prematurity, hyperbilirubinemia, hypoxia, low-birth weight, immunological conditions, infectious diseases, etc. Before proposing any method of management, parents should be informed about the variation among patients and the changes that may appear in some children's audition over time. Sigh language, speech and language therapy, hearing-aids, and cochlear implantation have been used in the treatment of AD. In general, AD is rather refractory to conventional amplification and cochlear implantation has been found an effective method of management in young implanted children with severe/profound deafness and AD. However, the situation is more complicated and challenging in milder hearing losses.

CONCLUSION

The selected and proposed 30 related articles published in the International Journal of Pediatric Otorhinolaryngology aim to stimulate the related research in order to further explore the etiology, pathophysiology, and management of AD.

Impact of the presence of auditory neuropathy spectrum disorder (ANSD) on outcomes of children at three years of age

OBJECTIVE

To determine the influence of the presence of auditory neuropathy spectrum disorder (ANSD) on speech, language, and psycho-social development of children at three years of age.

DESIGN

A population-based, longitudinal study was performed on outcomes of children with hearing impairment (LOCHI) in Australia. The demographic characteristics of the children were described, and their developmental outcomes were evaluated at three years of age. Performance of children with ANSD was compared with that of children without ANSD in the LOCHI study.

STUDY SAMPLE

There were 47 children with ANSD in the study sample.

RESULTS

Sixty-four percent of children with ANSD have hearing sensitivity loss ranging from mild to severe degree, and the remaining have profound hearing loss. At three years, 27 children used hearing aids, 19 used cochlear implants, and one child did not use any hearing device. Thirty percent of children have disabilities in addition to hearing loss. On average, there were no significant differences in performance level between children with and without ANSD. Also, the variability of scores was not significantly different between the two groups.

CONCLUSIONS

There was no significant difference in performance levels or variability between children with and without ANSD, both for children who use hearing aids, and children who use cochlear implants.

Masking effects in patients with auditory neuropathy-possible involvement of suppression mechanism caused by normal outer hair cell function

OBJECTIVE

Variations in the effects of masking noise were evaluated in different pathologies of sensorineural hearing loss.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral center.

PATIENTS

Fifty-five ears of 30 patients with sensorineural hearing loss who underwent noise audiometry in the Department of Otolaryngology-Head and Neck Surgery, Tohoku University Hospital, since 2010, because of complaints of hearing difficulty in noisy environments.

MAIN OUTCOME MEASURES

Masked threshold for narrow band and white noise.

RESULTS AND DISCUSSION

Masking effects in patients with auditory neuropathy were significantly larger than those in patients with other types of hearing losses. Masking effects of broad band white noise were greater than those of narrow band noise. Masking effects could be observed for white noise even in the elevated unmasked threshold region, where little contribution of excitatory masking effect would be expected. The present findings support the idea that the suppression mechanism caused by normal outer hair cell function is important in the masking phenomenon in patients with auditory neuropathy.

Cochlear implantation in unique pediatric populations

PURPOSE OF REVIEW

Over the last decade, the selection criteria for cochlear implantation have expanded to include children with special auditory, otologic, and medical problems. Included within this expanded group of candidates are those children with auditory neuropathy spectrum disorder, cochleovestibular malformations, cochlear nerve deficiency, associated syndromes, as well as multiple medical and developmental disorders. Definitive indications for cochlear implantation in these unique pediatric populations are in evolution. This review will provide an overview of managing and habilitating hearing loss within these populations with specific focus on cochlear implantation as a treatment option.

RECENT FINDINGS

Cochlear implants have been successfully implanted in children within unique populations with variable results. Evaluation for cochlear implant candidacy includes the core components of a full medical, audiologic, and speech and language evaluations. When considering candidacy in these children, additional aspects to consider include disorder-specific surgical considerations and child/caregiver counseling regarding reasonable postimplantation outcome expectations.

SUMMARY

Cochlear implants are accepted as the standard of care for improving hearing and speech development in children with severe-to-profound hearing loss. However, children with sensorineural hearing loss who meet established audiologic criteria for cochlear implantation may have unique audiologic, medical, and anatomic characteristics that necessitate special consideration regarding cochlear implantation candidacy and outcome. Individualized preoperative candidacy and counseling, surgical evaluation, and reasonable postoperative outcome expectations should be taken into account in the management of these children.

Restoration of auditory evoked responses by human ES-cell-derived otic progenitors

Deafness is a condition with a high prevalence worldwide, produced primarily by the loss of the sensory hair cells and their associated spiral ganglion neurons (SGNs). Of all the forms of deafness, auditory neuropathy is of particular concern. This condition, defined primarily by damage to the SGNs with relative preservation of the hair cells, is responsible for a substantial proportion of patients with hearing impairment. Although the loss of hair cells can be circumvented partially by a cochlear implant, no routine treatment is available for sensory neuron loss, as poor innervation limits the prospective performance of an implant. Using stem cells to recover the damaged sensory circuitry is a potential therapeutic strategy. Here we present a protocol to induce differentiation from human embryonic stem cells (hESCs) using signals involved in the initial specification of the otic placode. We obtained two types of otic progenitors able to differentiate in vitro into hair-cell-like cells and auditory neurons that display expected electrophysiological properties. Moreover, when transplanted into an auditory neuropathy model, otic neuroprogenitors engraft, differentiate and significantly improve auditory-evoked response thresholds. These results should stimulate further research into the development of a cell-based therapy for deafness.

Bilirubin induces auditory neuropathy in neonatal guinea pigs via auditory nerve fiber damage

Bilirubin can cause temporary or permanent sensorineural deafness in newborn babies with hyperbilirubinemia. However, the underlying targets and physiological effects of bilirubin-induced damage in the peripheral auditory system are unclear. Using cochlear functional assays and electron microscopy imaging of the inner ear in neonatal guinea pigs, we show here that bilirubin exposure resulted in threshold elevation in both compound action potential (CAP) and auditory brainstem response (ABR), which was apparent at 1 hr and peaked 8 hr after drug administration. The threshold elevation was associated with delayed wave latencies and elongated interwave intervals in ABR and CAP. At 72 hr postinjection, these measures returned to control levels, except for the CAP amplitude. Cochlear microphonics remained unchanged during the experiment. Morphological abnormalities were consistent with the electrophysiological dysfunction, revealing fewer auditory nerve fibers (ANFs) in the basal turn, myelin sheath lesions of spiral ganglion neurons (SGNs) and ANFs, and loss of type 1 afferent endings beneath inner hair cells (IHCs) without loss of hair cells at 8 hr posttreatment. Similar to the electrophysiological findings, morphological changes were mostly reversed 10 days after treatment, except for the ANF reduction in the basal turn. These results suggest that hyperbilirubinemia in neonatal guinea pigs impaired auditory peripheral neuromechanisms that targeted mainly the IHC synapses and the myelin sheath of SGNs and their fibers. Our observations indicate a potential connection between hyperbilirubinemia and auditory neuropathy.

A positive wave at 8 ms (P8) and modified auditory brainstem responses measurement in auditory neuropathy spectrum disorder

OBJECTIVE

Auditory neuropathy spectrum disorder (ANSD) is characterized by absent or atypical auditory brainstem responses (ABR), recordable otoacoustic emissions and/or cochlear microphonics. Modification of ABR stimuli is discussed to improve wave V synchronization in ANSD patients.

DESIGN

Ten ANSD children (seven unilateral) underwent ABR measurement with an alternating stimulus (40.5s(-1)), constant rarefaction and condensation stimuli, a reduced click-rate (11.1s(-1)) and a chirp-stimulus.

RESULTS

The results showed no remarkably better synchronization with modified stimuli. Whereas higher levels showed no synchronization, reproducible positive waves at 8 ms (P8) at intensities of 65-85 dB were found in six patients with all stimuli.

CONCLUSIONS

We suggest an ipsilateral auditory origin of the positive potentials at 8 ms. They could be characteristic of synchronization abnormalities in some cases of ANSD.

Inhalation of hydrogen gas attenuates ouabain-induced auditory neuropathy in gerbils

AIM

Auditory neuropathy (AN) is a hearing disorder characterized by abnormal auditory nerve function with preservation of normal cochlear hair cells. This study was designed to investigate whether treatment with molecular hydrogen (H(2)), which can remedy damage in various organs via reducing oxidative stress, inflammation and apoptosis, is beneficial to ouabain-induced AN in gerbils.

METHODS

AN model was made by local application of ouabain (1 mmol/L, 20 mL) to the round window membrane in male Mongolian gerbils. H(2) treatment was given twice by exposing the animals to H(2) (1%, 2%, and 4%) for 60 min at 1 h and 6 h after ouabain application. Before and 7 d after ouabain application, the hearing status of the animals was evaluated using the auditory brainstem response (ABR) approach, the hear cell function was evaluated with distortion product otoacoustic emissions (DPOAE). Seven days after ouabain application, the changes in the cochleae, especially the spiral ganglion neurons (SGNs), were morphologically studied. TUNEL staining and immunofluorescent staining for activated caspase-3 were used to assess the apoptosis of SGNs.

RESULTS

Treatment with H(2) (2% and 4%) markedly attenuated the click and tone burst-evoked ABR threshold shift at 4, 8, and 16 kHz in ouabain-exposed animals. Neither local ouabain application, nor H(2) treatment changed the amplitude of DPOAE at 4, 8, and 16 kHz. Morphological study showed that treatment with H(2) (2%) significantly alleviated SGN damage and attenuated the loss of SGN density for each turn of cochlea in ouabain-exposed animals. Furthermore, ouabain caused significantly higher numbers of apoptotic SGNs in the cochlea, which was significantly attenuated by the H(2) treatment. However, ouabain did not change the morphology of cochlear hair cells.

CONCLUSION

The results demonstrate that H(2) treatment is beneficial to ouabain-induced AN via reducing apoptosis. Thus, H(2) might be a potential agent for treating hearing impairment in AN patients.

[Auditory synaptopathy/neuropathy: clinical findings and diagnosis]

Auditory synaptopathy/neuropathy (AS/AN) is a special subtype of sensorineural hearing disorders with heterogeneous phenotypes and underestimated incidence. AS/AN generally develops in infancy, occasionally in adulthood. Symptoms include fluctuating, mostly bilateral hearing loss and abnormally reduced speech comprehension, especially in noisy environments. Within audiological assessments, patients with AS/AN present otoacoustic emissions (TEOAE; DPOAE) and cochlear microphonics (CM), absence of stapedius reflexes (SR) as well as absent or pathologically altered auditory evoked brainstem potentials (ABR). Children with AS/AN cannot be identified within OAE-based newborn hearing screening programs. Clinical findings, transtympanic electrocochleography (ECoG) and further diagnostic tools permit further identification of individual characteristics. In individual cases conventional amplification and the use of FM systems may improve hearing and communication skills. If these interventions, accompanied by intensive hearing, speech and language therapy are unsuccessful, cochlear implants (CI) or alternative forms of communication may be useful options for rehabilitation.

Audiologic management of auditory neuropathy spectrum disorder in children: a systematic review of the literature

PURPOSE

This review summarizes current evidence related to the audiologic management of children with auditory neuropathy spectrum disorder (ANSD).

METHOD

A systematic search of the literature was conducted in 25 electronic databases (e.g., PubMed, CINAHL, and ERIC) using key words such as auditory neuropathy, auditory neuropathy spectrum disorder, auditory neuropathy/dyssynchrony, and hearing loss. Eighteen studies met the inclusion criteria by addressing 1 or more of 8 clinical questions. Studies were evaluated for methodological quality, and data regarding participant, intervention, and outcome variables are reported.

RESULTS

Fifteen of the 18 studies addressed the use of cochlear implantation, and 4 addressed conventional acoustic amplification. All participants demonstrated improved auditory performance; however, all 18 studies were considered exploratory, and many had methodological limitations.

CONCLUSION

The clinical evidence related to intervention for ANSD is at a very preliminary stage. Additional research is needed to address the efficacy of acoustic amplification and cochlear implantation in children with ANSD and the impact of this disorder on developmental outcomes.

Risk factors for auditory neuropathy spectrum disorder in NICU infants compared to normal-hearing NICU controls

OBJECTIVES

To evaluate independent etiologic factors associated with auditory neuropathy spectrum disorder (ANSD) in infants who have been admitted to the neonatal intensive care unit (NICU) compared to normal-hearing controls.

STUDY DESIGN

Case-control study.

METHODS

We included all infants (n = 9) with the ANSD profile admitted to the NICU of Sophia Children's Hospital between 2004 and 2009. Each patient was matched with four normal-hearing controls of the same gender and postconceptional age. The following possible risk factors were studied: birth weight, dysmorphic features, APGAR scores (at 1, 5, and 10 minutes), respiratory distress (IRDS), cytomegalovirus (CMV) infection, sepsis, meningitis, cerebral bleeding, hyperbilirubinemia requiring phototherapy, peak total bilirubin level, furosemide, dexamethason, vancomycin, gentamycin, and tobramycin administration.

RESULTS

Nine infants met the ANSD criteria in one or both ears. IRDS (P = .02), meningitis (P = .04), and vancomycin administration (P = .009) were significantly increased in infants with ANSD compared to controls.

CONCLUSIONS

In high-risk NICU infants IRDS, meningitis and vancomycin administration are associated with auditory neuropathy spectrum disorder.

Screening mutations of OTOF gene in Chinese patients with auditory neuropathy, including a familial case of temperature-sensitive auditory neuropathy

BACKGROUND

Mutations in OTOF gene, encoding otoferlin, cause DFNB9 deafness and non-syndromic auditory neuropathy (AN). The aim of this study is to identify OTOF mutations in Chinese patients with non-syndromic auditory neuropathy.

METHODS

73 unrelated Chinese Han patients with AN, including one case of temperature sensitive non-syndromic auditory neuropathy (TS-NSRAN) and 92 ethnicity-matched controls with normal hearing were screened. Forty-five pairs of PCR primers were designed to amplify all of the exons and their flanking regions of the OTOF gene. The PCR products were sequenced and analyzed for mutation identification.

RESULTS

Five novel possibly pathogenic variants (c.1740delC, c.2975_2978delAG, c.1194T>A, c.1780G>A, c.4819C > T) were identified in the group of 73 AN patients, in which two novel mutant alleles (c.2975_2978delAG + c.4819C > T) were identified in one Chinese TS-NSRAN case. Besides, 10 non-pathogenic variants of the OTOF gene were found in AN patients and controls.

CONCLUSIONS

Screening revealed that mutations in the OTOF gene account for AN in 4 of 73(5.5%) sporadic AN patients, which shows a lower genetic load of that gene in contrast to the previous studies based on other populations. Notably, we found two novel mutant alleles related to temperature sensitive non-syndromic auditory neuropathy. This mutation screening study further confirms that the OTOF gene contributes to ANs and to TS-NSRAN.

Auditory steady state response in auditory neuropathy

Review:

Auditory neuropathy is a disorder characterised by preservation of outer hair cell function, with normal otoacoustic emissions and/or cochlear microphonics, but an absent or distorted auditory brainstem response.

Purpose:

This study aimed to objectively assess hearing thresholds in patients with auditory neuropathy, using the auditory steady state response.

Materials and methods:

Thirteen patients with auditory neuropathy and 15 normal hearing subjects were examined. Audiological evaluation included basic audiological tests, otoacoustic emissions, auditory brainstem response and auditory steady state response.

Results:

In the auditory neuropathy patients, the auditory brainstem response was absent in 11 patients, while the auditory steady state response was absent in only three.

Conclusion:

The auditory steady state response may serve as a valuable objective measure for assessing the hearing threshold across different frequencies in patients with auditory neuropathy. We recommend that auditory steady state response be used to complete the evaluation of patients with auditory neuropathy.

Temperature-sensitive auditory neuropathy associated with an otoferlin mutation: Deafening fever!

Transient deafness associated with an increase in core body temperature is a rare and puzzling disorder. Temperature-dependent deafness has been previously observed in patients suffering from auditory neuropathy. Auditory neuropathy is a clinical entity of sensorineural deafness characterized by absent auditory brainstem response and normal otoacoustic emissions. Mutations in OTOF, which encodes otoferlin, have been previously reported to cause DFNB9, a non-syndromic form of deafness characterized by severe to profound prelingual hearing impairment and auditory neuropathy. Here we report a novel mutation in OTOF gene in a large family affected by temperature-dependent auditory neuropathy. Three siblings aged 10, 9 and 7 years from a consanguineous family were found to be affected by severe or profound hearing impairment that was only present when they were febrile. The non-febrile patients had only mild if any hearing impairment. Electrophysiological tests revealed auditory neuropathy. Mapping with microsatellite markers revealed a compatible linkage in the DFNB9/OTOF region in the family, prompting us to run a molecular analysis of the 48 exons and of the OTOF intron-exon boundaries. This study revealed a novel mutation p.Glu1804del in exon 44 of OTOF. The mutation was found to be homozygous in the three patients and segregated with the hearing impairment within the family. The deletion affects an amino acid that is conserved in mammalian otoferlin sequences and located in the calcium-binding domain C2F of the protein.