An isolated and sporadic auditory neuropathy (auditory nerve disease): report of five patients

Temperature-Dependent Auditory Neuropathy: Is it an Acoustic Uhthoff-like Phenomenon?; A Case Report

Objectives:

We describe the case of a young girl in whom transient deafness occurred when her core body temperature rose.

Methods:

The patient was referred for a series of audiological and neurologic evaluations performed over time in both afebrile and febrile states, as well as after a stress test (with a treadmill) in which the body temperature rise simulated the febrile state.

Results:

The patient was found to have a temporary bilateral hearing loss, but had normal distortion product otoacoustic emissions. Moreover, auditory brain stem responses revealed the absence of neural synchrony when her core body temperature increased.

Conclusions:

These results are consistent with a temperature-dependent auditory neuropathy, a rare condition in which patients show normal outer hair cell function and abnormal neural function of the eighth cranial nerve. The symptom is reminiscent of Uhthoff's phenomenon, which is described as transient visual loss and is usually observed in multiple sclerosis. This case of temperature-dependent auditory neuropathy is noteworthy because it sheds light on a disorder of which there have been few reports in the literature. We discuss its similarity to Uhthoff's phenomenon.

Molecular approach of auditory neuropathy

INTRODUCTION

Mutations in the otoferlin gene are responsible for auditory neuropathy.

OBJECTIVE

To investigate the prevalence of mutations in the mutations in the otoferlin gene in patients with and without auditory neuropathy.

METHODS

This original cross-sectional case study evaluated 16 index cases with auditory neuropathy, 13 patients with sensorineural hearing loss, and 20 normal-hearing subjects. DNA was extracted from peripheral blood leukocytes, and the mutations in the otoferlin gene sites were amplified by polymerase chain reaction/restriction fragment length polymorphism.

RESULTS

The 16 index cases included nine (56%) females and seven (44%) males. The 13 deaf patients comprised seven (54%) males and six (46%) females. Among the 20 normal-hearing subjects, 13 (65%) were males and seven were (35%) females. Thirteen (81%) index cases had wild-type genotype (AA) and three (19%) had the heterozygous AG genotype for IVS8-2A-G (intron 8) mutation. The 5473C-G (exon 44) mutation was found in a heterozygous state (CG) in seven (44%) index cases and nine (56%) had the wild-type allele (CC). Of these mutants, two (25%) were compound heterozygotes for the mutations found in intron 8 and exon 44. All patients with sensorineural hearing loss and normal-hearing individuals did not have mutations (100%).

CONCLUSION

There are differences at the molecular level in patients with and without auditory neuropathy.

Evaluation of inner hair cell and nerve fiber loss as sufficient pathologies underlying auditory neuropathy

Auditory neuropathy is a hearing disorder characterized by normal function of outer hair cells, evidenced by intact cochlear microphonic (CM) potentials and otoacoustic emissions (OAEs), with absent or severely dys-synchronized auditory brainstem responses (ABRs). To determine if selective lesions of inner hair cells (IHCs) and auditory nerve fibers (ANFs) can account for these primary clinical features of auditory neuropathy, we measured physiological responses from chinchillas with large lesions of ANFs (about 85%) and IHCs (45% loss in the apical half of the cochlea; 73% in the basal half). Distortion product OAEs and CM potentials were significantly enhanced, whereas summating potentials and compound action potentials (CAPs) were significantly reduced. CAP threshold was elevated by 7.5dB, but response synchrony was well preserved down to threshold levels of stimulation. Similarly, ABR threshold was elevated by 5.6dB, but all waves were present and well synchronized down to threshold levels in all animals. Thus, large lesions of IHCs and ANFs reduced response amplitudes but did not abolish or severely dys-synchronize CAPs or ABRs. Pathologies other than or in addition to ANF and IHC loss are likely to account for the evoked potential dys-synchrony that is a clinical hallmark of auditory neuropathy in humans.

The frequency of auditory neuropathy detected by universal newborn hearing screening program

OBJECTIVE

Auditory neuropathy/auditory dyssynchrony (AN/AD) has become a well-accepted clinical entity. The combined use of oto-acoustic emissions (OAEs) and auditory brainstem response (ABR) testing in the universal newborn hearing screening (UNHS) has led to the easy recognition of this disorder. Although, we are now able to diagnose AN/AD reliably, little is known about its epidemiology, etiology, and especially the frequency of its occurrence. The primary goal of this study was to determine the frequency of AN/AD in the Western Anatolian region of Turkey. The secondary goal was to compare the detection rate of AN/AD before and after the implementation of the UNHS in the audiology department of Dokuz Eylul University Hospital.

METHOD

Between 2005 and 2007, among the 23,786 newborns who were screened by automated click evoked oto-acoustic emissions (a-CEOAE) and automated auditory brainstem responses (a-ABRs), 2236 were referred to our department. All necessary audiological tests were performed for all the referred newborns. Among them, babies with deficient or abnormal ABR in combination with normal OAEs were considered as having AN/AD. These babies were evaluated with additional diagnostic audiological tests. Furthermore, comparison of the incidence of children diagnosed with AN/AD before and after the implementation of UNHS in our audiology department was also performed.

RESULTS

Among the referred newborns, 65 had abnormal or deficient ABR test results. Ten of these 65 newborn babies (mean diagnostic age: 5.7 months) with hearing impairment showed electrophysiological test results that were consistent with AN/AD. The frequency of AN/AD in these 65 children with hearing loss was 15.38%. Moreover, the frequency of AN/AD within UNHS was found to be 0.044%. Seven of the 10 babies with AN/AD had hyperbilirubinemia as a risk factor, which is a high rate to be emphasized. On the other hand, the retrospective investigation of children diagnosed with AN/AD in the same audiology department between 1999 and 2005 (i.e. before the implementation of UNHS) revealed only 7 children, with an average diagnostic age of 34 months.

CONCLUSION

After implementing the UNHS, the incidence of AN/AD in the audiology department increased from 1.16 to 4.13. Furthermore, the age of diagnosis of AN/AD decreased from 34 months to 5.7 months. This study shows that AN/AD, when screened, is a comparatively common disorder in the population of hearing-impaired infants. While newborn hearing screening provides early detection of babies with hearing loss, it also helps to differentiate AN/AD cases when the screening is performed with both a-ABR and automated oto-acoustic emission (a-OAE) tests. Thus, the routine combined use of a-ABR and a-OAE tests in UNHS programs, especially for the high-risk infants, can provide better detection of newborns with AN/AD. Furthermore, hyperbilirubinemia is merely an association and maybe etiologically linked.

Einseitige auditorische Neuropathie

Auditory neuropathy presents with normal otoacoustic emissions combined with pathological findings in brainstem evoked response audiometry. Normally, the auditory neuropathy is bilateral. We report about a 9 year old child where we could diagnose a unilateral deafness in spite of regular TEOAE and DPOAE. No reproducible biosignals were seen when the right ear was stimulated with alternating click stimuli at a level of 80 dB. On the left side, the latency of the potentials was normal. A cranial MRI showed normal anatomy. In order to determine a unilateral deafness, objective tests (e.g., OAE, BERA) and subjective tests should be used.

Newborn hearing screening in the NICU: profile of failed auditory brainstem response/passed otoacoustic emission

OBJECTIVE

Incidence of a specific pattern of auditory responses, absent auditory brainstem responses (ABRs) and present otoacoustic emissions (OAEs), in newborn hearing screening in a regional perinatal center neonatal intensive care unit (NICU) is described. This profile, labeled auditory neuropathy or auditory dyssynchrony (AN/AD), is a dysfunction in neural/brainstem transmission that occurs in individuals whose outer hairs cells are functioning normally. Although the AN/AD profile has been associated with various risk factors, incidence and prediction are unknown.

METHOD

Analysis of electrophysiologic measures and medical record reviews of the first 22 months of the universal newborn hearing-screening program was conducted. Association of the AN/AD profile was evaluated with the following factors: gender, gestational age, ototoxic drug regimen, low birth weight, hyperbilirubinemia, hydrocephalus, low Apgar score, anoxia, respiratory distress syndrome, pulmonary hypertension, intraventricular hemorrhage, multiple birth, seizure activity, and family history.

RESULTS

One hundred fifteen (24.1%) of the 477 infants failed the ABR in 1 or both ears and passed OAEs bilaterally. Comparisons of infants fitting the AN/AD profile with those not fitting the AN/AD profile were negative with 3 exceptions: those with hyperbilirubinemia and those who were administered vancomycin or furosemide. A logistic-regression analysis model failed to predict which infants would be at risk for the AN/AD profile either unilaterally or bilaterally.

CONCLUSIONS

Screening of NICU infants should be conducted with ABR first, followed by OAE after failure on ABR. Because the incidence of the AN/AD profile was found to be 24% in this at-risk population, additional study is warranted.

Auditory Neuropathy or Endocochlear Hearing Loss?

AIMS

The purpose of the study was to define boundaries between endocochlear hearing loss and auditory neuropathy in children with congenital profound hearing loss and positive otoacoustic emissions.

PATIENT

A child presented with bilateral profound hearing loss, which was confirmed by the absence of evoked auditory potentials at 110 dB and with conserved otoacoustic emissions. The lack of any relevant medical history, a normal neurologic pediatric examination, and the improvement obtained with powerful hearing aids suggested an endocochlear cause. Genetic testing identified mutations in OTOF, responsible for the DFNB9 recessive form of hearing loss.

RESULTS

In recent years, cases of children with hearing loss associated with positive otoacoustic emissions have been labeled as "auditory neuropathy." Classically, this form of hearing loss is refractory to the use of hearing aids and cochlear implants. Mutations in OTOF lead to inner hair cells dysfunction, whereas the outer hair cells are initially functionally preserved. As this form of endocochlear hearing loss can be detected at a molecular level, genetic testing can be proposed for cases of nonsyndromic auditory neuropathy, as those children could benefit from cochlear implantation.

CONCLUSION

It is advisable to reserve the term "auditory neuropathy" for patients who present hearing loss and conserved otoacoustic emissions in the context of a neurologic syndrome or for children with suggestive perinatal history. In other cases, genetic testing for mutations in OTOF should be carried out.

Cochlear implantation in an adult patient with auditory neuropathy

We present a case report of effective cochlear implantation for an adult patient with auditory neuropathy. A 34-year-old man developed bilateral hearing loss at approximately 10 years of age. His speech discrimination score was very severe despite only moderate sensorineural hearing loss. Absence of auditory brainstem responses (ABR) and preservation of distortion product otoacoustic emissions (DPOAE) were confirmed by our audiological examinations. After cochlear implantation, good responses for electrically evoked compound action potential (EAP) and electrically evoked ABR (EABR) were observed. Postoperatively, his audiological performance was significantly improved. We conclude that cochlear implantation can be a valid option for patients with auditory neuropathy.

Auditory neuropathy/auditory dys-synchrony in school children with hearing loss: frequency of occurrence

OBJECTIVE

The frequency of occurrence of a recently identified hearing disorder, auditory neuropathy/auditory dys-synchrony (AN/AD), was investigated in children with hearing impairment in Hong Kong.

METHODS

In this study, 56 students, aged 7-18 years, attending primary divisions in schools for the hearing impaired were screened using otoacoustic emission procedures.

RESULTS

One student in the study group was found to have intact outer hair cell function. A detailed diagnostic assessment of this case strongly suggested AN/AD was involved. Combining the study results with those of a previously conducted survey in Hong Kong, the frequency of occurrence of AN/AD in children attending schools for the hearing impaired was estimated to be 2.44% (3 out of 123 children screened). Estimates of the frequency of occurrence of AN/AD in various other educational settings in Hong Kong were also derived.

CONCLUSIONS

The study indicates that AN/AD is not an extremely rare disorder. Educational audiologists and other health care professionals need to be actively involved in the identification and management of AN/AD. Research should be directed at technological innovations that may help to overcome the limitations of present screening procedures, in order to more accurately identify the disorder.

Primary auditory neuropathy - an enigma

OBJECTIVES

To report audiological and neuroradiological findings in patients with primary auditory neuropathy (PAN) from a tertiary institution in south India.

MATERIAL AND METHODS

The auditory profiles in 24 patients were analyzed along with neurological and radiological findings.

RESULTS

Puretone audiometry showed varied hearing acuity and configuration. The syllable recognition score (n=15) was above 80% except in three. The dichotic digit test (n=11) showed bilateral suppression except in two who showed unilateral suppression. The auditory brainstem responses and the acoustic stapedius reflex were absent with distortion product otoacoustic emission (DPOAE) present in all. The neurological and radiological studies were normal.

CONCLUSION

The audiological profile is consistent with the presence of DPOAE and absence of acoustic stapedius reflex and auditory brainstem responses. In patients with adequately preserved syllable recognition in quiet conditions, there was a significantly poor performance on dichotic digit test. As these patients had no neurological deficits and absence of specific etiological factors, we propose to use the term PAN for this entity.

Auditory neuropathy : Diagnostic and therapeutic challenge report of first series of four cases from india

Auditory neuropathy (AN), a recently described clinical entity, is a sensorineural disorder where the patient has hearing loss with impaired word discrimination out of proportion to pure tone loss in the pressence of abnormal / absent auditory brain stem responses, and normal outer hair cell as measured by otoacoustic emissions and / cochlear microphonics. It is essential that the practicing, ENT surgeon have a high degree of suspicion of AN in patients complaining of difficulty in understanding speech with hearing loss and audiological evidence of dissociation between pure-tone and speech audiometry. Appropriate newer diagnostic tests of ABR and OAE and /or CM for confirmation of AN is essential. We present a series of four patients with auditory neuropathy from a tertiary care teaching hospital. This is the first Series of 4 cases of this clinical entity from the Indian subcontinent.

Cochlear implantation in patients with auditory neuropathy of varied etiologies

OBJECTIVES/HYPOTHESIS

Auditory neuropathy is a relatively recently described pattern of hearing loss characterized by preservation of outer hair cell function despite absent brainstem auditory evoked responses. Intact outer hair cell function is demonstrated by the presence of otoacoustic emissions and/or a measurable cochlear microphonic on electrocochleography, whereas no synchronous neural activity (absent action potentials) is seen on acoustically evoked brainstem auditory evoked response testing. The study reviews the authors' experience with six patients diagnosed with auditory neuropathy, four of whom have undergone cochlear implantation.

MATERIALS AND METHODS

A retrospective review of all medical and audiological charts at the University of Virginia Hospitals (Charlottesville, VA) was performed to identify patients who have undergone cochlear implantation or have been diagnosed with auditory neuropathy, or both.

RESULTS

Six patients with hearing loss attributable to auditory neuropathy were identified, four of whom have undergone cochlear implantation. Causes varied, including congenital, infectious, and idiopathic origins. Adults demonstrated subjective auditory perception on promontory stimulation, whereas no repeatable brainstem auditory evoked response waveforms could be demonstrated on pediatric promontory stimulation testing. Patients with implants demonstrated implant-evoked brainstem auditory evoked responses and improved audiological performance.

CONCLUSIONS

The six cases presented in the study represent varied causes and, probably, varied sites of lesions of auditory neuropathy. Promontory stimulation has been valuable, particularly in adults. Cochlear implantation allows the opportunity to provide a supraphysiological electrical stimulation to the auditory nerve, with the hope of reintroducing synchronous neural activity. Greater confidence and enthusiasm for cochlear implantation in appropriately selected patients with auditory neuropathy are gained through experience with such diverse cases.

Electrocochleography in auditory neuropathy

Auditory neuropathy (AN) is a disorder characterized by the absence or the severe impairment of the auditory brainstem responses (ABRs) together with the preservation of otoacoustic emissions and/or cochlear microphonic (CM). We recorded transtympanic electrocochleography (ECohG) evoked by 0.1 ms clicks in one young adult and in four children having distortion product otoacoustic emissions and absent ABRs. In all but one patient CM and summating potential (SP) were present with normal threshold, and their amplitudes appeared comparable to or higher than the values obtained from subjects with normal hearing. The compound action potential (CAP) was absent in two patients while in one subject CM and SP were followed by a highly desynchronized neural activity. A broad CAP was found in two children and the threshold appeared clearly elevated in one of them, while it showed only a mild elevation in the other. No correlation was found between CAP and behavioral thresholds. These results suggest that ECohG can be useful in AN diagnoses since it is the only reliable tool in evaluating the auditory peripheral function in the presence of a desynchronized ABR.