|Year : 2014 | Volume
| Issue : 3 | Page : 119-122
Clinical presentation and audiologic findings in pediatric auditory neuropathy
Navneet Gupta1, Deepanshu Gurnani2, Vikas Sinha2, Pawan Sharma2, Sachin Jindal2, Ambuj Pandey2
1 Departments of ENT and Head and Neck Surgery, Acharya Sri Chandra College of Medical Sciences and Hospital, Jammu, Jammu and Kashmir, India
2 Departments of ENT and Head and Neck Surgery, M. P. Shah Government Medical College, Jamnagar, Gujarat, India
|Date of Web Publication||16-Jul-2014|
Department of ENT and Head and Neck Surgery, M. P. Shah Government Medical College, Jamnagar, Gujarat
Source of Support: None, Conflict of Interest: None
Aim: of the study was to rule out audiologic findings, related etiologies and its effect in pediatric patients having hearing deficits that are most likely due to a neuropathy of the eighth nerve. Study Design: Retrospective neo-natal hearing screening programme based. Subject and Methods: Subjects include 30 children aged from 0 yrs to 12 yrs, were tested with pure tone audiometry, behavioral observation audiometry, free-filed audiometry, speech audiometry, auditory brainstem response, and click evoked otoacoustic emissions. Results: Pure tone and free-field testing revealed 40 ears (66.67%, n = 60) with sloping type, sensorineural hearing loss, 20 ears (33.3%, n = 60) had flat configuration. Out of this 18 (6%, n = 30) subject showed bilateral similar configuration (either bilateral sloping type/ flat type of audiogram). Rest 12 (40%, n = 30) subject showed bilateral different pattern. 10 (33.3%, n = 30 children demonstrated fair to poor word discrimination scores and the other 2 (6.67%, n = 30) had fair to good word discrimination. For other rest of 18 (60%, n = 30) children speech test couldn't be performed because of age limit and poor speech and language development. Out of 30 subjects 28 (93.3%, n = 30) showed normal distortion product Otoacoustic emissions and 2(6.67%, n = 30) subjects showed absent emissions. Conclusions: All thirty children demonstrated absent or marked abnormalities of brainstem auditory evoked potentials which suggest cochlear outer hair cell function is normal; mostly lesion is located at the eighth nerve or beyond. Generally auditory neuropathy is associated with different etiologies and it is difficult to diagnose auditory neuropathy with single audiological test; sufficient test of battery is required for complete assessment and diagnosis of auditory neuropathy
Keywords: Auditory brainstem response, Auditory neuropathy, Evoked otoacoustic emissions, Hearing loss
|How to cite this article:|
Gupta N, Gurnani D, Sinha V, Sharma P, Jindal S, Pandey A. Clinical presentation and audiologic findings in pediatric auditory neuropathy. Indian J Otol 2014;20:119-22
|How to cite this URL:|
Gupta N, Gurnani D, Sinha V, Sharma P, Jindal S, Pandey A. Clinical presentation and audiologic findings in pediatric auditory neuropathy. Indian J Otol [serial online] 2014 [cited 2020 Sep 29];20:119-22. Available from: http://www.indianjotol.org/text.asp?2014/20/3/119/136852
| Introduction|| |
Traditionally, hearing loss has been defined by its origin and site of lesion. It has also divided into different types in accordance with its neural involvement, that is, conductive, mixed type and sensorineural type. Though mixed type hearing loss depicts both conductive and sensory components in it, but in sensorineural type of hearing loss, pure cochlear neural involvements are very common. Further sensorineural hearing loss (SNHL) comprises two aspects of disorder based on the site of lesion, whether it is cochlear or retro-cochlear (areas beyond cochlea). Retro-cochlear region composes all superior auditory pathways and structures except cochlea, that is, from cochlear nucleus to auditory cortex.
Auditory neuropathy (AN) is an unusual disorder in which patients demonstrate hearing loss for pure tones, difficulty in word discrimination irrespective of pure-tone loss, absent or abnormal auditory brainstem responses (ABRs), and usually normal outer hair cell function as measured by otoacoustic emissions (OAEs) and cochlear microphonic.  A neuropathy usually refers to a disease of the peripheral nerve or nerves, but the auditory nerve itself is not always affected in AN spectrum disorders.  The hallmark of AN, a neural type of hearing loss, is preservation of OAEs and abnormal or absent ABRs. Most patients with SNHL are found to have a sensory type of hearing loss, and numerous genes for both syndromic and nonsyndromic forms have been identified.
It is estimated that at least 50% of congenital hearing loss is due to hereditary factors. Approximately, 70% of hereditary hearing loss is nonsyndromic. Patterns of inheritance of nonsyndromic hearing loss can be autosomal recessive, autosomal dominant, X-linked, and mitochondrial. 
Auditory neuropathy may accompany peripheral neuropathy in a variety of dominant syndromes such as Charcot-Marie-Tooth disease More Details  and Friedreich's ataxia,  G6PD. AN unassociated with peripheral neuropathy most commonly occurs as a sporadic or recessive trait,  but X-linked recessive  and autosomal dominant  forms have also been seen and described. Furthermore, the etiology of AN is vast, which may include prematurity, hyperbilirubinemia, anoxia, hypoxia, congenital brain anomalies, ototoxic drug exposure, and genetic factors.  It is estimated that approximately 40% of cases have an underlying genetic basis, which can be inherited in both syndromic and nonsyndromic conditions.
| Methods|| |
A group of pediatric children were enrolled. These children were selected from various medical, neo-natal, pediatric, audiological and ENT setup and also from neonatal hearing screening program. Majority of children were having prenatal, perinatal, postnatal, or related medical history. Complete audiological test battery were administered in these children.
This study sample consists of 30 children aged ranges from 0 to 12 years, among whom 9 (30%, n = 30) children were referred from different audiology clinic over 1-year period, had significant signs and symptoms of auditory difficulty. Other 21 (70%, n = 30) children were referred from periodic newborn screening program and other pediatric and medical setup, had taken for suspected hearing loss. Among 30 children, there are 20 boys (66.67%, n = 30) and 10 girls (33.3%, n = 30). 9 (30%, n = 30) children had history of postnatal medical complications and had kept in incubator for a long time. Despite hearing loss; some of the audiological signs were syndromic in origin and others nonsyndromic in nature. Early diagnosis of referred children revealed that all children were initially diagnosed with SNHL. Further audiological assessment of all 30 children confirmed that they have absent or abnormal ABRs and normal OAEs, suggestive of normal outer hair cell functioning.
One child developed normal speech and language until 18 months, after he had severe jaundice his speech and language development ceased, although he still responded to loud music and also often showed selective listening. Five (16.67%, n = 30) children showed history of neo-natal jaundice and admitted to neonatal intensive care unit for certain period of time. Seven (23.3%, n = 30) children had related history of delayed birth cry and low birth weight. Two (6.67%, n = 30) of the children diagnosed with Friedreich's. Other 2 (6.67%, n = 30) of the children had history of recurrent pneumonia and seizure before diagnosis of hearing loss. 4 (13.3%, n = 30) had history of birth hypoxia/seizure which further diagnosed with delayed mile stone and cerebral palsy. One (3.33%, n = 30) of the children has congenital hydrocephalus; lumbar puncture was done on the 12 th day of child's age. 1 (3.33%, n = 30) of the children reported with G6PD. Rest 7 (23.3%, n = 30) subjects didn't report any significant history.
| Audiologic Testing|| |
Standard pure-tone audiometry testing was carried out for the frequencies 250, 500, 1000, 2000, 4000, and 8000 Hz for 20 children. Since, the subject group age ranges from 0 to 12 years. 10 (33.3%, n = 30) children were not cooperative during pure-tone audiometry, so they had gone for behavior observation audiometry and free field audiometry. Masked bone conduction testing couldn't be accomplished for all the children. Speech audiometry testing was not possible for 10 (33.3%, n = 30) children who had little or limited spoken language. In click-evoked OAEs, the distortion product OAEs was determined in 6 octave bands in response to signal to-noise ratio of at least 4 dB and waveform reproducibility in at least three octave bands of >75%.
Auditory brainstem evoked potentials were recorded in two channel setup with four electrode configuration, that is, two electrode on both sided mastoid processes, one electrode on fore head as ground point and one at vertex to optimize detection of wave V. Band pass from 30 or 100 Hz to 4000 Hz was used to detect principle ABR waves. Click stimuli were rarefaction clicks presented monaurally at rates from 11.1 to 33.3/s and at intensities from 55 dBnHL to 85 dBnHL and in most cases, 95 dBnHL. Repeated wave replicability testings were administered to cross-check the ABR wave forms. Different averages were documented for wave interpretation throughout testing. Electrode generated impedance value and artifact rate were eventually monitored to maintain test-retest reliability. Latency-intensity function test, interpeak latency, and wave amplitude were taken into account for better diagnosis.
| Results|| |
The audiological results of 30 children for pure-tone audiometric testing, word discrimination scores, click-evoked otoacoustic emission and auditory brainstem responses
The 40 ears had sloping type of hearing loss, 20 ears had flat configuration (S.N. in nature). Severity ranged from mild to profound. In 18 (60%, n = 30) youngest children, there was insufficient spoken language or limited vocabulary skill, word discrimination could not be assessed and is assumed to be poor on this basis. Of the remaining 12 (40%, n = 30) children, 10 (33.3%, n = 30) had poor-to-fair word discrimination. 2 (6.67%, n = 30) of the subjects had very good word discrimination (88-90%).
Almost all the 28 (93.3%, n = 30) children had showed absent or abnormal ABR waves with presence of normal evoked OAEs as per the audiological characteristics of AN, except 2 (6.67%, n = 30) of the subjects, in spite of having moderately severe hearing loss, subjects were present with absent of evoked OAE [Figure 1].
|Figure 1: Pattern of hearing loss in 60 ears ; n = 30 children. (X axis shows no of ears) (40 ears; n = 20 children showed sloping hearing loss, 20 ears; n = 10 children showed flat hearing loss)|
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A 6-year-old boy child who developed progressive hearing loss at the age of 4 years after a brain insult with history of meningitis and episodic seizures. His pure-tone audiogram reveals bilateral mild to moderately severe SNHL with poor speech discrimination scores (20% right and 5% left). Evoked auditory potentials showed completely absent ABR to clicks or tone bursts up to 95-dBnHL.
Most of the patients had pure-tone hearing loss ranging from mild to severe degrees, poor speech discrimination, absent or severely abnormal ABRs, and usually normal click-evoked OAEs. Magnetic resonance imaging of the brain revealed no brainstem or eighth cranial nerve abnormalities to account for the electrophysiologic findings. A total of 30 children were identified with AN.
| Discussion|| |
Almost all our 28 (93.3%, n = 30) children had shown presence of normal evoked OAEs in which 23 (76.6%, n = 30) children were related to some or other medical history and 7 (23.3%, n = 30) children were not carrying any significant history. Doyle et al. in 1998 conducted a retrospective study on eight pediatric patients and identified having hearing deficits that are most likely due to a neuropathy of the eighth nerve. Retrospective review of audiologic findings in eight children with AN reveals five children had sloping SNHL, two with high frequency loss, and one with a mild, flat configuration. Six children demonstrated poor word discrimination scores, and the other two had fair to good word discrimination. All eight children had normal distortion product and transient OAEs. All eight children demonstrated absent or marked abnormalities of brainstem auditory evoked potentials (BAEPs).  Deltenre et al. in their study have reported three children with early onsets and major neo-natal illnesses without any BAEP neural component who all retained isolated cochlear microphonic potentials as well as click-evoked OAEs.  Berlin et al. described three patients having AN as part of Charcot-Marie-Tooth disease, a hereditary sensori-motor neuropathy.  Spoendlin described the temporal bones of two individuals with Friedreich's ataxia.  He noted that the organ of Corti was normal, but that there was damage to the spiral ganglion cells in these patients. In their study, Hallpike et al. also they found normal hair cells, but degeneration of spiral ganglion cells and auditory nerve fibers in a patient with hereditary hearing loss, poor speech comprehension, and peripheral neuropathy.  The point concern to these researchers was that the ABR abnormalities were far disproportion to the pure-tone loss. The localization of the disorder to the eighth nerve could not be made at that time, as methods for defining outer hair cell function were not yet widely available (OAEs) or not routinely used (cochlear microphonics). Kraus et al. felt that these cases probably had neuropathology of the auditory brain stem.  Cases of absent ABR in the presence of normal hearing had been identified earlier. More recently, additional cases of adult and pediatric AN have been found ([Sininger et al.] presented at the American Speech Language Hearing Association Convention, Anaheim, CA, November, 1993).  The incidence of AN not yet known, but is seen infrequently relative to sensory hearing loss. However, it is possible that some individuals who were diagnosed with SNHL before without OAEs testing have undetected neuropathy. Thus, we recommend routine OAEs and screening ABR testing in hearing screening program, children who diagnosed with hearing loss or having any significant medical history.
| Conclusion|| |
We incurred the previous and ongoing trends, clinical presentation and audiological findings of pediatric AN, along with its most obvious etiology and their subsequent affects on hearing and communication. AN is a spectrum disorder usually associated with various syndromes and other pathological sign and symptoms. This unique disorder affects speech-language development in pediatrics by impairing normal hearing mechanism, thus, results in poor speech discrimination. Previous studies have concluded that AN in pediatrics usually occurred due to prenatal and post natal infections and complications such as neuropathy at eight cranial nerve, hypoxia, meningitis etc. With course of advance studies, clinical audiologists as well as otolaryngologists should be aware of its nature and complications before diagnosis of this unusual disorder. Even though as per recent studies OAEs might be absent in patient with AN, still OAEs and screening ABR are key tests and should be include in newborn screening program to keep a vigil eye on its incidence and for facilitating early identification, which would help in contribute some additional sorts of intervention to this disorder.
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