early detection of a hearing problem with a diagnostic tool like newborn hearing screening test is important .
early detection can bring improvements in hearing ability and language development of children by promoting the use of rehabilitation strategies including hearing aid and cochlear implant .
auditory neuropathy is characterized by abnormal auditory brainstem response ( abr ) and normal otoaoustic emission ( oae ) responses .
although auditory neuropathy manifests as various patterns in pure tone and speech audiometry , most patients have very poor word discrimination function.1 ) we present a case of auditory neuropathy improved in a child who was diagnosed with moderate hearing loss by abr testing at 16 months of age , but who presented normal pure tone threshold and speech discrimination score 3 years after wearing hearing aids .
a six - year - old boy presented to the outpatient clinic with abnormalities of hearing and language development .
no congenital anomalies were evident at birth . however , he was not able to speak until 16 months of age and his response to external sound stimuli was slow .
he showed no abr - response to 65 db nhl click stimuli at 16 months age . since then he had worn a hearing aid in the right ear ( fig .
1 ) . at 25 months of age , aided hearing threshold was about 30 db hl in sound field pure tone audiometry ( fig .
he wore the hearing aid for another 2 years . at 5 years , 10 months of age , he visited our hospital for a hearing evaluation .
his parents related that his hearing function seemed to have improved with time , because he had no difficulty communicating with others without a hearing aid .
abr test showed no click sound response in both ears at 90 db nhl ( fig .
transient evoked otoacoustic emission showed response reproducibility of 88% ( right ear ) and 95% ( left ear ) , and normal distortion product otoacoustic emissions responses were reported ( fig .
however , normal pure tone threshold was evident at both ears ; speech reception threshold was 22 db ( right ear ) and 26 db ( left ear ) and speech discrimination score was 96% ( right ear ) and 88% ( left ear ) ( fig .
4 ) . he was recommended to stop wearing the hearing aid . a language development test conducted at 7 years
, 4 months of age revealed an age equivalent of 6 years on expressive vocabulary test and 5 years on receptive vocabulary test .
the concept of auditory neuropathy was first introduced by starr , et al.1 ) in 1996 to describe 10 patients , including infants and adolescents , showing normal oae results , abnormal abr results and poor speech discrimination score .
auditory neuropathy is characterized by the auditory pathway lesion in the inner hair cells , the junction between the inner hair cells and the nerve , and the spiral ganglion or the auditory nerve in the presence of normal outer hair cell function .
, auditory neuropathy is described as peripheral neuropathy resulting from the demyelination of auditory nerves .
demyelinating lesions decrease the speed of neurotransmission , which in turn impairs nerve stimulation responses of the brain stem and decreases the synchronized activity of the entire auditory nerve activity , leading to unusual waveforms.1,2 ) auditory neuropathy accounts for nearly 2.4 - 15% of all childhood sensorineural hearing loss .
auditory neuropathy most often occurs in both ears among infants aged 2 years or younger although it can occur in adults.3 ) more recently , auditory neuropathy has been increasingly referred to as auditory neuropathy spectrum disorder in recognition of its heterogeneity .
these risk factors include hypoxia , preterm birth , hyperbillirubinemia , ototoxic medication use and neurological diseases , such as mitochondrial disease .
especially , hyperbilirubinemia is a leading cause of auditory neuropathy.4 ) infants with one of these risks need to undergo oae testing , especially when they have a poor abr roche , et al.5 ) reported the relationship of radiologic findings with auditory neuropathy in 118 patients ; radiologic abnormalities were observed in 64% and 23% of patients examined using magnetic resonance imaging ( mri ) group and computed tomography , respectively .
the most common abnormality in mri is the absence of the auditory nerve , followed by brain lesion .
mri is the most important radiologic tool in deciding on a course of treatment and assessing the prognosis of auditory neuropathy . in this case ,
the treatment for childhood auditory neuropathy includes hearing aids , language therapy and regular hearing test - based monitoring .
also , cochlear implant can be considered in case of poor outcomes.6 ) kim , et al.7 ) compared outcomes of six children with auditory neuropathy and four children with sensorineural hearing loss after cochlear implant , and reported no difference in hearing recovery outcomes between the two groups .
fulmer , et al.8 ) also reported no significant difference in hearing improvement following cochlear implant in 10 patients with auditory neuropathy and 10 patients with sensorineural hearing loss .
for infants , abr waveforms can be improved with time , so hearing conditions should be tested and examined regularly .
dunkley , et al.9 ) introduced a case in which a child showed pure tone threshold average of 35 db hl and normal word discrimination test 5 years after the diagnosis of audiometry neuropathy based on abr waveforms of 50 db nhl with normal oae at 1 week of age .
psarommatis , et al.10 ) also chronicled the improvement of auditory neuropathy in 20 children of 25 patients who had abr waveforms of more than 75 db nhl and normal oae .
of the 20 children , 12 exhibited abr less than 40 db nhl and one child had 50 db nhl but normal results in other hearing tests .
berlin , et al.11 ) studied 260 children with auditory neuropathy and found that 13 ( 5% ) had no problem in language development and ended up needing no treatment , even hearing aids .
the patient in the present case also showed typical clinical features of auditory neuropathy including non - response for abr in addition to normal oae results .
however , hearing improved to the extent that he had normal hearing for puretone and speech audiometry , and language development was only mildly delayed compared to other children in the same age group .
we suggest following observation on a regular basis and reassessment of audiologic status and language development .
 newborn hearing screening test is very important in the early diagnosis of childhood hearing loss because it affects language development . 
 auditory neuropathy is a spectrum disorder characterized by abnormal auditory brainstem response but preserved otoacoustic emission and cochlear microphonics . 
 in general , auditory neuropathy patients have poor word discrimination and variable patterns of pure tone audiometry . 
 we report on a patient with auditory neuropathy diagnosed at 16 months of age and started wearing hearing aids , but showed normal pure tone and speech audiometric findings 3 years later . 
 close follow - up for patients with auditory neuropathy is recommended . 