Auditory neuropathy spectrum disorder (ANSD) is a disease with many unknowns and difficulties in the diagnosis and treatment process for ENT physicians and audiologists since 1996 when it was first defined.
Each answer obtained during the investigation of this disease reveals many new question marks and reveals how little we know about the functioning of the auditory system.
ANSD clinically;
(1) hearing loss of any level, often bilateral,
(2) Demonstration of normal function of outer hair cells by otoacoustic emission (OAE) and / or cochlear microphonic (KM) responses,
(3) Abnormally evoked responses starting from ABR wave I,
(4) Poor Speech Discrimination Scores (SDS) that are inconsistent with the audiogram,
(5) It is a table characterized by inability to obtain acoustic reflexes ipsilaterally and contralaterally at 110 dB HL.
It is thought that the ANSD may originate from the inner hair cells, the disorder in the synapse between the inner hair cell and the VIII nerve, or the auditory nerve itself.In some cases, it can be seen as a reflection of the effects in all or part of these regions.
In pure tone audiometry, results that vary from normal hearing thresholds to thresholds compatible with severe hearing loss and a precise audiogram shape are obtained.Most patients report that they have difficulties in understanding speech, especially in noisy environments. Speech discrimination scores in these patients are obtained poor scores, inconsistent with hearing thresholds.
Hearing loss can be constant over time or show fluctuations.
Figure 1: Audiogram and tympanometry results of a patient diagnosed with auditory neuropathy.
Normal findings are obtained for OAE and CM responses. Based on this feature, it is reported that outer hair cells function normally and / or there is inner hair cell or 8th cranial nerve pathology depending on ABR findings. Especially the presence of OAE responses in patients and the presence of CM in the ABR performed afterwards are considered among the most important criteria in diagnostic terms.
Figure 2: Left ear OAE responses of the same patient.
Figure 3: Right ear OAE responses of the same patient The patient is wearing a hearing aid in her/ his right ear.
Although the ABR responses should not be obtained due to the basic definition, the wave V can be observed minimally in 20% of the patients, which can be considered as the presence of partial synchronization, but in some of the patients, the wave V is not observed in the ABR in the first tests, while the wave V formation is observed over time.
Figure 4: ABR findings of a patient diagnosed with right ear ANSD.
Waves 1 and 2 were taken in alternate polarity in the patient. Waves 3 and 4 are taken in rarefaction and condensation polarity and CMs are observed. Waves 3 and 4 are observed in rarefaction and condensation polarity and CMs are observed.
