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Cochlear microphonics recording during ABR threshold testing in children

Abstract Objective: It is agreed that the cochlear microphonic (CM) arises mainly from the normal outer hair cells (OHCs) in cochlea. The aim of this research is to study the CM characteristics in different hearing profiles and reflect the usefulness of recording CM simultaneously during Auditory Brainstem Response (ABR) threshold testing in children. Methods: This is a retrospective study that included 33 cases comprised of children with autism spectral disorders (ASD), children with cochlear sensorineural hearing loss (SNHL), children with auditory neuropathy spectrum disorder (ANSD) and 41 normal hearing healthy children as controls. The children’s ages ranged from 0.5 to 96 months. Both the CM and ABR waves were simultaneously recorded using alternating split polarity ABR. Results: CM amplitudes and thresholds in normal hearing children with ASD did not significantly differ from normal hearing healthy children. CM were preserved in children with ANSD despite the absence of distortion product OAE responses, but in a significantly lower amplitude than those with DPOAE. There was no statistically significant correlation between the children’s ages and CM amplitude at any intensity level and in any of the different child groups, except in the controls where there was a statistically significant negative correlation between the children’s ages and CM amplitude at 70dBnHL, while there was a statistically significant positive correlation between the children’s ages and CM threshold. There were no differences in the CM amplitude between the two ears at any intensity level in all of the different groups of children. Conclusion: Children with ASD showed comparable outer hair cell function to normal hearing healthy children, reflecting absence of any peripheral hyperacusis due to loudness recruitment. CM should always be searched for when testing young children when there is absence of ABR response with absence or presence of otoacoustic emissions, to avoid any false negative results for ANSD. CM can be preserved in children with SNHL with loudness recruitment. This finding could be confused with ANSD, so CM should be traced down to its threshold for an appropriate diagnosis.