Extra-tympanic Electrocochleography in Auditory Neuropathy Spectrum Disorder

Abstract

Objective: Compare electrocochleography (ECochG) recordings obtained simultaneously at the round window (RW) and tympanic membrane (TM) in patients with auditory neuropathy spectrum disorder (ANSD) in order to validate a noninvasive method for assessing site of lesion in these patients. Better understanding of site of lesion may help optimize intervention strategy and ultimately, performance among ANSD children.

Method: ECochG responses were recorded simultaneously at the TM and RW using single pulse and trains of clicks and tone-burst stimuli during cochlear implantation in ANSD children. Recorded potentials included the cochlear microphonic (CM) and nerve compound action potential (CAP). Correlation between RW and TM ECochG recordings were analyzed using Pearson correlation test.

Results: ECochG responses were successfully recorded at both the TM and RW simultaneously from 7 ANSD patients using all 4 paradigms. Both sites (TM and RW) revealed similar response patterns although RW responses were at least 1 order of magnitude greater than the TM responses. For all patients and conditions tested, the TM and RW ECochG recordings were significantly correlated in 88% of cases. A clear CAP was recorded from a subset of patients. Also, in the click train condition, in patients with a CAP response, the amplitude was noted to rapidly decrease following the first 3 to 4 stimuli.

Conclusion: RW ECochG recordings have larger amplitudes and better morphology than TM recordings, but still showed positive correlation in most cases. The CAP morphology recorded from a subset of our subjects is consistent with previous literature. CAP amplitude decrement in the click train condition indicates neural adaptation in ANSD.