Intraoperative Electrocochleographic Characteristics of Auditory Neuropathy Spectrum Disorder in Cochlear Implant Subjects.

Craig A Buchman,Christopher K Giardina,Kevin D Brown,Zachary J Bastian,Douglas C Fitzpatrick,Tatyana E Fontenot,Oliver F Adunka,William J Riggs,Joseph P Roche,Michael S Harris

doi:10.3389/fnins.2017.00416

Abstract

Auditory neuropathy spectrum disorder (ANSD) is characterized by an apparent discrepancy between measures of cochlear and neural function based on auditory brainstem response (ABR) testing. Clinical indicators of ANSD are a present cochlear microphonic (CM) with small or absent wave V. Many identified ANSD patients have speech impairment severe enough that cochlear implantation (CI) is indicated. To better understand the cochleae identified with ANSD that lead to a CI, we performed intraoperative round window electrocochleography (ECochG) to tone bursts in children (n = 167) and adults (n = 163). Magnitudes of the responses to tones of different frequencies were summed to measure the “total response” (ECochG-TR), a metric often dominated by hair cell activity, and auditory nerve activity was estimated visually from the compound action potential (CAP) and auditory nerve neurophonic (ANN) as a ranked “Nerve Score”. Subjects identified as ANSD (45 ears in children, 3 in adults) had higher values of ECochG-TR than adult and pediatric subjects also receiving CIs not identified as ANSD. However, nerve scores of the ANSD group were similar to the other cohorts, although dominated by the ANN to low frequencies more than in the non-ANSD groups. To high frequencies, the common morphology of ANSD cases was a large CM and summating potential, and small or absent CAP. Common morphologies in other groups were either only a CM, or a combination of CM and CAP. These results indicate that responses to high frequencies, derived primarily from hair cells, are the main source of the CM used to evaluate ANSD in the clinical setting. However, the clinical tests do not capture the wide range of neural activity seen to low frequency sounds.

Highlights

Auditory neuropathy spectrum disorder (ANSD) is a hearing dysfunction characterized by an apparent discrepancy between the measures of cochlear and neural function when viewed by surface electrode auditory brainstem response (ABR) testing
For frequencies of 1,000 Hz and lower, the proportions of ears with significant responses were nearly universal for ANSD cases, and were ∼80% of ears in the other groups
The magnitudes of the responses (Figure 2D) were higher to all frequencies in the ANSD ears compared to the others

Summary

Introduction

Auditory neuropathy spectrum disorder (ANSD) is a hearing dysfunction characterized by an apparent discrepancy between the measures of cochlear and neural function when viewed by surface electrode auditory brainstem response (ABR) testing. Healthy hair cells are identified by the presence of otoacoustic emissions (OAEs) and/or cochlear microphonic (CM) in ABR testing, coupled with small or absent wave V (Kaga et al, 1996; Starr et al, 1996; Berlin et al, 1998; Rance et al, 1999; Teagle et al, 2010). While high frequencies may be useful in diagnosis, most of the ECochG responses in CI subjects, in both children and adults, are to low frequencies (Fitzpatrick et al, 2014; McClellan et al, 2014; Formeister et al, 2015). To compare ANSD with nonANSD subjects, responses to both high and low frequencies must be obtained. We recorded responses to tones across the frequency range in CI subjects, both children and adults, with and without ANSD

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