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Cochlear microphonics from auditory brainstem responses of infants with auditory neuropathy spectrum disorder Smith, Kyle


Objectives: The cochlear microphonic (CM) is a bioelectric potential detectable through early latency auditory brainstem responses (ABR). It has been described as large in amplitude and long in duration in auditory neuropathy spectrum disorder (ANSD), a complex form of hearing loss. ANSD is identified through a combination of diagnostics, including but not limited to present otoacoustic emissions (OAEs) and/or a robust CM, and absent/abnormal ABR. Based on previous literature, this study hypothesized that CMs would differ significantly between infants with ANSD and normal-hearing infant data from well-baby, and neonatal intensive care unit (NICU) populations; it further hypothesized that CM/ABR wave V (CM/V) amplitude ratios would not differ significantly across ANSD groups presenting with and without OAEs. Design: Retrospective analysis was performed on click-ABR recordings from 16 infants with ANSD (24 ears; mean 3.5 months, corrected) for comparison to published normative data. ANSD was identified by the presence of OAEs (OAE+) and absent/abnormal ABR, and by CM presence with abnormal/absent ABR and support from later behavioral results for infants with absent OAEs (OAE-). Waves were analyzed by comparing condensation and rarefaction polarities to highlight the CM. Proposed CM/V ratio values for ANSD identification were also explored. Results: Mean CM durations were significantly longer in combined ANSD ears (4.197 ± 1.154ms) than normally-hearing well-baby (0.73 ± 0.3ms) and NICU (0.82 ± 0.51ms) infants. CM amplitudes were significantly larger in ANSD (0.322 ± 0.173µV) than well-baby (0.24 ± 0.09µV), but not NICU (0.26 ± 0.13µV) infants. OAE+ and OAE- ANSD ears did not differ significantly in CM duration or amplitude but did differ significantly in mean CM/V ratios (6.602 ± 2.987, 2.040 ± 1.112, respectively). Ratios correctly identified ANSD in 16 of 19 ANSD ears with a wave V. Conclusions: Significant group differences in CM duration suggest that this measure could be useful for identification of ANSD in infants. CM amplitude was less definitive, with confounds between datasets. The CM/V ratios failed to correctly categorize all OAE- infants for which the measure would be most applicable. Results should be viewed with caution given the retrospective nature and limited sample size of the analysis.

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