We are delighted to invite you to Kyle Smith’s MSc thesis oral defense.
When: Monday 27 August, 2018 at 2:00 PM
Where: Friedman Building, Room 354
Title: “Cochlear Microphonics from Auditory Brainstem Responses of Infants with Auditory Neuropathy Spectrum Disorder”
MSc Candidate: Kyle Smith
Committee: Anthony Herdman, Navid Shahnaz, and Rae Riddler
Abstract
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 or abnormal ABR. Based on previous literature, this study hypothesized that CMs would differ significantly between infants with ANSD and normal-hearing infants from well-baby, and neonatal intensive care unit (NICU) populations; it further hypothesized that CMs and 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). ANSD was identified by the presence of OAEs (OAE+) and absent/abnormal ABR, and through comprehensive physiological and later behavioral diagnostic analysis for infants with absent OAEs (OAE-). Waves were analyzed using split-alternating methods for comparing condensation and rarefaction polarities to highlight the CM. Proposed values for identification of ANSD with CM/V ratios were also explored.
Results: Mean CM durations were found to be significantly longer in ANSD (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- groups did not differ significantly in CM duration or amplitude but did differ significantly in mean CM/V ratio values (6.602 ± 2.987, 2.040 ± 1.112, respectively). Ratios correctly identified ANSD in 16 of 19 ANSD ears with an identifiable 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 notable 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 of the analysis and limited sample size.