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Comparative analysis of auditory brainstem response and hearing aid fitting thresholds in auditory neuropathy… Parfett, Alicia 2018

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COMPARATIVE ANALYSIS OF AUDITORY BRAINSTEM RESPONSE AND HEARING AID FITTING THRESHOLDS IN AUDITORY NEUROPATHY SPECTRUM DISORDER by  Alicia Parfett  B.Sc., The University of Victoria, 2012  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Audiology and Speech Sciences)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  October 2018   © Alicia Parfett, 2018  ii   The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis/dissertation entitled:  Comparative Analysis of Auditory Brainstem Response and Hearing Aid Fitting Thresholds in Auditory Neuropathy Spectrum Disorder  submitted by Alicia Parfett in partial fulfillment of the requirements for the degree of Master of Science in Audiology and Speech Sciences  Examining Committee: Dr. Anthony Herdman, Professor and Electrophysiologist Supervisor  Dr. Navid Shahnaz, Professor and Clinical Audiologist Supervisory Committee Member  Alison Beers, Clinical Pediatric Audiologist Supervisory Committee Member iii  Abstract  Objectives. In cases of auditory neuropathy spectrum disorder (ANSD), clinicians may defer amplification until reliable behavioural thresholds can be obtained, as auditory brainstem response (ABR) assessment often overestimates thresholds. Limited research has investigated the correlation between ABR-estimated and behavioural thresholds. This study aims to retrospectively quantify the management practices found in ANSD patients identified through the British Columbia Early Hearing Program (BCEHP). The relationship between ABR and hearing aid (HA) fitting thresholds will be investigated for evidence to support using ABR thresholds to inform early intervention.   Methods. BCEHP patient data was obtained for the 28 children diagnosed with ANSD between 2008 and 2015. Information such as clinical demographics and the use of hearing technology was extracted. The age of diagnosis and intervention was reviewed for 1-3-6 month benchmark compliance. ABR and HA fitting threshold data was collected, and comparative analysis was performed.   Results. Analysis revealed that the average age of ANSD diagnosis was 7.8 months corrected (range: 1.5 – 69 months), and the average time between diagnosis and amplification was 10 months (SD: 15 months). Comparative analysis revealed that while delaying amplification is appropriate for the majority of ANSD patients, fitting to ABR-estimated thresholds may be suitable in a small subset. iv  Conclusions. HA fitting for ANSD infants is often delayed beyond 6 months of age. Study results suggest that in some cases, ABR thresholds may be sufficient to generate prescriptive targets for amplification. Further research is needed to corroborate these findings and provide support for early intervention based on ABR-thresholds.    v  Lay Summary  Early intervention for hearing loss by 6 months of age is associated with improved speech and language outcomes. Hearing levels can be estimated for young infants using ABR assessment, except in cases of ANSD where ABR thresholds have not typically been used to predict behavioural thresholds. The correlation between ABR thresholds and behavioural thresholds in cases of ANSD is not known.  Consequently, many infants and young children with ANSD are delayed in receiving amplification until hearing thresholds can be measured using behavioural testing.  This study will retrospectively compare ABR-estimated thresholds to hearing aid fitting thresholds for a population of young children with ANSD, in an attempt to improve clinical practice and outcomes for this population. vi  Preface  This thesis was carried out in collaboration with my supervisor Dr. Anthony Herdman, and my research colleague Kyle Smith. Dr. Herdman conceptualized the study and advised on the project’s development, including study design and statistical measurements.   Deidentified subject data was provided by the British Columbia Early Hearing Program (BCEHP) in association with BC Children’s Hospital (BCCH). Deidentification was carried out by Marlina Anderson at the BCCH. Review of patient data was conducted by Kyle Smith and myself in order to identify and categorize the information pertinent to our respective studies. As the sole author of this text, I was responsible for the project’s design, calculations and analysis.  Ethics approval was provided by the UBC Children's & Women’s Research Ethics Board. Study titles: Auditory evoked potentials (AEPs) in infants and children with normal hearing and hearing loss, certificate Number: H14-01969, and evaluating hearing in infants and children with ANSD, certificate number: H18-01605.  Funding was provided through UBC Faculty of Medicine internal funds grant. No conflicts of interest were declared. vii  Table of Contents  Abstract ........................................................................................................................................ iii Lay Summary ................................................................................................................................. v Preface ........................................................................................................................................... vi Table of Contents ......................................................................................................................... vii List of Tables .................................................................................................................................. x List of Figures ............................................................................................................................... xi List of Symbols & Abbreviations ............................................................................................... xii Acknowledgements .................................................................................................................... xiii Dedication .................................................................................................................................... xiv Chapter 1: Introduction ................................................................................................................ 1 1.1 Assessment and Presentation of ANSD ........................................................................... 1 1.2 Intervention and Management of ANSD ......................................................................... 2 1.2.1 Potential Risks of Overamplification ...................................................................... 3 1.2.2 Current Challenges in Management Strategies ....................................................... 4 1.3 Critical Periods for Early Language Development .......................................................... 5 1.4 Purpose of the Study ........................................................................................................ 6 Chapter 2: Methods ....................................................................................................................... 7 2.1 Source Data ...................................................................................................................... 7 2.1.1 BCEHP Screening Protocol ..................................................................................... 8 2.1.2 Diagnosis of ANSD ................................................................................................. 8 2.2 Variables for Comparative Analysis ................................................................................ 9 viii  2.2.1 Age of Hearing Loss and ANSD Diagnosis ............................................................ 9 2.2.2 Age of Protocol-Required ABR Thresholds for Hearing Aid Programming ........ 10 2.2.3 Age of Fitting with Hearing Aids .......................................................................... 10 2.2.4 Hearing Aid Fitting Thresholds ............................................................................. 11 2.2.5 Cumulative ABR Thresholds ................................................................................. 12 2.2.6 Hearing Technology Management Strategies ........................................................ 12 2.3 Comparative Analyses ................................................................................................... 13 2.3.1 Age Differences between Hearing Loss Diagnosis and Hearing Aid Fitting ........ 13 2.3.2 Age Differences between Protocol-Required ABR Thresholds and the Provision of Hearing Aids ..................................................................................................................... 13 2.3.3 Threshold Differences between ABR and Hearing Aid Fitting Thresholds .......... 13 2.3.3.1 Threshold Differences over Time ...................................................................... 14 2.3.3.2 Threshold Differences per Frequency ............................................................... 14 2.3.3.3 Threshold Differences at the Final Hearing Aid Fitting .................................... 15 Chapter 3: Results ....................................................................................................................... 16 3.1 Population Demographics .............................................................................................. 16 3.1.1 ANSD Clinical Demographics .............................................................................. 16 3.1.2 Risk Factors for Hearing Loss ............................................................................... 18 3.2 Diagnosis of ANSD ....................................................................................................... 18 3.2.1 BCEHP Screening Outcomes ................................................................................ 18 3.2.2 Age of Hearing Loss and ANSD Diagnosis .......................................................... 19 3.3 Intervention and Management of ANSD ....................................................................... 21 3.3.1 Age of Fitting Hearing Aids .................................................................................. 21 ix  3.3.2 Summary of Clinical Milestones in ANSD Hearing Aid Users ............................ 22 3.3.3 Time between Diagnoses and Hearing Aid Intervention ....................................... 24 3.3.4 Time between Protocol-Required ABR Thresholds and HA Intervention ............ 26 3.3.5 Differences between ABR Thresholds and HA Fitting Thresholds ...................... 27 3.3.6 Hearing Technology Management Strategies ........................................................ 31 Chapter 4: Discussion .................................................................................................................. 33 4.1 Population Demographics & Risk Factors .................................................................... 33 4.2 Newborn Hearing Screening Outcomes ........................................................................ 34 4.3 Diagnoses and Intervention of ANSD ........................................................................... 35 4.4 Comparative Analysis of Cumulative ABR and Final HA Fitting Thresholds ............. 37 4.5 Hearing Technology Management Strategies in ANSD ................................................ 38 Chapter 5: Conclusion ................................................................................................................. 39 References ..................................................................................................................................... 41  x  List of Tables  Table 2.1 Comparative Analysis for Composite ABR and HA Fitting Thresholds ...................... 11 Table 2.2 Comparative Analysis for Composite ABR and HA Fitting Thresholds at 2.0 kHz ..... 15 Table 3.2 Clinical Demographics for 28 Children Identified with ANSD .................................... 17 Table 3.3 Hearing Loss Risk Factors Identified in an ANSD Population ..................................... 18 Table 3.1 Screening Outcomes for 28 Children Identified with ANSD ........................................ 19  xi  List of Figures  Figure 3.1 a) Age of Hearing Loss Diagnoses in 28 Patients b) Age of ANSD Diagnosis in 26 Patients ........................................................................................................................................... 20 Figure 3.2 Age of Hearing Technology Intervention for 11 ANSD Patients ................................ 22 Figure 3.3 Summary of Diagnosis and Management Milestones in 11 ANSD Patients ............... 23 Figure 3.4 Time between Intervention and a) Diagnosis of a Hearing Loss b) Diagnosis of ANSD ....................................................................................................................................................... 25 Figure 3.5 Time between Protocol-Required ABR Thresholds and Intervention for 10 Patients . 27 Figure 3.6 The Average Difference between Hearing Aid Fitting Thresholds and Cumulative ABR Thresholds over Time ........................................................................................................... 28 Figure 3.7 Frequency Specific Average Differences between ABR and Hearing Aid Fitting Thresholds at a) 2.0 kHz b) 0.5 kHz and c) 4.0 kHz ..................................................................... 29 Figure 3.8 Average Difference between Cumulative ABR and Final HA Fitting Thresholds ...... 30 Figure 3.9 Hearing Technology Management Strategies in an ANSD Population ....................... 32  xii  List of Symbols & Abbreviations Abbreviation/Symbol Definition AABR Automated auditory brainstem response ABR Auditory brainstem response ANSD Auditory neuropathy spectrum disorder AOAE Automated otoacoustic emissions ASR Acoustic stapedial reflex BCCH British Columbia Children’s Hospital BCEHP British Columbia Early Hearing Program CI Cochlear implant CM Cochlear microphonic CMV Cytomegalovirus dB Decibel dB HL Decibels hearing level dB eHL Decibels estimated hearing level dB nHL Decibels normal hearing level DNT Did not test DPOAE Distortion product optoacoustic emissions Dx Diagnosis EHDI Early hearing detection and intervention  EID HL Early-identified hearing loss HA Hearing aid HL Hearing loss Hx History Hz Hertz kHz Kilohertz (1000 Hz) OAE Otoacoustic emissions SNHL Sensorineural hearing loss WNL Within normal limits  xiii  Acknowledgements  I wish to thank my supervisor Dr. Anthony Herdman for giving me this opportunity to research, learn and challenge myself. His enthusiasm, guidance and support throughout this project have been crucial to its fruition. Thank you to the members of my supervisory committee; Dr. Navid Shahnaz and Alison Beers, for the time spent reviewing this document and for providing me with such valuable feedback. I also wish to thank the staff and clinicians at BCCH for gathering the data that made this project possible.   A special thank you to the “Thesis Buddies”; Kyle Smith, Angela Ryall and Martine Schlagintweit for sharing this journey with me. I could not have made it through these long work days without your encouragement and company. I would also like to extend that same appreciation to the remaining classmates who make up the “AUDI Family”; I am forever grateful we ended up in the same class. Thank you for your humor and teamwork over these last two years!  And of course, a prodigious thank you to my family and friends. Your love and support are what make any of my accomplishments possible.   xiv  Dedication    To my family & friends, for your continuous love and support. ~ And in loving memory of my Poh Poh,  Cheung Hop Lee Chan. 1  Chapter 1: Introduction Auditory neuropathy spectrum disorder (ANSD) is a type of hearing impairment characterized by the presence of a compromised auditory neural pathway despite normal outer hair cell function. The prevalence of ANSD ranges between 1-10 % of children identified with a permanent childhood hearing loss (Kirkim, Serbetcioglu, Erdag, & Ceryan, 2008; Gary Rance, 2005a). ANSD is an umbrella diagnosis that encompasses a range of lesions that can occur within the inner hair cell, at the synapse between the inner hair cell and the VIII nerve, or along the VIII nerve itself (Berlin, Hood, Morlet, Rose, & Brashears, 2003a; Starr, Picton, Sininger, Hood, & Berlin, 1996). Due to variability in the site of lesion, the etiology of ANSD is widely heterogenous and may not be limited to one cause. Known risk factors associated with ANSD include prematurity, jaundice, low birth weight, certain antibiotics and diuretics, and most predominately; hypoxia and hyperbilirubinemia (Beutner, Foerst, Lang-Roth, von Wedel, & Walger, 2007; I. Bielecki, Horbulewicz, & Wolan, 2012; Madden, Rutter, Hilbert, Greinwald Jr, & Choo, 2002a). However, cases of ANSD with no known risk factors have also been reported (Bielecki et al., 2012).   1.1 Assessment and Presentation of ANSD Traditionally, a diagnosis of ANSD is made based on the presence of otoacoustic emissions (OAEs) or a cochlear microphonic (CM) in conjunction with abnormal or absent auditory brainstem (ABR) recordings. Acoustic reflexes are often absent (Starr et al., 1996). ANSD can occur bilaterally or unilaterally, with pure tone thresholds that range from normal to profound (Madden, Rutter, Hilbert, Greinwald Jr, & Choo, 2002b; Gary Rance, 2005b). Audiometric thresholds are typically unable to predict speech perception performance, with patients often 2  demonstrating disproportionately poorer speech thresholds (Barreira-Nielsen, Fitzpatrick, & Whittingham, 2016; Starr et al., 1996). Although individuals with ANSD can display a range of auditory capabilities, the most commonly reported symptoms include difficulty hearing in background noise, fluctuating hearing sensitivity and poor speech perception (Rance, 2005; Starr et al., 1996).  1.2 Intervention and Management of ANSD In the absence of intervention with hearing technology, only a small percentage of the children with ANSD would be expected to develop normal speech and language (Berlin et al., 2010). If elevated hearing thresholds are confirmed for this population, a hearing aid trial is often recommended. Cochlear implant candidacy may be explored in cases where children are not making appropriate gains in speech and language development. Success with acoustic amplification is reportedly inconsistent; some pediatric patients show improvements in speech and language, while others only gain minimal benefit (Berlin et al., 2010; Gary Rance, Cone-Wesson, Wunderlich, & Dowell, 2002). Cochlear implants (CIs) may be a suitable intervention for ANSD populations, as the electrical stimulation may provide greater synchronization along the auditory nerve (Hartmann, Topp, & Klinke, 1984; Trautwein, Sininger, & Nelson, 2000; Zhou, Abbas, & Assouline, 1995). The reported benefits provided by CIs are also variable within this population. Some studies have indicated similar post-implantation outcomes to group-matched ANSD versus sensorineural hearing loss (SNHL) peers (Breneman, Gifford, & DeJong, 2012), while others have demonstrated poorer post-implantation outcomes for the group with ANSD (He et al., 2013; Rance & Barker, 2008). Comparable outcomes have also been obtained between CIs and hearing aids (HAs) within the ANSD population (Rance & Barker, 2008). It 3  may be that the site and degree of lesion along the auditory pathway influence success with intervention, but further studies are needed to corroborate this theory.   1.2.1 Potential Risks of Overamplification Historically, there has been a common belief among some clinicians that the nature of ANSD places patients at a greater risk for overamplification, especially in those who are too young to provide reliable behavioural feedback. To reduce the risk of inadvertently damaging residually functioning cochlear structures, recommendations presented in early literature have included fitting hearing aids with low gain (Hood, 1998), only providing low gain amplification in one ear (Berlin, 1999) or providing no amplification at all (Berlin, 1995). With more recent literature showing the potential benefits of amplification in ANSD populations, many clinicians are pursuing a bilateral amplification trial for their patients, but continue to be cautious with the amount of gain they provide. Although hearing threshold elevations due to overamplification were documented in some pediatric SNHL cases (Macrae, 1991; Macrae, 1995), to date there is no conclusive scientific evidence validating the provision of low-gain amplification within the pediatric ANSD population. In addition, the retention of OAE responses after hearing aid use has been documented (Sininger, Starr, & Starr, 2001). Currently, there are no evidence-based guidelines dictating how to best deviate from a standard fitting prescription. Given that young infants and children are less likely to have consistent hearing aid use (Moeller, Hoover, Peterson, & Stelmachowicz, 2009; Elizabeth A. Walker et al., 2013), and are more likely to be in quieter environments, the concern of increased hearing loss due to overamplification may not be fully substantiated. However, this conjecture would need to be evaluated in future research. For clinicians, management of ANSD is a delicate trade-off between providing audibility that 4  facilitates auditory development and the perceived risk of causing harm through overamplification.  1.2.2 Current Challenges in Management Strategies Due to the variability in etiology and auditory performance among individuals with ANSD, the habilitative process is not standardized; audiological management and language recommendations are individualized, closely monitored and frequently reviewed (Barreira-Nielsen et al., 2016; Berlin, Hood, Morlet, Rose, & Brashears, 2003b; Roush, Frymark, Venediktov, & Wang, 2011). Universal newborn hearing screening programs with subsequent electrophysiological (ABR) assessment for young infants has facilitated early identification of ANSD. While ANSD can be identified early, the ability to estimate hearing levels is not possible until children are older and able to provide behavioural audiological thresholds. Cortical Auditory Evoked Potentials (CAEPs) are currently being investigated as an option to more accurately estimate hearing thresholds for infants with ANSD (He, Teagle, Roush, Grose, & Buchman, 2013); however, a caveat to this form of testing is that CAEP morphology is affected by the age and state of the child (Stapells, 2011). As a result, provision of amplification for children with ANSD is often postponed until reliable behavioural thresholds can be obtained. For typically-developing infants, behavioural audiometry can be completed as early as 6 months using visual reinforcement audiometry (Katz, Burkard, & Medwetsky, 1985); however, for children with ANSD, where the comorbidity of developmental delays and medical conditions is high, behavioural audiological thresholds are often not confirmed until much later. As a result, children with ANSD are often delayed in accessing the audibility required for speech and language development. 5  1.3 Critical Periods for Early Language Development Language acquisition begins with the detection and differentiation of an auditory signal. Fetuses are able to listen and learn in utero, and as neonates this exposure enables them to discriminate and show a preference for their own mother’s voice (DeCasper, Lecanuet, Busnel, Granier-Deferre, & Maugeais, 1994), as well as their own native language (Kisilevsky et al., 2009; Mehler et al., 1988). Language maturation continues postpartum with the categorization and discrimination of phonemes. Within the first year of life there is a critical period for phonemic development. At 6 to 8 months of age infants are able to discriminate between all phonemes, from 8 to 12 months this capacity wanes, and by 12 months of age infants are typically limited to recognizing the phonemic contrasts present only in their native language (Werker & Tees, 1984).  The perceptions emerging during this time lay the foundation for language accession and can even predict future language capabilities (Tsao, Liu, & Kuhl, 2004). Auditory input within the first year of life has pivotal implications for later language and aural communication abilities. Even transient obstructions of the auditory signal by otitis media has been shown to affect speech perception and future syntactic and semantic processing (Clarkson, Eimas, & Marean, 1989; Zumach, Chenault, Anteunis, & Gerrits, 2011). In the case of permanent hearing loss, the importance of timely intervention becomes especially important. Early identified children who are fit with and consistently wear appropriate amplification by 6 months of age have significantly better language outcomes than children who receive intervention after 6 months (Yoshinaga-Itano, Sedey, Coulter, & Mehl, 1998).   6  1.4 Purpose of the Study Early auditory access is essential for speech and language development. Because behavioural hearing thresholds can be lower than ABR-estimated hearing thresholds for infants with ANSD, clinicians will often defer fitting with amplification until behavioural threshold information can be obtained. There is currently no known correlation between ABR-estimated and behavioural hearing thresholds for children with ANSD. In addition, more evidence is needed to better understand the variability in diagnostic presentation and best management strategies for infants and young children with ANSD. This information would help guide clinicians’ decision-making processes. Thus, this study aimed to retrospectively quantify the scope and diversity of infants and young children with ANSD identified through the British Columbia Early Hearing Program (BCEHP). This included calculating the average time taken for a diagnosis of ANSD as well as fitting with amplification with respect to the 1, 3 and 6 month benchmarks outlined by the BCEHP. Common influences contributing to delays in meeting these goals will be identified. Intervention and management practices within the population will also be examined; specifically, the differences between ABR and hearing aid fittings thresholds will be investigated to determine whether hearing aid fitting can proceed based on ABR-estimated hearing thresholds in cases of ANSD. This study will hopefully contribute towards the larger goal of ensuring that infants and young children with ANSD are able to meet the 1-3-6 benchmarks for early identification and intervention. 7  Chapter 2: Methods 2.1 Source Data Clinical data for pediatric patients diagnosed with ANSD between 2008 and 2015 were retrospectively collected for this study from British Columbia Children’s Hospital (BCCH) in Vancouver, British Columbia. Chart review was performed to extract patient demographic information, medical data pertaining to risk factors for hearing loss, hearing screening results, and audiological assessment results such as auditory brainstem response (ABR), otoacoustic emission (OAE), tympanometry clinical data. ABR reports and OAEs were used to confirm the audiologist’s original diagnosis of ANSD based on current BCEHP criteria. Tympanometry results (when reported) were used to determine middle-ear status during ABR and behavioral testing, but was not used for any subsequent analyses. Patient demographics (presented in the Results section) included biological sex, age, profile of ANSD (bilateral/unilateral), presentation of ANSD (classic/presumptive), risk factors, and the use of hearing technology devices. Categorization of classic versus presumptive presentation of ANSD is discussed below under Diagnosis of ANSD. Patients who were born outside of the province and/or lacked chart data indicating early participation with BCEHP were excluded from the study. One patient with cochlear nerve aplasia was excluded. Chart records obtained through BCCH revealed that 35 children had been identified with ANSD between 2008 and 2015 but only 28 met the inclusion criteria for this study.   8  2.1.1  BCEHP Screening Protocol The BCEHP offers universal newborn hearing screening using a two-stage screening protocol.  The program aims to screen all babies born in British Columbia by one month of age. For babies born in regular maternity wards or home births (termed Well-Babies), automated otoacoustic emission (AOAE) is used as the first stage of screening; babies from this group who fail first stage screening receive a repeat screening with automated auditory brainstem response (AABR). For infants who spend at least 48 hours in the neonatal intensive care unit (NICU), screening is performed using only AABR. With the exception of infants who are at risk for late-onset permanent hearing loss, if a baby passes screening in both ears then no further testing is required.  Babies who do not pass first stage screening are offered second stage screening; babies who do not pass second stage screening are referred for diagnostic ABR assessment.  2.1.2 Diagnosis of ANSD Based on chart review, the assessment battery for sensorineural hearing loss included distortion product otoacoustic emissions (DPOAEs), immittance testing, ABR, as well as behavioural pure-tone and speech perception testing whenever possible. Medical consultation and imaging were conducted as needed. To be included in this dataset, clinicians would have made a diagnosis of ANSD in accordance with the BCEHP protocol (BCEHP, 2012), where ANSD is confirmed when OAEs are present in conjunction with absent or abnormal ABR waveforms. In cases where OAEs were absent in the presence of absent or abnormal ABR waveforms, but a cochlear microphonic (CM) was clear, then a presumptive diagnosis of ANSD was made. Because OAEs can be affected by the presence of even mild middle ear pathology or residual vernix caseosa in the external ear canal (Thornton, Kimm, Kennedy, & Cafarelli-Dees, 1993), absent OAEs do not 9  rule-out a diagnosis of ANSD. In a small proportion of reported ANSD cases, OAEs have been absent or degraded over time even when middle-ear pathology was not a contributing factor (Berlin et al., 2010). For the purpose of summarizing patient demographics all patients were sorted into one of the following two categories; patients with present OAEs and absent/abnormal ABR wave V’s were categorized as “classic ANSD”, while patients who had absent OAEs but present CMs were categorized as “presumptive ANSD”.  2.2 Variables for Comparative Analysis 2.2.1 Age of Hearing Loss and ANSD Diagnosis Clinical data such as OAEs, audiograms, ABR session files and accompanying clinical reports were reviewed for the 28 patients diagnosed with ANSD to determine the age at initial diagnosis of hearing loss as well as the age at subsequent diagnosis of ANSD. All ages are reported in corrected months unless otherwise indicated. The age of identified hearing loss was based on the age of the child at the first diagnostic ABR demonstrating elevated hearing thresholds, or the age of the child at the first elevated audiogram, whichever came first. The age of diagnosis of ANSD was based on the age of the child when all BCEHP criteria for a diagnosis of ANSD had been fulfilled, typically after assessment by click-ABR had been performed. Patients were assigned values of 0 or 1 within one-month categories, a “1” if a diagnosis was made by that month or a “0” if a diagnosis was still pending. The subsequent months following a patient’s diagnosis were also assigned a “1” value. For each one-month category the number of 0s and 1s was summed and plotted. Two known ANSD patients in the sample population were still in the process of being diagnosed with ANSD between 2008 and 2015 and were only excluded from the analysis for age of ANSD diagnosis. 10  2.2.2 Age of Protocol-Required ABR Thresholds for Hearing Aid Programming The OAEs, ABR and clinical reports of 28 ANSD patients were reviewed to determine the age of the child when the minimum threshold requirements had been obtained. In accordance with BCEHP guidelines for ABR assessment in cases of permanent hearing loss, requirements have been fulfilled when thresholds at 2000 and 500 Hz have been confirmed in each ear, given that “amplification can be fit conservatively if only 2 thresholds are known until such time as other thresholds are established” (BCEHP, 2012). The purpose of obtaining this age variable was to identify the time interval between when ABR thresholds for a minimum of 500 and 2000 Hz were established and when a child was fit with amplification.   2.2.3 Age of Fitting with Hearing Aids  The audiograms, clinical reports and hearing aid verification printouts were examined to identify the age each infant was first fit with hearing aids. This analysis included patients who were late-identified with hearing loss, or who later received a cochlear implant. The age of intervention was based on the recorded age on verification printouts or extrapolated from clinical information provided in chart data. Within one-month categories starting at one month of age, patients were assigned a “1” if an intervention was provided by that month, or a “0” if hearing technology was deferred. The subsequent months following a patient’s fitting with amplification were assigned a “1” value. For each one-month category the number of 0s and 1s was summed and plotted. Any patient who did not receive technology or whose use of technology is unknown was excluded from this investigation.  11  2.2.4 Hearing Aid Fitting Thresholds For each patient, the clinical reports, clinician notes, and verification printouts were reviewed to determine the hearing thresholds used at the each hearing aid fitting. Upon review of accompanying audiograms, not all fittings were based on ear-specific data, but for the purpose of this analysis, hearing thresholds used to generate prescriptive targets did not differentiate soundfield from ear-specific thresholds. Due to the nature of the retrospective review, clinical decision-making rationale was not always known. An example of entered hearing thresholds used in the comparative analysis for a single patient can be seen in Table 2.1.  Table 2.1 Comparative Analysis for Composite ABR and HA Fitting Thresholds    Right Ear  Left Ear   0.5 kHz 1.0 kHz 2.0 kHz 4.0 kHz  0.5 kHz 1.0 kHz 2.0 kHz 4.0 kHz ABR (dB eHL) Test 1   >75   DNT  >30  Test 2 85  70 65 Composite   85   70  65             Hearing Aid (dB HL) 1st Fitting 40 - 50 -  50 - 55 - 2nd Fitting 50 55 25 50  - 50 30 40            Comparative Analysis (dB HL - dB eHL) 1st Fitting   -35   -20  -10  2nd Fitting -60  - -35 Average Difference per Fitting 1st Fitting -22 2nd Fitting -48 12  2.2.5 Cumulative ABR Thresholds ABR waveforms and accompanying clinical reports for each patient were reviewed. Data-permitting, ABR thresholds at 0.5, 1.0, 2.0, and 4.0 kHz for each ear was determined. As seen in Table 2.1., when multiple ABR assessments were conducted, a composite final ABR threshold estimate was determined based on the best threshold measured at each frequency, as would be done clinically. Only thresholds with a clear wave V response were used for comparison to hearing aid fitting thresholds, with the following exceptions; in instances where a wave V response was reported for a range of intensities, (e.g., 60-70 dB eHL at 2.0 kHz) the highest reported intensity was selected, as a response was more likely to be present. If the ABR data indicated no response at a high stimulus level, then a threshold value of 5 dB above this level was used in the calculations (e.g., for an ABR threshold determined to be >105 dB eHL based on no response to stimuli at this level, then a threshold value of 110 dB eHL was used).   2.2.6 Hearing Technology Management Strategies Audiograms, clinical reports and hearing aid verification printouts were examined in order to identify the type of hearing equipment prescribed and fit. Equipment used included hearing aids, frequency-modulation (FM) systems and cochlear implants. If no equipment had been fit, chart review was conducted to identify the clinical rationale. The number of patients using each strategy alone or in combination was summed and illustrated.   13  2.3 Comparative Analyses 2.3.1 Age Differences between Hearing Loss Diagnosis and Hearing Aid Fitting  The method for determining the age of identified hearing loss and the age of fitting with hearing aids within this population was previously outlined (see section 2.2.1). In order to evaluate the time to intervention that occurred within this population, the difference between these two periods was calculated. Differential statistics (average, min, max and median) was performed.   2.3.2 Age Differences between Protocol-Required ABR Thresholds and the Provision of Hearing Aids The purpose of this analysis was to determine the time interval between the earliest possible provision of hearing aids (based solely on confirmation of ABR thresholds at 0.5 and 2.0 kHz in each ear) and the age at which hearing aids were fit. One hearing aid recipient was excluded from evaluation because threshold ABR data was unavailable. The difference between the age of protocol-required ABR thresholds and the age of intervention with hearing aids was calculated and differential statistics (average, min, max and median) were performed.  2.3.3 Threshold Differences between ABR and Hearing Aid Fitting Thresholds Analyses were conducted on nine hearing aid users identified with bilateral ANSD, looking at the difference between ABR-estimated thresholds and thresholds used for hearing aid fitting. The ABR-estimated thresholds and hearing aid fitting thresholds of one cochlear implant user were also included in this analysis. Subject S08, a bilateral ANSD hearing aid user who later received a cochlear implant was excluded from this analysis, as ABR threshold data was not available for review. Thresholds were not often obtained for all frequencies (0.5, 1.0, 2.0, and 4.0 kHz).   14  2.3.3.1 Threshold Differences over Time Composite ABR-estimated thresholds were subtracted from the audiological thresholds used for hearing aid fitting. The difference between the ABR thresholds and the hearing aid fitting thresholds was averaged across both ears and across available frequencies, giving a single numerical value, the “average difference” per child fit. An example provided in Table 2.1 outlines the calculations used for the comparative analysis described. A positive value for the average difference suggests that composite ABR thresholds were lower than hearing aid fitting thresholds, while a negative value suggests that composite ABR thresholds were greater than fitting thresholds. The average difference value at each patient’s fitting was calculated and plotted over time.   2.3.3.2 Threshold Differences per Frequency Frequency-specific (0.5, 1.0, 2.0, and 4.0 kHz) composite ABR thresholds were subtracted from each hearing aid fitting threshold at the corresponding frequency. For each patient, the difference between the composite ABR and hearing aid fitting thresholds at a single frequency was averaged across both ears and all fittings. This resulted in a single numerical value per frequency representing the average difference between ABR and hearing aid fitting thresholds over time for each child. An example provided in Table 2.2 outlines the calculations used for the frequency-specific comparative analysis described. Frequency specific data at 0.5 and 4.0 kHz was not available for all subjects. None of the subjects had frequency specific data at 1.0 kHz. Interpretation of the average difference value has been previously outlined in Section 2.3.3.1.   15  Table 2.2 Comparative Analysis for Composite ABR and HA Fitting Thresholds at 2.0 kHz  2.3.3.3 Threshold Differences at the Final Hearing Aid Fitting Composite ABR thresholds were subtracted from the thresholds used at the final hearing aid fitting. The difference between the ABR thresholds and hearing aid fitting thresholds was averaged across both ears and available frequencies, giving a single numerical value, the “average difference” at the final hearing aid fitting. Interpretation of the average difference value has been previously outlined in Section 2.3.3.1.   Right Ear  Left Ear   0.5 kHz 1.0 kHz 2.0 kHz 4.0 kHz  0.5 kHz 1.0 kHz 2.0 kHz 4.0 kHz ABR (dB eHL) Composite  85   70  65             Hearing Aid (dB HL) 1st Fitting 40 - 50 -  50 - 55 - 2nd Fitting 50 55 25 50  - 50 30 40            Comparative Analysis (dB HL - dB eHL) 1st Fitting   -35   -20  -10  2nd Fitting -60  - -35   Average Difference Across Fittings and Between Ears  at 2.0 kHz -35 16  Chapter 3: Results 3.1 Population Demographics 3.1.1 ANSD Clinical Demographics See Table 3.2 for a summary of demographic information for this ANSD population. Within the sample there were roughly equal numbers of males (50%) and females (39%), with only a small proportion of patients whose biological sex could not be identified from the deidentified charts (11%). Bilateral ANSD was more common (61%) than unilateral ANSD (39%). The majority of patients (n = 15, 54%) fit the classic ANSD diagnosis criteria, while a smaller group (n = 11, 39%) fit the presumptive ANSD diagnosis criteria due to the absence of OAEs. A larger number of the patients spent time in the NICU (68%). Many of the infants (n = 20, 71%) had risk factors for ANSD and seven patients (25%) had no known risk factors.     17   Characteristic Number (n = 28) Percentage (%) Biological Sex    Male 14 50  Female 11 39  Data Not Available 3 11     ANSD Profile     Bilateral 17 61  Unilateral 11 39     Presentation of ANSD     Classic 15 54  Presumptive 11 39  Data Not Available 2 7     Birth Status    NICU 19 68  Well Baby 8 29  Data Not Available 1 3     Risk Factors    Present 20 71  Not Present 7 25  Data Not Available 1 4 Table 3.1 Clinical Demographics for 28 Children Identified with ANSD   18  3.1.2 Risk Factors for Hearing Loss The scope of risk factors present within this population are detailed in Table 3.3. The three most common risk factors were prematurity (54%), low birth weight (25%) and respiratory ventilation (25%). Hyperbilirubinemia, cerebral palsy, family history of hearing loss and the use of ototoxic antibiotics were found in 11% of this population. The least common risk factor was cytomegalovirus (CMV) infection, which only occurred in 7% of the subjects.    Risk Factors Number  (n = 28) Percentage  (%) Present 20 71  Prematurity (< 37 weeks) 15 54  Low Birth Weight (< 1500 g) 7 25  Respiratory Ventilation 7 25  Hyperbilirubinemia 3 11  Ototoxic Antibiotics 3 11  Cerebral Palsy 3 11  Family History 3 11  CMV Infection 2 7 Absent  7 26 Unknown History  1 4 Table 3.2 Hearing Loss Risk Factors Identified in an ANSD Population  3.2 Diagnosis of ANSD 3.2.1 BCEHP Screening Outcomes The hearing screening results for 28 patients who participated in the BCEHP screening program are summarized in Table 3.1. Twenty-five infants (89%) did not pass their newborn hearing screening. These patients were primarily NICU residents; only 6 of the 25 infants who failed 19  hearing screening were well-babies. Three subjects (11%) passed their hearing screening, but these may have been false-negatives. Two of these 3 infants had risk factors for hearing loss and were referred for audiological monitoring through the BCEHP. The first was a well-baby with a family history of hearing loss and was later diagnosed with ANSD at 24 months. The second patient was a NICU graduate with multiple risk factors, including history of ototoxic antibiotics; this infant was diagnosed with ANSD at 10 months of age. The third infant passed hearing screening as a well-baby with no known risk factors for hearing loss and was discharged from the BCEHP; this child was later referred for hearing assessment at 5 years of age due parental concern.   Screening Result Number (n) Percentage (%) Pass 3 11 Refer 25 89 Table 3.3 Screening Outcomes for 28 Children Identified with ANSD  3.2.2 Age of Hearing Loss and ANSD Diagnosis The age at which our sample population (n = 28) was diagnosed with hearing loss is illustrated in Figure 3.1a and diagnosed with ANSD (n = 26) is illustrated in Figure 3.1b. By 3 months of age 75% of the subjects had been diagnosed with a hearing loss, which increased to 89% by 6 months of age. The rate of hearing loss diagnosis after this time declined and by 12 months 92% of the population had been identified. The average age for a hearing loss diagnosis was 5.6 months with a standard deviation of 12.8 months. Two outlier patients were diagnosed after 12 months of age; both were patients who had passed their newborn hearing screening.   20  a)    b)    Figure 3.1 a) Age of Hearing Loss Diagnoses in 28 Patients b) Age of ANSD Diagnosis in 26 Patients  Following identification of hearing loss, the average time to a diagnosis of ANSD was 2 months (range <1 month – 13.3 months). There were several outliers within our population that skewed the group average. The age at which each infant was diagnosed with ANSD is illustrated in Figure 3.1 b). Over a 24-month span, there was a steady rise in ANSD diagnoses from one to six 3 14 21 23 25 25 25 25 25 26 26 26 26 27 282514753 3 3 3 3 2 2 2 210510152025301 2 3 4 5 6 7 8 9 10 11 12 13-23 24 67Number of PatientsAge (months)Diagnosed with Hearing Loss Hearing Diagnosis Pending6 12 16 19 19 21 21 21 22 22 22 23 23 24 24 25 26262014107 75 5 5 4 4 43 3 2 210510152025301 2 3 4 5 6 7 8 9 10 11 12 13 14-15 16 17-28 29 69Number of PatientsAge (months)Diagnosed with ANSD ANSD Diagnosis Pending21  months, during which most of the diagnoses occurred. By 3 months of age 46% of the children had been diagnosed with ANSD, and by 6 months 73% of the population had been captured. This was followed by a slower rise in ANSD diagnoses, likely due to the challenges of testing a medically-complex infant population. The average age of an ANSD diagnosis was 7.8 months (range: 1.5 - 69 months).   3.3 Intervention and Management of ANSD 3.3.1 Age of Fitting Hearing Aids Within the sample of 28 patients, 11 were fit with hearing aids. The age at which hearing aids were first fit is illustrated in Figure 3.2.  The average age of hearing aid fitting was 15.1 months (SD: 12.7) but the distribution was highly skewed due to two patients being late identified with ANSD. None of the subjects had been fit with hearing aids by 6 months of age. Between 6 and 11 months of age, there was a steep rise from 0-73% in hearing aid provision to the infants. After 12 months of age, three of the future hearing aid users had yet to receive amplification. All three were NICU graduates with complicated medical histories. Two of the 3 infants demonstrated hearing thresholds within normal limits during early behavioural testing, which likely prolonged hearing aid recommendation and fitting.   22    Figure 3.2 Age of Hearing Technology Intervention for 11 ANSD Patients  3.3.2 Summary of Clinical Milestones in ANSD Hearing Aid Users Figure 3.3 illustrates the age at which the eleven ANSD hearing aid users met the following clinical milestones: hearing loss diagnosis, ANSD diagnosis, protocol-required ABR thresholds and fitting with hearing aids. Patient S08’s chart did not contain protocol-required ABR information, but all other data was available. For the majority of these patients, ABR assessments and the subsequent diagnoses of hearing loss and ANSD occurred in close succession. Patient S06 was initially diagnosed with sensorineural hearing loss and therefore received hearing aids prior to a diagnosis of ANSD. Patient S09, S10, and S11 all experienced significant delay in fitting with hearing aids. All three patients were NICU graduates, with patient S09 and patient S10 having complicated medical histories and ongoing developmental delays that made behavioural testing difficult to obtain. Patient S10 and patient S11 1 3 6 7 8 8 8 9 9 10 1111 11 11 11 11 11108543 3 32 210246810121 2 3 4 5 6 7 8 9 10 11 12 13-17 18 19-31 32 47Number of PatientsAge (months)H. Technology Provided H. Technology Deferred23  demonstrated hearing levels near or within normal limits during initial behavioural testing, which likely prolonged amplification recommendations and fitting.    Figure 3.3 Summary of Diagnosis and Management Milestones in 11 ANSD Patients   0 5 10 15 20 25 30 35 40 45 50S11S10S09S08S07S06S05S04S03S02S01Age (months)Hearing Aid RecipientsAge of Protocol-required ABR Age of Hearing Loss Dx Age of ANSD Dx Age of Intervention24  3.3.3 Time between Diagnoses and Hearing Aid Intervention  The time interval between hearing loss identification and hearing aid fitting for 11 patients was calculated; the average time interval was 12 months with a standard deviation of 14 months. The presence of several outliers, as seen in Figure 3.4a), resulted in a right-tailed distribution. The majority of patients (n = 8) were fit with hearing aids within 5 to 8 months of hearing loss diagnosis.   The time between a patient’s ANSD diagnosis and hearing aid intervention is illustrated in Figure 3.4b). One patient was fit with hearing aids 5 months prior to the ANSD diagnosis. The average time interval between ANSD diagnosis and fitting with hearing aids was 10 months with a standard deviation of 15 months. With the exception of the 3 outliers, most infants (n = 8) were fit with hearing aids within 1 to 7 months following their diagnosis of ANSD.   25  a)     b)     Figure 3.4 Time between Intervention and a) Diagnosis of a Hearing Loss b) Diagnosis of ANSD  00.511.522.533.51 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45Number of PatientsTime between Hearing Loss Diagnosis and Intervention (months)00.511.522.5-5 -3 -1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45Number of PatientsTime between ANSD Diagnosis and Intervention (months)26  3.3.4 Time between Protocol-Required ABR Thresholds and HA Intervention The BCEHP Amplification Protocol requires that fitting of hearing aids be based on a minimum of two confirmed thresholds per ear (2000 Hz and 500 Hz), and that hearing aids can be fit using a clinician’s best judgement if only two thresholds are known for a given ear until additional thresholds are established. The time interval between obtaining ABR thresholds at a minimum of 2000 and 500 Hz (sufficient for hearing aid programming in a population with sensorineural hearing loss) and the age each patient with ANSD was fit with a hearing aid is illustrated in Figure 3.5. One hearing aid recipient was excluded from analysis because protocol-required ABR threshold data was unavailable. The average time interval between protocol-required ABR thresholds and fitting with hearing aids was 13 months, with a standard deviation of 14 months; however, the distribution is highly skewed. Excluding outliers, the majority of patients (n = 7) experienced a 5 to 8-month delay between the age they met protocol-required ABR thresholds for hearing aid programming, and when they were fit with hearing aids.   27    Figure 3.5 Time between Protocol-Required ABR Thresholds and Intervention for 10 Patients  3.3.5 Differences between ABR Thresholds and HA Fitting Thresholds A comparative analysis was conducted to determine the degree of difference between the composite ABR thresholds and behavioural thresholds used for hearing aid programming for 10 subjects with bilateral ANSD fit binaurally with hearing aids. Figure 3.6 illustrates the difference between cumulative ABR thresholds and hearing aid programming thresholds for each of the 10 subjects over time. Considerable variation in differences between thresholds can be observed both between and within patients. Three patients had data from only one hearing aid fitting available for analysis. The majority of patients (n = 6) showed an overall trend of their hearing aid fitting thresholds being below ABR thresholds, indicated by a negative average difference value, while four patients, S03, S04, S09 and S10, showed generally positive average difference values and likely have similar values between ABR and HA thresholds.  00.511.522.533.51 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45Number of PatientsAge disparity between obtaining protocol-ABR thresholds and Intervention (months)28   Figure 3.6 The Average Difference between Hearing Aid Fitting Thresholds and Cumulative ABR Thresholds over Time   The average difference between ABR-estimated thresholds and hearing aid fitting thresholds was examined by frequency. Figure 3.7a) illustrates the difference between thresholds at 2.0 kHz, averaged over time for each subject. The minority (n = 4) of the patients had an averaged difference within 20 dB (+/- 10 dB), which suggests that in these patients, the cumulative ABR thresholds were similar to the HA fitting thresholds. The majority of patients (n = 6) had an average threshold difference greater than -10 dB, all with hearing aid fitting thresholds lower (i.e. better) than ABR-estimated thresholds. Figure 3.7b) and Figure 3.7c) shows the difference between thresholds at 0.5 kHz and 4.0 kHz, respectively, for subjects with this data available. At both of these frequencies, subjects S03 and S04 have averaged differences within 20 dB (+/- 10 dB), while the remaining three subjects in each category had averaged differences greater than  -10 dB.  -70-60-50-40-30-20-1001020300 10 20 30 40 50 60 70Average Difference between ABR and HA Fitting ThresholdsCorrected Age (mo)S01 S02 S03 S04 S05 S06 S07 S09 S10 S1129   a)  b)  c)      Figure 3.7 Frequency Specific Average Differences between ABR and Hearing Aid Fitting Thresholds at a) 2.0 kHz b) 0.5 kHz and c) 4.0 kHz -39-475 8-39-45-25-58-25-50-40-30-20-1001020Average Difference at 2.0 kHzS01 S02 S03 S04 S05 S06 S07 S09 S10 S11-40-45-29-25-50-45-40-35-30-25-20-15-10-50Average Difference at 0.5 kHzS03 S04 S05 S07 S11-461 0-43-30-50-40-30-20-10010Average Difference at 4.0 kHzS01 S03 S04 S05 S1130  Comparative analysis was conducted on the most recent hearing aid fitting available within the data reviewed for this study. The average age at the latest hearing aid fitting was 36 months (range: 9 - 72 months, SD: 23 months). Figure 3.8 demonstrates the range of average differences among patients at that time. The majority of patients (n = 6) had large negative values for the average difference, which indicates that their behavioural thresholds were likely lower than their ABR-estimated thresholds. A small distribution of patients (n = 4) had smaller, positive values for the average difference, which suggests that their ABR-estimated thresholds were similar to the thresholds used in their latest hearing aid fitting.     Figure 3.8 Average Difference between Cumulative ABR and Final HA Fitting Thresholds  -32-6503-39-45-2005-24-70-60-50-40-30-20-10010Average Difference at Final HA FittingS01 S02 S03 S04 S05 S06 S07 S09 S10 S1131  3.3.6 Hearing Technology Management Strategies The different types of hearing equipment used within this population was reviewed and is summarized in Figure 3.9. Hearing aids were worn by 9 subjects; with 2 of the 9 using an FM system in addition to hearing aids. Four of the bilateral ANSD patients had been assessed for cochlear implant candidacy, but to date only two subjects had been implanted (both bilaterally). Review of chart records also indicated that several patients within the bilateral and unilateral population (n = 2, 4 respectively) were too young at the time of chart review to begin behavioural testing; hearing equipment was not fit in the absence of behavioural hearing thresholds. One child with bilateral ANSD had recently provided consistent behavioural thresholds; amplification had been recommended but had not yet been fit at the time of the chart review. There were two remaining children with bilateral ANSD who had not been able to demonstrate reliable behavioural hearing thresholds thus far; these children had yet to be fit with amplification. For the children with unilateral ANSD, 64% of the patients were not using technology; note that these children all had normal hearing thresholds in one ear.  32    Figure 3.9 Hearing Technology Management Strategies in an ANSD PopulationANSD ProfileBilateral (n = 17)HA (n = 9)HA and FM(n = 2)HA Only(n = 7)Bilateral CI (n = 2)No Technology (n = 6)Soundfield WNL(n = 1)Inconsistent Behavioural (n = 2)Consistent Behavioural (n =1)Too Young for Behavioural(n = 2)Unilateral (n = 11)No Technology (n = 11)Monitoring Hearing Status(n = 7)Too Young for Behavioural(n = 4)33  Chapter 4: Discussion 4.1 Population Demographics & Risk Factors Clinical data for 28 young children identified with ANSD through the BCEHP was retrospectively reviewed. The demographics reported in Table 3.2 were congruent with characteristics typically observed within this population. There were roughly equal numbers of male and female subjects; consistent with literature suggesting that the prevalence of ANSD is not influenced by biological sex (Ching et al., 2013; Sininger et al., 2001).   Bilateral ANSD was present in 61% of the population, while 39% had unilateral ANSD. The proportion of children with unilateral ANSD  within our sample population was much higher compared to the proportion of cases of unilateral ANSD reported in literature, which ranges between 2.02% (Narne, Prabhu, Chandan, & Deepthi, 2014) to 22.2% (Bielecki, Horbulewicz, & Wolan, 2012) within ANSD populations. Seven of the 11 subjects reviewed in the current study with unilateral ANSD were well-babies. Because many universal newborn hearing screening programs initially screen the well-baby population with automated OAEs, well-babies with ANSD may be more likely to falsely pass hearing screening due to the increased likelihood of having OAEs despite the presence of hearing loss. The population reviewed in this study seemed to have a higher representation of well-babies with unilateral ANSD compared to what is typically reported in the literature.   The risk factors types and the distribution of percentages identified in Table 3.3 were in agreement with those previously reported (Bielecki et al., 2012; Madden et al., 2002; Narne et al., 2014). These results revealed that there are a variable number of risk factors for ANSD; 34  likely arising from the complexity of early life events and the comorbidity of disorders within this population.  4.2 Newborn Hearing Screening Outcomes All 28 subjects reviewed in this study received a newborn hearing screening through the BCEHP. Twenty-five of the infants did not pass hearing screening (89%). Two of the 3 infants in our study who passed their newborn hearing screening were screened with automated OAEs in well-baby nurseries. OAEs will detect infants with SNHL but can fail to detect infants with neural hearing loss, such as ANSD (Hayes, Sininger, & Northern, 2008). As a result, ANSD patients are likely to pass the first stage of hearing screening and not receive further audiological assessment. Although we cannot clearly confirm that ANSD was present at the time of the passed hearing screenings, Berg et al. (2011) showed that the number of well-baby nursery infants with ANSD who would have passed an automated OAE screening but were instead captured using an automated ABR screening protocol was less than1%. Because of this low incidence of ANSD among well-babies, they concluded that the higher costs needed to implement universal automated ABR hearing screening could not be justified. Future screening protocols may consider the use of wideband pressurized acoustic stapedial reflex (ASR) thresholds, which provide clinically relevant measures in newborn hearing assessments (Hunter, Keefe, Feeney, & Fitzpatrick, 2017). The use of ASR screening could increase the capture rate of well-babies with ANSD, who are likely to have absent reflexes despite present OAEs.      35  The importance of promoting greater awareness of speech and language milestones cannot be overemphasized. Public education and professional outreach could greatly facilitate parent-initiated referrals to capture missed well-babies. This was how one of the three infants who passed hearing screening in our sample population was later identified.  The remaining two infants had risk factors for delayed-onset hearing loss and had been referred for audiological monitoring according to BCEHP protocol.   4.3 Diagnoses and Intervention of ANSD Review of our sample population revealed that 75% had been diagnosed with  hearing loss by the age of 3 months, and 89% had been diagnosed by 6 months. If we consider that the majority of our population received a clinical diagnosis for hearing loss by 3 months of age, it is plausible that the swift provision of amplification would have theoretically placed these ANSD infants within the recommended timeframe for countering language delays (Yoshinaga-Itano, Sedey, Coulter, & Mehl, 1998). However, it is important to consider that no studies to date have investigated the correlation between intervention timelines and language outcomes in infants with ANSD. This would be an important direction for future studies to explore in order to make timely and effective management recommendations.    The average age of hearing loss diagnosis within our sample population was 7.8 months. Once diagnosed with hearing loss, it took an average of 2 months to obtain a diagnosis of ANSD. By 3 months of age 36% of the population had an ANSD diagnosis, and by 6 months this had increased to 73%. There is a large discrepancy in the average age of ANSD diagnosis; values of under 3 months of age (Ching et al., 2013; Rance & Barker, 2008), 7.5 months of age (Barreira-36  Nielsen et al., 2016) and over a year (Jeong, Kim, Kim, Bae, & Kim, 2007) have been reported. The variation in time to diagnosis was likely due to differences in the screening and diagnostic protocols used by the hospitals and early hearing programs from which data is collected.  By the age of 6 months, many of the infants within our population had been diagnosed with hearing loss, but none had received an intervention with hearing aids. The average age of hearing aid fitting within our population was 15.1 months (SD: 12.7), falling along reported ranges of 6.2 months (Ching et al., 2013), 13.73 months (Walker, McCreery, Spratford, & Roush, 2016) and 17.3 months (Barreira-Nielsen et al., 2016). It is evident that children with ANSD are fit with amplification later than their counterparts with more typical sensorineural hearing loss. Figure 3.3 illustrates the wide time interval between the ages of identification and fitting with amplification for our sample of children with ANSD. There are likely many factors responsible for delays within ANSD populations, but two more likely contributors identified within our study were 1) the comorbidity of medical complications and developmental delays within this population and 2) the deferment of hearing aid fitting until reliable behavioural thresholds could be obtained, which was often hampered by the aforementioned complications. Given the frequency of these features in cases of ANSD, should patients with ANSD follow the same 1-3-6 benchmarks as children with more typical forms of hearing loss? Based on medical complexity alone, the average age of diagnosis and hearing aid intervention in sensorineural NICU populations is often later than in well-babies (Dalzell et al., 2000). Re-evaluating and determining appropriate intervention targets for the ANSD population was beyond the scope of this study but should be pursued in future research.   37  4.4 Comparative Analysis of Cumulative ABR and Final HA Fitting Thresholds The unreliability of ABR in ANSD patients has made deferral of amplification until behavioural testing a common clinical strategy. However, postponing intervention to mitigate potential overamplification might have its own repercussions on auditory and language development. Within our patient sample (n = 10), the average delay between protocol-required ABR and fitting with amplification was 13 months (SD: 14 mo). Due to the importance of timely intervention for early language development (Yoshinaga-Itano, Sedey, Coulter, & Mehl, 1998), this study aimed to quantify the degree of difference between ABR and HA fitting thresholds. As Figure 3.7 illustrates, the degree of difference is widely variable both between patients, and within patients over time. Many of the subjects (n = 6) were prescribed hearing aid targets that were lower than ABR thresholds, implying that clinicians were correct in delaying amplifications until behavioural thresholds could be obtained. For a smaller subset of subjects (n = 4), however; the small average difference values shown in Figure 3.8 suggest that ABR thresholds were close to hearing aid fitting thresholds. It is possible that for some patients with ANSD, early amplification based on ABR thresholds may be appropriate, but strategies to identify these patients are not known at this time. Given the limitations of retrospective review, the data presented in this study does not warrant changes to current clinical ANSD management strategies without further corroborating research. If clinicians were to pursue initial fitting using ABR thresholds, careful behavioural observations and monitoring would be necessary. Strong communication and teamwork between families and clinicians would be critical to the success of early amplification until reliable behavioural testing can be achieved.   38  4.5 Hearing Technology Management Strategies in ANSD The heterogeneity of ANSD requires individualized management, as seen in Figure 3.9. The hearing equipment utilized by children with ANSD is similar to equipment used by children with more typical SNHL. The one notable exception is the increased number of young children with ANSD who are not fit with hearing aids based on infant ABR assessment and as a result experience a longer delay before adequate audibility can be provided. Further investigation is needed to help clinicians facilitate auditory and linguistic development during this waiting period for children with ANSD. Interim solutions could place greater focus on alternative communication strategies such as signed English and cued speech (Cone-Wesson, 2001) or improving the signal-to-noise ratios with FM devices (Hood, 2003) until such time that amplification can be provided.    39  Chapter 5: Conclusion ANSD is a highly variable disorder, in both clinical presentation and etiology. Hearing aid fitting for this population is often delayed, in part due to the frequency of complicated birth histories and medical comorbidities. ABR testing has proven unreliable for estimating behavioural hearing thresholds in infants with ANSD and many clinicians will defer fitting with amplification until reliable behavioral thresholds can be obtained. However, timely intervention for hearing loss is critical for language development. Clinicians are forced to balance the risk of inappropriate amplification with the risk of reduced audibility.    For the majority of ANSD subjects investigated within this study, clinicians were correct in delaying the provision of amplification until behavioural thresholds could be obtained. However, results from this study suggest that for a small subset of patients, early hearing aid fitting with ABR-estimated thresholds may have been appropriate. If follow-up studies are able to corroborate these findings and provide a way to identify which factors influence the correlation of ABR-estimated to behavioural hearing thresholds, the average age of fitting amplification for children with ANSD may decrease.   The heterogeneity and low incidence of ANSD often makes it challenging for researchers to draw uniform conclusions. As a retrospective study, we were able to access a larger sample size, but were limited to the clinical data available. We had minimal control over potential confounds amongst the key variables used in the comparative analysis, such as the threshold information available in ABR testing, or the fittings made by the prescribing audiologist. Future research 40  would ideally control for these confounds, perhaps by conducting longitudinal studies with a pre-determined assessment and management protocol.   41  References Barreira-Nielsen, C., Fitzpatrick, E. M., & Whittingham, J. (2016). 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