(PP508) Physiologic Responses Over Time in Patients with Auditory Neuropathy, Auditory Synaptopathy

Auditory neuropathy/auditory synaptopathy (AN/AS) is associated with interrupted inner ear, synaptic, and/or neural function, affecting the integrity of signals that reach the brain. In this study, longitudinal changes in physiologic responses were characterized in infants and children with confirmed bilateral AN/AS.  Otoacoustic emission, auditory brainstem response, cochlear microphonic, and middle-ear muscle reflex findings were consistent with patterns associated with AN/AS. A substantial proportion of patients showed changes in responses over time that included fluctuation, improvement, and worsening. Identifying patterns of change in physiologic responses over time is valuable in clinical decision making and management.


Summary: 

Objectives: This study investigated changes in physiologic responses over time in patients with confirmed bilateral auditory neuropathy/auditory synaptopathy (AN/AS). The physiologic responses examined were otoacoustic emissions (OAE), auditory brainstem responses (ABR), cochlear microphonics (CM), and middle-ear muscle reflexes (MEMR). Associations among these measures were also evaluated.

Rationale: The prevalence of hearing loss from birth is estimated at 1.7 in every 1,000 infants (CDC, 2018). Of these infants, 10-20% are diagnosed with AN/AS. While the characteristics of physiologic responses associated with AN/AS have been described, changes in responses over time for these patients has not been fully explored. An understanding of the changes in physiologic responses over time will provide guidance in diagnosis, intervention, and expected outcomes.

Design: This retrospective study cohort included AN/AS patients (n=90 ears) whose data were collected from their medical records for inclusion in the Vanderbilt Auditory Neuropathy/Auditory Synaptopathy Database in the Hood Lab at Vanderbilt University. Subjects were divided into two cohorts, one exploring OAE and MEMR results (n=34 ears) and the other exploring ABR and CM results (n=58 ears). Data were analyzed for changes over time within subjects and associations among measures. Descriptive analyses were used to describe the findings.

Results: The majority (84%) of ABRs were absent with CM responses present as expected in patients with AN/AS. A comparison of data from the first and last tests indicated that the ABR changed from an “absent” to “abnormal” classification in 12% of subjects, consistent with evidence of improvement in neural synchrony. For MEMR, 62.5% of the subjects had absent responses with no change over time, 12.5% were elevated with no change, 18.75% changed from absent to elevated, and 6.25% changed from elevated to absent. Among the subjects with elevated MEMRs, 25% of the ears also demonstrated an improvement in the ABR over time. For the OAE data, 56% of subjects showed no change in test results, 26% showed worsening, and 18% showed fluctuation over time. Review of OAE data as a function of age indicated that the number of subjects with absent OAEs increased with age.

Conclusions: The results of this study indicate observable changes in physiologic measures over time in patients with bilateral AN/AS. Knowledge about changes over time in patients with AN/AS is valuable in supporting accurate evaluation and management planning. Future research will focus on exploring the associations among physiologic responses, behavioral metrics, patient characteristics including predictive risk factors, and speech and hearing outcomes.