Recovery of Abnormal ABR in Neonates and Infants at Risk of Hearing Loss

Abstract

The purpose of this retrospective study is to present the clinical experience of a single institution on the recovery of ABR thresholds in a large population of neonates and infants at risk of hearing loss. Potential prognostic factors associated with this phenomenon were also investigated. Out of 2248 high risk infants, 384 had abnormal ABR at initial hearing evaluation and 168 of them had absent ABR or a threshold ≥80 dBnHL. From this subgroup, a significant percentage showed complete or partial recovery on reexamination (32.7% and 9.3%, resp.), performed 4-6 months later. The presence of normal otoacoustic emissions was associated with the ABR restoration on reexamination. Moreover, the very young age at the initial hearing screening seems to be related to higher probabilities of false positive ABR. The potential recovery of hearing in HR infants raises concerns about the very early cochlear implantation in HR infants less than one year. Such a treatment modality should be decided cautiously and only after obtaining valid and stable objective and subjective hearing thresholds. This holds especially true for infants showing an auditory neuropathy profile, as they presented a much greater probability of ABR recovery.

Figure 1

Schematic flow chart of the results of the study. ¹Replicable waveform at 40 dBnHL within the expected latencies.

Figure 2

Audiological data from a HR infant of the early years of this study (risk indicators: prematurity, low birth weight, hyperbilirubinemia/phototherapy, and asphyxia). (a) Initial ABR recordings showing atypical waveforms at 90, 80, and 70 dBnHL (from above downwards). “Atypical” ABR waveforms were not a rare finding among infants suffering from AN who eventually showed full ABR restoration. We use the term “atypical” to describe any unexpected waveform, consisting of unpredictable yet reproducible waves. The black arrow denotes such a waveform. (b) Normal otoacoustic emissions were obtained bilaterally within the same session. (c) Last ABR testing at the age of 20 months. Typical and replicable waveforms were elicited at 60 and 40 dBnHL bilaterally (full ABR recovery). Information from the parents and behavioral audiometry validated the presence of normal hearing threshold.

Figure 3

Serial ABR measurements, otoacoustic emissions and MRI findings of an infant with type I Chiari malformation. (a) ABR recordings at the initial hearing assessment (age of 2.5 months). Waveforms were obtained at 90 dBnHL on the left and 80 dBnHL on the right ear. (b) ABR findings 5 months later (age of 7.5 months). Waveforms were elicited bilaterally at 50 dBnHL. (c) At the same time, normal otoacoustic emissions were recorded on the right side and partial response on the left. (d) Last ABR session after 10 months (age of 18 months). Typical ABR waveforms were recorded at 40 dBnHL bilaterally, a finding which corresponds to “normal” ABR threshold and which is considered a strong indication of normal hearing. (e) Coronal MRI image of the same infant at age of 7 months, depicting enlargement of lateral ventricles (black arrows) and herniated cerebellar tonsils (white arrow). In this case, the ABR thresholds recovered completely.