Aiding and occluding the contralateral ear in implanted children with auditory neuropathy spectrum disorder

The challenges associated with auditory neuropathy spectrum disorder (ANSD) are due primarily to temporal impairment and therefore tend to affect perception of low- to midfrequency sounds. A common treatment option for severe impairment in ANSD is cochlear implantation, and because the degree of impairment is unrelated to degree of hearing loss by audiometric thresholds, this population may have significant acoustic sensitivity in the contralateral ear. Clinically, the question arises as to how we should treat the contralateral ear in this population when there is acoustic hearing-should we plug it, amplify it, implant it, or leave it alone?

The purpose of this study was to examine the effects of acute amplification and plugging of the contralateral ear compared to no intervention in implanted children with ANSD and aidable contralateral hearing. It was hypothesized that due to impaired temporal processing in ANSD, contralateral acoustic input would interfere with speech perception achieved with the cochlear implant (CI) alone; therefore, speech perception performance will decline with amplification and improve with occlusion.

Prospective within-subject comparison. Adaptive speech recognition thresholds (SRTs) for monosyllable and spondee word stimuli were measured in quiet and in noise for the intervention configurations.

Nine children treated at the Medical College of Wisconsin Koss Cochlear Implant Program participated in the study. Inclusion criteria for this study were children diagnosed with ANSD who were unilaterally implanted, had aidable hearing in the contralateral ear (defined as a three-frequency pure-tone average of ≤80 dB HL), had at least 1 yr of cochlear implant experience, and were able to perform the speech perception task.

We compared SRT with the CI alone to SRTs with interventions of cochlear implant with a contralateral hearing aid (CI+HA) and cochlear implant with a contralateral earplug (CI+plug).

SRTs were measured and compared within subjects across listening conditions. Within-subject comparisons were analyzed using paired t-tests, and analyses of predictive variables for effects of contralateral intervention were analyzed using linear regression.

Contrary to the hypothesis, the bimodal CI+HA configuration showed a significant improvement in mean performance over the CI-alone configuration in quiet (p = .04). In noise, SRTs were obtained for six subjects, and no significant bimodal benefit was observed (p = .09). There were no consistent effects of occlusion observed across subjects and stimulus conditions. Degree of bimodal benefit showed a significant relationship with performance with the CI alone, with greater bimodal benefit associated with poorer CI-alone performance (p = .01). This finding, however, was limited by floor effects.

The results of this study indicate that children with ANSD who are experienced cochlear implant users may benefit from contralateral amplification, particularly for moderate cochlear implant performers. It is unclear from these data whether long-term contralateral hearing aid use in real-world situations would ultimately benefit this population; however, a hearing aid trial is recommended with assessment of bimodal benefit over time. These data may help inform clinical guidelines for determining optimal hearing configurations for unilaterally implanted children with ANSD, particularly when considering candidacy for sequential cochlear implantation.