Cochlear implantation in adults with asymmetric hearing loss

Abstract

Objective: Bilateral severe to profound sensorineural hearing loss is a standard criterion for cochlear implantation. Increasingly, patients are implanted in one ear and continue to use a hearing aid in the nonimplanted ear to improve abilities such as sound localization and speech understanding in noise. Patients with severe to profound hearing loss in one ear and a more moderate hearing loss in the other ear (i.e., asymmetric hearing) are not typically considered candidates for cochlear implantation. Amplification in the poorer ear is often unsuccessful because of limited benefit, restricting the patient to unilateral listening from the better ear alone. The purpose of this study was to determine whether patients with asymmetric hearing loss could benefit from cochlear implantation in the poorer ear with continued use of a hearing aid in the better ear.

Design: Ten adults with asymmetric hearing between ears participated. In the poorer ear, all participants met cochlear implant candidacy guidelines; seven had postlingual onset, and three had pre/perilingual onset of severe to profound hearing loss. All had open-set speech recognition in the better-hearing ear. Assessment measures included word and sentence recognition in quiet, sentence recognition in fixed noise (four-talker babble) and in diffuse restaurant noise using an adaptive procedure, localization of word stimuli, and a hearing handicap scale. Participants were evaluated preimplant with hearing aids and postimplant with the implant alone, the hearing aid alone in the better ear, and bimodally (the implant and hearing aid in combination). Postlingual participants were evaluated at 6 mo postimplant, and pre/perilingual participants were evaluated at 6 and 12 mo postimplant. Data analysis compared the following results: (1) the poorer-hearing ear preimplant (with hearing aid) and postimplant (with cochlear implant); (2) the device(s) used for everyday listening pre- and postimplant; and (3) the hearing aid-alone and bimodal listening conditions postimplant.

Results: The postlingual participants showed significant improvements in speech recognition after 6 mo cochlear implant use in the poorer ear. Five postlingual participants had a bimodal advantage over the hearing aid-alone condition on at least one test measure. On average, the postlingual participants had significantly improved localization with bimodal input compared with the hearing aid-alone. Only one pre/perilingual participant had open-set speech recognition with the cochlear implant. This participant had better hearing than the other two pre/perilingual participants in both the poorer and better ear. Localization abilities were not significantly different between the bimodal and hearing aid-alone conditions for the pre/perilingual participants. Mean hearing handicap ratings improved postimplant for all participants indicating perceived benefit in everyday life with the addition of the cochlear implant.

Conclusions: Patients with asymmetric hearing loss who are not typical cochlear implant candidates can benefit from using a cochlear implant in the poorer ear with continued use of a hearing aid in the better ear. For this group of 10, the 7 postlingually deafened participants showed greater benefits with the cochlear implant than the pre/perilingual participants; however, further study is needed to determine maximum benefit for those with early onset of hearing loss.

Figures

Figure 1

Individual audiometric thresholds as a function of frequency are shown for each participant. Unaided thresholds are open symbols with dashed lines, the better ear as triangles and the poorer ear as squares. Aided better ear thresholds are filled triangles with solid lines. Poorer ear post-implant thresholds with a CI are filled squares with solid lines.

Figure 2

Group mean speech recognition scores (CNC words, HINT sentences in noise, TIMIT sentences in noise and TIMIT sentences in quiet) pre-implant and at six months post-implant are shown for the seven postlingual participants. Scores are shown in black for the poorer hearing ear that was implanted, in white for the better hearing ear with a HA, and in gray for the participants' everyday listening condition (bimodal at the post-implant interval).

Figure 3

Group mean adaptive HINT scores in restaurant noise at the six-month interval for all postlingual participants are shown in the left panel. Individual participants' scores are shown in the right panel for the four participants who had both pre- and post-implant testing. Scores are expressed as SNR and are shown in black for the poorer hearing ear that was implanted, in white for the better hearing ear with a HA, and in gray for the participants' everyday listening condition (bimodal at the post-implant interval).

Figure 4

Individual participants' speech recognition scores (CNC words, HINT sentences in noise, TIMIT sentences in noise and TIMIT sentences in quiet) are shown for the three pre/perilingual participants pre-implant, and at six and 12 months post-implant. Scores are shown in black for the poorer hearing ear that was implanted, in white for the better hearing ear with a HA, and in gray for the participants' everyday listening condition (bimodal at the post-implant interval).

Figure 5

Individual pre/perilingual participants' adaptive HINT scores in restaurant noise are shown. Scores are expressed as SNR and are shown in black for the poorer hearing ear that was implanted, in white for the better hearing ear with a HA, and in gray for the participants' everyday listening condition (bimodal at the post-implant interval).

Figure 6

Group mean RMS error scores are shown in the left panel for the postlingual participants. Individual RMS error scores for the pre/perilingual participants are shown in the right panel. Scores are shown in black for the poorer hearing ear that was implanted, in white for the better hearing ear with a HA, and in gray for the participants' everyday listening condition (bimodal).

Figure 7

Individual participants' localization results are shown for the conditions CI-alone (filled squares, left panels), HA-alone (filled triangles, middle panels), and bimodal (filled circles, right panels) at six months post-implant. Symbols represent mean responses in degrees azimuth. X-axis represents the location of the stimuli and the Y-axis, the location of the response. The RMS error score for each participant and condition is noted in the upper left hand corner of each panel. Significant differences between the HA-alone and bimodal conditions are indicated with asterisks in the lower right hand corner of the bimodal panels.

Figure 8

Average ratings for the three sections of the SSQ (Speech as diamonds, Spatial as squares, Quality as triangles) for postlingual participants are shown in the left panel. Individual results for pre/perilingual participants are shown in the right panel at pre-implant and at six and 12 months post-implant.