Abstract
In this work we describe the experimental protocol set up to obtain very good results in speech performance and in time course, with a subject presenting profound bilateral sensorineural hearing loss with low-frequencies preservation. We used a bimodal stimulation with a like-hybrid modality. Auditory functions have been analyzed by standard tonal and speech audiometry tests, and verbal perception test. The fitting protocol permitted the subject to reach a perception at 65 dB of 100% in a very short time. The subject showed a sufficient recovery of the language spectral information and a good integration of verbal information with high consonantal recognition is present. This case report shows the importance to realize a correct cochlear implant fitting and that, in the case of bimodal stimulation, it is very important to obtain the mutual adjustment of the two hearing aids. Moreover, this study enhances the importance of realizing a preservative surgery to make the most of cochlear implants capacity.
1
Introduction
Binaural hearing is an essential property of the auditory system and evidence for binaural benefits is well documented in normal hearing subjects . Actually, cochlear implants (CI) are the treatment frequently utilized for subjects with severe to profound hearing loss. In the last years, for bilaterally affected subjects, the use of bimodal listening, combining electric (E) and acoustic (A) devices, using a CI in one ear and an acoustic hearing aid (HA) in the non-implanted ear has been increasing . Benefits with bimodal stimulation are controversial and vary across patients. In some cases a noteworthy increase in speech performances has been obtained , but in other cases very few benefits have been obtained . The variability is present also in the time necessary for adaption to the dual type of stimulation. Several studies have reported that most EA benefits occur in about 6 months . The use of bimodal strategy seems particularly useful for unilateral cochlear implant (CI) users that have substantial residual low-frequency hearing in the contralateral ear . In this case report the very good results obtained in speech performance and in time course, with a subject presenting a profound bilateral sensorineural hearing loss with low-frequencies preservation, are described. In particular, the protocol set up to obtain the best performances is detailed.
2
Case report
The examined subject, male, Caucasian, 26 years old, reported a profound, congenital, bilateral sensorineural form of hearing loss with reasonable maintenance of low frequencies. The subject, moreover, presented some other pathological aspects: tetralogy of Fallot, hydrocephalus and scoliosis.
The subject had used analogic HA since two years old. Then, in 2003, the analogic HA has been exchanged for a digital HA at the Audiology Unit of University Federico II of Naples with poor results. In fact, the subject in study showed small quantitative improvement, but worse verbal perception performances. This worsening was due to a very low recovery of frequencies higher than 1000 Hz. In 2007, the subject received cochlear implant (CI) in the worse ear: MXM model with 20 electrodes for stimulation. After this operation the subject received a bimodal stimulation, without obtaining sufficient performances for the tonal recovery ( Fig. 1 ). So, the subject returned for clinical controls to the Unit of Audiology of University Federico II of Naples.
A preliminary test for the CI determined a loudness absence for the first three apical electrodes: frequencies from 195 to 586 Hz. So, these three electrodes have been deactivated and the entire range of frequencies has been put back in the remaining 17 electrodes.
The therapeutic protocol carried out, then, consisted in a very slow path for the adaptation to the sonory world. To obtain this, the CI has been analyzed as in a first control, realizing a new starting fitting–mapping but, maintaining the bimodal stimulation.
Also in this case, the verbal perception, notwithstanding a good tonal recovery, resulted very low with a level of perception at 65 dB of only 10% with free field vocal audiometry using bisyllabic words.
To obtain better performances it has been decided to use the bimodal stimulation with a like-hybrid modality with the aim of using the CI for the transduction of high frequencies stimulation and the HA for the low frequency. The audiogram of the contralateral ear to the CI suggested to use the implant from 1000 Hz and the contralateral HA only for frequencies under 1000 Hz. To avoid losing the tonotopicity of implant it has not been deactivated the electrodes from 20 to 12 (from 195 to 977 Hz) but levels of the electrical stimulation of these electrodes generate no loudness. This approach has permitted the remaining 11 electrodes to transduce frequencies higher than 977 Hz. Moreover, the CI frequential range has been restricted to 6576 Hz.
For the contralateral HA frequencies up to 800 Hz have been stressed, while the higher frequencies have been compressed. The subject declared immediately that the sound was more lovely. The vocal test, realized a few minutes after the application of this experimental protocol, has shown a good improvement in audiological performances obtaining an increasing of the perception level at 65 dB from 10% to 60%. From this point started a fitting protocol that permitted the subject to reach a perception at 65 dB of 100% ( Fig. 2 ). The verbal perception test with bimodal stimulation has given the results shown in Table 1 .
| Test | CI + HA | Only CI |
|---|---|---|
| Vowels identification | 100 | 45 |
| Phonemic confusion matrices | 52 | 10.5 |
| Partial identification with vowels exchange | 100 | 20 |
| Partial identification with consonants exchange | 66 | – |
| Bisyllabic words identification | 94 | 20 |
| Sentences identification | 94 | – |
| Sentences understanding | 90 | – |
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