BackgroundAuditory neuropathy (AN) is a recently recognized hearing disorder characterized by intact outer hair cell function, disrupted auditory nerve synchronization and poor speech perception and recognition. Cochlear implants (CIs) are currently the most promising intervention for improving hearing and speech in individuals with AN. Although previous studies have shown optimistic results, there was large variability concerning benefits of CIs among individuals with AN. The data indicate that different criteria are needed to evaluate the benefit of CIs in these children compared to those with sensorineural hearing loss. We hypothesized that a hierarchic assessment would be more appropriate to evaluate the benefits of cochlear implantation in AN individuals.MethodsEight prelingual children with AN who received unilateral CIs were included in this study. Hearing sensitivity and speech recognition were evaluated pre- and postoperatively within each subject. The efficacy of cochlear implantation was assessed using a stepwise hierarchic evaluation for achieving: (1) effective audibility, (2) improved speech recognition, (3) effective speech, and (4) effective communication.ResultsThe postoperative hearing and speech performance varied among the subjects. According to the hierarchic assessment, all eight subjects approached the primary level of effective audibility, with an average implanted hearing threshold of 43.8 ± 10.2 dB HL. Five subjects (62.5%) attained the level of improved speech recognition, one (12.5%) reached the level of effective speech, and none of the subjects (0.0%) achieved effective communication.ConclusionCIs benefit prelingual children with AN to varying extents. A hierarchic evaluation provides a more suitable method to determine the benefits that AN individuals will likely receive from cochlear implantation.
The degree of overlap among cochlear nerve fibers stimulated by different electrodes results in electrode interaction, which has been shown to have a significantly deleterious effect on speech recognition performance in multi-electrode cochlear implant users. The Nucleus CI24R(CS) Contour array, which lies substantially closer to the modiolus than the CI24M straight array, is expected to exhibit narrower excitation patterns. The neural response telemetry (NRT) 3.0 software provides a method of measuring the spread of neural excitation by presenting the masker and probe pulses on different intra-cochlear electrode bands. Nine pairs of children, using Nucleus CI24M/CI24R(CS) cochlear implants with a similar etiology and duration of deafness, insertion depth, age of implantation and loudest acceptable presentation level (LAPL) in NRT sessions, participated in the study. Profiles of the spread of neural excitation stimulated at the LAPL at 3 probe locations were examined for each pair of the 2 types of electrode array. The spread of neural excitation with respect to array type and location revealed significant effects (p < 0.001; p = 0.002) and no interaction between array type and probe location (p = 0.559). The results demonstrated that the Contour array improved electrode discrimination, especially for the electrodes at the basal end of the cochlea. The findings have implications for future electrode array design and current implant mapping strategies.
After using the CI for 6 months, the hearing ability of both subjects was improved by the CI with an average post-implant threshold of 35 dB and 44 dB, respectively. The woman made significant progress in speech recognition with an open-set spondee recognition score of 55% and sentence recognition in quiet score of 90%. Sentence recognition in noise scores were 94% (SNR = +10 dB), 88% (SNR = +5 dB), and 80% (SNR = 0 dB). The boy achieved improved recognition scores for monosyllables (40%) and disyllables (26%), but poor sentence recognition both in quiet (0%) and in noise (0%).
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