Criteria for cochlear implantation (CI) is a constant topic of debate. The UK traditionally had relatively restrictive guidance, although this has been greatly improved by more recent guidance released in 2019. Nevertheless, because of the lack of evidence for cost-effectiveness, there remains no provision for patients with single-sided deafness. Patients with bilateral hearing loss who are out of criteria based on the better hearing ear (i.e. those with asymmetrical hearing loss) are intuitively more likely to benefit than those with normal hearing in the better hearing ear (particularly those with progressive hearing loss). Children, similarly, with their greater neural plasticity, may see greater benefit. Therefore the outcomes of studies such as this, looking at speech and language outcomes in implanted children with asymmetric hearing loss, are important as if they do not show significant improvement, prospects for expanding CI criteria seem slim. This study retrospectively identified 26 children who underwent CI surgery over a four-year period. The worse-hearing ear was implanted. Patients with cognitive impairment, auditory neuropathy and cochlear nerve hypoplasia were excluded. A number of patients were likely to have progressive hearing loss; specifically 42% had enlarged vestibular aqueduct. The mean threshold in the better-hearing ear was 62dB (92dB in the implanted ear). Outcome measures included a range of speech and language scoring tests. The broad range of outcome measures in the CI literature, particularly regarding speech development, makes comparison with other studies difficult. However, it is pleasing to see that these patients’ speech and language improved. There are limitations to the study, however. Firstly, the definition of asymmetric hearing loss doesn’t make it clear whether or not single-sided deafness (i.e. those with normal hearing in the non-implanted ear) are included. This is highly relevant, although the mean threshold of 62dB when those with thresholds greater than 70dB were excluded, means this is likely not a significant factor. There are limitations in terms of length of follow-up and, in particular, the lack of a comparison group to see whether there may be language development in those simply managed with bilateral hearing aids. Also, only a subset of patients were assessed using the same speech and language measure, which makes interpretation of results more difficult. Whilst these drawbacks mean this study is unlikely to inform many funding bodies’ next assessment of CI criteria, the data, and the fact that eight of the 26 underwent sequential implantation during follow-up, reassures those parents and clinicians considering implantation in these cases.
Cochlear implantation in asymmetric hearing loss
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