The very nature of a dead region (DR) in a cochlea means that they are often found in patients who are eligible for cochlear implants. However, a variety of different hearing configurations are found in those with DRs because of off-frequency listening. Dead regions are not only present in those patients with profound losses but can also occur in patients with moderate to severe hearing losses. Some patients with DRs may be eligible for a cochlear implant whilst others are not. The team in Cambridge Implant Centre in the UK carried out TEN testing (a test which is used to identify a DR in audiology clinics) and implanted 40 patients with DRs whose speech perception scores met the cochlear implant criteria but their pure-tone audiometric thresholds did not meet criteria. They found that the average score on speech perception testing of the DR group improved after cochlear implantation and there was no significant difference in the amount of improvement between the DR group and matched patients who met the traditional audiological criteria for cochlear implantation. TEN testing could therefore be a useful addition to the battery of tests used in a cochlear implant assessment.
It may help to identify those that have DRs who may benefit from cochlear implantation despite their audiograms being outside of audiological criteria.
It should be noted that this study was conducted using the old criteria for cochlear implantation (detailed in the NICE TA166 guidance); since then there has been a new publication of guidance (NICE TA566). When the team went back and reviewed their results, they found that 14 out of the 40 patients did not meet the new audiological criteria for TA566. However, these 14 patients still experienced an improvement post-implant in speech perception, thus the findings of this paper remain relevant.