Electrophysiological evaluation of the adult patient with cochlear implant: correlation with functional results

Cochlear implants (CI) provide the opportunity for post-lingually deafened adults to regain a part of their auditory communicative skills. Despite significant improvements in average performance there remains a considerable amount of unpredictable inter-subject variability. Most previous studies seeking to predict post-operative speech understanding have been handicapped by heterogeneous patient populations with variable devices, speech processing strategies, speech discrimination tests or clinical rehabilitation programs. The use of varying clinical programs, particularly different devices, can influence the usefulness of performance predictors. Electronics and electrode designs have evolved over time, leading to improved speech perception for the whole group of CI recipients. Another possible explanation for the broad variety in performances after implantation could be related to differences in peripheral nerve excitability. This activity could be estimated by measuring the widths of spread of excitation profiles through neural response telemetry. The study group was made up of 20 adult subjects who underwent CI surgery by the same otosurgeon and were rehabilitated by the same speech therapist at Pisa CI centre in the period from 2000 to 2011. In all these patients a Cochlear® perimodiolar electrode array was used, an array with 22 electrode contacts directed towards the inner wall of the scala tympani. The only variation was in the surgical insertion procedure, advance off stylet and in-stylet technique. One of this study's aims was to compare electrophysiological data to audiological outcomes in a CI adult population in order to find a specific method to predict future audiological outcomes from first programme mapping. To investigate dependence between excitability and patient benefits (described as speech understanding results) all the patients were submitted to a neural response telemetry and spread of excitation width on all the odd electrodes, evaluated with logopedical test using the new MAP performed on the basis of behavioural cues. All these data were compared to audiological outcomes. Another goal to achieve was to find a correlation between neural response telemetry and width of spread of excitation in 11 electrodes out of 22 measured. The measure of spread of excitation is not commonly used in the follow up of a CI population, but it could be of great importance in difficult cases such as non-collaborative patients and to study patients who do not achieve the expected results. In this context we tried to statistically demonstrate that as the SOE width increases, audiological performances of the patient declines. Finally, we compared all patient maps and their performances in order to find a correlation between MAP's modifications and their audiological outcomes