Neural Recovery Function of the Auditory Nerve in Cochlear Implant Surgery: Comparison between Prelingual and Postlingual Patients

THIEME 444 Original Research Neural Recovery Function of the Auditory Nerve in Cochlear Implant Surgery: Comparison between Prelingual and Postlingual Patients Bettina Carvalho1 Gislaine Richter Minhoto Wiemes1 Rogerio Hamerschmidt1 1 Hospital Paranaense de Otorrinolaringologia, Curitiba, Paraná, Brazil Int Arch Otorhinolaryngol 2020;24(4):e444–e449. Abstract Keywords ► cochlear implants ► prelingual hearing loss ► postlingual hearing loss ► neural response telemetry Address for correspondence Bettina Carvalho, Master, Hospital Paranaense de Otorrinolaringologia, Avenida República Argentina, 2069, Água Verde, Curitiba, PR, 80620-010, Brazil (e-mail: ). Introduction Cochlear implants (CIs) enable objective measures of the neural function in implanted patients through the measurements of the neural response telemetry (NRT) and of the Auditory nerve Recovery Function (REC). These measurements help in programming the speech processor and understanding the auditory system. Objective To compare the NRT and the REC in prelingual and postlingual implanted patients. Methods An observational, descriptive and prospective study was carried out. The NRT and the REC (through the T0, A, and tau parameters) were evaluated in individuals submitted to CI surgery, who were divided into two groups: prelingual and postlingual patients. Results In total, 46 patients were evaluated. Data analysis showed no statistically significant difference between the NRT measurements and the T0, A, and Tau of the REC in the comparison between the two groups, except for the NRT in the basal cochlear region. Conclusion There was no statistically significant difference in the REC in pre- and postlingual patients. Introduction The age at the onset of deafness is one of the most important factors in the evaluation of a patient with hearing loss (HL). Regarding this aspect, HL can be classified according to the period of language acquisition as prelingual or postlingual. It is said to be prelingual when it occurs before the acquisition of the bases of oral language, and it is postlingual when it occurs after the acquisition of language, when the patient already has an established linguistic code.1 Auditory deprivation in prelingual HL may affect the development of the auditory neural pathways, since the maturation of these pathways depends on stimulation. This deprivation compromises the maturation of the central auditory pathways, received April 29, 2019 accepted December 26, 2019 Luiz Patrial Netto1 DOI https://doi.org/ 10.1055/s-0040-1702974. ISSN 1809-9777. as well as the development of speech and language skills2. In postlingual HL, the neural pathways are already formed, and there is an auditory memory, so, in general, there is no regression of the language due to hearing deprivation. The development of speech perception and language acquisition, as well as the success of the CI rehabilitation, both in children with prelingual HL and in adults with pre- or postlingual HL, depends on some determinant factors,3 but since the ganglion cells of the auditory nerve are considered the elements that effectively respond to the electrical stimulus released by the CI, the participation of the ganglion cells is the differential factor in the individual’s ability to achieve success with the use of the CI.4 Copyright © 2020 by Thieme Revinter Publicações Ltda, Rio de Janeiro, Brazil Neural Recovery Function of the Auditory Nerve in Cochlear Implant Surgery Both the neural function of the cochlear nerve as well as the number, distribution, and functionality of the remaining neural cells must be in sufficient quantity to enable the electrical stimulation to be transmitted to the cerebral cortex5. This functionality can be evaluated through speech performance or electrophysiological tests. Initial studies6–8 compared the performance with the CI between postlingual and prelingual adult patients. They observed worse responses in the performance of prelingual patients. Other studies9,10 have shown that only prelingual children who are implanted early (before 6 years of age) have achieved full speech recognition in an open set, with an even better performance than the postlingual patients. In the first 6 years of age, a period of high neuronal plasticity9,10 was reached with CI stimulation, close to that of a normal listener. Ching et al11 showed the benefit of early intervention for language development, helping to ensure early amplification and enable cochlear implantation after the diagnosis. The possibility of performing CI in small children makes it necessary to use objective measurements to aid in the programming of the speech processor. One of them is neural response telemetry (NRT), through which the electrically-evoked compound action potential (ECAP) is obtained using the implant itself to elicit the stimulus and record the responses to study the remaining neural properties12 without the need to sedate the patient.13 The refractory recovery function (REC) can be extracted from the action potential of the neural fibers in response to the use of a pulse with a gap between the main stimulus and the masker.14 The REC is measured by an exponential function with three parameters: ‘T0’, ‘A’ and ‘tau’. T0 is the absolute refractory period (in μs); A is the maximum amplitude of the neural response at the maximum saturation level (in μV); and tau is the recovery time constant during the relative refractory period (in μs). It is important to consider the interaction between the three parameters.14–16 The objective of the present study was to evaluate and compare the NRT and the REC of pre- and postlingual implanted patients. Methods An observational, prospective and descriptive study was carried out, with the approval of the institutional Ethics Committee on Research in Human Beings under the CAAE: 69604917.2.0000.5529, registered under CEP 185/2017. Our institution is an ear, nose and throat (ENT) specific hospital, and the study took place from January to November 2017. Carvalho et al. The study included participants undergoing CI surgery, who were divided into two groups: 1. Prelingual: congenital HL or HL that occurred before the acquisition of language; 2. Postlingual: HL that occurred after the acquisition of language. We included patients who were submitted to the CI and to the intraoperative assessments that are part of our routine (►Table 1). The indications for the CI are well known in the literature. There was no randomization of the patients, because the groups were based on preexisting conditions (age of acquisition of language). No patients were lost to follow-up. The CI used was the Freedom Implant Contour Advance CI24RE (CA) (Cochlear Ltd, Sidney, Australia), and, to record the impedances, the ECAP and the REC, we used the Custom Sound EP 4.4 software (Cochlear Ltd.), which controls the parameters of stimulation and recording, and is installed in a computer coupled to the portable programming inter (...truncated)