Audiological Features of Auditory Neuropathy Spectrum Disorders

Objective: Auditory neuropathy spectrum disorder (ANSD) is hearing dysfunction with a broad spectrum of audiological clinical features and rehabilitation outcomes. Electrocochleography and electrically evoked auditory brainstem responses (eABR) are useful tool to predict site of lesion and type of ANSD (synaptopathy or neuropathy), especially in cases with unknown etiology of ANSD. Therefore, the aim of this study was to evaluate the applicability of intracochlear electrocochleography and eABR registration after cochlear implantation for revealing electrophysiological features of different forms of ANSD and predicting rehabilitation outcomes. Material and methods: 22 children with ANSD of different etiology were enrolled in the study. Intracochlear electrocochleography and eABR registration after cochlear implantation were performed in 23 ears. Seven children had OTOF-related ANSD, 2 children - cochlear nerve deficiency, in 8 cases ANSD probably was due to prematurity, in 1 – due to hyperbilirubinemia, 4 cases were with unknown etiology of ANSD. Results: Cochlear microphonic was recordable in 21 cases. The summating and compound action potentials were recordable in 7 cochlear implant users. There was diversity in electrocochleography results within the group of children with the same etiology of ANSD. On the other hand, there were cases when electrocochleography results were almost identical even in patients with different etiology and pathophysiology of ANSD. The eABR were registered in 7 children with OTOF-related ANSD and in 9 children with perinatal risk factors. Presence of eABRs in OTOF-related cases matches the pathophysiology of auditory synaptopathy. In 3 ears with hypoplastic cochlear nerve eABRs were absent or partially recordable only in bipolar mode of stimulation of basal turn. In children with unknown etiology in 2 cases eABRs were recordable from all stimulated electrodes (auditory synaptopathy) and in other 2 cases were absent (auditory neuropathy). Rehabilitation outcomes after cochlear implantation corresponded to the results of eABR registration and were better among children with eABRs. Conclusions: Intracochlear electrocochleography does not provide a reliable differentiation of different types of ANSD. Registration of eABRs in monopolar stimulation mode from intracochlear electrodes is valuable for differentiating ANSD types and predicting outcomes of cochlear implantation in children with ANSD.