Differences in Intracochlear Electrocochleography Signal Characteristics of Meniere’s Disease, Noise-Induced Hearing Loss, and Sudden Sensorineural Hearing Loss

Objectives: To perform a detailed analysis of intracochlear electrocochleography (IC ECochG) traces in subjects with one of three specific etiologies of hearing loss (Meniere’s disease, noise-induced hearing loss NIHL, and sudden sensorineural hearing loss) undergoing cochlear implantation (CI), to gain new insights into the site of dysfunction in each. Design: We conducted a retrospective clinical cohort study examining IC ECochG traces in 27 adult and pediatric cochlear implant recipients with a diagnosis of either NIHL, Meniere’s disease, or sudden sensorineural hearing loss (SSNHL). We analyzed the IC ECochG waveforms of cochlear microphonic (CM), auditory nerve neurophonic (ANN), summating potential (SP), and compound action potential in response to a 500 Hz pure-tone stimulus. The ECochG responses were qualitatively and quantitatively analyzed across 11 intracochlear recording electrodes, and comparisons between groups made by Kruskal–Wallis comparison of mean ranks. Results: The CM amplitude in subjects with NIHL was significantly larger (27.6 μV) than in subjects with Meniere’s disease (7.2 μV) and sudden sensorineural hearing loss (9.0 μV) ( p = 0.0092). Compared with Meniere’s disease and SSNHL, the NIHL group also demonstrated preservation of the expected intracochlear tonotopic relationship, with larger amplitude microphonics recorded from more deeply inserted electrodes. Likewise, this group demonstrated large, positive SPs with progressive enlargement approaching the cochleotopic place. Taken together, these results are suggestive of a surviving population of apical hair cells in this group. In contrast with the SP in the NIHL group, subjects with Meniere’s disease and SSNHL had smaller SPs ( p = 0.0014). SPs in these groups also demonstrated negative polarities with loss of the expected cochleotopic distribution. To estimate the function of the auditory nerve relative to the hair cells, the ANN/CM ratio was explored. Herein, significant differences arise between the Meniere’s disease group (average ANN:CM = 0.36) and the sudden sensorineural hearing loss group (average ANN:CM = 1.08) ( p = 0.0301) suggesting relative neural function is better in the SSNHL than the Meniere’s group, and that the drivers of a negative polarity SP in this group may be related to inner hair cell dysfunction. Conclusions: IC ECochG is an effective tool for investigating residual function in the cochlea following cochlear implantation. Our results reveal significant differences in the function of cochlear generators between subjects with Meniere’s disease, SSNHL, and NIHL, which may reflect differing lesion sites.