Cochlear implant in immune mediated inner ear diseases: impedance variations and clinical outcomes

OBJECTIVE: Immune-mediated inner ear disease (IMIED) is characterized by severe/profound hearing loss. Although IMIED might lead to cochlear disorders with modification of electrode impedance these patients are ideal candidates for cochlear implant (CI). The aim of the study was to evaluate whether impedance values and impedance fluctuations over time were significantly higher in IMIED patients treated with CI compared to the control group. METHOD: The sample was composed of CI patients with severe/profound hearing loss: a study group (SG) of IMIED patients (31 ears) and a control group (CG) of patients with hearing loss not related to their immune system (31 ears). Audiological performance and impedance values were measured and compared amongst groups at 3, 6, 12 and 18 months following the fitting sessions. RESULTS: Speech perception was significantly better for SG in word and sentence recognition in quiet. Impedance values were, on average, significantly higher for apical and middle electrode segments in SG compared to CG at the 3 month follow-up and were maintained over a longer time period. Additionally, a subset of SG patients ( active patients ) experienced significantly greater impedance fluctuation corresponding to clinical symptom reactivation. DISCUSSION AND CONCLUSION: IMIED patients achieved good audiological performance. However, the surgical intervention could change the inner ear environment, causing impedance fluctuations and, consequently, more frequent CI fittings. Additionally, impedance evaluation could be utilised as an early warning sign of IMIED recurrence and as an aid to therapeutic decision-making.