Long-term stability of electrical stapedial reflex and electrodes impedance in children with MED-EL cochlear implants

Background: The purpose of this study was to investigate changes in electrical evoked stapedial reflex thresholds (ESRTs) and electrodes impedance over time in children with MED-EL cochlear implants. Methods: In this study, 60 kids were included, while 15 kids were excluded because their cases did not fit the requirements. Patients who received MED-EL cochlear implants were monitored postoperatively over 5 years to determine whether or not their electrical evoked stapedial reflex thresholds (ESRT) and electrode impedance remained stable. Results: At the initial fitting, electrodes 4, 5, 6, 8, and 9 showed significantly different impedances, while electrodes 1, 2, 3, 7, 10, 11, and 12 showed no significantly different impedances. Excluding electrode 12, all electrodes showed a statistically significant difference in ESRT at three and 6 months. All electrodes, except electrodes 7 and 8, showed no difference between ESRT and the behaviorally based MAP most comfortable level (MCL). After three months, there was a highly significant difference between ESRT and the behavioral MAP for the audiometric frequencies 500, 1000, 2000, and 4000 Hz. Conclusion: Particularly at 3 and 6 months, there was a considerable decrease in electrode impedance, which stabilized throughout the course of the remaining follow-up period. Nearly all the electrodes showed a significant variation in ESRT between 3 and 6 months, but over the subsequent 5 years, ESRT essentially stabilized. Additionally, there was no difference between behavioral-based MAP and ESRT MCL; nevertheless, after 3 months, there was a highly significant difference between ESRT and the behavioral MAP at the 500, 1000, 2000, and 4000 Hz audiometric frequencies.