Electrically evoked auditory brainstem responses in children with sequential bilateral cochlear implants.

Objective: To examine the effect of sequential bilateral cochlear implantation on auditory brainstem maturation and the effect of age in receiving the second implant (CI2). Study Design: Prospective cohort study. Setting: Tertiary academic referral center. Patients: Thirty prelingually deaf children, who received their first implant (CI1) at a mean age of 1.8 year and their CI2 at a mean age of 5.3 years. Intervention: Sequential bilateral cochlear implantation. Main Outcome Measure: Electrically evoked auditory brainstem responses on the 2 implant sides were measured intraoperatively and postoperatively after 6, 12, and 24 months of bilateral implant use. Results: Electrically evoked auditory brainstem response latencies on the 2 implants were compared within subjects over time. Wave III did not show any significant differences between the 2 sides, whereas Wave V was initially prolonged on the CI2 side compared with the CI1 side. Although still apparent, this interaural latency difference of Wave V was no longer significant after 12 and 24 months. Interwave interval Ill to V latencies remained significantly prolonged on the CI2 side. Age in receiving the CI2 did not account for the individual differences in latencies for all waveforms. Conclusion: The present data suggest that auditory brainstem maturation will occur after a relatively long period of unilateral deafness irrespective of the age in receiving the CI2. Because some abnormalities were still seen at the upper part of the brainstem, our results indicate that the CI2 side has not caught up with the CI1 side. Nevertheless, within our follow-up time, interaural (interwave) latencies decrease significantly, and longer-term data might reveal that the CI2 eventually will catch up with the CI1 side.