Auditory brainstem implant: Part I. Auditory performance and its evolutionover time

Objective: Evaluation of auditory performance and its evolution over time i n patients with the auditory brainstem implant. Study Design: Prospective study. Setting: Tertiary referral center. Patients and Methods: Between May 1996 and April 2000, 14 patients with neu rofibromatosis type 2 underwent implantation with a multichannel auditory b rainstem implant. Auditory performance data were obtained in 13 patients wh o had used their device on a regular daily basis for 1 to 41 months (averag e 19 months). Hearing evaluation was based on the results of four tests (vo wel confusion, consonant confusion, Freiburger numbers, and speech-tracking test), which were performed with and without lip-reading at regular interv als after device activation. Results: 12 patients received auditory sensation through the auditory brain stem implant immediately after device activation. In one patient, because o f postoperative electrode migration, device activation was not successful. In this case, after the electrode array was repositioned, activation was su ccessful. The results of the audiovisual mode 2 weeks after device activati on revealed a lip-reading enhancement above the chance level in about 50% o f the patients in the vowel confusion and speech-tracking tests and in 70% of the patients in the consonant confusion test. Lip-reading enhancement im proved within the first 6 months and then entered a plateau phase, which wa s more prominent in the monosyllabic vowel and consonant tests. In the audi tory alone mode, more than half of the patients showed their first positive result in the vowel test 3 months after device activation, but it took abo ut 6 months until half of the patients revealed a result above the chance l evel in the consonant and Freiburger numbers tests. Open set speech recogni tion,in the auditory alone mode (in the speech-tracking test) was not commo n and happened relatively late (within 1 year or later). Discussion and Conclusion: Although auditory sensation appeared immediately after device activation, a period of 6 months was necessary for relearning and adaptation of the central auditory system to the altered form of audit ory information presented by the auditory brainstem implant.