Results From a Second-Generation Vestibular Implant in Human Subjects: Diagnosis May Impact Electrical Sensitivity of Vestibular Afferents.

Objective: Auditory and vestibular outcomes after placement of a vestibular-cochlear implant in subjects with varying causes of vestibular loss.

Study Design: Prospective case study.

Setting: Tertiary referral center.

Patients: Three human subjects received a vestibular-cochlear implant. Subject 1 had sudden hearing and vestibular loss 10 years before implantation. Subjects 2 and 3 had bilateral Menière's disease with resolution of acute attacks. All subjects had severe-profound deafness in the implanted ear and bilateral vestibular loss.

Intervention: Vestibular-cochlear implant with electrode positions confirmed by CT.

Main Outcome Measures: Electrically-evoked vestibular and cochlear compound action potentials (ECAPs), speech perception, and electrically-evoked slow-phase eye velocities.

Results: Subject 1 had no vestibular ECAP, but normal cochlear ECAPs and cochlear implant function. She had minimal eye-movement with vestibular stimulation. Subject 2 had vestibular ECAPs. This subject had the largest eye velocities from electrical stimulation that we have seen in humans, exceeding 100 degrees per second. Her cochlear implant functions normally. Subject 3 had vestibular and cochlear ECAPs, and robust eye-movements and cochlear implant function.

Conclusion: The etiology of vestibular loss appears to have a profound impact on sensitivity of vestibular afferents in distinction to cochlear afferents. If this dichotomy is common, it may limit the application of vestibular implants to diagnoses with preserved sensitivity of vestibular afferents. We speculate it is due to differences in topographic organization of Scarpa's versus the spiral ganglion. In two subjects, the second-generation device can produce higher velocity eye movements than seen in the four subjects receiving the first-generation device.