Electrical Vestibular Co-stimulation by Lateral Wall Cochlear Implant Electrode Arrays

Hypothesis and background: The objective of this study was to analyze cervical and ocular vestibular-evoked myogenic potentials to electrical stimulation (e-cVEMPs and e-oVEMPs) by straight lateral wall cochlear implant electrodes with respect to response numbers, amplitudes, latencies, and thresholds. Methods: E-VEMPs were recorded in adult Synchrony cochlear implant (CI) patients stimulating with electric pulse trains. The stimulation electrode was successively varied between apical stimulation at electrode E3, medial stimulation at E6, and basal stimulation at E10 and E11. VEMPs to bone conducted vibration (BCV) were recorded as a reference in all participants. Results: The study included 20 ears (cases) of 19 patients (mean age of 54.8 y, SD: 11.3 y). E-VEMPs could be measured in 18 cases (95%), and VEMPs to BCV were elicited in 12 cases (60%). Response rates to basal stimulation at E10 and E11 were higher compared with medial and apical stimulation. The difference was significant for e-cVEMPs. For basal stimulation, e-VEMP amplitudes were comparable to BCV-stimulated VEMPs and increased with increasing stimulation level. E-VEMP thresholds were within clinical fitting levels for basal stimulation electrodes and close to or below hearing thresholds for some participants. Conclusion: Vestibular co-stimulation by straight lateral wall electrodes was demonstrated by the presence of e-VEMPs in 95% of participants. Basal electrode contacts are more likely to lead to vestibular co-stimulation compared with medial and apical electrodes, and vestibular co-stimulation can occur before electric stimuli become audible. Vestibular co-stimulation can, therefore, occur during daily CI use, while the effect on everyday balance function is unknown yet.