Vestibular Co-stimulation in Adults with a Cochlear Implant.

BACKGROUND: Vestibular co-stimulation is a side effect of cochlear implant stimulation. The electrical currents delivered by the cochlear implant can spread toward the vestibular system and thus stimulate it. The aim of the study is to evaluate whether it is feasible to functionally restore the balance by modifying the vestibular co-stimulation. METHODS: Four adult patients, who had received a commercially available cochlear implant previously, were enrolled. Counterbalanced biphasic pulses were presented as bursts or as an amplitude-modulated biphasic pulse train (modulation frequencies ranging from 1 to 500 Hz) at the participant's upper comfortable level for electrical stimulation. Subjective sensations and vestibular-mediated eye movements were used for evaluating the possible effects of vestibular co-stimulation. RESULTS: One participant experienced a cyclic tilting of his head in response to an amplitude-modulated biphasic pulse train with a modulation frequency of 2 and 400 Hz. However, during a follow-up visit, the sensation could not be replicated. CONCLUSION: Subjective vestibular sensations or vestibular-mediated eye movements could not be electrically evoked with a commercially available cochlear implant in 4 adult patients with almost normal vestibular function. Therefore, customized design of the hard-, firm-, and/or software of the commercially available cochlear implant might be necessary in order to electrically restore vestibular performance.

The relationship between cochleovestibular function tests and endolymphatic hydrops grading on MRI in patients with Menière's disease.

PURPOSE: In this retrospective study the relationship between cochleovestibular function and a magnetic resonance imaging (MRI-) based classification system of endolymphatic hydrops was investigated. METHODS: Seventy-eight patients with unilateral definite Menière's disease who underwent MRI were included. The parameters of Pure Tone Audiometry (PTA), caloric irrigation test, cervical vestibular evoked myogenic potentials, and video Head Impulse Test were compared between the grades of endolymphatic hydrops (EH) and perilymphatic enhancement (PE) on MRI. RESULTS: The low-frequency PTA was significantly different between cochlear EH grades I and II (p = 0.036; Grade I: mean (Standard Deviation, SD) = 51 decibel Hearing Level (dB HL) (18 dB HL); Grade II: mean (SD) = 60 dB HL (16 dB HL)), and vestibular EH grades 0 and III (p = 0.018; Grade 0: mean (SD) = 43 dB HL (21 dB HL); Grade III: mean = 60 dB HL (10 dB HL)). The ipsilateral caloric sum of ears with vestibular EH grade I (n = 6) was increased with regards to vestibular EH grades 0 (p = 0.001), II (p < 0.001), and III (p < 0.001) (Grade 0: mean (SD) = 24°/s (15°/s); Grade I: mean (SD) = 47°/s (11°/s); Grade II: mean (SD) = 21°/s (13°/s); Grade III: mean (SD) = 16°/s (8°/s)). CONCLUSION: According to these results we can conclude that only the highest grades of cochlear and vestibular EH seem to be associated with decreased cochleovestibular functioning.