The effect of cochlear implants on vestibular-evoked myogenic potential responses and postural stability

Current spread by electrical stimulation via inserted cochlear implant (CI) electrodes and the consequential increase in sound input can affect the equilibrium of patients. The aim of the present study was to clarify the effect of CIs on the equilibrium of patients through cervical vestibular-evoked myogenic potential (cVEMP) testing and static stabilometry performed with the CIs turned on (CI-on) and off (CI-off). This prospective study included nine adult patients who underwent unilateral cochlear implantation surgery at our institution. cVEMP testing and stabilometry were performed before surgery and repeated after surgery in the CI-on and CI-off modes. Before surgery, cVEMP responses were diminished in five of the nine patients (55.6%), while the results of stabilometry were poor in six patients (66.7%). After surgery, both cVEMP responses and stabilometry findings in the CI-off mode exhibited significant deterioration relative to the preoperative results (cVEMP: 7/9, 77.8%; stabilometry: 7/9, 77.8%). However, in the CI-on mode, there were significant improvements in both test results relative to the findings in the CI-off mode for all patients. CIs compensated for the surgical trauma-induced deterioration in static postural stability when turned on, resulting in a considerable improvement. Our findings suggest that postoperative cVEMP testing in the CI-on and CI-off modes will enable more accurate assessment of the saccule–inferior vestibular nerve system function after cochlear implant surgery.