Impact of cochlear implantation on peripheral vestibular function in adults

Cochlear implantation may have a detrimental effect on vestibular function and residual hearing. Our goal was to investigate the impact of cochlear implantation on peripheral vestibular function and the symptomatology that ensues.

A prospective observational study included all adults undergoing cochlear implantation by the same operator between July 2014 and December 2015, with pre- and postoperative (4 months) neurovestibular balance examination comprising a questionnaire and clinical tests [head impulse test (HIT), head-shaking test (HST), skull vibration test (SVT)] and instrumental tests [caloric test of the lateral semicircular canal and cervical vestibular-evoked myogenic potentials (cVEMP)].

Twenty-two patients were included, with a mean age of 62 years and sex-ratio of 1.2. Before implantation, 50% of subjects (n=11) reported at least one episode of vertigo associated with balance disorder during their life. After implantation, there were 11 cases of vertigo but only one patient described persistent discomfort related to vertigo 4 months after surgery. Patients with impaired vestibular function after 4 months, taking all symptoms together, were all aged more than 75 years. HIT was abnormal in 18% of cases before implantation and in 59% after (P=NS). HST showed nystagmus in one patient both before and after surgery. Only 18% of patients showed nystagmus induced by SVT before surgery, increasing to one-third after surgery (P=NS). Caloric test of the lateral canal showed hypofunction in 50% of cases before surgery, including 10% of cases with areflexia. This rate increased after surgery to 58%, with 18% areflexia (P=NS). cVEMPs were not detected in 68% of cases before implantation and this rate increased to 86% after surgery (P=NS). There were no significant associations (P>0.05) between test results and symptoms.

In the medium term, although older subjects more frequently presented vestibular disorder, cochlear implantation induced little vertigo or balance disorder, sometimes even improving vestibular function. However, vestibular disorders were frequent preoperatively and increased postoperatively. We tested vestibular function on different stimulation frequencies and yet found no correlation between postoperative test results and postoperative vertigo.