Bionic Ears & Dizziness: Examining the Impact of Cochlear Implantation on Vestibular Function

Abstract

Cochlear implantation (CI) is regarded as an effective and life-changing intervention for individuals with bilateral severe to profound hearing loss. The success of CI has seen an expansion of its candidacy criteria in recent times. Vestibular dysfunction and vertigo are known to occur following CI. However, current literature reports wide variability in the prevalence of post-CI vestibular dysfunction with few studies examining all five vestibular end-organs. The primary aim of this thesis is to enhance understanding of post-CI vestibular dysfunction and vertigo using clinical history and a battery of modern audio-vestibular tests: three-dimensional video head impulse testing (3D vHIT), vestibular evoked myogenic potentials (VEMP), home audiometry and home video-oculography (VOG).

The use of 3D vHIT and both cervical and ocular VEMPs demonstrate that CI can have impacts on all five vestibular end-organs with lateral canal function most affected. Coupled with findings of stable home audiometry and direction-changing nystagmus on home VOG, these tests reveal post-CI secondary endolymphatic hydrops as the main cause of post-CI episodic spontaneous vertigo. Finally, patients with sudden sensorineural hearing loss (SSNHL) increasingly proceed with CI. Such patients are characterised by relative preservation of utricular and lateral canal function, loss and spontaneous recovery of posterior canal function. There is a trend in evidence gathered thus far, that those with SSNHL have a higher frequency of post-CI vertigo compared to controls.

The findings of this thesis establish the unique clinical and vestibular test profile of CI recipients which previously had limited opportunities for characterisation. It highlights an effective method for pre- and post-CI vestibular assessment, demonstrates the clinical utility of novel technologies, and identifies some risk factors and causes of post-CI vertigo that assist counselling and management of this distinct patient group.