Vestibular Evoked Myogenic Potential Characteristics in Common Vestibular Disorders

Intense sound and vibration evokes small reflexes from the neck and eye muscles, reflecting activation of vestibular-otolith receptors. These responses provide the basis for two clinical tests of balance function, referred to as cervical- and ocular- vestibular evoked myogenic potentials (cVEMPs and oVEMPs). As relatively new tests, their diagnostic role has not been fully explored. The primary aim of this thesis was to identify test and stimulus combinations that improve the sensitivity and specificity of VEMP testing, whilst differentiating between different causes of vertigo and imbalance. Patients with Ménière’s disease, vestibular migraine, superior canal dehiscence, vestibular schwannoma, and vestibular neuritis were recruited from neurology outpatient clinics at the Royal Prince Alfred Hospital in Sydney, Australia from 2009-2015. Each study identified specific stimulus/VEMP combinations that enhanced the sensitivity of VEMP testing, as well as revealing patterns of otolith dysfunction that characterised each disorder. Ménière’s disease was characterised by impaired saccular and largely preserved utricular function, whereas in vestibular migraine otolith function was usually preserved and symmetrical. Superior canal dehiscence was unique with its high frequency augmentation effects and prolonged oVEMP latencies to skull-tap stimulation. For vestibular schwannoma larger than 14 mm, impaired function of both otolith organs was common. Abnormal utricular, but spared saccular function, was most often observed in patients with vestibular neuritis. The findings of this thesis provide new insight into how test parameters can be manipulated to enhance the sensitivity of VEMP testing in the clinical setting. The different patterns of saccular and utricular involvement contribute significantly to the clinician’s ability to separate different vestibular disorders