Vestibular dysfunction in patients with auditory neuropathy detected by vestibular evoked myogenic potentials

Masseter and cervical vestibular evoked myogenic potentials in individuals with auditory neuropathy

OBJECTIVE

This study aimed to explore the functional integrity of vestibulo-masseteric and sacculo-collic reflex pathways in individuals with Auditory Neuropathy (AN). The study also aimed at finding the correlation between mVEMP and cVEMP response parameters for AN and healthy individuals.

DESIGN

Standard group comparison research design.

STUDY SAMPLE

Individuals with AN (n = 20); age-gender matched healthy individuals (n = 20) were recruited. Each participant underwent routine audiological evaluation; mVEMP and cVEMP testing. mVEMP and cVEMP were recorded using 500 Hz tone burst stimulus for all the participants.

RESULTS

Most of the AN individuals had no mVEMP (ipsilateral & contralateral - 60%; bilateral - 50%) and cVEMP (60%) responses. There was no significant association (p > 0.05) between the duration of AN with mVEMP and cVEMP findings. However, a significant correlation (p < 0.05) was found for EMG rectified amplitude of mVEMP and cVEMP in AN.

CONCLUSION

The results of this study suggested an impaired function of the vestibulomassteric and sacculocollic reflex pathways in individuals with AN. Vestibular evaluation should be included as a part of the regular test battery for individuals with AN.

Is galvanic VEMP a prediction of the nerve origin and damage in patients of vestibular schwannoma

BACKGROUND

Recent studies proved that certain proportions of vestibular schwannoma (VS) originated other than vestibular nerve of the eighth cranial nerve.

AIMS/OBJECTIVES

Unlike air-conducted sounds (ACS) and bone-conducted vibration (BCV), galvanic vestibular stimulation (GVS) evokes vestibular evoked myogenic potentials (VEMPs) from the vestibular nerve.

MATERIALS AND METHODS

Case-control study was conducted in unilateral VS patients pre-operatively. Healthy ears were controls. Patients examined ACS, BCV and GVS ocular VEMP (oVEMP) and cervical VEMP (cVEMP), caloric test, video head impulse test (vHIT), suppression head impulse paradigm (SHIMP) and pure tone audiometry (PTA).

RESULTS

Seven (26.9%) tumors affected left ear and 19 (73.1%) on the right(p < .05). Response rates in VS group were statistically lower than control except for ACS-cVEMP (p < .05). Response rates of VEMPs in VS patients decreased with the tumor size grows. But not all BCV and GVS VEMPs disappeared in the largest tumor group. Abnormal rates of caloric test, vHIT gains and SHIMP were found.

CONCLUSIONS AND SIGNIFICANCE

Response rates of GVS VEMPs decreased with the residual functional nerve fibers. GVS VEMPs help to differentiating labyrinthine and retro-labyrinthine lesions. GVS combined with BCV VEMPs probably reflex the tumor origin from the eighth cranial nerve and/or the remaining vestibular function.

[To address on the refined and individualized comprehensive evaluation of inner ear function]

Auditory and vestibular function detection technology is the premise and key to the diagnosis and management for inner ear diseases. Concurrent damage to the auditory and vestibular system occurs in many inner ear diseases. The general points and issues on hearing and vestibular function tests, as well as the clinical significance of refined and individualized comprehensive evaluation of inner ear function are described in this paper.

The audiovestibular profile of Brown-Vialetto-Van Laere syndrome

BACKGROUND

Brown-Vialetto-Van Laere syndrome, a rare disorder associated with motor, sensory and cranial nerve neuropathy, is caused by mutations in riboflavin transporter genes SLC52A2 and SLC52A3. Hearing loss is a characteristic feature of Brown-Vialetto-Van Laere syndrome and has been shown in recent studies to be characterised by auditory neuropathy spectrum disorder.

METHOD

This study reports the detailed audiovestibular profiles of four cases of Brown-Vialetto-Van Laere syndrome with SLC52A2 and SLC52A3 mutations. All of these patients had auditory neuropathy spectrum disorder.

RESULTS

There was significant heterogeneity in vestibular function and in the benefit gained from cochlear implantation. The audiological response to riboflavin therapy was also variable, in contrast to generalised improvement in motor function.

CONCLUSION

We suggest that comprehensive testing of vestibular function should be conducted in Brown-Vialetto-Van Laere syndrome, in addition to serial behavioural audiometry as part of the systematic examination of the effects of riboflavin.

Retro-labyrinthine Lesion Site Detected by Galvanic Vestibular Stimulation Elicited Vestibular-evoked Myogenic Potentials in Patients with Auditory Neuropathy

OBJECTIVE

Auditory neuropathy (AN) is a unique pattern of hearing loss with preservation of hair cell function. The condition is characterized by the presence of otoacoustic emissions (OAE) or cochlear microphonic (CM) responses with severe abnormalities of the auditory brainstem response (ABR). The vestibular branches of the VIII cranial nerve and the structures innervated by it can also be affected. However, the precise lesion sites in the vestibular system are not well characterized in patients with AN.

METHODS

The air-conducted sound (ACS) vestibular-evoked myogenic potentials (VEMPs) and galvanic vestibular stimuli (GVS)-VEMPs were examined in 14 patients with AN.

RESULTS

On examination of VEMPs (n=14, 28 ears), the absent rates of ACS-cervical VEMP (cVEMP), ACS-ocular VEMP (oVEMP), GVS-cVEMP, GVS-oVEMP and caloric test were 92.9% (26/28), 85.7% (24/28), 67.9% (19/28), 53.6% (15/28), and 61.5% (8/13), respectively. Impaired functions of the saccule, inferior vestibular nerve, utricle, superior vestibular nerve, and horizontal semicircular canal were found in 25.0% (7/28), 67.9% (19/28), 32.1% (9/28), 53.6% (15/28) and 61.5% (8/13) patients, respectively. On comparing the elicited VEMPs parameters of AN patients with those of normal controls, both ACS-VEMPs and GVS-VEMPs showed abnormal results in AN patients (such as, lower presence rates, elevated thresholds, prolonged latencies, and decreased amplitudes).

CONCLUSION

The study suggested that patients with AN often have concomitant vestibular disorders. Retro-labyrinthine lesions were more frequently observed in this study. GVS-VEMPs combined with ACS-VEMPs may help identify the lesion sites and facilitate detection of areas of vestibular dysfunction in these patients.

Similarities and Differences Between Vestibular and Cochlear Systems - A Review of Clinical and Physiological Evidence

The evoked response to repeated brief stimuli, such as clicks or short tone bursts, is used for clinical evaluation of the function of both the auditory and vestibular systems. One auditory response is a neural potential - the Auditory Brainstem Response (ABR) - recorded by surface electrodes on the head. The clinical analogue for testing the otolithic response to abrupt sounds and vibration is the myogenic potential recorded from tensed muscles - the vestibular evoked myogenic potential (VEMP). VEMPs have provided clinicians with a long sought-after tool - a simple, clinically realistic indicator of the function of each of the 4 otolithic sensory regions. We review the basic neural evidence for VEMPs and discuss the similarities and differences between otolithic and cochlear receptors and afferents. VEMPs are probably initiated by sound or vibration selectively activating afferent neurons with irregular resting discharge originating from the unique type I receptors at a specialized region of the otolithic maculae (the striola). We review how changes in VEMP responses indicate the functional state of peripheral vestibular function and the likely transduction mechanisms allowing otolithic receptors and afferents to trigger such very short latency responses. In section "ELECTROPHYSIOLOGY" we show how cochlear and vestibular receptors and afferents have many similar electrophysiological characteristics [e.g., both generate microphonics, summating potentials, and compound action potentials (the vestibular evoked potential, VsEP)]. Recent electrophysiological evidence shows that the hydrodynamic changes in the labyrinth caused by increased fluid volume (endolymphatic hydrops), change the responses of utricular receptors and afferents in a way which mimics the changes in vestibular function attributed to endolymphatic hydrops in human patients. In section "MECHANICS OF OTOLITHS IN VEMPS TESTING" we show how the major VEMP results (latency and frequency response) follow from modeling the physical characteristics of the macula (dimensions, stiffness etc.). In particular, the structure and mechanical operation of the utricular macula explains the very fast response of the type I receptors and irregular afferents which is the very basis of VEMPs and these structural changes of the macula in Menière's Disease (MD) predict the upward shift of VEMP tuning in these patients.

Diagnosing vestibular hypofunction: an update

Unilateral or bilateral vestibular hypofunction presents most commonly with symptoms of dizziness or postural imbalance and affects a large population. However, it is often missed because no quantitative testing of vestibular function is performed, or misdiagnosed due to a lack of standardization of vestibular testing. Therefore, this article reviews the current status of the most frequently used vestibular tests for canal and otolith function. This information can also be used to reach a consensus about the systematic diagnosis of vestibular hypofunction.