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

ObjectivesThis study aimed to determine vestibular involvement in patients with auditory neuropathy (AN) using ocular vestibular evoked myogenic potential (oVEMP), cervical vestibular evoked myogenic potential (cVEMP), caloric tests, video Head Impulse Tests (vHIT), and Suppression Head Impulse Paradigm (SHIMP) tests.MethodsTwenty-two patients with AN (study group) and 50 age-and-gender-matched healthy subjects (control group) were enrolled. All patients underwent air-conducted sound oVEMP and cVEMP tests. In the study group, 20 patients underwent a caloric test, 10 patients underwent a video Head Impulse Test (vHIT), and nine patients underwent the Suppression Head Impulse Paradigm (SHIMP) test.ResultsSignificant differences in VEMP abnormalities were found between the two groups. Most AN patients showed no VEMP response, while only a few patients showed VEMP responses with normal parameters. Some AN patients presented abnormal VEMP parameters, including thresholds, latencies, and amplitudes. The abnormal rate (including no response and abnormal parameters) was 91% in the cVEMP test and 86% in the oVEMP test. No significant difference was found between oVEMP and cVEMP abnormalities. AN patients exhibited a 70% abnormal rate in the caloric test. Most AN patients showed normal VOR gains. Most patients showed no overt corrective saccades in vHIT, and exhibited normal anticompensatory saccades in the SHIMP test.ConclusionMany AN patients experience vestibular dysfunction, which may be detected by using a vestibular functional test battery.SignificanceVEMP abnormalities might reflect the status and degree of vestibular involvement in AN.     

EMG responses in the soleus muscles evoked by unipolar galvanic vestibular stimulation

This study compared the effects of transmastoid galvanic stimulation with unilateral galvanic stimulation of vestibular afferents. We recorded the effects on soleus EMG occurring at short (SL) and medium (ML) latency, both in normal subjects and in patients with previous unilateral vestibular neurectomy. Unipolar cathodal and anodal stimulation on the same side produced opposite effects for both SL and ML responses. Responses to unilateral cathodal or anodal stimulation were smaller, but otherwise resembled those of transmastoid stimulation with the cathode or the anode placed on the same side, respectively. Unilateral cathodal stimulation resulted in a larger SL response, which occurred at shorter latency than unilateral anodal stimulation. With unipolar stimulation on the side of previous vestibular nerve section, typical SL and ML responses were absent. With stimulation of the intact side, the patients showed smaller SL responses than normal subjects with unilateral stimulation. The larger responses to unilateral cathodal compared to unilateral anodal stimulation are consistent with previous reports that cathodal stimulation produces an increase and anodal a decrease in vestibular nerve firing. The smaller SL responses in the patients may be a consequence of central nervous system reorganization following unilateral vestibular nerve section.     

EMG responses evoked by the termination of galvanic (DC) vestibular stimulation: 'off-responses'.

OBJECTIVE: Vestibular responses in soleus electromyography (EMG) evoked by the sudden onset of galvanic (DC) stimulation ('on-responses') have been described in detail previously. The aim of the present study was to describe responses in soleus triggered by the termination of galvanic stimulation ('off-responses'). METHODS: In 10 healthy human subjects, we studied responses to transmastoid (bilateral) stimuli of 200 ms and 2 s average duration and 3 or 4 mA intensity. We obtained both on- and off-responses using the same raw data. EMG activity was recorded onto tape while current pulses of systematically varying duration were delivered. Averaged on-responses were obtained by triggering from the beginning of the current pulses. Averaged off-responses were obtained by triggering from the termination of the current pulses. RESULTS: Short-latency (SL) and medium latency (ML) off-responses were both obtained in all but one study. The SL and the ML components of the off-responses were present and had similar latencies and amplitudes, but opposite excitability, to the on-responses obtained with the same stimuli. CONCLUSIONS: Off-responses to galvanic vestibular stimulation can be recorded from soleus EMG. Our findings imply that vestibular SL and ML reflex responses in the legs are dependent on the change in the rate of vestibular nerve discharge, not its absolute level. Both on- and off-responses have properties appropriate to a role in maintaining body stability.     

Vestibular evoked myogenic potentials in multiple sclerosis patients.

OBJECTIVES: Vestibular evoked myogenic potentials (VEMPs) are saccular responses to loud acoustic stimuli and are recordable from the sterno-cleido-mastoid muscle ipsilaterally to the stimulated ear. This study aimed to investigate VEMPs in patients suffering from multiple sclerosis (MS), and to compare these findings with both clinical and instrumental data. METHODS: We recorded VEMPs from 70 MS patients, whose clinical data were retrospectively evaluated for the possible occurrence of: past and current (with respect to VEMP recording) brainstem and/or cerebellar symptoms; current brainstem and/or cerebellar signs. Sixty-five patients underwent brainstem auditory evoked potentials (BAEPs) recording; 63 of the same patients underwent saccadic eye movement recording and subjective visual vertical (SVV) evaluation. RESULTS: VEMPs were abnormal in 31%, BAEPs in 38% and SVV in 21% of the patients. Saccadic eye movements showed a possible brainstem dysfunction in 44.4% of the patients. There was no correlation between the occurrence of abnormalities and the technical means of detection. The same held true for correlations with clinical data, with the exception of the BAEPs; these proved to be more frequently abnormal in patients presenting at neurological examination with brainstem and/or cerebellar signs that were possibly related to the complaint of dizziness. CONCLUSIONS: VEMPs should be considered a useful complementary neurophysiological tool for the evaluation of brainstem dysfunction.     

Ocular vestibular evoked myogenic potentials produced by impulsive lateral acceleration in unilateral vestibular dysfunction

Objective

To deduce the connectivity underlying ocular vestibular evoked myogenic potentials (OVEMPs) recorded from two sites and produced by lateral transmastoid stimulation in patients with unilateral vestibular dysfunction.

Methods

OVEMPs were recorded using lateral impulsive stimuli delivered by a hand-held minishaker placed at the mastoid. Twelve patients were tested using the typical OVEMP recording montage placed inferior to the eyes. In a subset of 6 patients, recordings were also made using a lateral electrode montage. The majority of patients were tested following surgery for inner ear disease. Patient responses were compared to those in normal subjects under similar recording conditions.

Results

For the inferior montage, regardless of which mastoid was stimulated, deficits were observed only from the eye opposite the affected ear. In contrast, OVEMPs recorded using the lateral electrode montage showed changes on both sides.

Conclusions

OVEMPs produced using lateral transmastoid stimulation and recorded from beneath the eyes are generated by a crossed vestibulo-ocular pathway while the projections underlying the lateral responses are likely to be bilateral.

Significance

The vestibular-ocular connectivity underlying the OVEMPs recorded from inferior and lateral recording sites differs. For clinical use, the inferior recording site is the simplest to interpret.     

Vestibular evoked myogenic potentials in patients suffering from an unilateral acoustic neuroma: a study of 170 patients.

OBJECTIVE: To determine the value of investigating the vestibular evoked myogenic potentials (VEMP's) induced by clicks and 500 Hz short tone burst (STB) for the diagnosis of acoustic neuromas. METHODS: We studied the average responses to 100dB clicks and 500 Hz STB in the ipsilateral sternomastoid muscle. Ninety-five healthy subjects and 170 patients suffering from a unilateral acoustic neuroma were included in that study. Caloric and audiometric tests results were also analyzed. RESULTS: Thirty-six/170 patients (21.2%) exhibited normal responses to clicks and to STB whereas 134/170 (78.8%) gave abnormally low or no responses. 78/170 (45.9%) showed no responses to both clicks and STB. In 56/170 patients (32.9%), VEMP's induced by high level clicks and STB were discordant: STB VEMP's were either normal (n=32) or low (n=24) in patients with an abnormal response to clicks (no response n=40 or low response n=16). In contrast, STB-induced VEMP's were always normal in cases of normal responses to clicks. No strong, systematic correlation could be found between saccular nerve dysfunction and either the degree of 4-8 kHz hearing loss or the extent of horizontal canalar impairment. CONCLUSIONS: These data indicate that high level clicks and STB provide complementary information about the functionality of the saccular nerve. Clicks are useful to detect a minor saccular nerve dysfunction. In cases in which there is no response to clicks, STB gives valuable information about a potential residual function of the saccular nerve.     

Asymmetry of balance responses to monaural galvanic vestibular stimulation in subjects with vestibular schwannoma

ObjectiveWe investigated the potential of galvanic vestibular stimulation (GVS) to quantify lateralised asymmetry of the vestibulospinal pathways by measuring balance responses to monaural GVS in 10 subjects with vestibular schwannoma and 22 healthy control subjects.MethodsSubjects standing without vision were stimulated with 3 s, 1 mA direct current stimuli delivered monaurally. The mean magnitude and direction of the evoked balance responses in the horizontal plane were measured from ground-reaction forces and from displacement and velocity of the trunk. Vestibular-evoked myogenic potentials (VEMPs) to 500 Hz air and bone-conducted tones were also recorded.ResultsIn healthy subjects, the magnitudes of the force, velocity and displacement responses were not significantly different for left compared to right ear stimulation. Their individual asymmetry ratios were always <30%. Subjects with vestibular schwannoma had significantly smaller force, velocity and displacement responses to stimulation of the affected compared with non-affected ear. Their mean asymmetry ratios were significantly elevated for all three measures (41.2 ± 10.3%, 40.3 ± 15.1% and 21.9 ± 14.6%).ConclusionsAsymmetry ratios of balance responses to monaural GVS provide a quantitative and clinically applicable lateralising test of the vestibulospinal pathways.SignificanceThis method offers a more clinically relevant measure of standing balance than existing vestibular function tests which assess only vestibuloocular and vestibulocollic pathways.     

Recording of vestibular myogenic evoked potentials in patients with disturbed inner function

In this study, we measured VEMP in patients with disturbed function of inner ear. We studied 4 patients with unilateral sensorineural deafness and normal excitability of vestibular organs; 6 persons with unilateral weakness of vestibular function and 10 healthy subjects. We found that in patients with unilateral weakness of vestibular function VEMPs had short latencies and diminished amplitudes whereas in patients with unilateral deafness VEMPs were unchanged. These data strongly suggested that VEMPs were generated by stimulation of vestibular and not cochlear part of inner ear-sacculus. Our data confirm that VEMPs are a highly objective technique, simple, secure and comfortable for patients to assess the vestibulo-spinal connections.     

Postural and muscle responses to galvanic vestibular stimulation reveal a vestibular deficit in adolescents with idiopathic scoliosis

One of the most appealing hypotheses around the aetiopathogenesis of adolescent idiopathic scoliosis attributes the development of the spine deformity to an imbalance in the descending vestibulospinal drive to the muscles resulting in a differential mechanical pull on the spine during the early life stages. In this study, we explored this hypothesis by examining postural and muscle responses to binaural bipolar galvanic vestibular stimulation (GVS) of randomly alternating polarity. Adolescents diagnosed with idiopathic scoliosis (n = 12) and healthy age‐matched controls (n = 12) stood quietly with feet together (stance duration 66–102 s), eyes closed and facing forward, while 10 short (2s), transmastoidal, bipolar square wave GVS pulses (0.3–2.0 mA) of randomly alternating polarity were delivered at varying time intervals. Responses depicted in the electromyographic (EMG) activity of bilateral axial and appendicular muscles, vertical reaction forces and segment kinematics were recorded and analysed. Scoliotic patients demonstrated smaller ankle muscle responses and a delayed postural shift to the right relative to controls during anode right/cathode left GVS. When GVS polarity was reversed, patients had a greater soleus short‐latency response on the left anodal side, while the rest of the muscle and postural responses were similar between groups. Vestibular stimulation also evoked greater head and upper trunk sway in scoliotic compared with healthy adolescents irrespective of stimulus polarity. Results provide new preliminary evidence for a vestibular imbalance in adolescents with idiopathic scoliosis that is compensated by somatosensory, load‐related afferent feedback from the lower limbs during the latter part of the response.     

Ocular vestibular evoked myogenic potentials induced by air-conducted sound in patients with acute brainstem lesions

ObjectiveThe ocular vestibular-evoked myogenic potential (oVEMP), a recently documented otolith-ocular reflex, is considered to reflect the central projections of the primary otolithic afferent fibers to the oculomotor nuclei. The aim of our study is to define air-conducted sound oVEMP abnormality in patients with acute brainstem lesions and to determine the brainstem structures involved in the generation of oVEMPs.MethodsIn response to air-conducted tone burst sounds (ACS), oVEMP was measured in 52 patients with acute brainstem lesions. Individualized brainstem lesions were analyzed by means of MRI-based voxel-wise lesion-behavior mapping, and the probabilistic lesion maps were constructed.ResultsMore than half (n = 28, 53.8%) of the patients with acute brainstem lesions showed abnormal oVEMP in response to ACS. The majority of patients with abnormal oVEMPs had lesions in the dorsomedial brainstem that contains the medial longitudinal fasciculus (MLF), the crossed ventral tegmental tract (CVTT), and the oculomotor nuclei and nerves.ConclusionMLF, CVTT, and the oculomotor nuclei and nerves appear to be responsible for otolith-ocular responses in the brainstem.SignificanceComplemented to cervical VEMP for the uncrossed otolith-spinal function, oVEMP to ACS may be applied to evaluate the crossed otolith-ocular function in central vestibulopathies.     

Unit responses evoked in the amygdala and striatum by electrical stimulation of the medial geniculate body

Unit activity was recorded from cells and cell clusters in the amygdala and striatum in response to electrical stimulation of the medial geniculate body (MGB) in rats anesthetized with chloral hydrate. Responses were mostly excitatory and were evoked against a relatively silent background (i.e., the units seldom fired between stimuli). The shortest latency responses were recorded in the caudate putamen (CPU), lateral amygdaloid nucleus (AL), and amygdalostriatal transition area (AST). Longer latency responses were obtained from neurons in the basolateral (ABL), basomedial (ABM), and central (ACE) nuclei of the amygdala. Moreover, while responses were evoked in AL, AST, and CPU with 300-500 microA stimuli delivered once every 10 sec, more intense and higher-frequency stimuli were required to obtain responses in ABL, ABM, and ACE. These findings are consistent with anatomical tracing studies showing that AL, AST, and CPU receive direct projections from the MGB and related acoustic processing areas of the thalamus but that ACE, ABL, and ABM do not.     

Vestibular evoked myogenic potentials and their clinical utility in patients with amyotrophic lateral sclerosis

ObjectiveTo evaluate the diagnostic value of vestibular evoked myogenic potentials (VEMPs) in the assessment of brainstem function integrity in patients with amyotrophic lateral sclerosis (ALS).MethodsThis was a prospective case-control study including 30 definite or probable ALS patients divided into two groups (with or without brainstem involvement) and 30 healthy controls. Cervical (c-), masseter (m-) and ocular VEMP (o-VEMP) measurements were obtained for all the participants.ResultsThe c-VEMP mean p13 and n23 were significantly prolonged in the ALS patients. The interside peak differences in p13 and n23 of c-VEMP and in n10 and p15 of o-VEMP were significantly prolonged. The rates of alteration in c-VEMP, m-VEMP and o-VEMP in the ALS patients were 67%, 40%, and 45%, respectively. The ALS patients with brainstem involvement had a significantly higher percentage of VEMP abnormalities than did those without brainstem involvement (p = 0.027).Conclusionsc-VEMP is a sensitive tool to detect lower levels of brainstem involvement. Impairments in o-VEMP and m-VEMP indicate involvement of the upper brainstem. The use of combined VEMPs may provide useful insights into the pathophysiological mechanism of ALS.SignificanceVEMPs may be useful in the evaluation of brainstem dysfunction in ALS patients.     

Vestibular hypersensitivity to sound in superior canal dehiscence: large evoked responses in the legs produce little postural sway.

OBJECTIVE: Patients with superior canal dehiscence (SCD) typically have enhanced sound-evoked vestibular reflexes, such as vestibulo-collic and vestibulo-ocular reflexes. We wished to investigate whether sound-evoked lower limb EMG responses and postural sway are also enhanced in this condition. METHODS: Eight patients with CT confirmed SCD (11 affected ears) and 8 age-matched normal controls participated. Three sound-evoked responses were measured; vestibulo-collic reflexes (i.e. vestibular-evoked myogenic potentials, VEMPs), lower limb vestibulo-spinal reflexes and body sway (centre of pressure in mm). Sound stimuli were 500 Hz air-conducted tone bursts of varying lengths (VEMPs: 2 ms; vestibulo-spinal: 20 ms; sway: 1s and 200 ms) set at fixed levels above each subject's VEMP threshold. RESULTS: SCD patients had very large VEMP and vestibulo-spinal responses following high intensity stimulation, but at the matched intensity of 15 dB above threshold amplitudes were similar in both SCD patients and controls. The amplitude of both responses increased linearly with increasing stimulus intensity in both groups. Large ( approximately 20mm), stereotyped sway responses were present in only one (atypical) patient with high intensity stimulation. Small ( approximately 2mm) sway responses were present in the remaining patients, and began immediately following the vestibulo-spinal responses. CONCLUSIONS: Despite the presence of large vestibular reflexes, there is usually very little body sway in response to loud sounds in SCD patients. SIGNIFICANCE: Large short-latency vestibulo-spinal reflexes in SCD do not necessarily evoke large sway responses.     

Tonic eye movements induced by bilateral and unilateral galvanic vestibular stimulation (GVS) in guinea pigs

Galvanic vestibular stimulation (GVS) stimulates primary vestibular afferents innervating the semicircular canals (SCCs) and otoliths found in the inner ear of humans and other mammals, including guinea pigs. To determine which pathways contribute to eye movements generated by this artificial vestibular stimulation in guinea pigs, low current intensities of GVS were passed either bilaterally between the tensor-tympani muscles of the two ears (up to 30 μA) or unilaterally between one tensor-tympani electrode and an indifferent on the back of the neck (up to 60 μA). Both forms of GVS were found to selectively generate tonic eye movements without nystagmus, characteristic of the otolith-ocular reflex; the axis of eye rotation did not align with any semicircular canal plane, but was oriented close to the expected axis of eye rotation that would occur in response to the net stimulation of otolith afferents. The induced eye rotation was predominantly vertical with a smaller horizontal deviation and very little torsion. Consistent with the results of previous human studies, the tonic eye movements were found to exhibit bilateral gain enhancement, whereby bilateral GVS generated twice the amplitude of eye rotation as unilateral anodal or cathodal stimulation alone. Eye movement responses to unilateral GVS were symmetrical in amplitude during equivalent intensities of anodal and cathodal stimulation, consistent with the known responses of more regularly and intermediately discharging primary vestibular afferents to GVS. These results together suggest that more regularly discharging otolith-ocular projections may mediate the tonic changes in eye position induced during maintained, low-intensity GVS in guinea pigs.     

Short latency vestibular potentials evoked by electrical round window stimulation in the guinea pig

Short-latency potentials evoked by round window electrical stimulation were recorded in guinea pig by means of vertex-pinna skin electrodes using averaging techniques. Constant current shocks of 20 microseconds or 50 microseconds (25-300 microA) were used to evoke both auditory and vestibular brain-stem potentials. Pure auditory potentials, comparable to those evoked by acoustic clicks, were obtained by 20 microseconds electrical stimuli and disappeared during an auditory masking procedure made with a continuous white noise (110 dB SPL). Short latency potentials labeled V1, V2 and V3 were obtained by 50 microseconds electrical stimuli during an auditory masking procedure. This response disappeared after specific vestibular neurectomy, whereas the auditory response evoked by acoustic clicks or by electrical stimulation remained unchanged, suggesting that these latter potentials had a vestibular origin.     

Perception of the vertical in patients with right hemispheric lesion: effect of galvanic vestibular stimulation

Patients with right-brain injury present, more frequently in the acute phase, with a deviation of the subjective vertical (SV) contralateral to the lesion. The aim of this study was to investigate the influence of galvanic vestibular stimulation (GVS) on this disorder. Twelve patients presenting with a right hemispheric lesion, seven with neglect (N+) and five without (N-) were compared to eight control subjects. They had to orient vertically a luminous rod in darkness, in three galvanic stimulation (1.5 mA) conditions: cathode left, cathode right and no stimulation (baseline). Without stimulation, the patients' SV, and especially that of N+, showed an anticlockwise deviation. In comparison with baseline values, GVS induced a deviation toward the side opposite to the cathode in the three groups. In the patients, the deviation was of larger amplitude and appeared greater for left than for right cathodic stimulation. In conclusion, we showed an influence of vestibular stimulation on the SV of right brain-injured patients, especially when spatial neglect was present. As left cathodic stimulation can reduce the SV deviation associated with spatial neglect, such a tool could be introduced in rehabilitation.     

Ocular vestibular evoked myogenic potentials: The effect of head and body tilt in the roll plane

ObjectiveTo explore effects of whole-head/body tilt in the roll plane on ocular-vestibular evoked myogenic potentials (oVEMP).MethodsTwenty healthy subjects were randomly tilted in an Eply Omniax rotator across a series of eight angles from 0° to 360° (at 45° separations) in the roll plane. At each position, oVEMPs to air-conducted (AC) and bone-conducted (BC) stimulation were recorded from unrectified infra-orbital surface electromyography during upward gaze. oVEMP amplitudes, latencies and amplitude asymmetry were compared across each angle of orientation.ResultsHead orientation had a significant effect on oVEMP reflex amplitudes for both AC and BC stimulation (p < 0.001). For both stimuli there was a trend for lower amplitudes with increasing angular departure from the upright position. Mean amplitudes decreased by 42.6–56.8% (AC) and 23.2–25.5% (BC) when tilted 180°. Roll-plane tilt had a significant effect on amplitude asymmetry ratios recorded in response to AC stimuli (p < 0.001), indicating a trend for lower amplitudes from the dependent (down) ear. Amplitude asymmetry ratios for BC stimuli were unaffected by head and body orientation.ConclusionsThe results confirm an effect of head and body orientation on oVEMP reflexes recorded in response to air- and bone-conducted stimuli.SignificanceThe upright position yields an optimal oVEMP response.