Otolithic and canal functions assessment during the acute phase of benign paroxysmal positional vertigo.

PURPOSE: Assess otolith and canal involvement in patients with Benign Paroxysmal Positional Vertigo (BPPV) during the acute phase. METHODS: Ninety patients with BPPV in the acute phase underwent a vestibular assessment that included an assessment with videonistagmography, video Head Impulse Test (vHIT) to evaluate horizontal and vertical semicircular canals, and ocular vestibular evoked myogenic potentials (oVEMPs) for the otolithic function. RESULTS: Ninety patients had an involvement of the posterior canal, fifty-five out of ninety patients presented a BPPV of the right ear. No asymmetry of the otolithic functions was found for the utricular macula. Furthermore, no reduction of the Vestibular Ocular Reflex gain was found for the examined canal functions. CONCLUSIONS: The lack of asymmetry suggests that during the acute phase of BPPV, the otolithic function is balanced between the affected and unaffected ears. Moreover, the preserved VOR gain for the examined canal functions suggests that the VOR responses for the examined channels were intact.

Vestibular function after vestibular neuritis.

OBJECTIVE: To measure horizontal semicircular canal function over days, weeks, and months after an acute attack of vestibular neuritis. DESIGN: The video head impulse test (vHIT) was used to measure the eye movement response to small unpredictable passive head turns at intervals after the attack. STUDY SAMPLE: Two patients diagnosed with acute right unilateral vestibular neuritis. RESULTS: There was full restoration of horizontal canal function in one patient (A) as shown by the return of the slow phase eye velocity response to unpredictable head turns, while in the other patient (B) there was little or no recovery of horizontal canal function. Instead this second patient generated covert saccades during head turns. CONCLUSION: Despite the objective evidence of their very different recovery patterns, both patients reported, at the final test, being happy and feeling well recovered, even though in one of the patients there was clear absence of horizontal canal function. The results indicate covert saccades seem a successful way of compensating for loss of horizontal canal function after unilateral vestibular neuritis. Factors other than recovery of the slow phase eye velocity are significant for patient recovery.

Does unilateral utricular dysfunction cause horizontal spontaneous nystagmus?

The presence of spontaneous nystagmus in darkness with a strong horizontal component has been taken to indicate that there is asymmetrical function of the horizontal semicircular canals. If this horizontal spontaneous nystagmus can be suppressed by vision, then it is regarded as due to peripheral horizontal canal dysfunction. However, we report evidence from one patient (61-year-old male), who visited the MSA ENT Clinic, Cassino (FR) Italy, reporting acute, severe vertigo, postural unsteadiness, nausea and vomiting associated with right sudden hearing loss. The patient received instrumental audiovestibular testing to obtain objective measurements of his inner-ear receptors. At the time of the attack, the patient showed spontaneous nystagmus, mainly with horizontal and vertical components (3D infrared video-oculography). Video head-impulse tests of dynamic horizontal canal function showed that the functional status of both horizontal canals was within the normal range. Cervical VEMPs to 500 Hz bone-conducted vibration at Fz showed normal results; ocular VEMPs to the same stimulus showed a reduced n10 amplitude beneath the left eye, corresponding to the right ear. For this reason, the patient was diagnosed as having right unilateral selective utricular macula lesion due to labyrinthitis. There is considerable evidence of convergence of neural input from the otoliths onto horizontal canal neurons in the vestibular nuclei. The firing of such neurons could reflect either asymmetrical horizontal canal function or asymmetrical utricular function. The problem with this patient was not due to asymmetrical horizontal canal function, but only to asymmetrical utricular function, demonstrated by the results of the oVEMP test.

The clinical course of vestibular neuritis from the point of view of the ocular vestibular evoked myogenic potential.

BACKGROUND: Studying otolith functions after unilateral vestibular neuritis using ocular vestibular-evoked myogenic potentials and subjective visual vertical tests could give different results. METHOD: A total of 39 patients underwent a vestibular assessment that included the Dizziness Handicap Inventory and horizontal and vertical semicircular canal function testing with video head impulse testing, ocular vestibular-evoked myogenic potential testing, cervical vestibular-evoked myogenic potentials and subjective visual vertical testing. RESULTS: All patients showed a significant alteration (asymmetry ratio more than 40 per cent) for ocular vestibular-evoked myogenic potentials as well as for subjective visual vertical testing (more than -2° to more than +2°) during the acute phase, whereas after 72 hours from the acute vertigo attack normal values (asymmetry ratio less than 40 per cent) were found in 6 out of 39 patients for ocular vestibular-evoked myogenic potentials and 36 out of 39 for the subjective visual vertical (less than -2° to less than +2°). CONCLUSION: Ocular vestibular-evoked myogenic potentials are the most suitable test to evaluate otolith functions in patients with unilateral vestibular neuritis in the acute and sub-acute phase.

Ocular vestibular-evoked myogenic potential (oVEMP) to test utricular function: neural and oculomotor evidence.

A new test for utricular function has recently been introduced and validated, namely the ocular vestibular-evoked myogenic potential (oVEMP), which refers to the myogenic potentials recorded by surface EMG electrodes beneath both eyes in response to bone conducted vibration (BCV) of the head or air conducted sound (ACS). The oVEMP test differs from another vestibular-evoked myogenic potential recorded by surface EMG electrodes over the sternocleidomastoid muscles in that the cervical vestibular-evoked myogenic potential (cVEMP) due to saccular activation is measured. oVEMP is a reliable clinical test that relies on extensive physiological evidence from studies on guinea pigs, and in particular on recording the vestibular primary afferent responses to BCV, demonstrating that the same BCV causes similar eye movements in both guinea pigs and humans. This review briefly integrates the most recent physiological and behavioural evidence that substantiates the clinical use of oVEMP.

Ocular and cervical vestibular evoked myogenic potentials in response to bone-conducted vibration in patients with probable inferior vestibular neuritis.

BACKGROUND AND AIMS: Previous evidence shows that the n10 component of the ocular vestibular evoked myogenic potential indicates utricular function, while the p13 component of the cervical vestibular evoked myogenic potential indicates saccular function. This study aimed to assess the possibility of differential utricular and saccular function testing in the clinic, and whether loss of saccular function affects utricular response. METHODS: Following vibration conduction from the mid-forehead at the hairline, the ocular n10 component was recorded by surface electromyograph electrodes beneath both eyes, while the cervical p13-n23 component was recorded by surface electrodes over the tensed sternocleidomastoid muscles. RESULTS: Fifty-nine patients were diagnosed with probable inferior vestibular neuritis, as their cervical p13-n23 component was asymmetrical (i.e. reduced or absent on the ipsilesional side), while their ocular n10 component was symmetrical (i.e. normal beneath the contralesional eye). CONCLUSION: The sense organ responsible for the cervical and the ocular vestibular evoked myogenic potentials cannot be the same, as one response was normal while the other was not. Reduced or absent saccular function has no detectable effect on the ocular n10 component. On vibration stimulation, the ocular n10 component indicates utricular function and the cervical p13-n23 component indicates saccular function.

The basis for using bone-conducted vibration or air-conducted sound to test otolithic function.

Extracellular single neuron recordings of primary vestibular neurons in Scarpa's ganglion in guinea pigs show that low-intensity 500 Hz bone-conducted vibration (BCV) or 500 Hz air-conducted sound (ACS) activate a high proportion of otolith irregular neurons from the utricular and saccular maculae but few semicircular canal neurons. In alert guinea pigs, and humans, 500 Hz BCV elicits otolith-evoked eye movements. In humans, it also elicits a myogenic potential on tensed sternocleidomastoid muscles. Although BCV and ACS activate both utricular and saccular maculae, it is possible to probe the functional status of these two sense organs separately because of their differential neural projections. Saccular neurons have a strong projection to neck muscles and a weak projection to the oculomotor system. Utricular afferents have a strong projection to eye muscles. So measuring oculomotor responses to ACS and BCV predominantly probes utricular function, while measuring neck muscle responses to these stimuli predominantly probes saccular function.

Multiple dehiscences of bony labyrinthine capsule. A rare case report and review of the literature.

Multiple semicircular canal dehiscences are clinical entities characterised by vestibular and cochlear symptoms induced by enhanced sensitivity of labyrinthine receptors due to a multiple bone defect of the otic capsule. The case is presented of a 38-year-old male with bilateral posterior semicircular canal dehiscence associated with unilateral (right) superior semicircular canal dehiscence. The man suffered from vestibular (recurrent Tullio Phenomenon or sound-induced vertigo) and cochlear symptoms (persistent aural fullness associated with mixed hearing loss and disabling tinnitus).

Effect of bone-conducted vibration of the midline forehead (Fz) in unilateral vestibular loss (uVL). Evidence for a new indicator of unilateral otolithic function.

Recently, a new indicator of vestibular otolithic function has been reported: it is a series of negative-positive myogenic potentials recorded by surface electrodes on the skin beneath the eyes in response to bone-conducted vibration (BCV) delivered to the forehead at the hairline in the midline (Fz). The potential is called the ocular vestibular-evoked myogenic potential (oVEMP) and the first component of this (n10) is a small (approximately 8 microV), short latency (~ 10 ms), negative potential. In healthy subjects, who are looking up, the n10 responses to Fz bone-conducted vibration are symmetrical beneath the two eyes. In the present investigation, in 17 patients with unilateral surgical vestibular loss, marked asymmetries were observed between the n10 beneath the two eyes: n10 is small or absent beneath the eye on the side opposite the operated ear, confirming previous evidence that n10 is a crossed vestibulo-ocular response unlike p13 of bone-conducted vibration cervical VEMPs (cVEMPs) is a ipsilateral vestibular response and also it is absent in this type of subjects. These results, together with evidence from patients with superior vestibular neuritis allow us to conclude: the asymmetry of the n10 response to Fz bone-conducted vibration is an indicator of utricular macula/superior vestibular nerve dysfunction on the operated side in patients with unilateral vestibular loss.

Ocular and cervical vestibular-evoked myogenic potentials to bone conducted vibration in Ménière's disease during quiescence vs during acute attacks.

OBJECTIVE: Two indicators of otolithic function were used to measure dynamic otolith function in the same patients both during an acute attack of Ménière's disease (MD) and in the quiescent period between attacks. METHODS: The early negative component (n10) of the ocular vestibular-evoked myogenic potential (the oVEMP) to brief 500 Hz bone conducted vibration (BCV) stimulation of the forehead, in the midline at the hairline (Fz) was recorded by surface EMG electrodes just beneath both eyes while the patient looked up. It has been proposed that the n10 component of the oVEMP to 500 Hz Fz BCV indicates utricular function. It has been proposed that the early positive component (p13) of the cervical vestibular-evoked myogenic potential (the cVEMP) recorded by surface electrodes on both tensed SCM neck muscles to 500 Hz Fz BCV indicates saccular function. RESULTS: Sixteen healthy control subjects tested on two occasions showed no detectable change in the symmetry of oVEMPs or cVEMPs to 500 Hz Fz BCV. In response to 500 Hz Fz BCV 15 early MD patients tested at both attack and quiescent phases showed a dissociation: there was a significant increase in contralesional of n10 of the oVEMP during the attack compared to quiescence but a significant decrease in the ipsilesional p13 of the cVEMP during the attack compared to quiescence. CONCLUSIONS: During an MD attack, dynamic utricular function in the affected ear as measured by the n10 of the oVEMP to 500 Hz Fz BCV is enhanced, whereas dynamic saccular function in the affected ear as measured by the p13 of the cVEMP to 500 Hz Fz BCV is not similarly affected. SIGNIFICANCE: The MD attack appears to affect different otolithic regions differentially.

Prolonged bone-conducted vibration in superior semicircular canal dehiscence and in otosclerosis: comparison of the 3D eye movement evaluation.

Vibration-induced nystagmus, as clinical sign, was recently introduced in outpatient clinical practice for the study and evaluation of otoneurological patients. This response, which can only be evoked by bone conducted vibratory stimulation in the mastoid region or at the location on the forehead in the midline at the hairline, was essentially designed for patients with persistent unilateral vestibular deficit and was interpreted as the result of excitatory functional activity of the vestibular system on the non-affected side. Vibratory stimulation is, in fact, considered to reach both systems, which in the case of functional asymmetry, respond asymmetrically with greater excitatory activation on the more responsive side. On the other hand, little information is available concerning vibration-induced nystagmus in subjects with symmetrical vestibular function. The limited experience with this recently proposed test and incomplete knowledge regarding its mechanisms suggest that it must be investigated in clinical conditions, having a known pathophysiological basis: the responses obtained could help provide insight into the potential of this test and contribute to the diagnostic definition of the superior semicircular canal dehiscence or otosclerosis. Analysis of Vibration-induced nystagmus, recently proposed to study transmission of excitatory stimuli by bone conduction, may be appropriate for altered input caused by defects of the labyrinthine capsule. This promises to be an interesting new field of research.

A review of the scientific basis and practical application of a new test of utricular function--ocular vestibular-evoked myogenic potentials to bone-conducted vibration.

This is a review of recently published papers showing that bone-conducted vibration of the head causes linear acceleration stimulation of both inner ears and this linear acceleration is an effective way of selectively activating otolithic afferent neurons. This simple stimulus is used in a new test to evaluate clinically the function of the otoliths of the human inner ear. Single neuron studies in animals have shown that semicircular canal neurons are rarely activated by levels of bone-conducted vibration at 500 Hz which generate vigorous firing in otolithic irregular neurons and which result in a variety of vestibulo-spinal and vestibulo-ocular responses, and the latter is the focus of this review. In humans, 500 Hz bone-conducted vibration, delivered at the midline of the forehead, at the hairline (Fz), causes simultaneous and approximately equal amplitude linear acceleration stimulation at both mastoids and results in ocular-evoked myogenic potentials (oVEMPs) beneath both eyes. The first component of this myogenic potential, at a latency to peak of about 10 ms is a negative potential and is called n10 and, in healthy subjects, is equal in amplitude beneath both eyes, but after unilateral vestibular loss, the n10 potential beneath the eye opposite to the lesioned ear is greatly reduced or totally absent. n10 is a myogenic potential due to a crossed otolith-ocular pathway. In patients with total unilateral superior vestibular neuritis, in whom saccular function is largely intact (as shown by the presence of cervical vestibular evoked myogenic potentials (cVEMPs), but utricular function is probably compromised, there is a reduced n10 response beneath the contralesional eye, strongly indicating that n10 is due to utricular otolithic function.

Vestibular signs and symptoms of volumetric abnormalities of the vestibular aqueduct.

OBJECTIVE: The objective of this study was to identify a pattern of signs, symptoms and neuroradiological findings which would assist investigation of vestibular function (especially otolith function) in a group of adult patients with anatomical alterations of the endolymphatic aqueduct and sac. METHODS: Fifteen subjects affected by volumetric abnormalities of the vestibular aqueduct were selected from a cohort of patients referred to a tertiary referral neurotological centre between 1 January 2004 and 30 June 2006. All patients underwent accurate clinical history-taking and were evaluated using a standardised set of bedside and instrumental neurotological tests (i.e. audiometry, auditory brainstem response and vestibular evoked myogenic potentials). After these tests, each patient underwent computed tomography and magnetic resonance imaging in order to accurately evaluate the middle ear, labyrinthine capsule and internal auditory canals. These evaluations confirmed clinical suspicion of volumetric abnormalities of the vestibular aqueduct and endolymphatic sac. RESULTS: All the patients with a defined volumetric alteration in the region of the vestibular aqueduct and endolympatic sac reported a typical pattern of symptoms and signs. The most obvious and frequent symptoms in these patients were migraine-related vertigo (using the Neuhauser criteria, 10 of 15, 66.6 per cent), 'motion sickness' (12 of 15, 80 per cent), oscillopsia (nine of 15, 60 per cent) and dizziness (14 of 15, 93.3 per cent). Clinical examination results for the selected patients allowed some useful speculative conclusions. During neurotological evaluation, two instrumental methodologies were especially useful diagnostically: vestibular evoked myogenic potentials of the neck, and the mastoid vibration test at 100 Hz. CONCLUSIONS: Dysfunction of the vestibular aqueduct is suggested by symptomatology characterised by: migraine-related vertigo, unstable or recurring oscillopsia, lowering of the vestibular evoked myogenic potential threshold, hypoacusis, anamnestic report of motion sickness, and nystagmus induced by mastoid vibration and head-shaking. Computed tomography and magnetic resonance imaging are needed in order to confirm clinical suspicions.