Cervical and Ocular Vestibular-Evoked Myogenic Potentials in Patients With Intracochlear Schwannomas

Measurement of Ocular Vestibular Evoked Myogenic Potentials: Nasion Reference Montage as an Alternative to the Clinical Standard Montage

OBJECTIVE

To compare two novel electrode montages for ocular, vestibular evoked myogenic potential using single-nasion reference electrodes with the clinical standard montage.

STUDY DESIGN

Randomized crossover experiment.

SETTING

Tertiary referral center.

PARTICIPANTS

Sixty healthy participants.

INTERVENTION

Normal hearing and vestibular function were confirmed with an extensive test-battery. All ocular, vestibular evoked myogenic potential settings were measured with air-conducted tone bursts at 100-dB normal hearing level and a frequency of 500 Hz. Three electrode montages were measured in randomized order: the clinical standard montage ("S"), the nasion reference montage ("N"), and the nasion reference montage with a more lateral active electrode ("L"). Upgaze was standardized to 35 degrees.

MAIN OUTCOME MEASURES

Detection rate, latency of N1 and P1, peak-to-peak amplitude of N1 and P1, signal-to-noise ratio (SNR), asymmetry ratio (AR), concordance of expert assessment, and reliability.

RESULTS

All electrode montages showed detection rates greater than 90%. Latencies for "L" were shorter than for "S" and "N." Amplitudes and SNR for "S" and "N" were higher than for "L," whereas the values for "S" and "N" did not differ significantly. For AR, no significant differences between the montages were assessed. Concordance of experts ranged from 78% for "L" and 89.8% for "N." All montages provided excellent day-to-day reliability (intraclass correlation coefficient ≥0.9) for amplitudes and SNR.

CONCLUSIONS

Montage N could be a useful alternative to the clinical standard montage: although results are roughly equivalent, montage N requires one less electrode to do so.

Objective Neurological Testing Methods Used to Follow Up Vestibular Neuritis Depending on Different Factors

Purpose

We analyze the impact of different factors on clinical performance and prognosis in vestibular neuritis (VN) and explore indicators that could accurately reflect changes in patients' symptoms at different stages.

Methods

We observed patients with VN during the acute and recovery phases. Clinical symptoms, vertigo-related scales, neurological examination, vestibular function tests (caloric test, video head impulse test (vHIT), vestibular evoked myogenic potential (VEMP)), and the history of disease (underlying diseases, glucocorticoid therapy) were recorded at onset and at 4 and 12 weeks after onset in VN patients. Multiple linear regression analysis was used to identify vestibular function tests that had a linear regression relationship with the subjective quantitative results.

Results

At 4 weeks after onset, the group without underlying disease had better improvement in EEV, gain, and UW than the group with underlying disease (P < 0.05). There was a significant difference in the change in DHI, EEV, gain of the affected horizontal semicircular canal in the vHIT and unilateral weakness (UW) between the glucocorticoid treatment group and the no glucocorticoid treatment group (P < 0.05), and glucocorticoid treatment group was better. The change value in the gain of horizontal canals in the vHIT was mainly positively and linearly correlated with the EEV scores (P<0.001). Possible dynamic correlation between vHIT results and vestibular symptoms.

Conclusion

The absence of underlying disease and the receipt of glucocorticoid therapy significantly contributed to the improvement of objective vestibular function tests in the short term, while the improvement of subjective vertigo may correlate with the different objective measures and questionnaire. We believe that the improvement of the affected horizontal semicircular canal gain value in the vHIT can be used as a reference indicator of the degree of improvement of vestibular symptoms with superior vestibular neuritis.

Vestibular Impairment in Patients with Vestibular Schwannoma: A Journey through the Pitfalls of Current Literature

Vestibular Schwannoma is the most common tumour of Ponto Cerebellar Angle and is capable of strongly impacting the patient's quality of life. In recent decades, the proposals for the management of the disease have multiplied, just as the diagnostic capacity has improved. While in the past, the primary objective was the preservation of the facial function, and subsequently also of the auditory function, the attention to the vestibular symptomatology, which appears to be one of the main indicators of deterioration of quality of life, is still unsatisfactory. Many authors have tried to provide guidance on the best possible management strategy, but a universally recognized guideline is still lacking. This article offers an overview of the disease and the proposals which have advanced in the last twenty years, evaluating their qualities and defects in a critical reading.

Intralabyrinthine schwannomas: a two-case series and literature review with a focus on hearing rehabilitation

PURPOSE

Intralabyrinthine schwannomas (ILSs) are an uncommon finding. Diagnosis is challenging and no gold standard treatment exists yet. In this article, we present a two-cases series and review the latest available literature to assess the best diagnostic and therapeutic scheme.

METHODS

We reviewed the latest available literature assessing most frequent and relevant sets of symptoms, clinical features of the disease, diagnostic tests and imaging, possible treatments and after-surgery hearing rehabilitation techniques. We then compared literature data to our own series ones.

RESULTS

ILSs clinical presentation and development may overlap with other, more common otological conditions. Full audiometric battery test, electrophysiological study of VEMPS and MRI with contrast enhancement all appear to be critical to correctly diagnose these tumors. Several treatments exist: radiological follow-up, radiation therapy, full or partial surgical excision. Hearing rehabilitation is mostly accomplished through simultaneous cochlear implantation.

CONCLUSIONS

Our case-series data matches the available literature. ILSs are a rare type of vestibular schwannomas. Diagnosis in challenging and delayed in time as all the diagnostic tests, yet sensitive, are not specific for ILSs. The most suitable treatment seems to be surgical excision of these tumors followed by simultaneous cochlear implantation to restore hearing.

A Single Fast Test for Semicircular Canal Dehiscence—oVEMP n10 to 4000 Hz—Depends on Stimulus Rise Time

As previously reported, a single test measuring oVEMP n10 to 4000 Hz stimuli (bone-conducted vibration (BCV) or air-conducted sound (ACS)) provides a definitive diagnosis of semicircular canal dehiscence (SCD) in 22 CT-verified patients, with a sensitivity of 1.0 and specificity of 1.0. This single short screening test has great advantages of speed, minimizing testing time, and the exposure of patients to stimulation. However, a few studies of the 4000 Hz test for SCD have reported sensitivity and specificity values which are slightly less than reported previously. We hypothesized that the rise time of the stimulus is important for detecting the oVEMP n10 to 4000 Hz, similarly to what we had shown for 500 and 750 Hz BCV. We measured oVEMP n10 in 15 patients with CT-verified SCD in response to 4000 Hz ACS or BCV stimuli with rise times of 0, 1, and 2 ms. As a result, increasing the rise time of the stimulus reduced the oVEMP n10 amplitude. This outcome is expected from the physiological evidence of guinea pig primary vestibular afferents, which are activated by sound or vibration. Therefore, for clinical VEMP testing, short rise times are optimal (preferably 0 ms).

Proposal for a Unitary Anatomo-Clinical and Radiological Classification of Third Mobile Window Abnormalities

Introduction: An increased number of otic capsule dehiscence (OCD) variants relying on the third window pathomechanism have been reported lately. Therefore, a characterization of the anatomical structures involved and an accurate radiological description of the third window (TW) interface location have become essential for improving the diagnosis and appropriate therapeutic modalities. The purpose of this article is to propose a classification based on clinical, anatomical, and radiological data of third mobile window abnormalities (TMWA) and to discuss the alleged pathomechanism in lesser-known clinical variants.

Materials and Methods: The imaging records of 259 patients who underwent, over the last 6 years, a high-resolution CT (HRCT) of the petrosal bone for conductive hearing loss were analyzed retrospectively. Patients with degenerative, traumatic, or chronic infectious petrosal bone pathology were excluded. As cases with a clinical presentation similar to those of a TW syndrome have recently been described in the literature but without these being confirmed radiologically, we thought it necessary to be integrated in a separated branch of this classification as “CT - TMWA.” The same goes for certain intralabyrinthine pathologies also recently reported in the literature, which mimic to some extent the symptoms of a TW pathology. Therefore, we suggest to call them intralabyrinthine TW-like abnormalities.

Results: Temporal bone HRCT and, in some cases, 3T MRI of 97 patients presenting symptomatic or pauci-symptomatic, single or multiple, unilateral or bilateral OCD were used to develop this classification. According to the topography and anatomical structures involved at the site of the interface of the TW, a third-type classification of OCD is proposed.

Conclusions: A classification reuniting all types of TMWA as the one proposed in this article would allow for a better systematization and understanding of this complex pathology and possibly paves the way for innovative therapeutic approaches. To encompass all clinical and radiological variants of TMWA reported in the literature so far, TMWAs have been conventionally divided into two major subgroups: Extralabyrinthine (or “true” OCD with three subtypes) and Intralabyrinthine (in which an additional mobile window-like mechanism is highly suspected) or TMWA-like subtype. Along these subgroups, clinical forms of OCD with multiple localization (multiple OCD) and those that, despite the fact that they have obvious characteristics of OCD have a negative CT scan (or CT – TMWA), were also included.

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.

Bone conducted vibration is an effective stimulus for otolith testing in cochlear implant patients

BACKGROUND

Treatment with a cochlear implant (CI) poses the risk of inducing a behaviorally unmeasurable air-bone gap leading to false negative absence of cervical and ocular vestibular evoked myogenic potentials (cVEMPs, oVEMPs) to air conducted sound (ACS).

OBJECTIVE

To investigate VEMP response rates to ACS and bone conducted vibration (BCV) in CI patients and the applicability of the B81 transducer for BCV stimulation.

METHODS

Prospective experimental study including unilateral CI patients, measuring cVEMPs and oVEMPs to ACS and to BCV, comparing response rates, signed asymmetry ratios, latencies, and amplitudes.

RESULTS

Data of 13 CI patients (mean age 44±12 years) were analyzed. For the CI side, oVEMP and cVEMP response rates were significantly higher for BCV (77%cVEMP, 62%oVEMP) compared to ACS (23%cVEMP, 8%oVEMP). For the contralateral side, no difference between response rates to ACS (85%cVEMP, 69%oVEMP) and BCV (85%cVEMP, 77%oVEMP) was observed. Substantially higher asymmetries were observed for ACS (-88±23%for cVEMPs, -96±11%for oVEMPs) compared to BCV (-12±45%for cVEMPs, 4±74%for oVEMPs).

CONCLUSIONS

BCV is an effective stimulus for VEMP testing in CI patients. The B81 is a feasible stimulator.

Rare Disorders of the Vestibular Labyrinth: of Zebras, Chameleons and Wolves in Sheep's Clothing

The differential diagnosis of vertigo syndromes is a challenging issue, as many - and in particular - rare disorders of the vestibular labyrinth can hide behind the very common symptoms of "vertigo" and "dizziness". The following article presents an overview of those rare disorders of the balance organ that are of special interest for the otorhinolaryngologist dealing with vertigo disorders. For a better orientation, these disorders are categorized as acute (AVS), episodic (EVS) and chronic vestibular syndromes (CVS) according to their clinical presentation. The main focus lies on EVS sorted by their duration and the presence/absence of triggering factors (seconds, no triggers: vestibular paroxysmia, Tumarkin attacks; seconds, sound and pressure induced: "third window" syndromes; seconds to minutes, positional: rare variants and differential diagnoses of benign paroxysmal positional vertigo; hours to days, spontaneous: intralabyrinthine schwannomas, endolymphatic sac tumors, autoimmune disorders of the inner ear). Furthermore, rare causes of AVS (inferior vestibular neuritis, otolith organ specific dysfunction, vascular labyrinthine disorders, acute bilateral vestibulopathy) and CVS (chronic bilateral vestibulopathy) are covered. In each case, special emphasis is laid on the decisive diagnostic test for the identification of the rare disease and "red flags" for potentially dangerous disorders (e. g. labyrinthine infarction/hemorrhage). Thus, this chapter may serve as a clinical companion for the otorhinolaryngologist aiding in the efficient diagnosis and treatment of rare disorders of the vestibular labyrinth.