Abnormal cervical vestibular-evoked myogenic potential in anterior inferior cerebellar artery territory infarction: Frequency, pattern, and a determinant

Otoconial Degeneration After Transient Ischemia Induced by Four-Vessel Occlusion in Rats

BACKGROUND AND PURPOSE

Ischemia of the inner ear may damage the otoconia. However, no study has explored any changes in the configuration of otoconia after transient ischemia of the labyrinth.

METHODS

Nineteen 7-week-old Sprague-Dawley rats were randomly assigned to either the sham (n=5) or the experimental group (n=14). The rats in the experimental group were subjected to global ischemia for 20 minutes using a four-vessel occlusion model, and were sacrificed seven days after the procedure. The rats in the sham group were sacrificed without any procedure. The otolithic organs (utricle and saccule) were dissected out for scanning electron microscope.

RESULTS

The otolithic organs in the sham group showed their normal gross configuration with a dense clumping of otoconia with a normal hexagonal morphology and a smooth surface. The otolithic organs in the experimental group also maintained a grossly normal configuration, but each otoconia showed irregular surfaces with numerous cracks or furrows, especially in the periphery of the otoconial bed.

CONCLUSIONS

The current study showed that otoconial degeneration may occur even after transient ischemia of the labyrinth. This finding supports an association between cerebral ischemia and benign paroxysmal positional vertigo.

Separating posterior-circulation stroke from vestibular neuritis with quantitative vestibular testing

OBJECTIVE

To separate vestibular neuritis (VN) from posteriorcirculation stroke (PCS) using quantitative tests of canal and otolith function.

METHODS

Video Head-Impulse tests (vHIT) were used to assess all three semicircular canal pairs; vestibulo-ocular reflex (VOR) gain and saccade metrics were examined. Cervical and ocular-Vestibular-Evoked Myogenic Potentials (c- and oVEMP) and Subjective Visual Horizontal (SVH) were used to assess otolith function.

RESULTS

For controls (n = 40), PCS (n = 22), and VN (n = 22), mean horizontal-canal VOR-gains were 0.96 ± 0.1, 0.85 ± 0.3 and 0.40 ± 0.2, refixation-saccade prevalence was 71.9 ± 41, 90.7 ± 57, 209.2 ± 62 per 100 impulses and cumulative-saccade amplitudes were 0.9 ± 0.4°, 2.4 ± 2.2°, 8.0 ± 3.5°. Abnormality-rates for cVEMP, oVEMP and SVH were 38%, 9%, 72% for PCS, and 43%, 50%, 91% for VN. A gain ≤0.68, refixation-saccade prevalence of ≥135% and cumulative-saccade amplitudes ≥5.3° separated VN from PCS with sensitivities of 95.5%, 95.5%, and 81.8%, and specificities of 68.2%, 86.4% and 95.5%. VOR-gain and saccade prevalence when combined, separated VN from PCS with a sensitivity and specificity of 90.9%. Abnormal oVEMP asymmetry-ratios were of low sensitivity (50%) but high specificity (90.9%) for separating VN from PCS.

CONCLUSION

vHIT provided the best separation of VN from PCS. VOR-gain, refixation-saccade prevalence and amplitude were effective discriminators of VN from PCS.

SIGNIFICANCE

vHIT and oVEMP could assist early identification of the aetiology of Acute Vestibular Syndrome in the Emergency Room.

Vestibular evoked myogenic potentials (VEMP) captured in the forearm flexor muscles: a study of its feasibility and reference ranges

OBJECTIVE

To determine the central tendency measures and variability of vestibular evoked myogenic potential (VEMP) with regard to the latency and wave amplitude when potentials are captured from the flexor muscles of the forearm.

METHODS

Ten adult volunteers with normal hearing underwent examination of their forearm flexor muscles (right and left sides; 20 samples in total) for VEMP acquisition. To this end, 200 tone burst stimuli at a 500 Hz frequency and 95 dBnHL intensity were promediated.

RESULTS

No statistical differences were observed in VEMP responses acquired from the right and left forearm flexor muscles concerning P34 and N44 latencies (p=0.32 and 0.90, respectively). The mean latency obtained for the P34 wave component was 34.9 ms (±2.6), with a lower limit equal to 29.3 and an upper limit equal to 40.4 ms. The average latency of the N44 wave component was 43.6 ms (±2.1), with a lower limit of 39.1 ms and an upper limit of 48.1 ms. The results were consistent and had low variability, and showed an average asymmetry index of 15.4 (±10.7). These findings indicate that potentials may be investigated in different age groups and in specific clinical populations, such as pathologies that may alter the neuronal transmission of the inferior vestibular pathway, especially when a longer portion is observed.

CONCLUSIONS

VEMP recording from forearm flexors is both feasible and stable, with latency reference ranges between 29.3 and 40.4 ms for P34, and 39.1 and 48.1 ms for N44.

Enhancing research quality of studies on VEMPs in central neurological disorders: a scoping review

Common pitfalls in vestibular-evoked myogenic potential (VEMP) recording methods have been extensively outlined by several reviews. Conversely, the robustness of research methodology employed for the design and conduct of VEMP studies has never been appraised. To fill this void, we conducted a scoping review to map and evaluate the overall quality of the existing literature on VEMPs in central neurological disorders. Five databases were searched from inception to October 2018 for case-control studies on multiple sclerosis (MS), cerebellar and/or brainstem strokes, Parkinson's disease (PD), migraine, and tumors of the cerebellopontine angle. Study quality was assessed using the Agency for Healthcare Research and Quality criteria (AHRQ). The 11-criteria AHRQ scoring system revealed that PD studies achieved a score of 5/11, migraine and cerebellar and/or brainstem stroke a score of 4/11, MS and tumors of the cerebellopontine angle a score of 3/11. Age was found to be one of the main sources of case-control imbalance: compared with controls, cases were significantly older with a 3.6-yr difference in MS studies, 6 yr in PD, up to 12 yr in stroke and tumors. Regardless of pathological condition, case-control groups were found unmatched also by gender. Post hoc power calculations revealed that 53% of the studies achieved the minimum statistical power of 80%. This scoping review revealed low research quality across the literature on VEMPs in central neurological disorders. Scoping lines are provided on actions to be undertaken in future studies to establish a common methodological platform and enhance the quality of research in this field.

NEW & NOTEWORTHY Robust methodology is a prerequisite for any type of research, particularly for observational designs such as those employed in vestibular-evoked myogenic potential (VEMP) research. On these premises, this scoping review provides methodological guidelines to improve validity, accuracy and consistency of clinical outcomes from VEMP studies involving central nervous system disorders. In fact, the high risk for bias that is inherent to poor methodology threatens the validity of the findings of works that are technically sound but methodologically flawed.

Recent Advances in Cerebellar Ischemic Stroke Syndromes Causing Vertigo and Hearing Loss

Cerebellar ischemic stroke is one of the common causes of vascular vertigo. It usually accompanies other neurological symptoms or signs, but a small infarct in the cerebellum can present with vertigo without other localizing symptoms. Approximately 11 % of the patients with isolated cerebellar infarction simulated acute peripheral vestibulopathy, and most patients had an infarct in the territory of the medial branch of the posterior inferior cerebellar artery (PICA). A head impulse test can differentiate acute isolated vertigo associated with PICA territory cerebellar infarction from more benign disorders involving the inner ear. Acute hearing loss (AHL) of a vascular cause is mostly associated with cerebellar infarction in the territory of the anterior inferior cerebellar artery (AICA), but PICA territory cerebellar infarction rarely causes AHL. To date, at least eight subgroups of AICA territory infarction have been identified according to the pattern of neurotological presentations, among which the most common pattern of audiovestibular dysfunction is the combined loss of auditory and vestibular functions. Sometimes acute isolated audiovestibular loss can be the initial symptom of impending posterior circulation ischemic stroke (particularly within the territory of the AICA). Audiovestibular loss from cerebellar infarction has a good long-term outcome than previously thought. Approximately half of patients with superior cerebellar artery territory (SCA) cerebellar infarction experienced true vertigo, suggesting that the vertigo and nystagmus in the SCA territory cerebellar infarctions are more common than previously thought. In this article, recent findings on clinical features of vertigo and hearing loss from cerebellar ischemic stroke syndrome are summarized.

Vestibular evoked myogenic potentials and video head impulse test in patients with vertigo, dizziness and imbalance

The aim of this study was to compare vestibular evoked myogenic potentials (VEMP) and video head impulse test (vHIT) results in patients presenting with vertigo and dizziness. We retrospectively analyzed data of all patients with the chief complaint of vertigo, dizziness, or imbalance that underwent VEMP and vHIT from January 2015 to January 2016. A total of 117 patients (73 females, mean age 53.92±16.76) fulfilled inclusion criteria: group 1 included patients with the final diagnosis of vestibular neuritis (VN) (N=31 (16 right and 15 left VN)), group 2 included patients with the final diagnosis of vertigo of central origin (N=23) and group 3 included patients with the final diagnosis of unspecified dizziness (N=63). There was significant correlation between oVEMP asymmetry and asymmetry of the lateral canals 60ms gains on vHIT (r=0.225, p=0.026). Significant correlation between oVEMP and vHIT asymmetry was present in VN patients (r=0.749, p<0.001), while no correlation was found in the groups 2 and 3. oVEMP and vHIT lateral canals asymmetries were significantly greater in patients with vestibular neuritis. Furthermore, positive correlations of oVEMP amplitudes with 60ms gain of the lateral semicircular canal and slope of the anterior semicircular canal on vHIT, and cVEMP with slope of the posterior semicircular canal on the vHIT were found. These changes were significantly more pronounced in patients with vestibular neuritis. In conclusion, VEMPs and vHIT data should be used complementarily; asymmetry on both tests strongly supports peripheral vestibular system involvement.

Recent Advances in Understanding Audiovestibular Loss of a Vascular Cause

Acute audiovestibular loss is characterized by abrupt onset of prolonged (lasting days) vertigo and hearing loss. Acute ischemic stroke in the distribution of the anterior inferior cerebellar artery (AICA) is known to be the leading cause of acute audiovestibular loss. So far, eight subgroups of AICA territory infarction have been identified according to the patterns of audiovestibular dysfunctions, among which the most common pattern is the combined loss of auditory and vestibular functions. Unlike inner ear dysfunction of a viral cause, which can commonly present as an isolated vestibular (i.e., vestibular neuritis) or cochlear loss (i.e., sudden deafness), labyrinthine dysfunction of a vascular cause rarely results in isolated loss of vestibular or auditory function. As audiovestibular loss may precede the central symptoms or signs of an ischemic stroke in the posterior circulation, early diagnosis and proper management of audiovestiubular loss may provide a window to prevent the progression of infarction to larger areas of the posterior circulation. A clinician should consider the possibility that acute audiovestibular loss may herald impending AICA territory infarction, especially when patients have basilar artery occlusive disease close to the origin of the AICA on brain MRA. This review aims to highlight the recent advances in understanding audiovestibular loss of a vascular cause and to address its clinical significance.

Ischemic syndromes causing dizziness and vertigo

Dizziness/vertigo and imbalance are the most common symptoms of vertebrobasilar ischemia. Even though dizziness/vertigo usually accompanies other neurologic symptoms and signs in cerebrovascular disorders, a diagnosis of isolated vascular vertigo is increasing markedly by virtue of recent developments in clinical neurotology and neuroimaging. It is important to differentiate isolated vertigo of a vascular cause from more benign disorders involving the inner ear, since therapeutic strategies and prognosis differ between these two conditions. Over the last decade, we have achieved a marked development in the understanding and diagnosis of vascular dizziness/vertigo. Introduction of diffusion-weighted magnetic resonance imaging (MRI) has greatly enhanced detection of infarctions in patients with vascular dizziness/vertigo, especially in the posterior-circulation territories. However, well-organized bedside neurotologic evaluation is even more sensitive than MRI in detecting acute infarction as a cause of spontaneous prolonged vertigo. Furthermore, detailed evaluation of strategic infarctions has elucidated the function of various vestibular structures of the brainstem and cerebellum. In contrast, diagnosis of isolated labyrinthine infarction still remains a challenge. This diagnostic difficulty also applies to isolated transient dizziness/vertigo of vascular origin. Regarding the common nonlacunar mechanisms in the acute vestibular syndrome from small infarctions, individual strategies may be indicated to prevent recurrences of stroke in patients with vascular vertigo.

Vestibular-evoked myogenic potentials

The vestibular-evoked myogenic potential (VEMP) is a short-latency potential evoked through activation of vestibular receptors using sound or vibration. It is generated by modulated electromyographic signals either from the sternocleidomastoid muscle for the cervical VEMP (cVEMP) or the inferior oblique muscle for the ocular VEMP (oVEMP). These reflexes appear to originate from the otolith organs and thus complement existing methods of vestibular assessment, which are mainly based upon canal function. This review considers the basis, methodology, and current applications of the cVEMP and oVEMP in the assessment and diagnosis of vestibular disorders, both peripheral and central.

Vestibular evoked myogenic potentials (VEMPs) in central neurological disorders

Several types of acoustic stimulation (i.e. tone bursts or clicks), bone-conducted vibration, forehead taps, and galvanic stimulation elicit myogenic potentials. These can be recorded in cervical and ocular muscles, the so called vestibular evoked myogenic potentials (VEMPs). The cervical VEMP (cVEMP) resembles the vestibulo-collic reflex and the responses can be recorded from the ipsilateral sternocleidomastoid muscle. The ocular VEMP resembles the vestibulo-ocular reflex and can be recorded from extra-ocular muscles by a surface electrode beneath the contralateral infraorbital margin. Initially, the literature concerning VEMPs was limited to peripheral vestibular disorders, however, the field of VEMP testing is rapidly expanding, with an increasing focus on central neurological disorders. The current literature concerning VEMP abnormalities in central neurological disorders is critically reviewed, especially regarding the methodological aspects in relation to quality as well as the clinical interpretation of the VEMP results. Suggestions for further research are proposed as well as some clinically useful indications.

[Application of the new diagnostic tests for vertigo. Differentiated analysis of vestibular function]

Due to the development of new methods such as the vestibular evoked myogenic potential and the video head impulse tests, clinical vestibular diagnostic procedures are currently in an era of change. The spectrum of available techniques renders a specific, quantitative and objective analysis of vestibular reflexes possible for the first time. Moreover, a combination of different methods permits the assessment of different functional areas of the vestibular receptor. In addition to a topological diagnosis, the concept of a differentiated analysis of vestibular receptor function includes evaluation of frequency-specific functional areas (dynamic frequency analysis) and monitoring of temporal changes (time-dependent diagnostics). Consequently, the overall outcome of physiological tests can be viewed from a new perspective. This enables a comprehensive assessment of vestibulopathies in clinical practice and furthers the understanding of these disorders.

Vertigo in brainstem and cerebellar strokes

PURPOSE OF REVIEW

The aim of this study is to review the recent findings on the prevalence, clinical features, and diagnosis of vertigo from brainstem and cerebellar strokes.

RECENT FINDINGS

Patients with isolated vertigo are at higher risk for stroke than the general population. Strokes involving the brainstem and cerebellum may manifest as acute vestibular syndrome, and acute isolated audiovestibular loss may herald impending infarction in the territory of the anterior inferior cerebellar artery. Appropriate bedside evaluation is superior to MRI for detecting central vestibular syndromes. Recording of vestibular-evoked myogenic potentials is useful for evaluation of the central otolithic pathways in brainstem and cerebellar strokes.

SUMMARY

Accurate identification of isolated vascular vertigo is very important since misdiagnosis of acute stroke may result in significant morbidity and mortality, whereas overdiagnosis of vascular vertigo would lead to unnecessary costly work-ups and medication.

Audiovestibular loss in anterior inferior cerebellar artery territory infarction: a window to early detection?

Acute audiovestibular loss is a common neurotological condition that is characterized by sudden onset of severe prolonged (lasting days) vertigo and hearing loss and is diagnosed by the presence of canal paresis to caloric stimulation and sensorineural hearing loss on pure tone audiogram. Before 2000, papers on anterior inferior cerebellar artery (AICA) territory infarction focused mostly on associated brainstem and cerebellar findings, without a detailed description of neurotological findings. Since 2000, several reports have demonstrated that acute audiovestibular loss is an important sign for the diagnosis of AICA territory infarction. To date, at least eight subgroups of AICA infarction have been identified according to the pattern of neurotological presentations, among which the most common pattern of audiovestibular dysfunction is the combined loss of auditory and vestibular functions. Because audiovestibular loss may occur in isolation before ponto-cerebellar infarction involving AICA distribution, audiovestibular loss may serve as a window to prevent the progression of acute audiovestibular loss into more widespread areas of infarction in posterior circulation (mainly in the AICA territory). Clinician should keep in mind that acute audiovestibular loss may herald impending AICA territory infarction, especially when patients had basilar artery occlusive disease presumably close to the origin of the AICA on brain MRA, even if other central signs are absent and MRI does not demonstrate acute infarction.