Ocular vestibular evoked myogenic potentials in response to air-conducted 500 Hz short tones: Effect of stimulation procedure (monaural or binaural), age and gender

Decoding Age-Linked Masseter Vestibular Evoked Myogenic Potential Changes in Healthy, Aging Individuals

PURPOSE

The primary objective of this study was to assess how age influences masseter vestibular evoked myogenic potential (mVEMP) parameters by utilizing 500-Hz tone burst stimuli delivered through air conduction.

METHOD

The study involved 110 participants ranging from 15 to 60 years of age, grouped into five categories, all of whom had no previous issues related to their vestibular system. The participants were exposed to 500-Hz tone burst stimuli at 125 dB SPL through ER-3A inserts. These stimuli were presented to one ear at a time, with alternating polarity. A Tukey's honestly significant difference test was conducted to compare rectified and unrectified amplitude, along with latencies (P11 and N21) and the asymmetric ratio across all age groups. Additionally, a multivariate analysis of variance was performed to assess the impact of sex on the study variables.

RESULTS

All 110 participants (220 ears) in the study provided mVEMP responses, encompassing 100% of the subjects. The results revealed a significant reduction in both amplitude and latency extension for the P11 and N21 peaks. Interestingly, P11 latency was also prolonged in the youngest participants (Group 1), suggesting ongoing maturation of the system even beyond the age of 16 years. Moreover, a significant sex difference was observed in the P11 latencies. However, there were no substantial sex differences (p > .05) in N1 peak latency, peak-to-peak amplitude, rectified amplitude, and asymmetric ratio.

CONCLUSIONS

Changes in structure occur due to degeneration, and the quantity of vestibular sensory hair cells gradually diminishes with age. The rate of decline is faster in semicircular canals compared to end organs, as observed by Merchant et al. (2000). Following a linear degeneration starting at the age of 40 years, a continuous reduction in sensory cells and primary neurons takes place until approximately 40% of vestibular sensory cells are lost by the age of 75 years and insufficient maturation can lead to prolonged peaks and reduced amplitudes compared with those that are considered normal. Therefore, it is crucial to consider the age of the participants when making diagnoses and incorporate relevant correction factors based on age-related reference data.

Effects of aging on ocular vestibular-evoked myogenic potential using ER-3A insert earphone and B81 bone vibrator

Purpose

Aging is a process associated with degeneration and dysfunction of peripheral vestibular system or apparatus. This study aimed to investigate the influence of aging on ocular vestibular-evoked myogenic potential (oVEMP) response rates and recording parameters using the B81 bone vibrator and compare them with air conduction stimuli (ACS) oVEMP response characteristics.

Methods

In 60 healthy participants aged 10–71 years (mean age 39.9; 29 male participants), the oVEMP response was elicited using a B81 bone vibrator and an ER-3A insert earphone. The effects of age and stimulus on oVEMP response rates and recording parameters were evaluated.

Results

Response rates and amplitudes declined with aging using either ACS or bone-conducted vibration (BCV) stimulation, particularly in individuals over 60 years of age, whereas thresholds increased and N1 latencies were prolonged. BCV showed fewer risks of absent oVEMP response than ACS (p = 0.002). BCV acquired higher amplitudes (p < 0.001), lower thresholds, and shorter N1 and P1 latencies (all p < 0.001) than ACS.

Conclusions

The absence of an oVEMP response may be attributed to aging rather than a concurrent vestibular disorder. B81-BCV likely produces higher mechanical drives to the vestibular hair cells at safer and non-traumatic levels compared with ACS and therefore may be more likely to evoke a response in the elderly cohort, whose vestibular function and mechanical sensitivity have declined. Thus, B81-BCV stimulation is more effective and safer to elicit oVEMPs, and it should be recommended when ACS fails in the clinic, particularly in the elderly population.

Vestibular evoked myogenic potentials

Vestibular Evoked Myogenic Potentials (VEMP) are commonly recorded in patients experiencing vertigo or chronic instability. This test evaluates the patient's otolith function and is often combined with both Videonystagmography and Video Head Impulse Test. VEMP is a simple, reproducible test, in the absence of any pre-existing conductive hearing loss. Cervical VEMP explore both saccular function and the inferior vestibular nerve, whereas ocular VEMP assess utricular function and the superior vestibular nerve. In combination with previously described tests, VEMP allows characterization of vertigo and provides support for the diagnosis of superior semicircular canal dehiscence syndrome, Menière's disease, vestibular neuritis, vestibular schwannoma or idiopathic bilateral vestibulopathy. A good knowledge of these electrophysiological tests is essential in order to precisely assess the presence or absence of vestibular function impairment. We describe the test recording technique and the most common pitfalls in interpretation of the results. We then outline the results observed in various diseases impacting vestibular function.

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.

Sexual dimorphism in vestibular function and dysfunction

It has been recognized for some time that females appear to be overrepresented in the incidence of many vestibular disorders, and recent epidemiological studies further support this idea. While it is possible that this is due to a reporting bias, another possibility is that there are actual differences in the incidence of vestibular dysfunction between males and females. If this is true, it could be due to a sexual dimorphism in vestibular function and therefore dysfunction, possibly related to the hormonal differences between females and males, although the higher incidence of vestibular dysfunction in females appears to last long after menopause. Many other neurochemical differences exist between males and females, however, that could be implicated in sexual dimorphism. This review critically explores the possibility of sexual dimorphism in vestibular function and dysfunction, and the implications it may have for the treatment of vestibular disorders.

'Standard' versus 'nose reference' electrode placement for measuring oVEMPs with air-conducted sound: Test-retest reliability and preliminary patient results

OBJECTIVES

This study compared two electrode placements ('standard' versus 'nose reference' placement) for measuring oVEMPs, elicited by air-conducted 500Hz tone bursts. The test-retest reliability of both positions was evaluated and additionally both electrode placements were applied on a group of vestibular patients.

METHODS

Eighteen healthy volunteers (range of 20-25years) participated in the first part and were retested after one week for evaluation of the test-retest reliability. Eleven patients (range of 41-74years) with a variety of vestibular pathologies were tested once.

RESULTS

In the normal group, the nose reference electrode placement resulted in significantly larger peak-to-peak amplitudes (p<0.001), shorter n10 (p=0.001) and p15 (p<0.001) latencies and smaller 95% prediction intervals for the Inter-Ocular Ratio (IOR) ([-68, 68] for the standard position versus [-32, 32] for the nose reference position). Furthermore, an excellent amplitude and IOR test-retest reliability was observed with the nose reference configuration, as shown by the intraclass correlation coefficient (ICC), the coefficient of variation of the method error (CV_ME) and the minimal detectable differences (MDD). In the patient group, the same significant amplitude difference was found. Moreover, three patients presented with absent oVEMPs when recorded with the standard placement, whereas the nose reference placement could evoke a detectable oVEMP response.

CONCLUSIONS

This study demonstrated that a nose reference electrode position results in larger oVEMP amplitudes and achieves a better reliability for the most important clinical parameters (amplitude and IOR). Our patient data substantiate the possible clinical benefit of this position, but further systematic patient verification is required.

SIGNIFICANCE

The nose reference electrode position facilitates the detection of generally very small oVEMP responses and shows a high test-retest reliability, showing promising potential for future use in the vestibular clinic.