Vestibular Restoration and Adaptation in Vestibular Neuritis and Ramsay Hunt Syndrome With Vertigo

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 Nucleus Involvement in Patients With Acute Vertigo Due to Herpes Zoster Oticus or Vestibular Neuritis

OBJECTIVES

Herpes zoster oticus (HZO) typically provokes vestibular symptoms and is traditionally viewed as a cranial nerve equivalent of shingles, but in contrast to vestibular neuritis (VN), it is unclear whether the pathology of HZO is limited to the vestibular nerve (neuritis) or can also involve the brainstem (nucleitis).

METHODS

We retrospectively compared brain MRIs of patients with HZO with those of patients with VN to study radiologic changes in the brainstem.

RESULTS

Five of 10 patients with HZO showed signal abnormalities in the vestibular nuclei, which lie in multiple vascular territories, whereas no patients with VN exhibited such findings.

DISCUSSION

HZO may at least in part reflect vestibular nucleitis, as opposed to a pure neuritis.

Cochleo-Vestibular Disorders in Herpes Zoster Oticus: A Literature Review and a Case of Bilateral Vestibular Hypofunction in Unilateral HZO

The varicella-zoster virus (VZV), a member of the Herpesviridae family, causes both the initial varicella infection and subsequent zoster episodes. Disorders of the eighth cranial nerve are common in people with herpes zoster oticus (HZO). We performed a review of the literature on different databases including PubMed and SCOPUS, focusing on cochlear and vestibular symptoms; 38 studies were considered in our review. A high percentage of cases of HZO provokes cochlear and vestibular symptoms, hearing loss and vertigo, whose onset is normally preceded by vesicles on the external ear. It is still under debate if the sites of damage are the inferior/superior vestibular nerves and cochlear nerves or a direct localization of the infection in the inner ear. The involvement of other contiguous cranial nerves has also been reported in a few cases. We report the case of a patient with single-side HZO presenting clinical manifestations of cochleo-vestibular damage without neurological and meningeal signs; after 15 days, the patient developed a new episode of vertigo with clinical findings of acute contralateral vestibular loss. To our knowledge, only three other such cases have been published. An autoimmune etiology may be considered to explain these findings.

Vestibulo-ocular reflex gain improvements at peak head acceleration and velocity following onset of unilateral vestibular neuritis: Insights into neural compensation mechanisms

BACKGROUND AND AIMS

An acute unilateral peripheral vestibular deficit (aUPVD) due to vestibular neuritis causes deficient yaw axis vestibular ocular reflex (VOR) gains. Using video head impulse tests (vHITs), we examined phasic and tonic velocity gains of the VOR over time to determine if these differed at onset and during subsequent improvement.

METHODS

The VOR responses of 61 patients were examined within 5 days of aUPVD onset, and 3 and 7 weeks later using vHIT with mean peak yaw angular velocities of 177°/s (sd 45°/s) and mean peak accelerations of 3660°/s2 (sd 1300°/s2). The phasic velocity or acceleration gain (aG) was computed as the ratio of eye to head velocity around peak head acceleration, and the tonic velocity gain (vG) was calculated as the same ratio around peak head velocity.

RESULTS

aG increased ipsi-deficit from 0.45 at onset to 0.67 at 3 weeks and 7 weeks later, and vG increased ipsi-deficit from 0.29 to 0.51 and 0.53, respectively, yielding a significant time effect (p < 0.001). Deficit side aG was significantly greater (p < 0.001) than vG at all time points. Deficit side gain improvements in aG and vG were similar. Contra-deficit aG increased from 0.86 to 0.95 and 0.94 at 3 weeks and 7 weeks, and vG contra-deficit increased from 0.84, to 0.89 and 0.87, respectively, also yielding a significant time effect (p = 0.004). Contra-deficit aG and vG were normal at 3 weeks. Mean canal paresis values improved from 91% to 67% over the 7 weeks.

CONCLUSIONS

Acceleration and velocity VOR gains on the deficit side are reduced by aUPVD and improve most in the first 3 weeks after aUPVD onset. Deficit side aG is consistently higher than deficit side vG following an aUPVD, suggesting that acceleration rather than velocity sensitive compensatory neural mechanisms are predominant during the compensation process for aUPVD.

Clinical characteristics of patients with dizziness/vertigo showing a dissociation between caloric and video head impulse test results

OBJECTIVE

To explore the clinical characteristics of patients with dizziness/vertigo who showed a dissociation between the results of the caloric test and video head impulse test (vHIT).

METHODS

A total of 327 patients who complained of dizziness/vertigo were continuously included. All patients underwent both the horizontal vHIT (h-vHIT) and caloric tests. Of the 327 patients, 69 patients showed a dissociation between the results of the two tests, 4 patients were excluded because the interval between the two tests exceeded 7 days. Finally, 65 patients were included in the analysis.

RESULTS

Among the 65 patients, 55 (84.6%) patients showed a positive caloric test (+) with a negative h-vHIT (-), and 10 (15.4%) patients showed a negative caloric test (-) with a positive h-vHIT (+). Peripheral and central lesions were identified in 50 (90.9%) and 5 (9.1%) patients, respectively, in the caloric test (+)/h-vHIT (-) group; and central lesions were found in 6 (60%) patients in caloric test (-)/h-vHIT (+) group. The etiologies were unilateral peripheral vestibular dysfunction (n = 25), Meniere's disease (MD, n = 10), sudden hearing loss with vertigo (SHLV, n = 7), benign paroxysmal positional vertigo (n = 5), vestibular neuritis (n = 2), autoimmune inner ear disease (n = 1), vestibular migraine (VM, n = 3), multiple sclerosis (n = 1), and multiple system atrophy (n = 1) in the caloric test (+)/h-vHIT (-) group, which were SHLV (n = 3), MD (n = 1), VM (n = 1), episodic ataxia type 2 (n = 1), cerebellopontine angle tumor (N = 1), Parkinson's disease (n = 1), Persistent postural perceptual dizziness (n = 1), and posterior circulation ischemia (n = 1) in the caloric test (-)/h-vHIT (+) group.

CONCLUSION

Dissociation between the results of caloric test and h-vHIT is not uncommon. A positive caloric test with a negative h-vHIT occurred more frequently, and these patients mostly had peripheral vestibular lesions; while a negative caloric test with a positive h-vHIT was unusual, these patients had both peripheral and central lesions.

Long-Term Evolution of Vestibular Compensation, Postural Control, and Perceived Disability in a Population of Patients with Vestibular Neuritis

Objectives. The aim was to analyze and compare the compensatory process, vestibular dysfunction, postural control, and perceived disability in a population of patients with vestibular neuritis (VN). Material and Methods. This is a prospective and longitudinal study of 67 patients diagnosed with VN. Inclusion criteria were sudden onset of vertigo, unidirectional spontaneous horizontal nystagmus, and impairment in vestibular test. Exclusion criteria were imaging or clinical findings of any neurotologic disorder. All vestibular tests were performed; vHIT, vestibular evoked myogenic potentials (VEMPs), caloric test and computerized dynamic posturography (CDP), dizziness handicap inventory (DHI), and visual analogue scale (VAS) were also performed at every follow up. Results. We observed a correlation between the composite score of CDP and baseline vestibular function elicited either by caloric test, VEMPs, or vHIT. There was a significant correlation between baseline vestibular function and first visit questionnaire scores. The main gain recovery for the horizontal canal was 0.1 ± 0.04 for the first three months. After that, the gain recovery significantly decreased. The presence of covert and overt saccades’, latency and amplitude decreased, respectively, after the 6-month period, when compared to the baseline results. We also observed a decrease in the PR score from 3 months after the vestibular insult until the last follow up. We observed a significant decrease in DHI and VAS from the first visit until the last one. Those patients with an initial HC gain below 0.5 had significantly higher DHI and VAS scores at every follow up. Conclusions. There are different measurements that could become a complete measurement of the state of compensation, postural control, and disability of the patients. There is a time window in which the vestibular restoration could give us clinical insights regarding the management of VN patients.

Clinical value of the video head impulse test in patients with vestibular neuritis: a systematic review

PURPOSE

The aim of this systematic review was to evaluate the clinical application potential of the video head impulse test (vHIT) in diagnosing vestibular neuritis (VN).

METHODS

An electronic search was conducted in the following databases: Embase, MEDLINE, ScienceDirect, Google scholar, and the Cochrane Database of Systematic Reviews. Clinical studies were included in which an evaluation was made using vHIT either alone or in combination with other tests or bedside algorithms. Evaluations that were carried out using unvalidated tools were excluded. Only studies of patients with VN (superior, inferior, or in toto) were included. Screening of titles, abstracts, full texts, and data extraction were undertaken independently by pairs of reviewers. Included studies were quality appraised using a modified version of the Newcastle-Ottawa scale.

RESULTS

Results were reported according to the preferred reporting items for systematic reviews and meta-analyses. Our search yielded 1309 unique records, 21 of which remained after screening titles and abstracts. Sixteen studies were included, i.e., for a total of 933 patients including 474 patients with a diagnosis of VN.

CONCLUSIONS

The diagnostic value of vHIT is high for VN, as it is a high-frequency measurement tool. vHIT is a useful complement or alternative to caloric and rotational tests as an indicator of lesions of vestibular canal functioning, especially at the time of onset. This tool can provide useful clues about the clinical progress of recovery from the lesion through the value of the vestibulo ocular reflex gain and the consequent evolution of the saccade pattern, which allows the patient to stabilize vision on the retina.

The characteristics of vHIT gain and PR score in peripheral vestibular disorders

BACKGROUND

Clinical application of vHIT is limited due to a lack of interpretation of vHIT gain and saccades.

OBJECTIVES

This research focuses on comparing common vertigo diseases on vHIT gain and saccade divergence(PR score).

MATERIAL AND METHODS

We retrospectively reviewed 165 patients who have one definite diagnosis, good data quality, and can be read by MATLAB software. All patients were grouped into unilateral vestibular dysfunction (UVD), Meniere's disease (MD), vestibular migraine (VM), Ramsay Hunt Syndrome (RHS), bilateral vestibular hypofunction (BVH), benign paroxysmal positional vertigo (BPPV), and acoustic neuroma (AN). PR score was calculated by an open-source software HitCal.

RESULTS

The saccade detection rate is higher than the abnormal vHIT gain on UVD, MD, VM, RHS, BVH and BPPV. PR score combined with vHIT gain could separate the affected side in UVD and RHS. In the MD group, both vHIT gain and PR score have inconspicuous performance. We also found that different compensation levels and hearing loss status affect results.

CONCLUSIONS AND SIGNIFICANCE

vHIT gain combined with PR score enables a proper distinction among common vertigo diseases. PR score is more sensitive than the gain value on evaluating the physiological situation, vestibular compensation and disease progression.

[Ramsay Hunt syndrome]

Ramsay Hunt syndrome is a complication of varicella-zoster virus infection, which manifests by geniculate ganglion involvement. Clinical presentation of Ramsay Hunt syndrome includes virus affecting external ear by vesicular rash on the ear, ear pain and peripheral facial nerve paralysis. The review presents an analysis of etiology, clinical picture and diagnosis of the disease. The clinical features of combined cranial nerve involvement, contemporary treatment and prophylaxis options are described. Early diagnosis and medical therapy is a crucial factor for positive prognosis to improve damaged nerves in Ramsay Hunt syndrome.

Spontaneous Recovery of the Vestibulo-Ocular Reflex After Vestibular Neuritis; Long-Term Monitoring With the Video Head Impulse Test in a Single Patient

Vestibular rehabilitation of patients in whom the level of vestibular function is continuously changing requires different strategies than in those where vestibular function rapidly becomes stable: where it recovers or where it does not and compensation is by catch-up saccades. In order to determine which of these situations apply to a particular patient, it is necessary to monitor the vestibulo-ocular reflex (VOR) gains, rather than just make a single measurement at a given time. The video Head Impulse Test (vHIT) is a simple and practical way to monitor precisely the time course and final level of VOR recovery and is useful when a patient has ongoing vestibular symptoms, such as after acute vestibular neuritis. In this study, we try to show the value of ongoing monitoring of vestibular function in a patient recovering from vestibular neuritis. Acute vestibular neuritis can impair function of any single semicircular canal (SCC). The level of impairment of each SCC, initially anywhere between 0 and 100%, can be accurately measured by the vHIT. In superior vestibular neuritis the anterior and lateral SCCs are the most affected. Unlike after surgical unilateral vestibular deafferentation, SCC function as measured by the VOR can recover spontaneously after acute vestibular neuritis. Here we report monitoring the VOR from all 6 SCCs for 500 days after the second attack in a patient with bilateral sequential vestibular neuritis. Spontaneous recovery of the VOR in response to anterior and lateral SCC impulses showed an exponential recovery with a time to reach stable levels being longer than previously considered or reported. VOR gain in response to low-velocity lateral SCC impulses recovered with a time constant of around 100 days and reached a stable level at about 200 days. However, in response to high-velocity lateral SCC and anterior SCC impulses, VOR gain recovered with a time constant of about 150 days and only reached a stable level toward the end of the 500 days monitoring period.

Changes in Vestibulo-Ocular Reflex Gain After Surgical Plugging of Superior Semicircular Canal Dehiscence

Superior semicircular canal dehiscence (SCD), which is characterized by a “third mobile window” in the inner ear, causes various vestibular and auditory symptoms and signs. Surgical plugging of the superior semicircular canal (SC) can eliminate the symptoms associated with increased perilymph mobility due to the presence of the third window. However, the natural course of vestibular function after surgical plugging remains unknown. Therefore, we explored longitudinal vestibular function after surgery in 11 subjects with SCD who underwent SC plugging using the middle cranial fossa approach. Changes in vestibulo-ocular reflex (VOR) gain in all planes were measured over 1 year with the video head impulse test. We also evaluated surgical outcomes, including changes in symptoms, audiometric results, and electrophysiological tests, to assess whether plugging eliminated third mobile window effects. The mean VOR gain for the plugged SC decreased from 0.81 ± 0.05 before surgery to 0.65 ± 0.08 on examinations performed within 1 week after surgery but normalized thereafter. Four of seven subjects who were able to perform both VOR tests before surgery and immediately after surgery had pathologic values (SC VOR gain < 0.70). Conversely, the mean VOR gain in the other canals remained unchanged over 1 year. The majority of symptoms and signs were absent or markedly decreased at the last follow-up evaluation, and no complications associated with the surgery were reported. Surgical plugging significantly attenuated the air-bone gap, in particular at low frequencies, because of increased bone conduction thresholds and deceased air conduction thresholds. Moreover, surgical plugging significantly increased vestibular-evoked myogenic potential thresholds and decreased the ratio of summating potential to action potential in plugged ears. Postoperative heavily T2-weighted images were available for two subjects and showed complete obliteration of the T2-bright signal intensity in the patent SC lumen in preoperative imaging based on filling defect at the site of plugging. Our results suggest that successful plugging of dehiscent SCs is closely associated with a transient, rather than persistent, disturbance of labyrinthine activity exclusively involved in plugged SCs, which may have clinical implications for timely and individualized vestibular rehabilitation.

Manifestaciones clínicas del síndrome de Ramsay-Hunt en una serie de 20 casos

Introducción y objetivo: la experiencia clínica nos ha mostrado las distintas formas de presentación y la variabilidad sintomatológica que puede revelar el síndrome de Ramsay-Hunt o herpes zóster ótico. Las descripciones que ofrece la literatura nos han servido para corroborar los hallazgos de un conjunto de pacientes, cuyas características y evolución hemos ido reuniendo en el tiempo. Dada la importancia del tratamiento precoz, el objetivo de este trabajo ha consistido en realizar una exposición estructurada de este complejo síndrome con sus diversas manifestaciones. Método: estudio retrospectivo. Resultados: 20 pacientes ejemplifican los diferentes aspectos de este proceso. Discusión: se trata de una patología infrecuente, con una tríada sintomática patognomónica que consiste en otalgia, erupción vesicular y parálisis facial. Sin embargo, este síndrome no siempre se expresa de forma completa ni con la aparición de los síntomas en el orden indicado, añadiéndose con frecuencia otros cocleovestibulares. La posibilidad de que la infección se propague de forma centrífuga y centrípeta facilita el que se afecten otros nervios sensitivos y motores, ocasionando una polineuropatía craneal (herpes zóster cefálico) y raquídea o incluso, con mucha menor frecuencia, la aparición de una meningoencefalitis. No conocemos con precisión los mecanismos por los que progresa este proceso ni los factores desencadenantes, aunque en ocasiones les haya predisponentes. Establecer un diagnóstico es fundamental para iniciar el tratamiento, cuya precocidad facilita la resolución del proceso. Conclusiones: siendo la sospecha clínica la principal herramienta de un diagnóstico precoz, nos ha parecido de interés realizar esta revisión, dada la infrecuencia del herpes zóster ótico.

Misperception of the subjective visual vertical in neurological patients with or without stroke: A meta-analysis

BACKGROUND

The interpretation of the verticality of the environment is crucial for a proper body balance. The subjective visual vertical test (SVV) is a widely used method to determine the visual perception of the verticality, whose alteration has been related with poor functional status.

OBJECTIVE

To analyze the visual perception of the verticality in neurological patients in comparison with healthy controls.

METHODS

We searched PubMed, Scopus, and Scielo from the start of the databases until October 2017 and manually searched the reference lists of studies comparing SVV values between neurological patients and controls. Standardized mean difference (SMD) and subgroup analysis were used to analyze differences between neurological patients and healthy subjects and between stroke and non-stroke patients, respectively.

RESULTS

A total of 1,916 subjects from 31 studies were included. Neurological patients misestimate the true vertical in comparison with controls (SMD = 1.05; 95% CI: 0.81, 1.28). The misperception of the verticality was higher in stroke patients (SMD = 1.35; 95% CI: 1.02, 1.68) than in patients with other neurological conditions (SMD = 0.48; 95% CI: 0.29, 0.68).

CONCLUSIONS

Neurological patients showed a misperception of the verticality, estimated using the SVV. The neurological pathology that most alters the SVV is stroke.

Visual Performance and Perception as a Target of Saccadic Strategies in Patients With Unilateral Vestibular Loss

OBJECTIVES

To evaluate the ability of saccadic strategies developed during vestibular compensation to reduce the effect of an impaired vestibulo-ocular reflex (VOR) on a retinal smear and image motion sensation.

DESIGN

Twenty patients with unilateral vestibular loss were examined with a video head impulse test before and after vestibular rehabilitation (VR) with the use of gaze stabilization and refixation saccades training. Head and eye velocity functions were processed to infer the retinal eccentricity, and through its correlation with visual acuity (VA), several measurements are proposed to evaluate the influence of VR on saccades behavior and visual performance. To isolate the effect of saccades on the findings and avoid bias because of gain differences, only patients whose VOR gain values remained unchanged after VR were included.

RESULTS

Improved contribution of covert saccades and reduction of overt saccades latency were measured after VR. We found significant differences when assessing both the interval less than 70% VA (50.25 ms), which is considered the limit of a moderate low vision, and less than 50% VA (39.515 ms), which is the limit for severe low vision. Time to recover a VA of 75% (near normal) was reduced in all the patients (median: 56.472 ms).

CONCLUSION

Despite the absence of VOR gain improvement, patients with unilateral vestibular loss are able to develop saccadic strategies that allow the shortening of the interval of retinal smear and image motion. The proposed measurements might be of use to evaluate VR outcomes and visually induced impairment.

Recovery Pattern of High-Frequency Acceleration Vestibulo-Ocular Reflex in Unilateral Vestibular Neuritis: A Preliminary Study

Objective: To explore the recovery pattern of the high-frequency acceleration vestibulo-ocular reflex (VOR) function in unilateral vestibular neuritis (UVN).

Methods: Forty-seven consecutive patients with UVN were recruited within 10 days of symptom onset for this study. The high-frequency acceleration horizontal VOR function was assessed using the video head impulse test (vHIT). Patients returned for follow-up evaluation at ~6 months after the onset of symptoms. According to the dizziness handicap inventory questionnaire (DHI), the patients were classified into the normal to mild dizziness group (DHI score ≤30) and moderate to severe dizziness group (DHI score >30) at the follow-up. All the obtained horizontal vHIT gains and corrective saccades parameters were analyzed.

Results: vHIT results showed a significantly horizontal VOR gain recovery in UVN patients at the follow-up on the lesion side (p < 0.01). A significantly reduction in the occurrence of corrective saccades (overt and covert) and velocity of corrective saccades (overt and covert) were observed at the follow-up (p < 0.05). At the follow-up, the normal to mild dizziness group (DHI score ≤30) had a significantly higher normal rate of VOR gain, the mean vHIT gains and occurrence of isolated covert saccades (P < 0.05). Furthermore, the occurrence of mixed saccades and the mean velocity of covert saccades were significantly lower in normal to mild dizziness group (P < 0.05).

Conclusion: Apart from the recovery of the VOR gain, recovery pattern of corrective saccades can play a key role in vestibular compensate.

Clinical Validity of Quantified Visually Enhanced Vestibulo-ocular Reflex Test to Detect Horizontal Semicircular Canal Hypofunction

OBJECTIVE

To investigate the clinical validity of the mathematical measured VVOR test results to detect horizontal semicircular canal hypofunction.

STUDY DESIGN

Prospective, nonrandomized, observational study.

SETTING

Tertiary referral center, hospital.

PATIENTS

Consecutive patients on first time visit to otoneurology unit.

INTERVENTION(S)

Diagnostic.

MAIN OUTCOME MEASURE(S)

Values of statistical indicators of clinical validity for VVOR test to detect horizontal canal hypofunction were used considering vHIT horizontal aVOR gain values as gold standard.

RESULTS

Area under curve of ROC curve for quantified VVOR testing was 0.92. Head movement frequency on VVOR test and contralateral VVOR gain were identified as significant influence factors of (unilateral) VVOR gain (p < 0.0001) on statistical linear model.

CONCLUSIONS

According to the obtained results, the quantified VVOR test has excellent clinical validity for detecting angular horizontal VOR hypofunction.

Clinical Characteristics of Dizziness Associated with Acute Peripheral Facial Palsy

Background and Objectives

We aimed to assess the clinical significance of dizziness associated with acute peripheral facial palsy (APFP).

Subjects and Methods

Medical records of patients who visited an otorhinolaryngology clinic at a university hospital and were admitted for treatment of APFP between 2014 and 2016 were thoroughly reviewed.

Results

In total, 15.3% (n=15) of patients had dizziness. Continuous, rotatory dizziness without exacerbating factors was most common and frequently accompanied by nausea/vomiting. Dizziness disappeared within 1 week during the hospitalization period. Patients with Ramsay Hunt syndrome (31.0%) had dizziness more frequently than those with Bell’s palsy (8.7%). In addition, higher hearing thresholds and pain around the ear was reported more often in dizzy patients (p<0.05). Logistic regression analysis revealed that the initial House-Brackmann grade of facial paralysis was solely associated with final recovery, but dizziness was not associated with prognosis.

Conclusions

Patients with APFP may have transient dizziness in the early stage, which may be more frequently accompanied by worse hearing thresholds and/or pain around the ear. However, these symptoms including dizziness seem to be unrelated to final prognosis.

The Role of Predictability in Saccadic Eye Responses in the Suppression Head Impulse Test of Horizontal Semicircular Canal Function

Background

In the suppression head impulse paradigm (SHIMP) vHIT protocol, the participant is instructed to follow with his gaze a mobile target generated by a laser placed on the participant's head. Recent studies have reported that the refixation saccade latencies are in relation with the time evolution of the vestibular dysfunction in both (standard and SHIMP) procedures. We hypothesized that some central mechanisms like head impulse prediction could be one of the causes for the differences in the saccadic eye responses.

Methods

A prospective cohort non-randomized study was designed. For the SHIMP protocol, recorded with the ICS Impulse ver. 4.0^® (Otometrics A/S, Taastrup, Denmark) vHIT device, three different algorithms were performed: "predictable," "less predictable," and "unpredictable" depending on the target's predictability. A mathematical method was developed to analyze the SHIMP responses. The method was implemented as an additional tool to the MATLAB open source script for the extended analysis of the vHIT responses named HITCal.

Results

In cohort 1, 52 participants were included in "predictable" SHIMP protocol. In cohort 2, 60 patients were included for the "less predictable" and 35 patients for the "unpredictable" SHIMP protocol. The participants made more early saccades when instructed to perform the "predictable" paradigm compared with the "less predictable" paradigm (p < 0.001). The less predictable protocol did not reveal any significant difference when compared with the unpredictable protocol (p = 0.189). For the latency of the first saccade, there was statistical difference between the "unpredictable" and "predictable" protocols (p < 0.001) and between the "less predictable" and "predictable" protocols (p < 0.001). Finally, we did not find any relationship between the horizontal vestibulo-ocular reflex (hVOR) gain and the latency of the saccades.

Conclusion

We developed a specific method to analyze and detect early SHIMP saccades. Our findings offer evidence regarding the influence of predictability on the latency of the SHIMP saccadic responses, suggesting that early saccades are probably caused by a conditioned response of the participant. The lack of relationship between the hVOR gain and the latency of the saccades suggests that the predictive behavior that caused the early eye saccades are independent of the vestibular function.