A Novel Saccadic Strategy Revealed by Suppression Head Impulse Testing of Patients with Bilateral Vestibular Loss

Functional impact of bilateral vestibular loss and the unexplained complaint of oscillopsia

Introduction

The vestibulo-ocular reflex (VOR) stabilizes vision during head movements. VOR disorders lead to symptoms such as imbalance, dizziness, and oscillopsia. Despite similar VOR dysfunction, patients display diverse complaints. This study analyses saccades, balance, and spatial orientation in chronic peripheral and central VOR disorders, specifically examining the impact of oscillopsia.

Methods

Participants involved 15 patients with peripheral bilateral vestibular loss (pBVL), 21 patients with clinically and genetically confirmed Machado-Joseph disease (MJD) who also have bilateral vestibular deficit, and 22 healthy controls. All pBVL and MJD participants were tested at least 9 months after the onset of symptoms and underwent a detailed clinical neuro-otological evaluation at the Dizziness and Eye Movements Clinic of the Meir Medical Center.

Results

Among the 15 patients with pBVL and 21 patients with MJD, only 5 patients with pBVL complained of chronic oscillopsia while none of the patients with MJD reported this complaint. Comparison between groups exhibited significant differences in vestibular, eye movements, balance, and spatial orientation. When comparing oscillopsia with no-oscillopsia subjects, significant differences were found in the dynamic visual acuity test, the saccade latency of eye movements, and the triangle completion test.

Discussion

Even though there is a significant VOR gain impairment in MJD with some subjects having less VOR gain than pBVL with reported oscillopsia, no individuals with MJD reported experiencing oscillopsia. This study further supports that subjects experiencing oscillopsia present a real impairment to stabilize the image on the retina, whereas those without oscillopsia may utilize saccade strategies to cope with it and may also rely on visual information for spatial orientation. Finding objective differences will help to understand the causes of the oscillopsia experience and develop coping strategies to overcome it.

Video Suppression Head Impulses and Head Impulses Paradigms in Patients with Vestibular Neuritis: A Comparative Study

Background: This study aims to explore the clinical relevance of the Suppression Head Impulse Paradigm (SHIMP) to better understand if it represents an additional clinical value compared to the Head Impulse Paradigm (HIMP) in patients with vestibular neuritis (VN) in different stages of the disease. Methods: From January 2020 to June 2022, patients with unilateral VN were found in a database of an ENT vestibular clinic. Clinical presentation, vestibular test outcomes, therapy, and recovery were examined in medical records. Results: A total of 42 patients (16 Females, mean age 51.06 ± 12.96; 26 Male, mean age 62.50 ± 9.82) met the inclusion criteria and were enrolled in the study. The means of the VOR gain for both paradigms were respectively 0.38 ± 0.12 (SHIMP) and 0.46 ± 0.13 (HIMP) at T0 and 0.55 ± 0.20 (SHIMP) and 0.64 ± 0.19 (HIMP) at T1 for the lesional side. For the HIMP, the gain value <0.76 identified the affected side of VN with 100% sensitivity (92−100) and 100% specificity (91−100). For the SHIMP, the gain value <0.66 identified the affected side of VN with 100% sensitivity (92−100) and 100% specificity (91−100) and an AUC of 1.0 (0.96−1.0, p < 0.0001). Conclusion: The SHIMP paradigm has a diagnostic accuracy equal to the classic HIMP paradigm in patients with VN. The assessment of VOR slow phase velocity and vestibulo-saccadic interaction in patients with VN could be easier with the use of the SHIMPs paradigm. SHIMPs paradigm provides helpful information about the evaluation of VOR slow phase velocity and vestibulo-saccadic interaction as new recovery strategies in patients with VN.

The Clinical Use of the Suppression Head Impulse Paradigm in Patients with Vestibulopathy: A Systematic Review

Background: This review aims to explore the potential clinical application of the suppression head impulse paradigm (SHIMP) in patients with unilateral and bilateral vestibulopathy. Methods: An electronic search was conducted by two independent reviewers in the following databases: Embase, MEDLINE (PubMed), and Scopus. The screening of titles, abstracts, and full texts and data extraction were undertaken independently by pairs of reviewers. The included studies were quality appraised using a modified version of the Newcastle–Ottawa Scale. Results: The results were reported following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). Our search yielded 935 unique records, of which 16 remained after screening titles and abstracts. A total of 11 studies were included, covering a total of 418 participants (230 patients and 188 healthy participants). Conclusion: SHIMP could be a useful tool to diagnose a VOR alteration in patients with vestibulopathy in both the acute and chronic phases of vestibulopathy.

Correlation between subjective and objective measures in bilateral vestibulopathy

BACKGROUND

Bilateral vestibulopathy (BVP) is a chronic and potentially very disabling condition. The impact of the vestibular loss on quality of life (QoL) is variable and still up for discussion. However, previous studies have reported that BVP has a negative impact of QoL.

AIMS/OBJECTIVES

The aim of the study was to evaluate the association between vestibulo-ocular reflex (VOR) gain and saccade pattern and patient reported QoL.

MATERIALS AND METHODS

Ten patients fulfilling the Bárány criteria of BVP were included in the study. All patients underwent vestibular evaluation using Head Impulse Paradigm (HIMP) and Suppression Head Impulse Paradigm (SHIMP) and responded to Dizziness Handicap Inventory (DHI). DHI was used as a measurement for QoL.

RESULTS

Linear regression revealed a tendency to a correlation between lateral VOR-gain measured by HIMP or SHIMP and total DHI score. Covert saccades were related to low total DHI scores. No association was found between type of SHIMP saccade and QoL. No significant correlations were found.

CONCLUSION AND SIGNIFICANCE

A tendency was found towards a relationship between lateral VOR-gain by HIMP or SHIMP and total DHI score. The study also indicates that covert saccades are related to low impact on QoL.

Association Analysis of HIMP and SHIMP Quantitative Parameters in Patients With Vestibular Neuritis and Healthy Participants

Background: The Head Impulse Paradigm (HIMP) and Suppression Head Impulse Paradigm (SHIMP) are objective, quantitative methods that directly test the vestibulo-ocular reflex (VOR) and are increasingly becoming a standard in evaluating patients with vestibular disorders. Objective: The main objective was to assess the correlations between HIMP and SHIMP parameters in patients with superior vestibular neuritis (VN) and healthy participants. Additionally, the correlations between the parameters of each method were analyzed. Methods: A retrospective cohort, non-randomized study was designed. HIMP and SHIMP were performed on 40 patients with VN and 20 healthy participants (40 ears). HIMP and SHIMP parameters were measured and calculated. Pearson's or Spearson's correlations were used to establish the associations among them. Results: A strong positive correlation was found between HIMP and SHIMP gain (Pearson's r = 0.957, p = 0.000), while strong negative correlations were detected between HIMP and SHIMP saccade amplitudes (r = -0.637, p = 0.000) and percentages of overt saccades (r = -0.631, p = 0.000). In HIMP, strong and moderate positive correlations were identified between gain and saccade amplitude (R ² = 0.726, p = 0.000) and gain and saccade percentage (R ² = 0.558, p = 0.000), respectively. By contrast, an extremely weak positive correlation was observed between gain and latency (R ² = 0.053, p = 0.040). In SHIMP, strong and moderate positive correlations were found between gain and saccade percentage (R ² = 0.723, p = 0.000) and gain and saccade amplitude (R ² = 0.525, p = 0.000), respectively, but no correlation was detected between gain and latency (R ² = 0.006, p = 0.490). Conclusions: HIMP and SHIMP-related parameters were highly correlated (inter-method). Within each method (intra-method), moderate to strong correlations in VOR assessment were observed. These results further contribute to our understanding of the relationship between HIMP and SHIMP as well as to the diagnosis.

Vestibular contributions to the Romberg test: Testing semicircular canal and otolith function

Normal stance relies on three sensory inputs: vision, proprioception and vestibular function. The Romberg test, trying to stand with feet together and eyes closed, is familiar to every medical student as a test of distal proprioceptive impairment. It remains the best known of Romberg's many remarkable contributions to clinical neurology. In Romberg's time almost nothing was known about the function of the vestibular system. We now know that standing with the eyes closed on a compliant rather than a firm surface is more a test of vestibular than proprioceptive function. Peripheral vestibular function tests in clinical use today all rely on measurements of oligosynaptic brainstem reflexes. Short-latency eye rotations in response to rapid, brief head rotations (head impulses) give an accurate, robust and reproducible measure of the function of any and each of the six semicircular canals. Short-latency evoked potentials from sternomastoid and inferior oblique muscles in response to loud clicks or skull taps (vestibular evoked myogenic potentials) give an accurate and reproducible measure of the function of each and any of the four otolith organs. In the present paper, we briefly review what is now known about the anatomy and physiology of the peripheral receptors and brainstem pathways mediating these reflexes and examine how this knowledge can help interpret the Romberg test.

Suppression head impulse test paradigm (SHIMP) characteristics in people with Parkinson's disease compared to healthy controls

The suppression head impulse test paradigm (SHIMP) is a newly described indicator of vestibular function which yields two measures: vestibulo-ocular reflex (VOR) gain and a saccadic response. It is an alternative and complementary test to the head impulse test paradigm (HIMP). Parkinson's disease (PD) has known saccadic and central vestibular pathway dysfunction. This paper is the first description of SHIMP VOR gain and saccade characteristic in this population. This prospective observational study measured the SHIMP VOR gain and saccade characteristics in 39 participants with idiopathic PD and compared this to 40 healthy controls (HC). The effect of group, demographic variables and SHIMP characteristics were evaluated. SHIMP VOR gains were not significantly different between groups (p = 0.10). Compared to HC, the PD group mean SHIMP peak saccade velocity was significantly reduced by an average of 77.07°/sec (p < 0.001), and SHIMP saccade response latency was longer, with an average delay of 23.5 ms (p = 0.003). SHIMP saccade peak velocity was also associated with both head impulse velocity (p = 0.002) and SHIMP VOR gain (p = 0.004) variables, but there was no significant influence of these variables when SHIMP saccade peak velocity was considered as a predictor of PD (p = 0.52-0.91). VOR gains were unaffected by PD. PD-specific saccadic dysfunction, namely reduced peak saccade velocities and prolonged response latencies, were observed in the SHIMP-induced saccade responses. VOR gain using slow phase eye velocity is preferred as the indicator of vestibular function in the SHIMPs paradigm as non-vestibular factors affected saccade peak velocity.

Diagnosing vestibular hypofunction: an update

Unilateral or bilateral vestibular hypofunction presents most commonly with symptoms of dizziness or postural imbalance and affects a large population. However, it is often missed because no quantitative testing of vestibular function is performed, or misdiagnosed due to a lack of standardization of vestibular testing. Therefore, this article reviews the current status of the most frequently used vestibular tests for canal and otolith function. This information can also be used to reach a consensus about the systematic diagnosis of vestibular hypofunction.

Suppression Head Impulse Paradigm (SHIMP) in evaluating the vestibulo-saccadic interaction in patients with vestibular neuritis

PURPOSE

Evaluate the potential clinical application of the Suppression Head Impulse Paradigm (SHIMP) in evaluating the vestibulo-saccadic interaction in patients with vestibular neuritis (VN).

METHODS

A retrospective study was performed. Fifteen patients diagnosed with unilateral VN were identified from a database of ENT vestibular clinic from January 2011 to February 2020. Medical records were reviewed to determine clinical presentation, vestibular testing results, treatment, and recovery.

RESULTS

Fifteen patients (7 left ear, 8 right ear, mean age 58.73 ± 10.73, six female) met the inclusion criteria and were enrolled in the study. Significant differences were found in the within-subjects analysis at T1 in DHI score (p = 0.001), VOR gain (p < 0.005), and in the percentages of impulses containing a SHIMPs saccade when the head is passively turned toward the affected side (p = 0.001).

CONCLUSIONS

SHIMPs paradigm provides useful information about the value of vestibulo-saccadic interaction as new recovery strategies in patients with VN.

Motor style at rest and during locomotion in human

Humans exhibit various motor styles that reflect their intra- and interindividual variability when implementing sensorimotor transformations. This opens important questions, such as, At what point should they be readjusted to maintain optimal motor control? Do changes in motor style reveal the onset of a pathological process and can these changes help rehabilitation and recovery? To further investigate the concept of motor style, tests were carried out to quantify posture at rest and motor control in 18 healthy subjects under four conditions: walking at three velocities (comfortable walking, walking at 4 km/h, and race walking) and running at maximum velocity. The results suggest that motor control can be conveniently decomposed into a static component (a stable configuration of the head and column with respect to the gravitational vertical) and dynamic components (head, trunk, and limb movements) in humans, as in quadrupeds, and both at rest and during locomotion. These skeletal configurations provide static markers to quantify the motor style of individuals because they exhibit large variability among subjects. Also, using four measurements (jerk, root mean square, sample entropy, and the two-thirds power law), it was shown that the dynamics were variable at both intra- and interindividual levels during locomotion. Variability increased following a head-to -toe gradient. These findings led us to select dynamic markers that could define, together with static markers, the motor style of a subject. Finally, our results support the view that postural and motor control are subserved by different neuronal networks in frontal, sagittal, and transversal planes.NEW & NOTEWORTHY During human locomotion, motor control can be conveniently decomposed into a static and dynamic components. Variable dynamics were observed at both the intra- and interindividual levels during locomotion. Variability increased following a head-to-toe gradient. Finally, our results support the view that postural and motor control are subserved by different neuronal networks in the frontal, sagittal, and transversal planes.

A review on screening tests for vestibular disorders

Although many studies have reported on tests of the vestibular system a valid and reliable, evidence-based screening battery for easy clinical use remains elusive. Many screening tests attempt to assess the vestibulo-ocular reflex. Therefore, head shaking, the Dix-Hallpike maneuver, the supine roll test, and head impulse tests are discussed. Other tests address the spatial orientation functions of the vestibular system, such as the Bucket Test and the Fukuda Stepping test. Still, other tests are based on the known correlates with balance skills, both static and dynamic, such as tandem walking and the modern variation of the Romberg test, the modified Clinical Test of Sensory Interaction and Balance. This review provides a critical overview of the literature on some of these tests and their value for clinical use and in epidemiological studies.

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.

Laboratory examinations for the vestibular system

PURPOSE OF REVIEW

In the last decades, researchers suggested that clinical assessment of labyrinthine function in detail became easy thanks to video head impulse tests (VHITs), vestibular evoked myogenic potential test (VEMP) and video-oculography (VOG). It has been argued that they can replace electronystagmography, the caloric and rotatory chair tests. This review addresses the latest evaluations of these tests and the opportunities they offer, but also the limitations in clinical practice.

RECENT FINDINGS

The VHIT and suppression head impulse test (SHIMP) are under ideal circumstances able to accurately identify deficits of the VOR in 3D. However, in a relevant part of the patient population, pupil tracking is inaccurate, video-goggles slip and VOR quantification is problematic. The dissociation between the VHIT and caloric test suggests that these tests are complementary. A new 3D-VOG technique claims to quantify eye torsion better than before, opening multiple diagnostic possibilities. VEMPs remain difficult to standardize. Variability in normal cervical vestibular-evoked myogenic potential amplitude is large. VEMPs become smaller or absent with age, raising questions of whether there is a lower normal limit at all. Recent research shows that the labyrinth is directly stimulated in the MRI offering new opportunities for diagnostics and research.

SUMMARY

In clinical practice, the VHIT, SHIMP, VEMP and new 3D-VOG techniques improve diagnostic power. Unfortunately, technical issues or variability prevent reliable quantitative evaluation in a part of the regular patient population. The traditional caloric and rotatory chair test can still be considered as valuable complementary tests.

Full Spectrum of Reported Symptoms of Bilateral Vestibulopathy Needs Further Investigation-A Systematic Review

Objective

To systematically review the symptoms reported by patients with bilateral vestibulopathy (BV) in clinical studies and case reports. This would serve as the first step in establishing a validated patient-reported outcome measures (PROM) for BV.

Methods

A search on symptoms reported by patients with BV was performed in PubMed, and all publications covering these symptoms were included. Exclusion criteria comprised reviews and insufficient details about the frequency of occurrence of symptoms.

Results

1,442 articles were retrieved. 88 studies were included (41 clinical studies, 47 case reports). In consensus, 68 descriptions of symptoms were classified into 6 common and generic symptoms. Frequency of symptoms in clinical studies and case reports were reviewed, respectively; imbalance (91 and 86%), chronic dizziness (58 and 62%), oscillopsia (50 and 70%), and recurrent vertigo (33 and 67%). BV could be accompanied by hearing loss (33 and 43%) and tinnitus (15 and 36%). 15 clinical studies and 10 case reports reported symptoms beyond vestibular and hearing deficits such as limited social activities, depression, concentration, and memory impairment and reduced quality of life in general.

Conclusion

The literature on BV symptomatology mainly focuses on classic symptoms such as imbalance and oscillopsia, while only few report additional symptoms such as cognitive memory impairment and performing dual tasks. In fact, none of the reviewed clinical studies and case reports provided a comprehensive overview of BV symptoms. To develop a validated PROM, qualitative research using semi-structured and unstructured interviews is needed to explore the full spectrum of BV symptoms.

Cognitive Rehabilitation in Bilateral Vestibular Patients: A Computational Perspective

There is evidence that vestibular sensory processing affects, and is affected by, higher cognitive processes. This is highly relevant from a clinical perspective, where there is evidence for cognitive impairments in patients with peripheral vestibular deficits. The vestibular system performs complex probabilistic computations, and we claim that understanding these is important for investigating interactions between vestibular processing and cognition. Furthermore, this will aid our understanding of patients’ self-motion perception and will provide useful information for clinical interventions. We propose that cognitive training is a promising way to alleviate the debilitating symptoms of patients with complete bilateral vestibular loss (BVP), who often fail to show improvement when relying solely on conventional treatment methods. We present a probabilistic model capable of processing vestibular sensory data during both passive and active self-motion. Crucially, in our model, knowledge from multiple sources, including higher-level cognition, can be used to predict head motion. This is the entry point for cognitive interventions. Despite the loss of sensory input, the processing circuitry in BVP patients is still intact, and they can still perceive self-motion when the movement is self-generated. We provide computer simulations illustrating self-motion perception of BVP patients. Cognitive training may lead to more accurate and confident predictions, which result in decreased weighting of sensory input, and thus improved self-motion perception. Using our model, we show the possible impact of cognitive interventions to help vestibular rehabilitation in patients with BVP.

A Tool to Quantify the Functional Impact of Oscillopsia

Background

Individuals with bilateral vestibular hypofunction (BVH) often report symptoms of oscillopsia during walking. Existing assessments of oscillopsia are limited to descriptions of severity and symptom frequency, neither of which provides a description of functional limitations attributed to oscillopsia. A novel questionnaire, the Oscillopsia Functional Impact scale (OFI) was developed to describe the impact of oscillopsia on daily life activities. Questions on the OFI ask how often individuals are able to execute specific activities considered to depend on gaze stability in an effort to link functional mobility impairments to oscillopsia for individuals with vestibular loss.

Methods

Subjective reports of oscillopsia and balance confidence were recorded for 21 individuals with BVH and 48 healthy controls. Spearman correlation coefficients were calculated to determine the relationship between the OFI and oscillopsia visual analog scale (OS VAS), oscillopsia severity questionnaire (OSQ), and Activities-Specific Balance Confidence scale to demonstrate face validity. Chronbach’s α was calculated to determine internal validity for the items of the OFI. A one-way MANOVA was conducted with planned post hoc paired t-tests for group differences on all oscillopsia questionnaires using a corrected α = 0.0125.

Results

The OFI was highly correlated with measures of oscillopsia severity (OS VAS; r = 0.69, p < 0.001) and frequency (OSQ; r = 0.84, p < 0.001) and also with the Activities-Specific Balance Confidence scale (r = −0.84, p < 0.001). Cronbach’s α for the OFI was 0.97. Individuals with BVH scored worse on all measures of oscillopsia and balance confidence compared to healthy individuals (p’s < 0.001).

Conclusion

The OFI appears to capture the construct of oscillopsia in the context of functional mobility. Combining with oscillopsia metrics that quantify severity and frequency allows for a more complete characterization of the impact of oscillopsia on an individual’s daily behavior. The OFI discriminated individuals with BVH from healthy individuals.

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.