The Vestibular Implant: Quo Vadis?

Objective: To assess the progress of the development of the vestibular implant (VI) and its feasibility short-term. Data sources: A search was performed in Pubmed, Medline, and Embase. Key words used were “vestibular prosth*” and “VI.” The only search limit was language: English or Dutch. Additional sources were medical books, conference lectures and our personal experience with per-operative vestibular stimulation in patients selected for cochlear implantation. Study selection: All studies about the VI and related topics were included and evaluated by two reviewers. No study was excluded since every study investigated different aspects of the VI. Data extraction and synthesis: Data was extracted by the first author from selected reports, supplemented by additional information, medical books conference lectures. Since each study had its own point of interest with its own outcomes, it was not possible to compare data of different studies. Conclusion: To use a basic VI in humans seems feasible in the very near future. Investigations show that electric stimulation of the canal nerves induces a nystagmus which corresponds to the plane of the canal which is innervated by the stimulated nerve branch. The brain is able to adapt to a higher baseline stimulation, while still reacting on a dynamic component. The best response will be achieved by a combination of the optimal stimulus (stimulus profile, stimulus location, precompensation), complemented by central vestibular adaptation. The degree of response will probably vary between individuals, depending on pathology and their ability to adapt

Bilateral vestibulopathy and age:experimental considerations for testing dynamic visual acuity on a treadmill

Introduction: Bilateral vestibulopathy (BVP) can affect visual acuity in dynamic conditions, like walking. This can be assessed by testing Dynamic Visual Acuity (DVA) on a treadmill at different walking speeds. Apart from BVP, age itself might influence DVA and the ability to complete the test. The objective of this study was to investigate whether DVA tested while walking, and the drop-out rate (the inability to complete all walking speeds of the test) are significantly influenced by age in BVP-patients and healthy subjects. Methods: Forty-four BVP-patients (20 male, mean age 59 years) and 63 healthy subjects (27 male, mean age 46 years) performed the DVA test on a treadmill at 0 (static condition), 2, 4 and 6 km/h (dynamic conditions). The dynamic visual acuity loss was calculated as the difference between visual acuity in the static condition and visual acuity in each walking condition. The dependency of the drop-out rate and dynamic visual acuity loss on BVP and age was investigated at all walking speeds, as well as the dependency of dynamic visual acuity loss on speed. Results: Age and BVP significantly increased the drop-out rate (p ≤ 0.038). A significantly higher dynamic visual acuity loss was found at all speeds in BVP-patients compared to healthy subjects (p < 0.001). Age showed no effect on dynamic visual acuity loss in both groups. In BVP-patients, increasing walking speeds resulted in higher dynamic visual acuity loss (p ≤ 0.036). Conclusion DVA tested while walking on a treadmill, is one of the few “close to reality” functional outcome measures of vestibular function in the vertical plane. It is able to demonstrate significant loss of DVA in bilateral vestibulopathy patients. However, since bilateral vestibulopathy and age significantly increase the drop-out rate at faster walking speeds, it is recommended to use age-matched controls. Furthermore, it could be considered to use an individual “preferred” walking speed and to limit maximum walking speed in older subjects when testing DVA on a treadmill

Construct validity and reliability of the Bilateral Vestibulopathy Questionnaire (BVQ)

BackgroundThe Bilateral Vestibulopathy Questionnaire (BVQ) is a recently developed 54-item Patient Reported Outcome Measure (PROM) that evaluates the clinically important symptoms of bilateral vestibulopathy (BVP) and its impact on daily life. This study aimed to assess the construct validity and reliability of the BVQ in a large BVP cohort.MethodsPatients diagnosed with BVP were asked to complete a set of questionnaires, including the BVQ, the EuroQol-5D-5L, the Health Utilities Index, the Dizziness Handicap Inventory, the Hospital Anxiety and Depression Scale, and the Oscillopsia Severity Questionnaire. The construct validity of the BVQ was evaluated by confirmatory and exploratory factor analyses (CFA and EFA), followed by hypotheses testing and known groups validity. Structural properties were explored for each individual item. Reliability was assessed by testing the internal consistency of the BVQ constructs (Cronbach's alpha) and test–retest reliability [intraclass correlation coefficients (ICCs)].ResultsA total of 148 patients with BVP (50% women, mean age 66 years) completed the set of questionnaires. The CFA did not show a satisfactory model in the original BVQ. However, the EFA showed a four-factor solution with 20 Likert-scale items related to oscillopsia, imbalance, emotion, and cognition. The succeeding CFA provided evidence for construct validity and an acceptable model of fit. Hypothesis testing confirmed that this shortened version validly measures the constructs to be measured. Statistically significant differences in scores between known groups were found, providing further support for good construct validity. The structural properties were acceptable. Cronbach's alpha confirmed good internal consistency for the four constructs, ranging from 0.80 to 0.89. The ICCs of the 20 Likert-scale items and four visual analog scale (VAS) items were interpreted as good (range 0.76–0.93).ConclusionThis study showed evidence of good construct validity of the new shortened version of the BVQ, consisting of four constructs with a total of 20 Likert-scale items and four VAS items. The final 24-item BVQ proved to be a reliable and valid multi-item PROM that captures the clinically important symptoms of BVP and evaluates its impact on daily life. Consequently, the BVQ enables the gathering of high-level evidence of treatment effectiveness in a systematic and quantitative manner

Acute cortical deafness in a child with MELAS syndrome

Auditory impairment in mitochondrial disorders are usually due to peripheral sensorineural dysfunction. Central deafness is only rarely reported. We report here an 11-year-old boy with MELAS syndrome who presented with subacute deafness after waking up from sleep. Peripheral hearing loss was rapidly excluded. A brain MRI documented bilateral stroke-like lesions predominantly affecting the superior temporal lobe, including the primary auditory cortex, confirming the central nature of deafness. Slow recovery was observed in the following weeks. This case serves to illustrate the numerous challenges caused by MELAS and the unusual occurrence of acute cortical deafness, that to our knowledge has not be described so far in a child in this setting

Drafting a Surgical Procedure Using a Computational Anatomy Driven Approach for Precise, Robust, and Safe Vestibular Neuroprosthesis Placement-When One Size Does Not Fit All

OBJECTIVE: To design and evaluate a new vestibular implant and surgical procedure that should reach correct electrode placement in 95% of patients in silico. DESIGN: Computational anatomy driven implant and surgery design study. SETTING: Tertiary referral center. PARTICIPANTS: The population comprised 81 patients that had undergone a CT scan of the Mastoid region in the Maastricht University Medical Center. The population was subdivided in a vestibular implant eligible group (28) and a control group (53) without known vestibular loss. INTERVENTIONS: Canal lengths and relationships between landmarks were calculated for every patient. The relationships in group-anatomy were used to model a fenestration site on all three semicircular canals. Each patient's simulated individual distance from the fenestration site to the ampulla was calculated and compared with the populations average to determine if placement would be successful. MAIN OUTCOME MEASURES: Lengths of the semicircular canals, distances from fenestration site to ampulla (intralabyrinthine electrode length), and rate of successful electrode placement (robustness). RESULTS: The canal lengths for the lateral, posterior, and superior canal were respectively 12.1 mm ± 1.07, 18.8 mm ± 1.62, and 17.5 mm ± 1.23, the distances from electrode fenestration site to the ampulla were respectively 3.73 mm ± 0.53, 9.02 mm ± 0.90, and 5.31 mm ± 0.73 and electrode insertions were successful for each respective semicircular canal in 92.6%, 66.7%, and 86.4% of insertions in silico. The implant electrode was subsequently revised to include two more electrodes per lead, resulting in a robustness of 100%. CONCLUSIONS: The computational anatomy approach can be used to design and test surgical procedures. With small changes in electrode design, the proposed surgical procedure's target robustness was reached

Postural impairments in unilateral and bilateral vestibulopathy

Chronic imbalance is a major complaint of patients suffering from bilateral vestibulopathy (BV) and is often reported by patients with chronic unilateral vestibulopathy (UV), leading to increased risk of falling. We used the Central SensoriMotor Integration (CSMI) test, which evaluates sensory integration, time delay, and motor activation contributions to standing balance control, to determine whether CSMI measures could distinguish between healthy control (HC), UV, and BV subjects and to characterize vestibular, proprioceptive, and visual contributions expressed as sensory weights. We also hypothesized that sensory weight values would be associated with the results of vestibular assessments (vestibulo ocular reflex tests and Dizziness Handicap Inventory scores). Twenty HCs, 15 UVs and 17 BVs performed three CSMI conditions evoking sway in response to pseudorandom (1) surface tilts with eyes open or, (2) surface tilts with eyes closed, and (3) visual surround tilts. Proprioceptive weights were identified in surface tilt conditions and visual weights were identified in the visual tilt condition. BVs relied significantly more on proprioception. There was no overlap in proprioceptive weights between BV and HC subjects and minimal overlap between UV and BV subjects in the eyes-closed surface-tilt condition. Additionally, visual sensory weights were greater in BVs and were similarly able to distinguish BV from HC and UV subjects. We found no significant correlations between sensory weights and the results of vestibular assessments. Sensory weights from CSMI testing could provide a useful measure for diagnosing and for objectively evaluating the effectiveness of rehabilitation efforts and future treatments designed to restore vestibular function such as hair cell regeneration and vestibular implants

Bilateral vestibulopathy: a clinical update and proposed diagnostic algorithm

Bilateral vestibulopathy (BVP) is characterized by its heterogeneous and chronic nature with various clinical presentations and multiple etiologies. This current narrative review reflects on the main insights and developments regarding clinical presentation. In addition, it proposes a new diagnostic algorithm, and describes available and potential future therapeutic modalities

Etiologies and hearing status in bilateral vestibulopathy: a retrospective study of 315 patients

ImportanceThe development of a vestibular implant has reached milestones and seems to be a promising therapeutic tool for bilateral vestibulopathy (BV). Given the former lack of therapeutic options for BV, the disease has received scant attention in the previous research literature. It is therefore of major importance to gain more insight into the underlying pathology of BV. Furthermore, as some research groups specifically use a combined vestibulo-cochlear implant, the size of the group of BV patients with associated hearing loss is of special interest.ObjectivesThe study aimed to determine the definite and probable etiology in bilateral vestibulopathy (BV) patients and to report on their hearing status.DesignThis study involves multicenter retrospective study design.SettingThe research setting is at tertiary referral centers.ParticipantsConsecutive BV patients diagnosed at the Antwerp University Hospital between 2004 and 2018 at the Maastricht University Medical Center between 2002 and 2015 and at the Geneva University Hospital between 2013 and 2018, who met the BV diagnostic criteria of the Bárány Society.Main outcome measuresPrimary interests were the etiology and hearing status of BV patients. Moreover, the data of vestibular tests were examined (caloric irrigation, rotatory chair tests, and video-head impulse test).ResultsThe authors identified 315 BV patients, of whom 56% were male patients. Mean age at diagnosis was 58.6 ± 15.1 (range 7–91) years. The definite cause was determined in 37% of the patients and the probable cause in 26% of the patients. No cause was identified in 37% of BV patients. The largest subgroup included patients with genetic etiology (31%), most frequently COCH mutation. Only 21% of patients (n = 61) had bilateral normal hearing. Almost half of the patients (45%, n = 134) had profound hearing loss in at least one ear.ConclusionBV is a heterogeneous condition, with over a third of cases remaining idiopathic, and nearly three-quarters affected by hearing loss. COCH mutation is the most common non-idiopathic cause of BV in our population. Only 21% of our BV patients presented with bilateral normal hearing

Multidimensional restitution of the vestibular function with a vestibular implant

Bilateral loss of the vestibular (BV) function leads to chronic imbalance and oscillopsia. This condition has a significant negative impact on quality of life, indicating a need to remedy the lack of effective treatment. The concept of the vestibular implant (VI) has emerged, it consists of a modified cochlear implant stimulator with one up to three additional electrodes positioned in contact with the vestibular nerve. An external processor, fed with motion information captured by a head-fixed motion sensor, is connected to the implanted stimulator. Finally motion modulated electrical stimulation is delivered to the vestibular nerve. Up to now, 13 patients with a BV loss have been implanted. We demonstrated that it is possible to significantly improve or in certain cases to normalize the vestibulo-ocular reflex (VOR) gains. We further showed that the vestibulo-collic reflex could be elicited and that controlled postural responses could be obtained. Finally, the dynamic visual acuity (DVA) while walking has been significantly improved, or even normalized, in 6 subjects. This was the first demonstration of a functional rehabilitation. The presented results reflect the potential of the VI towards a clinically useful device. Moreover, by providing selective stimulations of the vestibular system, the VI opens doors to push the vestibular research beyond the traditional boundaries