Vestibular dysfunction in cochlear implant candidates: Prevalence and outcomes

Stimulation Crosstalk Between Cochlear And Vestibular Spaces During Cochlear Electrical Stimulation

OBJECTIVES

Possible beneficial "crosstalk" during cochlear implant stimulation on otolith end organs has been hypothesized. The aim of this case-control study is to analyze the effect of electrical cochlear stimulation on the vestibule (otolith end-organ), when using a cochleo-vestibular implant, comparing vestibular stimulation (VI) and cochlear stimulation (CI).

METHODS

Four patients with bilateral vestibulopathy were included. A double electrode array research implant was implanted in all cases. Dynamic Gait Index (DGI), VOR gain measured by using vestibular head impulse test (vHIT), acoustic cervical myogenic responses (cVEMP) recordings, and electrical cVEMP were used in all cases. Trans-impedance Matrix (TIM) analysis was used to evaluate the current flow from the cochlea to the vestibule.

RESULTS

While patients did not have any clinical vestibular improvement with the CI stimulation alone, gait metrics of the patients revealed improvement when the vestibular electrode was stimulated. The average improvement in the DGI was 38% when the vestibular implant was activated, returning to the normal range in all cases. Our findings suggest that any current flow from the cochlear space to the otolith organs was insufficient for effective cross-stimulation. The functional results correlated with the data obtained in TIM analysis, confirming that there is no current flow from the cochlea to the vestibule.

CONCLUSION

The only way to produce effective electrical otolith end-organ stimulation, demonstrated with this research implant, is by direct electrical stimulation of the otolith end organs. No effective cross-stimulation was found from cochlear electrode stimulation.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:2349-2355, 2024.

Vestibular Hypofunction Screening in Older Cochlear Implant Candidates

OBJECTIVE

Vestibular loss is associated with increasing age and hearing loss. Cochlear implantation (CI) may be performed in these patients; however, CI can induce vestibular hypofunction (VH) postoperatively. If CI is performed in the "better balancing ear," patients may experience vestibulopathy from new bilateral VH. The objective of this study was to evaluate the rates of VH in older CI candidates, thereby helping to identify patients at increased risk for bilateral VH after CI.

STUDY DESIGN

Retrospective cohort study from 2019 to 2022 of patients age 60 to 80 years old who underwent videonystagmography (VNG).

SETTING

Tertiary care neurotology practice.

METHODS

VNG, including spontaneous nystagmus, cervical vestibular evoked myogenic potential (cVEMP), caloric stimulation, and rotary chair, was reviewed and stratified by CI candidacy. Patients with prior CI or known vestibular diagnosis were excluded.

RESULTS

Thirty-three patients were CI candidates and 184 patients were controls. cVEMP demonstrated a significantly greater rate of unilateral VH in CI candidates (P = .018). Caloric stimulation demonstrated an elevated rate of bilateral VH and presbyvestibulopathy in CI candidates (P = .057 and P = .036, respectively). Rotary chair demonstrated a significantly higher rate of bilateral VH and incomplete vestibular compensation based on reduced gain and gain asymmetry, respectively, in CI candidates (P < .001 and P = .043, respectively). Mean bithermal slow phase velocity sum and rotary chair gain were significantly lower in the CI candidate group (P = .002 and P < .001, respectively). Preoperative identification of VH determined the side of implantation in 4 patients (15%).

CONCLUSION

VH and incomplete vestibular compensation are common and more frequently seen in CI candidates compared to age-matched controls. Vestibular screening can play a role in surgical counseling and planning, and should be considered in older patients undergoing CI.

Balancing Act: A Comprehensive Review of Vestibular Evaluation in Cochlear Implants

Cochlear implantation, a transformative intervention for individuals with profound hearing loss, has evolved significantly over the years. However, its impact on the vestibular system, responsible for balance and spatial orientation, remains a subject of ongoing research and clinical consideration. This narrative review highlights key aspects of vestibular evaluation in patients undergoing cochlear implantation. Preoperative vestibular assessment is crucial to establish baseline vestibular function and identify any pre-existing balance issues. Various tests, including caloric, rotational chair, vestibular-evoked myogenic potential, and video head impulse tests, play a vital role in evaluating vestibular function. The goal is to assess the risk of vestibular disturbances arising from the surgery, guide surgical planning, and detect pre-existing alterations that could be totally or partially compensated. While some patients experience minimal vestibular disruptions, others may encounter transient or persistent balance issues following cochlear implant surgery. Postoperative vestibular testing allows for the early detection of such disturbances, enabling timely interventions like vestibular rehabilitation and evaluating changes produced due to surgical complications or changes in the patient's prior conditions. Challenges in vestibular evaluation include individual variability in patient responses, the proximity of the cochlea to the vestibular system, and the need to tailor testing protocols to individual needs. Further research is essential to refine testing protocols, minimize vestibular disturbances, and improve outcomes for cochlear implant candidates. A multidisciplinary approach involving otolaryngologists, audiologists, and physical therapists is integral to comprehensive patient care in this context. In conclusion, vestibular evaluation in patients undergoing cochlear implantation is critical for optimizing surgical planning, managing postoperative issues, and enhancing the overall quality of life for individuals embarking on the journey of restored hearing.

Mild therapeutic hypothermia protects against inflammatory and proapoptotic processes in the rat model of cochlear implant trauma

OBJECTIVE

Mild therapeutic hypothermia (MTH) has been demonstrated to prevent residual hearing loss from surgical trauma associated with cochlear implant (CI) insertion. Here, we aimed to characterize the mechanisms of MTH-induced hearing preservation in CI in a well-established preclinical rodent model.

APPROACH

Rats were divided into four experimental conditions: MTH-treated and implanted cochleae, cochleae implanted under normothermic conditions, MTH only cochleae and un-operated cochleae (controls). Auditory brainstem responses (ABRs) were recorded at different time points (up to 84 days) to confirm long-term protection and safety of MTH locally applied to the cochlea for 20 min before and after implantation. Transcriptome sequencing profiling was performed on cochleae harvested 24 h post CI and MTH treatment to investigate the potential beneficial effects and underlying active gene expression pathways targeted by the temperature management.

RESULTS

MTH treatment preserved residual hearing up to 3 months following CI when compared to the normothermic CI group. In addition, MTH applied locally to the cochleae using our surgical approach was safe and did not affect hearing in the long-term. Results of RNA sequencing analysis highlight positive modulation of signaling pathways and gene expression associated with an activation of cellular inflammatory and immune responses against the mechanical damage caused by electrode insertion.

SIGNIFICANCE

These data suggest that multiple and possibly independent molecular pathways play a role in the protection of residual hearing provided by MTH against the trauma of cochlear implantation.

Vestibular dysfunction in pediatric patients with cochlear implantation: A systematic review and meta-analysis

Objective

Vestibular dysfunction may delay the achievement of balance and perception milestones in pediatric patients after cochlear implantation (CIM).

Methods

A strategic literature search was done following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We searched the PubMed, Medline, Embase, Web of Science, and Cochrane Library databases from inception to July 2022. Studies were included on the otoliths, semicircular canals, and balance function changes in children after CIM. Two reviewers independently assessed the level of evidence, methodological limitations, risk of bias, and characteristics of the cases. Matched pre- and postoperative vestibular functional test data, including ocular and cervical vestibular-evoked myogenic potential (oVEMP and cVEMP), caloric test, video head impulse test (vHIT), and Bruininks-Oseretsky Test 2 (BOT-2), were used to calculate the relative risk of vestibular disorders. Subgroup analyses were performed according to surgical approach, CIM device status, and etiology.

Results

Twenty studies that met the inclusion criteria were selected for the meta-analysis. We observed significant vestibular dysfunction in pediatric patients with CIM. The results showed a statistically significant increase in abnormal cVEMP response (RR = 2.20, 95% CI = 1.87, 2.58, P < 0.0001), abnormal oVEMP response (RR = 2.10, 95% CI = 1.50, 2.94, P < 0.0001), and abnormal caloric test results (RR = 1.62, 95% CI = 1.20, 2.19, P = 0.0018) after implantation. Statistically significant differences were not found in the vHIT test results of all three semicircular canals before and after the operation (P > 0.05). Regarding static and dynamic balance, we found significantly poorer BOT-2 scores in children with CIM than in the normal group (mean difference = −7.26, 95% CI = −10.82, −3.70, P < 0.0001).

Conclusion

The results showed that vestibular dysfunction might occur after CIM in pediatric patients. Some children experience difficulties with postural control and balance. Our results suggest that a comprehensive evaluation of vestibular function should be performed before and after CIM.