Cochlear Implants and Vestibular Screening
The Study
Vestibular dysfunction is one of the many risks of placing a cochlear implant (CI). However, the use of the physical exam to screen CI candidates for vestibular dysfunction is not studied enough. The study’s goal is to explore the preoperative role of the clinical head impulse test (cHIT) in subjects undergoing CI surgery evaluation.
Cochlear implants (CIs)
Cochlear implants (CIs) are biomedical devices that partially restore sound perception to those with hearing loss. Although they are considered to be generally safe, there are also known possible surgical side effects. For instance, iatrogenic damage to the vestibular system is a known risk of CI surgery. Unilateral vestibular defects can cause vertigo, and cognitive impairment, and increase the risk of falls. Due to vestibular redundancy and central compensatory mechanisms, most patients are able to functionally recover from unilateral vestibular loss. This also proves to be more consequential among elderly adults, who comprise a large portion of CI candidates.
The clinical head impulse test
The clinical head impulse test (cHIT) is a quick physical exam maneuver that is used as the standard VOR function test in the outpatient setting. Much of the existing literature describes cHIT and vestibular testing with respect to comparing pre-and post-CI differences but does not directly evaluate the utility of performing cHIT among cochlear implant candidates for the purposes of clinical decision-making. Despite the potential for iatrogenic vestibular hypofunction, cHIT is not a routine part of the pre-CI physical examination at many medical centers.
Study Design
The study includes a retrospective review of 64 adult cochlear implant candidate cases between 2017 and 2020 at a tertiary health care center. This study was approved by the Institutional Review Board at the University of California, San Francisco.
All patients underwent audiometric testing and evaluation by the senior author. Patients with an abnormal catch-up saccade contralateral to their worse hearing ear during cHIT were referred for formal vestibular testing. Outcomes included clinical and formal vestibular results, operated ear with regard to audiometric and vestibular results, and postoperative vertigo.
The researchers conducted a retrospective cohort study involving any patient who presented for evaluation of CI candidacy between 2017 and 2020 by the senior author. Patients were included for analysis if they were 18 years of age or older and were evaluated by the senior author for CI candidacy.
The exclusion criteria consisted of any CI candidate without a preoperative cHIT or oculomotor abnormalities on the exam; no patients were excluded from the analysis. A total of 64 CI candidacy cases were identified. The clinical records, audiograms, and available vestibular testing results were reviewed to identify demographic, otologic, vestibular, and clinicopathologic information. All CI candidates underwent a standardized algorithm for assessment and evaluation of vestibular function during their initial clinical visit.
The cHIT is a quick, easily administered, bedside test that assesses the VOR to assist clinicians in identifying unilateral or bilateral vestibulopathy. A patient with unilateral peripheral vestibular injury will reveal an abnormal catch-up saccade when the head is thrust towards the affected side. Patients with bilateral vestibular dysfunction will exhibit abnormal fixation saccades with head thrusts to either side.
During cochlear implant surgery, electrode insertion into the cochlea has the potential to damage adjacent vestibular organs through trauma, infection, or vascular damage. The risks of bilateral vestibular loss may be mitigated by avoiding implantation of the only balancing ear when the audiometric status is equal between the two ears; however, cHIT is not a standard aspect of the physical exam for CI candidacy.
Results
Among all CI candidates, 44% (n = 28) reported preoperative disequilibrium symptoms. Overall, 62% (n = 40) of the cHITs were normal, 33% (n = 21) were abnormal, and 5% (n = 3) were inconclusive. There was one patient who presented with a false positive cHIT. Among the patients who endorsed disequilibrium, 43% had a positive preoperative cHIT. Fourteen percent of the subjects (n = 9) without disequilibrium had an abnormal cHIT. In this cohort, bilateral vestibular impairment (71%) was more common than unilateral vestibular impairment (29%). In 3% of the cases (n = 2), surgical management was revisited or altered due to cHIT findings.
The study found that there is a high prevalence of vestibular hypofunction in the cochlear implant candidate patient population. Vestibular loss is often ipsilateral to the audiometrically worse hearing ear or present in both ears. Self-reported assessments of vestibular function are often not congruent with clinical head impulse test results. Precochlear implantation vestibular screening may help inform which side of implantation may preserve vestibular function if audiology and surgical considerations are held equal.
The results demonstrate a high prevalence (44%) of self-reported preoperative disequilibrium symptoms within the CI candidacy population. Among those who endorsed vertigo, dizziness, or imbalance, only 43% had a positive cHIT test on the preoperative exam. Interestingly, we found that 14% of the CI candidates denied any vestibular issues but had an abnormal cHIT result on the exam. 23% of the patients that reported disequilibrium had a normal cHIT.
The researchers found a slightly higher prevalence of vestibulopathy among our patient population than another recently published retrospective study involving 335 CI candidates.17 In our study, 33% of the patients (n = 21) had an abnormal cHIT whereas West et al.17 reported 25.7%. Fifteen patients had bilateral vestibular impairment (71%) and six patients had unilateral vestibular impairment (29%).
Among those with unilateral vestibular impairment, 83% (n = 5) of the time, it was ipsilateral to the audiometrically worse ear. Intuitively this makes sense since hearing and vestibular function are often comorbid. This may also explain why new-onset bilateral vestibulopathy after CI surgery seems to be rare despite the lack of preoperative vestibular screening. Audiometric function often correlates with worse vestibular function, so even in the absence of testing, one is likely to implant the worse vestibular ear. There was only one case where an abnormal cHIT result was contralateral to the audiometrically worse ear. There was also one other case where asymmetric vestibular dysfunction between the two ears influenced surgical decision-making.
There is a high prevalence of vestibular hypofunction in the CI candidate population. Self-reported assessments of vestibular function are often not congruent with cHIT results. Clinicians should consider incorporating cHITs as part of the preoperative physical exam to potentially avoid bilateral vestibular dysfunction in a minority of patients.
Oncology Related Tools
Other
Latest Research
