Sharon L. Cushing

Evidence of Vestibular and Balance Dysfunction in Children With Profound Sensorineural Hearing Loss Using Cochlear Implants

Objectives/Hypothesis: Similarities between the peripheral auditory and vestibular systems suggest that children with sensorineural hearing loss (SNHL) may demonstrate vestibular and balance impairments. This hypothesis was studied in 40 children with severe to profound SNHL and unilateral cochlear implants.

A test of static and dynamic balance function in children with cochlear implants: the vestibular olympics.

OBJECTIVES To determine the incidence of static and dynamic balance dysfunction in a group of children with profound sensorineural hearing loss receiving a cochlear implant and to assess the impact of cochlear implant activation on equilibrium. DESIGN Observational cross-sectional study of children with single-sided implants, tested under 2 conditions: (1) implant on and (2) implant off in a random order. SETTING Ambulatory setting within an academic, tertiary care childrens hospital. PARTICIPANTS Forty-one children (ages 4-17 years) with cochlear implants comprised the study group. Fourteen children with normal hearing served as controls. INTERVENTION All participants performed a standardized test of static and dynamic balance function (Bruininks-Oseretsky Test of Motor Proficiency 2 [BOT2], balance subset). Children with implants performed the BOT2 under the 2 randomized conditions. MAIN OUTCOME MEASURES Overall performance on the balance subset of the BOT2 and the influence of implant activation on performance. RESULTS The mean (SD) age-adjusted scale score for our control group was 17 (5) points (95% confidence interval [CI], 14-20), which was not significantly different (P = .15) from the published age-adjusted mean for the BOT2 balance subset (15 [5] points). The group that had undergone implantation, however, performed significantly more poorly (12 [ 6] points; 95% CI, 10-14) than either the control group or the published test mean (P = .004). Children with implants performed better with their implants on than with their implants off (mean [SD] difference, 1.3 [2.7] points; 95% CI, 0.3-2.3; P = .01). CONCLUSIONS Large differences exist in the balance ability of children with sensorineural hearing loss requiring cochlear implantation compared with age-matched controls. Implant activation, however, conferred a slight advantage in accomplishing balance-related tasks. These results substantiate the need to further quantify the baseline vestibular dysfunction of our study population of children with cochlear implants, as well as the impact of implant activation on the input and output of the vestibular system.

Neuromuscular consequences of reflexive covert orienting

Visual stimulus presentation activates the oculomotor network without requiring a gaze shift. Here, we demonstrate that primate neck muscles are recruited during such reflexive covert orienting in a manner that parallels activity recorded from the superior colliculus (SC). Our results indicate the presence of a brainstem circuit whereby reflexive covert orienting is prevented from shifting gaze, but recruits neck muscles, predicting that similarities between SC and neck muscle activity should extend to other cognitive processes that are known to influence SC activity.

Vestibular end-organ dysfunction in children with sensorineural hearing loss and cochlear implants: an expanded cohort and etiologic assessment.

Introduction Similarities between the peripheral auditory and vestibular systems suggest that children with sensorineural hearing loss (SNHL) may demonstrate associated vestibular impairments. The current study examines vestibular function in a previously reported cohort (n = 40) augmented by 113 children with profound SNHL. Methods The current study is prospective and cross-sectional with repeated measures. Horizontal canal function was assessed in response to caloric and rotational stimuli. Saccular function was examined using vestibular evoked myogenic potentials (VEMP). One hundred fifty-three children were tested; 119 had unilateral cochlear implants (CIs) at time of testing, and 34 were evaluated before CI. Results Horizontal semicircular canal function was abnormal in response to caloric stimuli in 50% (69/139), with a proportion (18/69, 26%) reflecting mild to moderate unilateral abnormalities. Severe hypofunction or areflexia occurred in 37% (51/139). Horizontal semicircular canal function in response to rotation was abnormal in 47% (64/139). Bilateral reduction in VOR gain was seen across frequencies in 29% (40/139) and 13% (18/139) demonstrated isolated high-frequency (≥2 Hz) loss. Saccular function was absent bilaterally in 21% (32/135) and unilaterally in 30% (40/135). All children with meningitis (n = 11) and 46% with radiologic cochleovestibular anomalies (n = 31) had horizontal canal dysfunction, whereas 45% and 46%, respectively, displayed saccular dysfunction. Unilateral dysfunction of the horizontal canal or the saccule was equally distributed between the implanted and nonimplanted ear (14:9 and 22:18, respectively), and the differences in proportions were not statistically significant. Conclusion Vestibular end organ dysfunction occurred in half of all children with profound SNHL. Approximately one-third of the subjects displayed severe abnormalities(bilateral and/or severe loss). The likelihood of vestibular end-organ dysfunction is highly dependent on etiology, with meningitis and cochleovestibular anomalies having the highest rates of severe dysfunction.

Vestibular end-organ and balance deficits after meningitis and cochlear implantation in children correlate poorly with functional outcome.

Objective: Assess vestibular and balance function in meningitis-induced profound sensorineural hearing loss (SNHL). Study Design: Prospective cohort study. Setting: Tertiary pediatric referral center. Patients: Nine pediatric participant with profound SNHL after bacterial meningitis with (8) and without (1) unilateral Cochlear implant. Main Outcome Measure(s): Horizontal canal function in response to caloric and high-frequency rotation (0.25-5 Hz). Saccular function assessed by the vestibular evoked myogenic potential. Static and dynamic balance performance on the balance subset of the Bruininsk-Oseretsky Test of Motor Proficiency 2. Labyrinthine ossification on computed tomography preimplant, with follow-up imaging in a subset (n = 7). Results: Horizontal canal function in response to caloric stimulation was abnormal in all children, with 5 of 8 demonstrating bilateral areflexia and 3 of 8 having asymmetric hypofunction with better function on the implanted side. In response to rotation, horizontal canal function was abnormal in all but 1 child (8 of 9). Saccular function, assessed by VEMP, was intact in most of the children (5 of 7). Static and dynamic balance (Bruininsk-Oseretsky Test of Motor Proficiency 2 scores) were significantly poorer in the meningitis group compared with both normal-hearing controls (p < 0.01) and children with SNHL of variable etiology and Cochlear implant (p < 0.01). Labyrinthine ossification was present in all cases, with variable extent, location, and progression. Conclusion: Vestibular function and balance are compromised in children with SNHL after meningitis. Whereas vestibular loss seems well compensated at low frequency through an overreliance on visual inputs, deficits surface during high-frequency rotation, particularly in dark. Saccular function seems less susceptible to damage from meningitis. Extent, location, and progression of ossification were variable. Despite profound dysfunction on objective testing, subjective limitations in functional balance were not reported, demonstrating the significant ability of children to compensate for even the most severe vestibular losses.

High-resolution cone-beam computed tomography: a potential tool to improve atraumatic electrode design and position.

Abstract Conclusions: Flat-panel cone-beam computed tomography (CBCT) is able to assess the trajectory of the implanted cochlear implant (CI) array. This is essential to determine specific effects of electrode design and surgical innovations on outcomes in cochlear implantation. CBCT is a non-invasive approach yielding similar data to histopathological analyses, with encouraging potential for use in surgical, clinical and research settings. Objectives: To examine the fidelity of CBCT imaging and custom 3D visualization in characterizing CI insertion in comparison to gold standard, histopathological examination. Methods: Eleven human temporal bones were implanted with the ‘Straight Research Array’ (SRA). Post-insertion, they were imaged with a prototype mobile C-arm for intraoperative CBCT. Post-acquisition processing of low-dose CBCT images produced high-resolution 3D volumes with sub-millimetre spatial resolution (isotropic 0.2 mm3 voxels). The bones were resin impregnated and sectioned for light microscopic examination. Dimensional electrode characteristics visible in section images were compared with corresponding CBCT images by independent observers. Results: Overall, CBCT demonstrated adequate resolution to detect: 1) scala implanted; 2) kinking; 3) number of intracochlear contacts; 4) appropriate ascension of the array; and overall confirms ideal insertion. CBCT did not demonstrate adequate resolution to detect reversal of electrode contacts or basilar membrane rupture.

Motor output evoked by subsaccadic stimulation of primate frontal eye fields

In addition to its role in shifting the line of sight, the oculomotor system is also involved in the covert orienting of visuospatial attention. Causal evidence supporting this premotor theory of attention, or oculomotor readiness hypothesis, comes from the effect of subsaccadic threshold stimulation of the oculomotor system on behavior and neural activity in the absence of evoked saccades, which parallels the effects of covert attention. Here, by recording neck-muscle activity from monkeys and systematically titrating the level of stimulation current delivered to the frontal eye fields (FEF), we show that such subsaccadic stimulation is not divorced from immediate motor output but instead evokes neck-muscle responses at latencies that approach the minimal conduction time to the motor periphery. On average, neck-muscle thresholds were ∼25% lower than saccade thresholds, and this difference is larger for FEF sites associated with progressively larger saccades. Importantly, we commonly observed lower neck-muscle thresholds even at sites evoking saccades ≤5° in magnitude, although such small saccades are not associated with head motion. Neck-muscle thresholds compare well with the current levels used in previous studies to influence behavior or neural activity through activation of FEF neurons feeding back to extrastriate cortex. Our results complement this previous work by suggesting that the neurobiologic substrate that covertly orients visuospatial attention shares this command with head premotor circuits in the brainstem, culminating with recruitment in the motor periphery.

Incidence and characteristics of facial nerve stimulation in children with cochlear implants.

Objectives: Electrical stimulation from a cochlear implant can spread beyond the auditory nerve. The aims of this study were to accurately measure facial nerve stimulation in pediatric implant users and to determine the characteristics and incidence of this unwanted activity. Part A consisted of a prospective study of a randomized sample of 44 pediatric implant users. Part B consisted of a retrospective analysis of 121 children with previously recorded electrically evoked auditory brainstem responses (EABR).

Low pediatric cochlear implant failure rate: contributing factors in large-volume practice.

OBJECTIVE To evaluate the rate of cochlear implant (CI) failure and CI reimplantation (CIri) in our population of children receiving implants by means of a technique that includes device fixation with suture to cortical bone. DESIGN Retrospective analysis from January 1990 to June 2010. SETTING Tertiary pediatric hospital. PATIENTS A total of 971 devices were provided to 738 children (5575 implant-years). INTERVENTIONS Cochlear implant explants and CIri. MAIN OUTCOME MEASURES Surgical findings at CIri were assessed by device model. The Pediatric Ranked Order Speech Perception score and the Phonetically Balanced Kindergarten score were used to make comparisons of hearing ability before and after CIri. RESULTS Thirty-four patients have undergone CIri in our pediatric center during the past 20 years. Excluding 7 of these patients who received their initial implant at other centers, our rate of CIri was 2.9%. Mean (SD) time to device failure was 61 (43) months. A disproportionately high number of patients (7 of 35 [20%]) requiring CIri had meningitis before implantation. After CIri, children maintained or improved their best speech performance measured before device failure, with only 2 children showing a significant reduction in speech perception after CIri. CONCLUSIONS A very low rate of failure occurs in children who receive CI devices, and several factors may account for this low rate. Children who develop meningitis before CI appear to be at an increased risk of device failure.

Dose-dependent suppression of the electrically elicited stapedius reflex by general anesthetics in children undergoing cochlear implant surgery.

BACKGROUND: Cochlear implants stimulate the auditory nerve to enable hearing. Determining appropriate upper and lower limits of stimulation is essential for successful cochlear implantation. The intraoperative evoked stapedius reflex threshold (ESRT) and evoked compound action potential (ECAP) are commonly used to determine the limits of implant stimulation. In this study, we evaluated the dose-related effects of sevoflurane, desflurane, isoflurane, and propofol on the intraoperative ESRT and ECAP. METHODS: Forty-four children aged 6 mo to 17 yr undergoing cochlear implantation were recruited. Each child was randomly assigned to receive sevoflurane, desflurane, isoflurane, or propofol. Evoked responses were measured by a blinded investigator at end-tidal anesthetic concentrations corresponding to 0, 0.75, and 1.5 age-adjusted minimum alveolar concentration administered in random sequence and at targeted blood concentrations of propofol of 0, 1.5, and 3.0 &mgr;g/mL. Data were analyzed using one-way repeated-measures analysis of variance. P < 0.05 was considered statistically significant. RESULTS: The ESRT increased dose dependently with increasing volatile anesthetic concentration (P < 0.01). The stapedius reflex was completely abolished by volatile anesthesia in more than half of children. Propofol minimally affected the ESRT. In contrast, the ECAP was unaffected by anesthesia. CONCLUSIONS: Volatile anesthetics suppress the stapedius reflex in a dose-dependent manner, suggesting that ESRT measurements acquired during volatile anesthesia will overestimate the maximum comfort level, which may cause discomfort postoperatively and adversely affect the child’s adaptation to the implant. We advise against the use of volatile anesthetics for measurement of the stapedius reflex threshold during cochlear implant surgery.