A review of cochlear implantation in mitochondrial sensorineural hearing loss

OBJECTIVE

Mitochondrial sensorineural hearing loss (SNHL) may be nonsyndromic (occurring in isolation), associated with the A1555G mutation in the MTRNR1 gene. Mitochondrial SNHL may also be syndromic, associated with the A3243G point mutation in the MTTL1 gene. In syndromic cases-mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS), maternally inherited diabetes and deafness, Kearns-Sayre syndrome, and chronic progressive external ophthalmoplegia-the SNHL compounds already existing disabilities. The genetic basis for mitochondrial SNHL and postulated sites of pathologic changes are discussed.

DATA SOURCES

Sources used were relevant clinical and basic science publications.

STUDY SELECTION

A search of the entire databases of Medline and Web of Science, using various subject headings and free-text terms, was used to identify patients with mitochondrial disease having cochlear implants.

DATA EXTRACTION

The data from publications were critically reviewed and tabulated to assess implantation outcomes.

DATA SYNTHESIS

The data were not amenable to formal meta-analysis or valid data summarization, other than descriptive statistics.

CONCLUSIONS

There is an increasing awareness of the prevalence of mitochondrial SNHL and its progressive nature. High-risk candidates warrant genetic testing and family screening. Correlating the data for mitochondrial SNHL as a treatable entity is important, and the authors present an overview of these patients successfully rehabilitated by cochlear implantation.

Aetiology of hearing loss and other related factors versus language outcome after cochlear implantation in children

OBJECTIVE

Cochlear implantation outcome in prelingually deafened children is highly variable. The objective of this study was to examine the relationship between the yearly improvements in speech and language scores after cochlear implantation in children, with the aetiology of the hearing loss and other related factors.

METHODS

We reviewed the case notes of children with early onset (0-2 years) of hearing loss, who were implanted in their first decade of life between 1992 and 2000 in Great Ormond Street Children Hospital. We assessed the relationship between the improvement of the receptive language and speech scores, on each year after implantation, with the aetiology of hearing loss and with the presence of additional medical problems.

RESULTS

Children with a syndromic diagnosis had lower speech and language improvement scores at years 4 and 5 after implantation than children with a hereditary-non syndromic or unknown diagnosis. Vision and vestibular problems were significant negative predictors for speech and language improvement scores. The disability score, i.e. an overall index of additional to the hearing loss problems, had a negative correlation with the speech and language improvement scores.

CONCLUSIONS

The presence of a syndromic diagnosis, vision or vestibular problems, and the overall level of additional to the hearing loss problems, may be negative prognostic indicators for speech and language improvement after implantation.

Vibration-induced ocular torsion and nystagmus after unilateral vestibular deafferentation

Vibration is an excitatory stimulus for both vestibular and proprioceptive afferents. Vibration applied either to the skull or to the neck muscles of subjects after unilateral vestibular deafferentation induces nystagmus and a shift of the subjective visual horizontal. Previous studies have ascribed these effects to vibratory stimulation of neck muscle proprioceptors. Using scleral search coils, we recorded three-dimensional eye movements during unilateral 92 Hz vibration of the mastoid bone or of the sternocleidomastoid (SCM) muscle in 18 subjects with chronic unilateral vestibular deficits after vestibular neurectomy or neuro-labyrinthitis. Nine subjects had lost function of all three semicircular canals (SSCs) on one side, and the other nine had lost function of only the anterior and lateral SSCs. Vibration of the mastoid bone or of the SCM muscle on either side induced an ipsilesional tonic shift of torsional eye position of up to 6.5 degrees during visual fixation, as well as a nystagmus with horizontal, vertical and torsional components in darkness. Subjects who had lost function of all three SSCs on one side showed a larger shift in ocular torsion in response to SCM vibration than did subjects who had lost function of only two SSCs. The difference between ocular torsion produced by ipsilesional muscle or bone vibration was not significantly different from that produced by contralesional bone or muscle vibration. The vibration-induced nystagmus rotation axis tended to align with the pitch (y) axis of the head in subjects who had lost only anterior and lateral SSC function, and with the roll (x) axis of the head in subjects who had lost function of all three SSCs. We propose that the previously described vibration-induced shift of the subjective visual horizontal can be explained by the vibration-induced ocular torsion, and that the magnitude of ocular torsion is related to the extent of the unilateral vestibular deficit. While altered proprioceptive inputs from neck muscles might be important in the mechanism of vibration-induced ocular torsion and nystagmus after unilateral vestibular deafferentation, vibratory stimulation of vestibular receptors in the intact labyrinth also appears to have an important role.

Consequences and assessment of human vestibular failure: implications for postural control

Labyrinthine afferents respond to both angular velocity (semicircular canals) and linear acceleration (otoliths), including gravity. Given their response to gravity, the otoliths are likely to have an important role in the postural functions of the vestibular apparatus. Unilateral vestibular ablation has dramatic effects on posture in many animals, but less so in primates. Nevertheless, bilateral vestibular lesions lead to disabling symptoms in man related to disturbed ocular and postural control and impaired perception of slopes and accelerations. While seimicircular canal function can be assessed through its effects on vestibular ocular reflexes, assessment of otolith function in man has traditionally been much more difficult. Recent definition of a short latency vestibulocollic reflex, activated by sound and appearing to arise from the saccule, shows promise as a new method of non-invasive assessment of otolith function.

Vestibulospinal control of posture

To better understand the role of the vestibular system in postural coordination, we compared the ability of subjects with complete, bilateral loss of vestibular function and age-matched control subjects to maintain equilibrium and postural orientation during sinusoidal displacements of the support surface at a variety of frequencies. We also examined the ability of visual or somatosensory-light touch information to substitute for missing vestibular information in dynamic postural coordination. The results suggest that vestibular information is used as a gravitational reference frame to prevent slow drift of the trunk in space during complex postural tasks. Furthermore, visual information or somatosensory information from light touch of a finger on a stable reference can significantly substitute for loss of vestibular function.

Protective effect of edaravone against streptomycin-induced vestibulotoxicity in the guinea pig

This study investigated alleviation of streptomycin-induced vestibulotoxicity by edaravone in guinea pigs. Edaravone, a free radical scavenger, has potent free radical quenching action and is used in clinical practice to treat cerebral infarction. Streptomycin was administered to the inner ear by osmotic pump for 24 h, and edaravone (n=8) or saline (n=6) was intraperitoneally injected once a day for 7 days. We observed horizontal vestibulo-ocular reflex as a marker of postoperative vestibular function. Animals injected with saline showed statistically smaller gains than those injected with edaravone. These results suggest that edaravone suppresses streptomycin-induced vestibulotoxicity.

Evaluating the dizzy patient: bedside examination and laboratory assessment of the vestibular system

Dizziness and imbalance are common presenting complaints to the neurologist. The lack of a systematic approach to the examination and laboratory evaluation of the vestibular system often leads to incorrect diagnoses and suboptimal care. With a basic understanding of vestibular physiology and proper examination techniques, a correct diagnosis can generally be made at the bedside. We review the principles of the neuro-otological examination, including assessment for static vestibular imbalance, dynamic vestibular function, provocative maneuvers, ocular motor examination, and vestibulospinal testing. The use of additional vestibular laboratory testing and neuroimaging is then considered to further localize and quantify abnormalities.

[Bilateral vestibular loss. Diagnosis and follow-up]

BACKGROUND

Atypical symptom in patients with bilateral vestibular loss is head movement-induced oscillopsia. The paucity of precise complaints in many patients is surprising. Therefore, bilateral loss of vestibular function is often undiagnosed.

PATIENTS

We report on the long-term follow-up in 29 patients. They were monitored for 2-7 years (mean: 4.5 years).

RESULTS

Of the 29 patients 16 described oscillopsia. All symptomatic patients had acute bilateral vestibular loss.Patients described that their symptoms improved over a period of 1-2 years. Improvement was not age dependent.

CONCLUSIONS

Otoneurologists should be aware of the particular clinical symptoms in bilateral vestibular loss. Regarding clinical features, compensation of bilateral vestibular loss seems to be unlikely only based on central compensatory eye movement reflexes. More likely perceptual adaptations and restriction of head movement are responsible for subjective improvement.

Hypotonia, congenital hearing loss, and hypoactive labyrinths

The records of all patients attending a neurosensory genetics clinic over an 11-year period were reviewed. Of the 450 patients seen, 31 presented with sensorineural hearing loss, hypotonia, and delay in the acquisition of motor milestones. Of these, 4 children were found who did not have an etiologic diagnosis such as Down syndrome or cerebral palsy. Vestibular testing revealed hypoactive labyrinthine function in all 4 of the cases, and careful imaging of the temporal bone showed anomalous development of the cochlea, vestibule, and semicircular canals in 3 of the 4 cases. None of the patients had ataxia, tremor, or significant nystagmus. Over time, the hypotonia improved in all, and none were felt to have cognitive deficits. These cases demonstrate that hypoactive labyrinthine function may be associated with hypotonia that is severe enough to result in delayed acquisition of motor milestones. The patients followed the typical remitting course of "benign congenital hypotonia." The distinguishing clinical feature is the presence of moderate to profound sensorineural hearing loss in all of the patients.

Effects of visual input on galvanic body sway test of unilateral vestibular deficiency in patients with unilateral vestibular schwannoma

OBJECTIVE

Galvanic body sway tests (GBSTs) are performed with eyes fixed and closed. However, quantitative effect of fixation on GBST has been unknown. The purpose of this study is to address this question.

METHODS

We evaluated GBSTs of patients with unilateral vestibular schwannomas and normal controls, while their eyes were open and closed. We evaluated three GBST parameters: maximum amplitude of the response, velocity and latency of the onset of response.

RESULTS

Closing the eyes diminished stability, resulting in increased amplitude and velocity of the responses. However, apparent contribution to the latency of response could not be found. Contribution of visual fixation seems to be greater in apparatus with vestibular hypo-function than without it. Unilateral weakness (UW) was calculated for each parameter, and significant correlation, between with eyes fixed and closed, was found only for velocity parameter.

CONCLUSION

Fixation would stabilize the body of subjects, and diminish GBST responses. GBST with and without fixation can be evaluated together, using certain coefficient. On the other hand, fixation would not have any contribution to the latency of the GBST response. When we evaluate vestibular dysfunction of patients with unilateral vestibular schwannomas, velocity parameter should be employed.

Effects of predictive mechanisms on head stability during forward trunk perturbation

While much is known about reflex and mechanical contributions to the control of head stability, little is known about predictive control. The goal of this experiment was to determine the contribution of predictive mechanisms to head stability in space, in the pitch plane, during forward trunk perturbations. Eleven standing healthy subjects had their trunk pulled forward by a load-pulley apparatus. The perturbation was either self-triggered or imposed (triggered by the experimenter). Subjects were exposed to two loads: 2% and 4% of their body weight. The contributions of torques acting on the head-neck system were inferred from head and trunk kinematics, neck muscle EMG, and the torques acting on the head, which were computed using inverse dynamics. The results showed that both the head and trunk moved less during the self-triggered than imposed condition during both loads for most of the participants. There was no evidence of predictive neck countertorque or increased neck muscle co-contraction during the self-triggered condition. These findings suggest that most of the subjects improved head stability in the self-triggered condition by reducing trunk motion and the associated interactive torque that perturbed the head.

Combined effect of vestibular and craniomandibular disorders on postural behaviour

A correlation has been reported in the dental literature between temporomandibular disorders and musculoskeletal abnormalities, however, the question whether they modify body postural sway remains controversial. In the present investigation, the Craniomandibular Index was used to evaluate the clinical extension of temporomandibular joint dysfunction and related problems in 40 patients with normal vestibular function and in 42 patients with peripheral vestibular disorders. Balance function was assessed by static posturography and body sway area was measured in two conditions: i) eye open, and g) eye closed. Data were compared to those of 40 healthy subjects. Postural control showed a significantly different behaviour between groups with an increase in average body sway in patients with craniomandibular disorders as opposed to controls (p < 0.005). Although the involvement of the stomatognathic apparatus was not quantitatively different in the two groups of patients, those also presenting a peripheral vestibular disorder exhibited greater average body sway than patients with only craniomandibular disorders (p < 0.005). The latter showed a greater average body sway than controls only in the trial with eyes closed (p < 0.05). The results demonstrated that craniomandibular alterations could produce moderate postural instability in patients with a normal vestibular function. Conversely, their association with peripheral vestibular disorders becomes a real challenge to the upright quiet stance probably due to a negative effect of somatosensory origin on the vestibulo-spinal reflex impairment.

[Audimont--a scientific research expedition to Mount Cho Oyu in the Himalayas]

Even though hearing and vestibular disorders at high altitude have been reported since 1938, their reasons are still unknown. During the Audimont Research Expedition the risk for cochlear and vestibular sensory cells has been quantified by otoacoustic emissions and videonystagmography. Vestibular disorders could not be observed up to 7050 meters. However, the outer hair cells in the inner ear showed a reduction of emissions at increasing height. The pattern of the inner ear reply, depending on the altitude, complies with an increase of the perilymphatic pressure. As the perilymphatic space corresponds directly to the subarachnoid space, the limitation of hearing thus appears to be a direct consequence of raised intracranial pressure.

Neurovestibular symptoms following space flight

Neurovestibular symptoms experienced by astronauts in the post-flight period were examined using data from medical debriefs contained in the NASA Longitudinal Study of Astronaut Health database. Ten symptoms were identified (clumsiness, difficulty concentrating, persisting sensation aftereffects, nausea, vomiting, vertigo while walking, vertigo while standing, difficulty walking a straight line, blurred vision, and dry heaves), of which eight were crossed with twelve demographic parameters (mission duration, astronaut gender, age, one-g piloting experience, previous space flight experience, g-suit inflation, g-suit deflation, in-flight space motion sickness, in-flight exercise, post-flight exercise, mission role, fluid loading). Three symptoms were experienced by a majority of subjects, and another two by more than a quarter of the subjects. Intensity of the symptoms was mild, suggesting that they are unlikely to pose a risk to the crew during landing and the post-flight period. Seven of the symptoms and eight of the parameters under study were found to be significantly associated with each other.

Unilateral examination of utricle and saccule function

Attention is directed towards the recently developed unilateral tests of saccular and utricular function. Together with the now widely used head-thrust test and the standard caloric test for semicircular canal function, these provide for a more comprehensive unilateral examination of labyrinth function. The efficacy of vestibular evoked myogenic potentials (VEMP) as a direct unilateral test of saccular function is currently being demonstrated in an increasing number of reports. Furthermore, the relevant neuronal pathways have been delineated in animal studies, so that all evidence points to the validity of the VEMP as a saccule-mediated response. Concerning utricular function, considerable headway has been made using the unilateral centrifugation paradigm. Testing is performed with a variable radius rotary chair with constant velocity rotation about the earth-vertical axis. Displacing the head by 3.5-4 cm from the rotation axis, the eccentrically positioned utricle is stimulated unilaterally by the resultant centrifugal force. This paradigm can be employed to elicit a utriculo-ocular response (UOR) or to permit measurement of the subjective visual vertical (SVV). More recently, it has also been demonstrated that testing during normal, on-centre yaw axis rotation is often sufficient to localise peripheral otolith dysfunction by means of SVV estimation. This test mode can be easily integrated into routine clinical testing. To illustrate the efficacy of such differential testing, the findings from two patients are presented that demonstrate for the first time an isolated unilateral utricular dysfunction.

[Mechanisms of physical rehabilitation of patients with vestibular disorders]

The following methods of rehabilitation of patients with equilibrium disturbance have been analysed: 1) nonspecific exercise; 2) specific physical training to enhance the flow of impulses providing formation of the mechanism of the vestibular function compensation at the subconscious level; 3) specific training on the stabilographic platform based on the biological feedback principle. It was found that the most effective recovery of the statokinetic function was achieved under combination of the above methods. The effect manifested both in subjective improvement of the patients' general condition and objective response as shown by functional computed stabilometry.

Evidence for interacting cortical control of vestibular function and spatial representation in man

The objective of this research was to determine the possible relation between deficits in spatial representation capability and vestibular function following cortical lesions. We thus investigated vestibulo-ocular behaviour in a group of 14 patients with unilateral cortical damage involving the occipito-temporo-parietal junction. Patients were divided in three sub-groups: (1) Group R+: five patients with right sided cortical lesions associated with a left hemi-neglect, (2) Group R-: four patients with right sided cortical lesions with no hemi-neglect and (3) Group L: five patients with left-sided cortical lesions. The patient groups were compared to a group of eight healthy age-matched subjects. The vestibulo-ocular reflex (VOR) was tested in complete darkness by rotating the subject around the vertical axis by sinusoidal rotation at different frequencies, and by steps of acceleration or deceleration. The nystagmus slow phase velocity was measured and plotted as a function of the head velocity and the VOR parameters including gain, bias, time constant and phase were calculated. The cortical lesions induced a significant VOR asymmetry in terms of: a directional preponderance of the VOR gain to the contralesion side, only during sinusoidal rotation, and, in contrast, a VOR bias and a directional preponderance of the VOR time constant and of the nystagmus frequency to the side of the cortical lesion. These latter VOR deficits were the most significant in the R+ group, i.e. in right cortical lesions with hemi-neglect syndrome. These results demonstrate in man, the existence of a cortical influence on vestibular function related to the mechanisms of spatial representation.

[Enlarged vestibular aqueduct syndrome in patients with hypoacusis and deafness]

In 1978 Valvassori and Clemis have reported that enlarged vestibular aqueduct can cause progressive perceptive hearing loss and finally deafness.

AIM

Analysis of CT scans of patients with cochlear implants. Analysis of radiological data of 120 implanted patients was performed. CT examinations were performed during qualification to cochlear implantation. Most of the CT scans were performed using high resolution computed tomography (HRCT). A special attention was paid to patients with progressive perceptive hearing loss and CT of two patients with "gusher" during CI surgery. In one case (6-years old girl with bilateral profound perceptive hearing loss diagnosed in 2nd year of age) an enlarged vestibular aqueduct was found radiologically. In the second case (16 years old girl with progressive perceptive hearing loss since 1st year of age) no enlarged vestibular aqueduct was detected. Diagnostics and treatment of enlarged vestibular aqueduct syndrome are presented.