Patterns of Auditory Abnormality in Multiple Sclerosis: Exemples de cas auditifs anormaux dans les scléroses en plaques

The Interaural Time Difference for High-Pass Filtered Noise and Its Relationship With Brainstem Dysfunction and Disability in Multiple Sclerosis

PURPOSE

Just noticeable difference for interaural time difference (JND-ITD) is a sensitive test to detect silent lesions and neural asynchrony along the auditory pathways among individuals with multiple sclerosis (MS), but it has not been studied with brainstem functional system scores (BFSS) and expanded disability status scale (EDSS). The study aims to assess the usefulness of JND-ITD thresholds in individuals with MS and relate to brainstem magnetic resonance imaging (MRI) lesions, BFSS, and disability (EDSS).

METHOD

Standard group comparison design was adapted to compare the JND-ITD thresholds between individuals with MS (n = 45) and age and gender-matched healthy participants (n = 45). All participants underwent case history, neurological examination including BFSS and EDSS scoring, MRI brain imaging, minimental state examination, routine audiological evaluation, and ITD testing for high-pass filtered noise stimuli.

RESULTS

Of the 36 MS participants with abnormal JND-ITD thresholds, 22 (48.9%) participants could not identify maximum JND-ITD values (1,280 μs) in the ITD task. Abnormal JND-ITDs thresholds (139-1,280 μs) were obtained in 14 (31.11%) participants with MS. The JND-ITD thresholds were significantly different between the healthy and MS group. No significant association was found between the presence of ITD abnormality with the presence of brainstem lesions (MRI) and brainstem dysfunction (BFSS). Also, this study did not find any relationship between JND-ITD thresholds with disability (EDSS).

CONCLUSIONS

This study supports the findings that JND-ITD for high-pass filtered noise is a sensitive test to detect lesions along the auditory system. Even though JND-ITD thresholds did not relate with BFSS and EDSS scores, JND-ITD abnormalities can be of great value in identifying lesions along the auditory system, especially in the early stages of MS, when clinical neurological examination does not show any signs of brainstem dysfunction, disability, and MRI without any lesions in the brain.

Mismatch Negativity in Children and Adolescents with Autism Spectrum Disorder

Introduction  Individuals with autism spectrum disorder (ASD) have abnormalities in auditory perception and sensitivity. The mismatch negativity (MMN) component of the evoked potential demonstrates a brain detection response to an auditory change due to memory, and enables the identification of changes in the auditory system. Objective  To analyze MMN responses in children and adolescents with ASD and compare them with those of a control group. Methods  Cross-sectional and comparative study. The sample was composed of 68 children and adolescents, divided into study group (SG), which contained those diagnosed with ASD, and the control group (CG), which contained those with typical development, normal hearing thresholds, and without hearing complaints. All participants were submitted to peripheral and central electrophysiological auditory evaluations. For the electrophysiological auditory evaluation and MMN recording, the electrodes were fixed in the following positions: Fz (active electrode), M1 and M2 (reference electrodes), and on the forehead (ground electrode). Auditory stimuli were presented in both ears simultaneously, with a frequency of 1,000 Hz for the frequent stimulus, and of 2,000 Hz for the rare stimulus, in an intensity of 80 dBNA. Results  Latency and amplitude values were increased in the SG, with a statistically significant difference in comparison with the CG. In the MMN analysis, there was no statistically significant difference in the comparison between right and left ears and between genders. Conclusion  Children and adolescents with ASD had higher latency and amplitude values in the MMN component than the individuals in the CG.

Auditory evoked potentials in children and adolescents with multiple sclerosis and neuromyelitis optica spectrum disorders

BACKGROUND

In children, an acute demyelinating disease may evolve as a multiphasic disease with multiple relapses, such as multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). The Brainstem Auditory Evoked Potentials (BAEP) and Long-Latency Auditory Evoked Potentials (LLAEP) contribute to the identification of either retrocochlear changes or other central auditory nervous system (CANS) changes.

OBJECTIVES

To characterize BAEP and LLAEP in children and adolescents with MS and NMOSD and verify the diagnostic values of these potentials in each of the demyelinating diseases.

METHODS

The 40 participants were divided into two study groups (SG1 - MS, SG2 - NMOSD) and two comparison groups (CG1 and CG2), matched for age (9 years-17 years and 11 months) and sex. Electrophysiological hearing assessment was performed with BAEP and LLAEP.

RESULTS

When SG1 and SG2 were compared with CG1 and CG2 regarding BAEP and LLAEP, both SG1 and SG2 presented a higher occurrence of changes. Also, individuals with MS had higher occurrences of BAEP changes, whereas individuals with NMOSD had a higher occurrence of LLAEP changes.

CONCLUSIONS

BAEP and LLAEP in children and adolescents with MS or NMOSD showed higher latencies and lower amplitudes of some components when these individuals were compared with their peers. These procedures were highly accurate to identify demyelinating diseases. BAEP results were more abnormal in individuals with MS, while LLAEP was so with NMOSD. These findings indicate that the auditory evoked potentials are important instruments for the differential diagnosis of MS and NMOSD, and valuable to monitor disease evolution.

Effectiveness of Brainstem Auditory Evoked Potentials Scoring in Evaluating Brainstem Dysfunction and Disability Among Individuals With Multiple Sclerosis

Purpose The brainstem dysfunction in multiple sclerosis (MS) often causes significant functional impairment leading to disability. This study aims to explore modified brainstem auditory evoked potential (BAEP) scores based on the pattern of BAEP abnormalities and relate with brainstem symptoms, brainstem functional system scores (BFSS), brainstem lesions, and disability. Method Forty-five participants with relapsing-remitting MS and 45 age- and gender-matched healthy controls underwent case history assessment, otoscopic examination, pure-tone audiometry, and BAEP testing. Also, neurological examination (Expanded Disability Status Scale, FSS scales) and magnetic resonance imaging were carried out on MS participants. Patterns of BAEP abnormalities were categorized and converted to BAEP scores. Results Out of 45 participants' brainstem symptoms, BFSS > 1, brainstem lesions (magnetic resonance imaging), and BAEP abnormalities were observed in 75.6%, 42.2%, 62.2%, and 55.56% of participants, respectively. Waves V and III abnormalities were more common among MS participants and showed a significant difference from the control group in the Mann-Whitney U test. Chi-square test did not show a significant association of BAEP abnormalities with brainstem symptoms and lesions but showed significant association with BFSS. The mean and standard deviation of BAEP scores in MS participants were 1.73 + 2.37. All healthy controls showed BAEP scores of 0. BAEP scores in MS participants showed significant correlation with BFSS scores and predict Expanded Disability Status Scale scores. Conclusion BAEP scores based on the pattern of BAEP abnormality can be a valid and useful measure in evaluating brainstem functions and predicting disability in MS.

Impaired Binaural Hearing in Adults: A Selected Review of the Literature

Despite over 100 years of study, there are still many fundamental questions about binaural hearing that remain unanswered, including how impairments of binaural function are related to the mechanisms of binaural hearing. This review focuses on a number of studies that are fundamental to understanding what is known about the effects of peripheral hearing loss, aging, traumatic brain injury, strokes, brain tumors, and multiple sclerosis (MS) on binaural function. The literature reviewed makes clear that while each of these conditions has the potential to impair the binaural system, the specific abilities of a given patient cannot be known without performing multiple behavioral and/or neurophysiological measurements of binaural sensitivity. Future work in this area has the potential to bring awareness of binaural dysfunction to patients and clinicians as well as a deeper understanding of the mechanisms of binaural hearing, but it will require the integration of clinical research with animal and computational modeling approaches.

The audiovestibular manifestations as early symptoms of multiple sclerosis: a scoping review of the literature

BACKGROUND

Multiple sclerosis (MS) is an immune-mediated, demyelinating disease of the nervous system, which may impact the audiovestibular pathway at different stages of the disease. The auditory and vestibular manifestations of MS as a presenting or early symptom are an area in which more investigation is needed.

AIMS

The aim of this review is to determine the auditory and vestibular symptoms, which may occur at the presenting stage of multiple sclerosis. This clinical knowledge will allow a clinician to facilitate early diagnosis and intervention of MS through appropriate onward referral. Audiological and vestibular test results, as well as magnetic resonance imagery results, will also be examined to try to determine the impact of MS on the auditory and vestibular pathways.

METHODS

A scoping search of the electronic databases PubMed, Scopus, Web of Science, ScienceDirect, and EBSCO was conducted in March 2020 to obtain studies specifically of patients with audiovestibular symptoms at the early or presenting stages of multiple sclerosis. Data was extracted from studies which met the inclusion criteria and studies were subsequently critically appraised and assessed for risk of bias.

RESULTS

Eighteen papers met the inclusion criteria for this study. Results of the study found that the most common audiovestibular manifestation as a presenting symptom of MS was unilateral, moderate-profound, fluctuating, and sudden sensorineural hearing loss across all frequencies (250 Hz-8000 Hz). Other symptoms include tinnitus, balance abnormalities, aural pain and aural fullness, which may accompany SSHL or occur independently. The peripheral involvement of the immune-mediated mechanisms of MS was suggested by peripheral findings in vestibular examination results and the involvement of wave I ABR in patients with irreversible hearing loss. Demyelinating lesions associated with MS were suggested by results obtained from evoked potentials measurements, including ABR, VEMPs, and MLR.

CONCLUSION

An understanding of the sensitivity of evoked potentials in the detection of demyelinating lesions as well as the most common audiovestibular presentations of the disease allows the practitioner to provide an appropriate onward referral for MRI which may lead to early diagnosis and intervention of MS. We suggest that there is enough evidence to include evoked potentials complementary to MRI in the detection and monitoring of MS. As the review suggests evidence of involvement of the immune-mediated mechanisms of MS on peripheral structures like the inner ear, further clinical research is recommended to explore this mechanism. Key points 1. The most common audiovestibular manifestation as an early symptom of MS was unilateral moderate to profound SSHL across all frequencies (250 Hz-8000 Hz). 2. Findings of the review indicated the involvement of the immune-mediated mechanisms of MS in the peripheral structures of the inner ear. 3. These findings included peripheral results in the vestibular test of the patients involved in the study and secondly, the three studies which reported an absence of full recovery of hearing loss were also three papers which within their ABR results showed abnormality of wave I 4. This is the first paper to support the theory (Di Stadio et al. 2018) [32] that immune-mediated processes of MS can spread to peripheral inner ear structures 5. The review highlighted the sensitivity of evoked potentials in detecting MS lesions in the presenting stage, particularly ABR which demonstrated that in instances in which hearing loss recovered ABR results remained abnormal.

Auditory brainstem response

The auditory brainstem response (ABR), consisting of five to six vertex-positive peaks with separation of about 0.8ms, is very sensitive to factors that affect conduction velocity and hence ABR wave latencies in the brainstem auditory pathways. In addition, disorders causing dissynchronization of neural activity result in an amplitude decrease or disappearance of ABR peaks. The opposite effects occur in the maturation process, which takes about 2 years postterm; here conduction velocity increases quickly to its adult value, but synaptic delays being sensitive to synchronous release of transmitter substance take considerably longer. In neurological disorders, those that cause dissynchrony, such as auditory neuropathy and vestibular schwannoma, Gaucher disease, and Krabbe disease, the (longer latency) ABR peaks are reduced or absent. Effects on neural conduction, resulting in increased ABR interwave latencies, are found in vestibular schwannomas, Bell's palsy, Duane retraction syndrome, Marcus Gunn ptosis, and various encephalomyopathies. These measures allow an assessment of the parts of the brainstem that are involved.

Sequential Bilateral Hearing Loss in Multiple Sclerosis

Objectives: We describe a case of multiple sclerosis presenting with sequential bilateral hearing loss.

Methods: A 46-year-old woman underwent a series of audiological and neurologic evaluations for sequential bilateral hearing losses that occurred 6 months apart.

Results: Initially, the patient suffered from sudden left hearing loss, and magnetic resonance imaging documented an enhancing lesion in the left middle cerebellar peduncle. Six months later, another episode of sudden vertigo, right hearing loss, and right facial palsy developed. Magnetic resonance imaging disclosed a new lesion in the right middle cerebellar peduncle.

Conclusions: Sequential bilateral hearing loss may be a manifestation of multiple sclerosis. In younger patients with sudden hearing loss, multiple sclerosis should be included in the differential diagnosis.

Hearing disorders in multiple sclerosis

Multiple sclerosis (MS) is a disease that is both a focal inflammatory and a chronic neurodegenerative disease. The focal inflammatory component is characterized by destruction of central nervous system myelin, including the spinal cord; as such it can impair any central neural system, including the auditory system. While on the one hand auditory complaints in MS patients are rare compared to other senses, such as vision and proprioception, on the other hand auditory tests of precise neural timing are never "silent." Whenever focal MS lesions are detected involving the pontine auditory pathway, auditory tests requiring precise neural timing are always abnormal, while auditory functions not requiring such precise timing are often normal. Azimuth sound localization is accomplished by comparing the timing and loudness of the sound at the two ears. Hence tests of azimuth sound localization must obligatorily involve the central nervous system and particularly the brainstem. Whenever a focal lesion was localized to the pontine auditory pathway, timing tests were always abnormal, but loudness tests were not. Moreover, a timing test that included only high-frequency sounds was very often abnormal, even when there was no detectable focal MS lesion involving the pontine auditory pathway. This test may be a marker for the chronic neurodegenerative aspect of MS, and, as such could be used to complement the magnetic resonance imaging scan in monitoring the neurodegenerative aspect of MS. Studies of MS brainstem lesion location and auditory function have led to advances in understanding how the human brain processes sound. The brain processes binaural sounds independently for time and level in a two-stage process. The first stage is at the level of the superior olivary complex (SOC) and the second at a level rostral to the SOC.

Alterations in early auditory evoked potentials in multiple sclerosis patients

Alterations in early auditory evoked potentials (EAEP) in individuals with demyelinating disease are suggestive of lesions in the brainstem.

AIM

this study aims to evaluate the prevalence of hearing disorders and altered EAEP in multiple sclerosis (MS) patients.

MATERIALS AND METHOD

sixteen female and nine male patients with a defined diagnosis of multiple sclerosis took part in this study. All individuals underwent hearing and EAEP tests. The wave forms were categorized according to Jerger (1986).

RESULTS

fifty EAEP tests were carried out; 70% were classified as type I (normal response) according to Jerger's criteria. Altered EAEP results in at least one ear were classified into types II, III, IV or V according to Jerger. Females accounted for 31.25% of alterations, and males 44.44%, adding up to 36% of all cases.

CONCLUSIONS

these findings stress the importance of looking at EAEP in cases where there is suspicion of demyelinating disease and in patients with a defined diagnosis for MS.

Auditory Efferent Function Is Affected in Multiple Sclerosis

OBJECTIVE

This study evaluated efferent medial olivocochlear (MOC) function in patients with multiple sclerosis (MS). Various afferent auditory abnormalities have been described in MS, but there is a paucity of data on efferent function. The brain stem is a site of predilection for MS plaques and the efferent MOC pathway may be affected at this level.

METHODS

The study included 30 patients who had normal hearing. According to MRI findings, they were divided into two groups: those with an identifiable brain stem lesion (n = 10) and those with MS lesions in other parts of the central nervous system but without demonstrable MS plaques in the brain stem (n = 20). MOC function was evaluated by the olivocochlear suppression test, using transient evoked otoacoustic emissions. All subjects underwent standard auditory tests, including pure-tone audiometry and recording of auditory brain stem evoked responses. Twenty-two healthy subjects with normal hearing, matched for age and gender, served as a reference group for the auditory data.

RESULTS

The results showed that 66.6% of all patients had reduced MOC function, particularly those (90%) with identified lesions of the brain stem on MRI. Furthermore, abnormal MOC function was found in 55% patients without evidence of a brain stem lesion on MRI.

CONCLUSIONS

This study provides the evidence for a deficit of efferent auditory function in the majority of patients with MS. Taking into consideration the possible roles of the MOC system in processing of auditory information, abnormal MOC suppression in patients with MS may explain a variety of auditory presentations that are currently largely overlooked. This study also highlights the diagnostic value of the MOC suppression test as a site-of-lesion diagnostic test in MS and in identifying subtle brain stem lesions undetected by MRI, suggesting that subtle brain stem lesions may exist and that the MOC suppression test is sufficiently sensitive to detect them. Accordingly, the MOC suppression test may provide a tool for an early diagnosis of MS.

Autoimmune Mouse Antibodies Recognize Multiple Antigens Proposed in Human Immune-Mediated Hearing Loss

HYPOTHESIS

Autoimmune diseased mice with hearing loss will have autoantibodies against the various cochlear antigens proposed in clinical autoimmune inner ear disease.

BACKGROUND

Serum antibodies of patients with hearing loss recognize several proteins that are proposed as possible antigenic targets in the ear. This often leads to a clinical diagnosis of autoimmune inner ear disease, although it is not clear how these antibodies cause inner ear disease. Therefore, to better understand the relationship of autoantibodies and ear disease, an examination was made of serum autoantibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse with hearing loss. Similar antibody patterns in the mouse would provide an animal model in which to investigate potential autoimmune mechanisms of this clinical ear disorder.

METHODS

Sera from MRL/MpJ-Fas(lpr) autoimmune mice and normal C3H mice were tested by the enzyme-linked immunosorbent assay technique for reactivity against various reported cochlear antigens: heat shock protein 70 (bovine, human, bacterial), laminin, heparan sulfate proteoglycan, cardiolipin, and collagen types II and IV.

RESULTS

The autoimmune mouse sera showed significantly greater antibody reactivity against all of the antigens when compared with normal mouse sera.

CONCLUSIONS

Serum antibodies from autoimmune mice recognized several putative autoantigens reported for patients with hearing loss, suggesting that comparable antigen-antibody mechanisms might be operating. However, the recognition of multiple antigens did not identify any one as being the specific target in autoimmune hearing loss. The correlation of antibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse and human studies indicates this animal model should aid further investigations into potential cochlear antigens in autoimmune hearing loss.

The binaural interaction component (BIC) in children with central auditory processing disorders (CAPD)

The detection of binaural interaction is of diagnostic interest in patients with central auditory processing disorders (CAPDs), as binaural hearing tasks are frequently affected in these patients. Owing to the comorbidity associated with disorders such as an attention-deficit hyperactivity disorder, pathological results in subjective tests often show extra-auditory factors such as reduced attention rather than impaired central auditory function. Therefore, objective measures for auditory processing disorders are essential. The binaural interaction component (BIC), which is the arithmetical difference between the sum of the monaurally evoked auditory potentials of each ear and the binaurally evoked brainstem potentials, has been used as an objective measure of binaural interaction in humans. BIC measurements can therefore be considered as a possible diagnostic tool in CAPD patients. One aim of the present study was to examine whether and to what extent BIC measurements are capable of differentiating between normal children and children 'at risk for CAPD'. BIC measurements were performed on 17 children at risk for CAPD and in a group of 25 children with normal results in the central audiometric tests used. Using the presence or absence of clearly demonstrable BIC waveforms as an indication of whether a CAPD is present or not, a sensitivity and specificity of 76% could be achieved. We conclude that BIC measurements might be of some diagnostic value in CAPD patients.

[Auditory evoked potentials evaluation of the brain stem in multiple sclerosis]

The aim of this study was to evaluate the incidence of auditory and neurotological disorders in multiple sclerosis (MS). Twenty female and 9 male with a definite diagnosis of multiple sclerosis without signs of involvement of the brain stem underwent an audiological and an early auditory evoked potentials (EAEP). The wave forms were classified according to Jerger's (1986) classification. In 58 EAEP it was found 55% of type I (normal response) according to Jerger's classification in both sexes. Considering as an abnormal response the EAEP classified in type II, III, IV or V according to Jerger in at least one side, it was found 60% of abnormalities in females and 56% in males, totalizing 58,62% of all the studied subjects. The authors emphasize the use of EAEP in MS.

Demyelination of Vestibular Nerve Axons in Unilateral Ménière's Disease

We conducted a study to determine whether vestibular nerves inpatients with unilateral Ménière's disease whose symptoms are refractory to medical management exhibit neuropathologic changes. We also endeavored to determine whether retrocochlear abnormalities are primary or secondary factors in the disease process. To these ends, we obtained vestibular nerve segments from five patients during retrosigmoid (posteriorfossa) neurectomy, immediately fixed them, and processed them for light and electron microscopy. We found that all five segments exhibited moderate to severe demyelination with axonal sparing. Moreover, we noted that reactive astrocytes produced an extensive proliferation of fibrous processes and that the microglia assumed a phagocytic role. We conclude that the possible etiologies of demyelination include viral and/or immune-mediated factors similar to those seen in other demyelinating diseases, such as multiple sclerosis and Guillain-Barré syndrome. Our findings suggest that some forms of Ménière's disease that are refractory to traditional medical management might be the result of retrocochlear pathology that affects the neuroglial portion of the vestibular nerve.

Successful prevention of retrocochlear hearing loss in murine experimental allergic encephalomyelitis with T cell receptor Vbeta8-specific antibody

Experimental allergic encephalomyelitis is an animal model of a T cell-mediated autoimmune disease -- for example, multiple sclerosis. We demonstrated that mice with experimental allergic encephalomyelitis developed retrocochlear hearing loss, and that the lesion of the auditory pathway might be related to T cell receptor Vbeta8-expressing T cells. To investigate whether anti-Vbeta8 antibody could prevent hearing loss, we carried out brain stem auditory evoked potential testing, histologic examinations, and flow cytometry in antibody-treated and control myelin basic protein-immunized B10.PL mice. The antibody was administered just before immunization of myelin basic protein. The disease incidence and severity were significantly reduced in the mice injected with the antibody. The results of brain stem auditory evoked potential testing, histologic examinations, and flow cytometry indicated that the depletion of Vbeta8-expressing T cells brings the prevention of hearing loss, as well as prevention of other neurologic deficits. The development of T cell receptor-specific antibody therapy might help treat retrocochlear hearing loss in multiple sclerosis.

Multiple sclerosis: a cause of sudden hearing loss

Sudden hearing loss is a clinical entity which has numerous aetiologies. In cases where the aetiology is not determined, evaluation and treatment of sudden hearing loss are very difficult. A case of probable multiple sclerosis with sudden hearing loss as the initial symptom is reported. The pure-tone audiometry showed a quasi-total sensorineural hearing loss in the left ear; the left side displayed only wave I in the auditory brainstem response (ABR). Electronystagmographic examination revealed hypometric dysmetria and saccadic pursuit abnormalities. Magnetic resonance imaging (MRI) showed high-intensity lesions with multiple foci. After steroid therapy, the patient's hearing loss, vertigo and visual problems improved, but the ABR findings remained unchanged. We have decided to present this case because of the interesting ABR finding revealing the presence of wave I and the absence of all other waves after the normalization of the hearing.

Brain stem auditory-evoked potentials of mice with experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is an experimental model for multiple sclerosis. In order to study autoimmune retrocochlear hearing loss, we performed brain stem auditory-evoked potential (BAEP) studies on EAE mice. The EAE was induced in B10.PL and (PL/J x SJL)F1 mice. In the BAEP study, all of the peak and interpeak latencies were prolonged significantly in the diseased mice. Hearing thresholds were slightly elevated in the immunized mice during the acute phase. Inflammatory and phagocytic cell infiltration, demyelination, and V beta 8.1, 8.2 T-cell receptor-positive cells were observed in the cochlear nerves or their proximity by histologic study. It is suggested that immunologic reactions identified with EAE also occurred in the cochlear nerve, and that these reactions were responsible for the hearing problems. It appears that EAE is a useful model system for studying autoimmune insults on the neural portion of the auditory system.

Clinical application of distorted speech audiometry

The clinical validity of four different low-redundant speech tests was calculated using four groups of 83 patients with retrocochlear or central auditory lesions. The speech tests used were: interrupted speech (7 or 10 interruptions/s) time-compressed speech and filtered speech. A comparison between patients and age-matched normal-hearing controls showed that the patients had significantly lower speech recognition score. The best sensitivity ratings of the tests were between 47% and 80%, the highest in patients with cerebellopontine angle tumours and temporal lobe lesions, and the lowest in vascular brainstem lesions. The speech tests with the highest sensitivity were 7 interruptions/s and time-compressed speech.

Lateralization and discrimination of dichotic clicks: evidence from patients with brainstem lesions and normal cohorts

The ability to lateralize and discriminate dichotic clicks was tested in multiple sclerosis patients with normal audiograms and in normal cohorts. Lateral position spread over a greater range with interaural level differences than with interaural time differences, and was related to the two asymmetries by different functions. Measures of binaural acuity were inversely related to the slopes of the two functions. One group of patients performed normally with both types of interaural asymmetry, another group performed normally only with level differences; a third group of patients could not perform normally with either.

Clinical correlates of brain-stem auditory evoked potential variables in multiple sclerosis. Relation to click polarity

The correlations between clinical signs and BAEP latency, amplitude and dispersion variables were investigated in 98 multiple sclerosis patients. A new dispersion variable, the wave IV-V "shape ratio" (SR IV-V), correlated most strongly with brain-stem signs (i.e., nystagmus). Severely reduced wave IV-V amplitude was frequently found in patients with vertical nystagmus or internuclear ophthalmoplegia, and interpeak latency (IPL) III-V correlated most strongly with cerebellar dysfunction (i.e., ataxia). The results may reflect different localizing ability among the various BAEP variables. The association between ataxia and increased IPL III-V was significantly stronger for BAEP to C clicks than to R clicks. Patients with abnormal BAEPs to one polarity (C or R) but not to the other, had significantly more clinical dysfunction than patients with normal BAEPs to both C and R clicks. Hence, C vs. R discordance may be interpreted to indicate possible brain-stem dysfunction.

The choice of ABR click polarity and amplitude variables in multiple sclerosis patients

Evoked brainstem responses (ABR) to 75 dB nHL condensation (C), rarefaction (R), and alternating (A = C+R) clicks were investigated in healthy subjects and in patients with multiple sclerosis. A new wave IV-V 'shape ratio' (SR IV-V) was most sensitive. SR IV-V correlated most strongly with clinical MS classification, and seemed to be rather specific for retrocochlear dysfunction. Wave IV-V amplitude was also more sensitive than the common IV-V amplitude ratio. The variability of latencies and interpeak latencies was lower in ABR to A clicks than in ABR to either R or to C clicks. In patients, fewer subcomponents were found in ABR to A than in ABR to R and C clicks. ABR to A clicks were on the average slightly more sensitive than either C or R click ABR. Our results suggest that both A-mode ABR and the 'dispersion' variable SR IV-V can be used without significant problems in the diagnosis of brainstem demyelination. A test protocol which requires ABR to both C and R clicks to be abnormal, will, however, be less sensitive, though probably more specific.

Eighth nerve signs in a case of multiple sclerosis

We evaluated a 25-year-old woman with multiple sclerosis who presented with the acute onset of a profound unilateral high-frequency, sensorineural hearing loss that resolved clinically within 10 days. Click-elicited brain stem-evoked responses were abnormal at the time of presentation and demonstrated only limited recovery over a follow-up period of 11 months. Magnetic resonance imaging disclosed a lesion in the eighth nerve root-entry zone and the cochlear nucleus. Our findings in this case support the hypothesis of eighth nerve root-entry zone involvement in sudden hearing loss in multiple sclerosis and reinforce the notion that click-elicited brain stem-evoked responses are useful primarily to evaluate the high-frequency regions of the auditory system.

Clinical application of brain-stem audiometry

Based on the examination of 249 consecutive patients, the usefulness of brain-stem response audiometry in a major audiological clinic was evaluated. Auditory brain-stem responses were performed either for hearing threshold determination (67 patients) or for assessment of retrocochlear hearing loss (182 patients). The results demonstrate that ABR is a reliable method for the estimation of hearing thresholds in non-cooperative subjects. The rate of false positives was 5% and no false negatives were found. In combination with caloric testing, ABR is considered a valuable testing procedure in the audiological clinic and it may form the basis for submission to brain imaging examination when a suspicion of retrocochlear hearing disorder is raised. Concerning the diagnosis of retrocochlear hearing disorder, no false negatives have yet been found, while a rate of 13% of false positives has been indicated.