Pure-tone auditory thresholds are not chronically elevated in multiple sclerosis

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.

An investigation of auditory processing in relapsing-remitting multiple sclerosis

Multiple sclerosis (MS) is one of the most common neurological diseases in North America and it is frequently associated with sensory processing difficulties, cognitive deficits, and psychiatric illness. While many studies have examined cognitive deficits in MS measured by behavioural responses and neuroimaging techniques, only a few studies have examined neurophysiological measures of auditory functioning in MS, such as the mismatch negativity (MMN). The MMN is an event-related potential that indicates automatic auditory change detection. This study examined whether MMN endpoints measured by electroencephalography (EEG) differ in individuals with relapsing-remitting MS compared to healthy controls and whether the symptomatology of MS, including symptoms of depression and fatigue, are related to MMN measures. A multi-feature MMN paradigm, which includes five distinct deviant tones, was used to assess auditory cortex function in MS. There were no significant differences in MMN amplitudes or latencies between the MS and control group (p < 0.05) and corresponding effect sizes were small. However, there was a correlation between reduced MMN amplitudes in response to an intensity deviant and physician-reported disability. The intensity MMN may be more sensitive to deterioration in this population. Ultimately, this study provides a comprehensive profile of early auditory processing abilities in MS and suggests that a reduction in the MMN response may be representative of disease severity in MS.

Discriminating spatialised speech in complex environments in multiple sclerosis

People with multiple sclerosis (pwMS) frequently present with deficits in binaural processing used for sound localization. This study examined spatial release from speech-on-speech masking in pwMS, which involves binaural processing and additional higher level mechanisms underlying streaming, such as spatial attention. 26 pwMS with mild severity (Expanded Disability Status Scale score <3) and 20 age-matched controls listened via headphones to pre-recorded sentences from a standard list presented simultaneously with eight-talker babble. Virtual acoustic techniques were used to simulate sentences originating from 0°, 20°, or 50° on the interaural horizontal plane around the listener whilst babble was presented continuously at 0° azimuth, and participants verbally repeated the target sentence. In a separate task, two simultaneous sentences both containing a colour and number were presented, and participants were required to report the target colour and number. Both competing sentences could originate from 0°, 20°, or 50° on the azimuthal plane. Participants also completed a series of neuropsychological assessments, an auditory questionnaire, and a three-alternative forced-choice task that involved the detection of interaural time differences (ITDs) in noise bursts. Spatial release from masking was observed in both pwMS and controls, as response accuracy in the two speech discrimination tasks improved in the spatially separated conditions (20° and 50°) compared with the co-localised condition. However, pwMS demonstrated significantly less spatial release (18%) than controls (28%) when discriminating colour/number coordinates. At 50° separation, pwMS discriminated significantly fewer coordinates (77%) than controls (89%). In contrast, pwMS had similar performances to controls when sentences were presented in babble, and for the basic ITD discrimination task. Significant correlations between speech discrimination performance and standardized neuropsychological scores were observed across all spatial conditions. Our findings suggest that spatial hearing is likely to be implicated in pwMS, thereby affecting the perception of competing speech originating from various locations.

Effects of multiple sclerosis on the audio-vestibular system: a systematic review

OBJECTIVE

Systematically investigate the effects of multiple sclerosis (MS) on the audio-vestibular system.

METHODS

Systematic review of literature investigating audio-vestibular conditions in persons with MS (PwMS) aged ≥18 years. PubMed, Scopus, NICE and Web of Science were searched. Randomised controlled trials, and cohort, case-control, observational and retrospective studies in English, published from 2000 to 21 November 2021, evaluated PwMS with at least one outcome (pure tone audiometry, auditory brainstem response, otoacoustic emissions, cortical auditory evoked potentials, functional MRI assessing auditory function, vestibular evoked myogenic potentials, videonystagmography, electronystagmography, posturography, rotary chair, gaps in noise, word discrimination scores, duration pattern sequence test), were included. Study selection and assessments of bias were independently conducted by two reviewers using the Risk of Bias Assessment Tool for Non-randomized Studies, Newcastle-Ottawa Scale (NOS) and the NOS adapted for cross-sectional studies.

RESULTS

35 studies were included. Auditory function was evaluated in 714 PwMS and 501 controls, vestibular function was evaluated in 682 PwMS and 446 controls. Peripheral auditory function results were contradictory between studies; some found abnormalities in PwMS, and others found no differences. Tests of brainstem and central auditory functions were more consistently found to be abnormal in PwMS. Most vestibular tests were reported as abnormal in PwMS, abnormalities were either peripheral or central or both. However, quantitative analyses could not be performed due to discrepancies between studies in results reporting, test stimulus and recording parameters.

CONCLUSIONS

Although abnormal results on auditory and vestibular tests were noted in PwMS, specific effects of MS on the audio-vestibular system could not be determined due to the heterogeneity between studies that restricted the ability to conduct any quantitative analyses. Further research with consistent reporting, consistent stimulus and consistent recording parameters is needed in order to quantify the effects of MS on the auditory and vestibular systems.

PROSPERO REGISTRATION NUMBER

CRD42020180094.

Axon-glia interactions in the ascending auditory system

The auditory system detects and encodes sound information with high precision to provide a high-fidelity representation of the environment and communication. In mammals, detection occurs in the peripheral sensory organ (the cochlea) containing specialized mechanosensory cells (hair cells) that initiate the conversion of sound-generated vibrations into action potentials in the auditory nerve. Neural activity in the auditory nerve encodes information regarding the intensity and frequency of sound stimuli, which is transmitted to the auditory cortex through the ascending neural pathways. Glial cells are critical for precise control of neural conduction and synaptic transmission throughout the pathway, allowing for the precise detection of the timing, frequency, and intensity of sound signals, including the sub-millisecond temporal fidelity is necessary for tasks such as sound localization, and in humans, for processing complex sounds including speech and music. In this review, we focus on glia and glia-like cells that interact with hair cells and neurons in the ascending auditory pathway and contribute to the development, maintenance, and modulation of neural circuits and transmission in the auditory system. We also discuss the molecular mechanisms of these interactions, their impact on hearing and on auditory dysfunction associated with pathologies of each cell type.

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.

Speech discrimination impairments as a marker of disease severity in multiple sclerosis

BACKGROUND

Multiple Sclerosis (MS) pathology is likely to disrupt central auditory pathways, thereby affecting an individual's ability to discriminate speech from noise. Despite the importance of speech discrimination in daily communication, it's characterization in the context of MS remains limited. This cross-sectional study evaluated speech discrimination in MS under "real world" conditions where sentences were presented in ecologically valid multi-talker speech or broadband noise at several signal-to-noise ratios (SNRs).

METHODS

Pre-recorded Bamford-Kowal-Bench sentences were presented at five signal-to-noise ratios (SNR) in one of two background noises: speech-weighted noise and eight-talker babble. All auditory stimuli were presented via headphones to control (n = 38) and MS listeners with mild (n = 20), moderate (n = 16) and advanced (n = 10) disability. Disability was quantified by the Kurtzke Expanded Disability Status Scale (EDSS) and scored by a neurologist. All participants passed a routine audiometric examination.

RESULTS

Despite normal hearing, MS psychometric discrimination curves which model the relationship between signal-to-noise ratio (SNR) and sentence discrimination accuracy in speech-weighted noise and babble did not change in slope (sentences/dB) but shifted to higher SNRs (dB) compared to controls. The magnitude of the shift in the curve systematically increased with greater disability. Furthermore, mixed-effects models identified EDSS score as the most significant predictor of speech discrimination in noise (odds ratio = 0.81; p < 0.001). Neither age, sex, disease phenotype or disease duration were significantly associated with speech discrimination performance in noise. Only MS listeners with advanced disability self-reported audio-attentional difficulty in a questionnaire designed to reflect auditory processing behaviours in daily life.

CONCLUSION

Speech discrimination performance worsened systematically with greater disability, independent of age, sex, education, disease duration or disease phenotype. These results identify novel auditory processing deficits in MS and highlight that speech discrimination tasks may provide a viable non-invasive and sensitive means for disease monitoring in MS.

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.

Audiovestibular Symptoms in Systemic Autoimmune Diseases

Immune-mediated inner ear disease can be primary, when the autoimmune response is against the inner ear, or secondary. The latter is characterized by the involvement of the ear in the presence of systemic autoimmune conditions. Sensorineural hearing loss is the most common audiovestibular symptom associated with systemic autoimmune diseases, although conductive hearing impairment may also be present. Hearing loss may present in a sudden, slowly, rapidly progressive or fluctuating form, and is mostly bilateral and asymmetric. Hearing loss shows a good response to corticosteroid therapy that may lead to near-complete hearing restoration. Vestibular symptoms, tinnitus, and aural fullness can be found in patients with systemic autoimmune diseases; they often mimic primary inner ear disorders such as Menière's disease and mainly affect both ears simultaneously. Awareness of inner ear involvement in systemic autoimmune diseases is essential for the good response shown to appropriate treatment. However, it is often misdiagnosed due to variable clinical presentation, limited knowledge, sparse evidence, and lack of specific diagnostic tests. The aim of this review is to analyse available evidence, often only reported in the form of case reports due to the rarity of some of these conditions, of the different clinical presentations of audiological and vestibular symptoms in systemic autoimmune diseases.

Balance in multiple sclerosis: relationship to central brain regions

Dizziness, postural instability, and ataxia are among the most debilitating symptoms of multiple sclerosis (MS), reflecting, in large part, dysfunctional integration of visual, somatosensory, and vestibular sensory cues. However, the role of MS-related supratentorial lesions in producing such symptoms is poorly understood. In this study, motor control test (MCT) and dynamic sensory organization test (SOT) scores of 58 MS patients were compared to those of 72 healthy controls; correlations were determined between the MS scores of 49 patients and lesion volumes within 26 brain regions. Depending upon platform excursion direction and magnitude, MCT latencies, which were longer in MS patients than controls (p < 0.0001), were correlated with lesion volumes in the cortex, medial frontal lobes, temporal lobes, and parietal opercula (r's ranging from 0.20 to 0.39). SOT test scores were also impacted by MS and correlated with lesions in these same brain regions as well as within the superior frontal lobe (r's ranging from - 0.28 to - 0.40). The strongest and most consistent correlations occurred for the most challenging tasks in which incongruent visual and proprioceptive feedback were given. This study demonstrates that supratentorial lesion volumes are associated with quantitative balance measures in MS, in accord with the concept that balance relies upon highly convergent and multimodal neural pathways involving the skin, muscles, joints, eyes, and vestibular system.

Subcortical pathways: Towards a better understanding of auditory disorders

Hearing loss is a significant problem that affects at least 15% of the population. This percentage, however, is likely significantly higher because of a variety of auditory disorders that are not identifiable through traditional tests of peripheral hearing ability. In these disorders, individuals have difficulty understanding speech, particularly in noisy environments, even though the sounds are loud enough to hear. The underlying mechanisms leading to such deficits are not well understood. To enable the development of suitable treatments to alleviate or prevent such disorders, the affected processing pathways must be identified. Historically, mechanisms underlying speech processing have been thought to be a property of the auditory cortex and thus the study of auditory disorders has largely focused on cortical impairments and/or cognitive processes. As we review here, however, there is strong evidence to suggest that, in fact, deficits in subcortical pathways play a significant role in auditory disorders. In this review, we highlight the role of the auditory brainstem and midbrain in processing complex sounds and discuss how deficits in these regions may contribute to auditory dysfunction. We discuss current research with animal models of human hearing and then consider human studies that implicate impairments in subcortical processing that may contribute to auditory disorders.

Multiple sclerosis: Left advantage for auditory laterality in dichotic tests of central auditory processing and relationship of psychoacoustic tests with the Multiple Sclerosis Disability Scale-EDSS

OBJECTIVE

To evaluate the central auditory processing disorders in patients with multiple sclerosis, emphasizing auditory laterality by applying psychoacoustic tests and to identify their relationship with the Multiple Sclerosis Disability Scale (EDSS) functions.

METHOD

Depression scales (HADS), EDSS, and 9 psychoacoustic tests to study CAPD were applied to 26 individuals with multiple sclerosis and 26 controls. Correlation tests were performed between the EDSS and psychoacoustic tests.

RESULTS

Seven out of 9 psychoacoustic tests were significantly different (P<.05); right or left (14/19 explorations) with respect to control. In dichotic digits there was a left-ear advantage compared to the usual predominance of RDD. There was significant correlation in five psychoacoustic tests and the specific functions of EDSS.

CONCLUSION

The left-ear advantage detected and interpreted as an expression of deficient influences of the corpus callosum and attention in multiple sclerosis should be investigated. There was a correlation between psychoacoustic tests and specific EDSS functions.

Myelin development, plasticity, and pathology in the auditory system

Myelin allows for the rapid and precise timing of action potential propagation along neuronal circuits and is essential for healthy auditory system function. In this article, we discuss what is currently known about myelin in the auditory system with a focus on the timing of myelination during auditory system development, the role of myelin in supporting peripheral and central auditory circuit function, and how various myelin pathologies compromise auditory information processing. Additionally, in keeping with the increasing recognition that myelin is dynamic and is influenced by experience throughout life, we review the growing evidence that auditory sensory deprivation alters myelin along specific segments of the brain's auditory circuit. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 80-92, 2018.

Unilateral olfactory sensitivity in multiple sclerosis

It is not known whether lateralized olfactory sensitivity deficits are present in MS. Since projections from the olfactory bulb to the olfactory cortex are largely ipsilateral, and since both functional imaging and psychophysical studies suggest that the right side of the brain may be more involved in olfactory processing than the left, we addressed this issue by administering well-validated tests of odor detection, along with tests of odor identification, to each side of the nose of 73 MS patients and 73 age-, gender-, and race-matched normal controls. We also determined, in 63 of the MS patients, whether correlations were present between the olfactory test measures and MRI-determined lesions in brain regions ipsilateral and contralateral to the nose side that was tested. No significant left:right differences in either olfactory sensitivity or identification were present, although in both cases mean performance was lower in the MS than in the control subjects (ps<0.0001). Scores on the two sides of the nose were positively correlated with one another (threshold r=0.56, p<0.0001; Identification r=0.71, p<0.0001). The percent of MS patients whose bilateral test scores fell below the 10th percentile of controls did not differ between the odor identification and detection threshold tests. Both left and right odor identification and detection test scores were weakly correlated with lesion volumes in temporal and frontal lobe brain regions (r's<0.40). Our findings demonstrate that MS does not differentially influence odor perception on left and right sides of the nose, regardless of whether sensitivity or identification is being measured. They also indicate that tests of odor identification and detection are similarly influenced by MS and that such influences are associated with central brain lesions.

Taste dysfunction in multiple sclerosis

Empirical studies of taste function in multiple sclerosis (MS) are rare. Moreover, a detailed assessment of whether quantitative measures of taste function correlate with the punctate and patchy myelin-related lesions found throughout the CNS of MS patients has not been made. We administered a 96-trial test of sweet (sucrose), sour (citric acid), bitter (caffeine) and salty (NaCl) taste perception to the left and right anterior (CN VII) and posterior (CN IX) tongue regions of 73 MS patients and 73 matched controls. The number and volume of lesions were assessed using quantitative MRI in 52 brain regions of 63 of the MS patients. Taste identification scores were significantly lower in the MS patients for sucrose (p = 0.0002), citric acid (p = 0.0001), caffeine (p = 0.0372) and NaCl (p = 0.0004) and were present in both anterior and posterior tongue regions. The percent of MS patients with identification scores falling below the 5th percentile of controls was 15.07 % for caffeine, 21.9 % for citric acid, 24.66 % for sucrose, and 31.50 % for NaCl. Such scores were inversely correlated with lesion volumes in the temporal, medial frontal, and superior frontal lobes, and with the number of lesions in the left and right superior frontal lobes, right anterior cingulate gyrus, and left parietal operculum. Regardless of the subject group, women outperformed men on the taste measures. These findings indicate that a sizable number of MS patients exhibit taste deficits that are associated with MS-related lesions throughout the brain.

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.

Deafness in patients with multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease and is considered the most debilitating neurological disorder among young adults. Sudden deafness has been reported in MS patients. This article describes cases of sudden deafness related to acute bouts in MS patients. A survey was conducted using 405 records of MS patients attended to at a reference center in the city of Rio de Janeiro between 2011 and 2012 to identify cases of sudden deafness. Seven patients were identified, 6 with a relapsing-remitting course and 1 with progressive disease at onset. Five patients had unilateral deafness and 2 bilateral. The recovery was complete in 4 and partial in 1, and there was no recovery in 2 patients. It was not possible to establish a topographical correlation between deafness and brainstem lesions. Audiometric examinations revealed severe hearing loss during the bout and recovery of hearing in 5 cases after remission.

Sound Lateralization Test Distinguishes Unimpaired MS Patients from Healthy Controls

There is an urgent need to develop a practical and reliable clinical measure of disease progression in early and mild MS. We hypothesized that a test of sound lateralization, which is exquisitely sensitive to transmission delays in auditory brainstem, could be more useful for detecting processing speed deficits in mildly impaired MS subjects than standard cognitive tasks. Objective. To develop a practical test of sound lateralization for the clinic and to compare performance of MS subjects with variable disability and healthy subjects on Sound Lateralization Test (SLT) and two speed-of-processing tasks. Design. 42 healthy controls and 90 subjects with clinically definite MS, divided into no, mild, and moderate disability strata, were administered the Symbol Digit Modalities Test (SDMT), and 3-second Paced Auditory Serial Addition Test (PASAT). Results. All of the tests showed an overall difference in performance between controls and the three MS groups, but only the SLT measured a significant difference between controls and the no disability group. Conclusion. SLT is rapidly applied, technically simple, and superior to standard processing speed tests for discriminating between healthy controls and nondisabled MS subjects. SLT should be investigated as an outcome measure in early-phase trials and for monitoring early disease progression in the clinic.

Recent onset disequilibrium mimicking acute vestibulopathy in early multiple sclerosis

The differential diagnosis of patients with acute unilateral vestibulopathy rests in the proper clinical assessment and use of selected tests of vestibular function. In case of a central nervous system lesion as in Multiple Sclerosis, the case shown here, it is of particular importance to observe congruency between severity of symptoms and signs and, of topographic diagnosis. We report a case of a 37-year-old woman with recent onset disequilibrium that after careful analysis of the different test results several incongruences were found; this prompted a radiological study that provided the clue to diagnosis. After treatment the patient recovered completely not only clinically but also in vestibular deficit.