Wave I of early auditory evoked potentials in multiple sclerosis

Role of acute cochlear neuritis in sudden hearing loss in multiple sclerosis

We report a patient with definite multiple sclerosis (MS) who developed unilateral sudden hearing loss coincident with exacerbation of central nervous system symptoms. Involvement of the peripheral cochlear nerve, suggested by auditory findings including auditory brainstem response, was confirmed by magnetic resonance imaging. The clinical, electrophysiological and neuroradiological abnormalities disappeared in response to steroid pulse therapy. These findings suggest that acute inflammatory demyelinative lesion of the peripheral cochlear nerve can occur in MS, manifesting sudden hearing loss.

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.

Hearing loss in multiple sclerosis: localization of the auditory pathway lesion according to electrocochleographic findings

Multiple sclerosis is known to affect the myelin of the auditory pathway resulting in acute hearing loss. Two cases of sudden deafness due to multiple sclerosis have been evaluated by conventional audiometry, brainstem auditory evoked response audiometry and transtympanic electrocochleography. The abnormalities of the compound action potential in both patients (enhanced latency, abnormal adaptation using fast stimulus rate) and the normal receptor potentials (cochlear microphonic, summating potential), as well as the absence of brainstem responses suggest a disturbance of synchronization at the level of the first auditory neurone. The electrocochleography provides valuable information for the topodiagnosis of this and other neural hearing losses, especially in the absence of reliable brainstem responses.

Effects of multiple sclerosis brainstem lesions on sound lateralization and brainstem auditory evoked potentials

Magnetic resonance (MR) imaging, brainstem auditory evoked potentials (BAEPs), and tests of interaural time and level discrimination were performed on sixteen subjects with multiple sclerosis (MS). Objective criteria were used to define MR lesions. Of the eleven subjects in whom no pontine lesions were detected and the one subject who had pontine lesions that did not encroach upon the auditory pathways, all had normal BAEPs and interaural level discrimination, although a few had abnormal interaural time discrimination. Of four subjects with lesions involving the pontine auditory pathway, all had both abnormal BAEPs and abnormal interaural time discrimination; one also had abnormal interaural level discrimination. Analysis of the data suggest the following: waves I and II are generated peripheral to the middle of the ventral acoustic stria (VAS); wave III is generated ipsilaterally in the region of the rostral VAS, caudal superior olivary complex (SOC) and trapezoid body (TB); and waves V and L are generated contralaterally, rostral to the SOC-TB. The region of the ipsilateral rostral SOC-TB is implicated as part of the pathway involved in the generation of waves V and L. Interaural time discrimination of both high and low frequency stimuli were affected by all brainstem lesions that encroached on auditory pathways. A unilateral lesion in the region of the LL affected interaural time discrimination for low-frequency stimuli less severely than bilateral lesions of the LL or a unilateral lesion of the VAS. The only interaural level discrimination abnormality occurred for a subject with a unilateral lesion involving the entire rostral VAS. It appears that detailed analysis of lesion locations coupled with electrophysiological and psychophysical data holds promise for testing hypotheses concerning the function of various human auditory brainstem structures.

Binaural auditory processing in multiple sclerosis subjects

In order to relate human auditory processing to physiological and anatomical experimental animal data, we have examined the interrelationships between behavioral, electrophysiological and anatomical data obtained from human subjects with focal brainstem lesions. Thirty-eight subjects with multiple sclerosis were studied with tests of interaural time and level discrimination (just noticeable differences or jnds), brainstem auditory evoked potentials and magnetic resonance (MR) imaging. Interaural testing used two types of stimuli, high-pass (> 4000 Hz) and low-pass (< 1000 Hz) noise bursts. Abnormal time jnds (Tjnd) were far more common than abnormal level jnds (70% vs 11%); especially for the high-pass (Hp) noise (70% abnormal vs 40% abnormal for low-pass (Lp) noise). The HpTjnd could be abnormal with no other abnormalities; however, whenever the BAEPs, LpTjnd and/or level jnds were abnormal HpTjnd was always abnormal. Abnormal wave III amplitude was associated with abnormalities in both time jnds, but abnormal wave III latency with only abnormal HpTjnds. Abnormal wave V amplitude, when unilateral, was associated with a major HpTjnd abnormality, and, when bilateral, with both HpTjnd and LpTjnd major abnormalities. Sixteen of the subjects had their MR scans obtained with a uniform protocol and could be analyzed with objective criteria. In all four subjects with lesions involving the pontine auditory pathway, the BAEPs and both time jnds were abnormal. Of the twelve subjects with no lesions involving the pontine auditory pathway, all had normal BAEPs and level jnds, ten had normal LpTjnds, but only five had normal HpTjnds. We conclude that interaural time discrimination is closely related to the BAEPs and is dependent upon the stimulus spectrum. Redundant encoding of low-frequency sounds in the discharge patterns of auditory neurons, may explain why the HpTjnd is a better indicator of neural desynchrony than the LpTjnd. Encroachment of MS lesions upon the pontine auditory pathway always is associated with abnormal BAEPs and abnormal interaural time discrimination but may have normal interaural level discrimination. Our data provide one of the most direct demonstrations in humans of relationships among auditory performance, evoked potentials and anatomy. We present a model showing that many of these interrelationships can be readily interpreted using ideas developed from work on animals, even though these relationships could not have been predicted with confidence beforehand. This work provides a clear advance in our understanding of human auditory processing and should serve as a basis for future studies.

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.

Demyelinating optic neuropathy with Miller-Fisher syndrome. The case for overlap syndromes with central and peripheral demyelination

The syndrome of ataxia, areflexia and ophthalmoplegia, or Miller-Fisher syndrome, has been considered to be a variant of Guillain-Barré syndrome with pathology restricted to the peripheral nervous system. A patient with Miller-Fisher syndrome and bilateral demyelinating optic neuropathy suggesting associated central nervous system pathology is presented. Clinical and experimental evidence regarding the association of central and peripheral nervous system demyelination is reviewed.

The acute deafness of definite multiple sclerosis: BAEP patterns

Of 705 patients with or suspected of multiple sclerosis who underwent evoked potential recording during a 5 year period, 12 patients with definite multiple sclerosis experienced an acute hearing loss during a relapse of the demyelinating disease. Hearing loss was unilateral in all of the 12 cases but one; tinnitus was associated with hearing loss in 9 of the 12 patients. Deafness is an unfrequent symptom in the course of multiple sclerosis, being estimated to be no more than 3% in large series of multiple sclerosis. Brain-stem auditory evoked potentials were recorded in all 12 patients, during the relapse with acute hearing loss in 4 of them, after the relapse with hearing loss in the 8 others. During the relapse with hearing loss, BAEP abnormalities were present ipsilateral to the hearing loss in all 4 patients, wave I being absent in 2 of them. BAEPs were drastically improved when recorded after the relapse with hearing loss in 2 of the 3 patients in whom repeated records were made. BAEPs were abnormal on the side of the previous hearing loss in 5 out of the 8 patients recorded after the relapse with hearing loss. Clinical and BAEP data suggest that, in accordance with the anatomical organization of the auditory pathways, the lesion causing unilateral hearing loss in multiple sclerosis could be situated in the cochlear nerve or close to its entry zone in the brain-stem. However, dissociation between unilateral hearing loss and a normal peak I and I-III interval may occur.