Brain stem auditory evoked potentials and blink reflexes in quiescent multiple sclerosis

The conditioned eyeblink reflex: a potential tool for the detection of cerebellar dysfunction in multiple sclerosis

The delayed conditioned eyeblink reflex, in which an individual learns to close the eyelid in response to a conditioned stimulus (e.g. a tone) relies entirely on the functional integrity of a cerebellar motor circuitry that involves the contingent activation of Purkinje cells by parallel and climbing fibres. Molecular changes that disrupt the function of this circuitry, in particular a loss of type-1 metabotropic glutamate receptors (mGlu1 receptors), occur in Purkinje cells of patients with multiple sclerosis and in mice with experimental autoimmune encephalomyelitis as a result of neuroinflammation. mGlu1 receptors are required for cerebellar motor learning associated with the conditioned eyeblink reflex. We propose that the delayed paradigm of the eyeblink conditioning might be particularly valuable for the detection of subtle abnormalities of cerebellar motor learning that are clinically silent and are not associated with demyelinating lesions or axonal damage. In addition, the test might have predictive value following a clinically isolated syndrome, and might be helpful for the evaluation of the efficacy of drug treatment in multiple sclerosis.

Supratentorial multiple sclerosis lesions affect the blink reflex test

INTRODUCTION

The Blink Reflex Test (BRT) is a neurophysiological examination used for evaluation of brainstem reflex circuits. MRI is the most precise modality for evaluation of MS lesion anatomy. Our study objective was to investigate how the functional results of the neurophysiological BRT relate to the anatomy of MS lesions in routine MRI studies.

METHODS

65 MS patients underwent the BRT within 2 months of a brain MRI showing demyelinating lesions.

RESULTS

The overall sensitivity of the BRT was 90.8%, while in patients with at least one brainstem lesion and no brainstem lesions it was 91.4% and 90%, respectively.

DISCUSSION

The presence of brainstem lesions does not significantly affect BRT sensitivity. This points to the influence of supratentorial MS lesions on the BRT. Gender, age, disease duration, type of MS, acuteness of an MS event and whether MS diagnosis was recent or not were not variables affecting the results.

A comparison of auditory evoked potentials derived from a monitor integrated module versus standard technique

PURPOSE

Measurement of brain stem auditory evoked potentials (BAEP) and midlatency auditory evoked potentials (MLAEP) using a new monitor integrated module was compared with an established device. The aim of this study was to evaluate if the new system could replace the more inconvenient established technique.

MATERIAL AND METHODS

MLAEP and BAEP were obtained from 19 anesthetized male patients using the AEP-Module for Monitor S/5 [GE, Helsinki, Finland (S/5)] and Neuropack 4 mini [Nihon Kohden, Tokyo, Japan (Neuropack)]. Significance of different results was calculated by paired t test. Bias was estimated by Bland-Altman statistics.

RESULTS

Latencies of BAEP were significantly shorter and amplitudes of BAEP were significantly higher for Neuropack. Mean latencies of MLAEP (Pa and Nb) were not significantly different (Pa 44.1+/-4.4 ms vs. 41.9+/-5.4 ms/Nb 66.4+/-5.6 ms vs. 62.8+/-6.5 ms), but methods are not interchangeable owing to great variability (Pa -13.16 to 8.94 ms, Nb -19.15 to 11.79 ms).

CONCLUSIONS

BAEP recorded by S/5 cannot be used for diagnostic interpretation using generally accepted normal values, but can be used for examining changes during the monitoring period. Mean values of Pa and Nb were not significantly different, but values of the S/5 varied above and below the values of Neuropack such that the measurements could not be used for diagnostic interpretation. However, this did not reduce their usefulness for determining adequate hypnosis.

Wavelet decomposition of the blink reflex R2 component enables improved discrimination of multiple sclerosis

OBJECTIVES

The blink reflex R2 component was subjected to wavelet decomposition for time feature extraction in order to classify the functional status of patients with multiple sclerosis.

METHODS

The blink reflex was recorded bilaterally with unilateral stimulation of the supra-orbital nerve in 37 normal subjects and 9 patients with multiple sclerosis (MS). The late component, R2, was subjected to time-frequency decomposition using the Daubechies-4 wavelet. Using the time-frequency coefficients, the mean time of the R2 wave as well as the standard deviation of the R2 interval were calculated in each trial. The wavelet transform enables noise reduction by allowing selective use of frequency bands with high signal-to-noise ratio for time feature extraction; therefore automatic estimation of time parameters is robust. The distribution densities of the mean and the standard deviation of the R2 wave duration for the set of trials for each subject were computed.

RESULTS

An appreciable difference in the densities of the two parameters extracted in the wavelet domain was seen between normals and patients. This is in contrast to the onset latency of R2 which poorly discriminates MS patients from normals.

CONCLUSION

The results suggest that the mean and standard deviation of the R2-time robustly estimated using wavelet decomposition can be used to support clinical diagnosis in tracking the functional status of patients with diseases like multiple sclerosis.

Auditory brain stem response and electrically elicited blink reflex in handicapped children

The auditory brain stem response and the blink reflex were studied in 35 handicapped children in order to evaluate brain stem function. The auditory brain stem response and the blink reflex were abnormal in 20 and 16 cases, respectively. Of these, 14 had both auditory brain stem response and blink reflex abnormalities. The prevalence of auditory brain stem response and blink reflex abnormalities was high in severely handicapped children with difficulty in chewing or swallowing. The blink reflex was abnormal in four of 32 sides with a normal auditory brain stem response and 15 of 23 sides with an abnormal auditory brain stem response threshold, which reflects hearing loss or brain stem dysfunction. We conclude that the combined application of these two noninvasive tests is useful not only to delineate the extent of brain stem lesions but also to determine whether or not patients with an abnormal auditory brain stem response threshold have brain stem dysfunction.

Electrically elicited blink reflex and early acoustic evoked potentials in circumscribed and diffuse brain stem lesions

In the present paper, the function of the brain stem in patients with brain stem lesions of various aetiology is investigated with electrophysiological methods. The clinical observations are supplemented by experimental investigations on cats, in which the blink reflex and the early acoustic evoked potentials were registered during the acute elevation of intracranial pressure. The findings in patients with circumscribed space-occupying lesions in the posterior fossa document that the registration of the BR and the BAEP have a functional diagnostic significance above and beyond the neurological and radiological investigation. In the case of the cerebellar space occupations, specific alterations could not be observed. On the contrary, the alterations of BR and BAEP indicate a general disturbance of brain stem function, possibly as a result of a general increase of intracranial pressure. In cerebellopontine angle tumours, both BR and BAEP showed specific alterations which were usually asymmetrical. The BR changes ipsilateral to the tumour are of major topodiagnostic significance, whereas the alterations of the contralateral potential are especially informative in the registration of BAEP. The alterations of BR and BAEP also allow an appraisal of the localization and extent of the lesion in primary space occupations in the brain stem: A pathological R1 indicates a pontine lesion, whereas pathological R2 responses are found in medullary and in oral pontine and mesencephalic lesions. In contrast to cerebellopontine angle tumours, the BAEP tends to show symmetrical alterations in primary brain stem lesions. The prolongations of interpeak latencies correspond to the brain stem segment concerned, and the same also applies to pathological amplitude reduction and deformations of individual potentials. In patients with localized brain stem damage, the reflex pathway of R2 is discussed on the basis of the BR findings. In contrast to the view held up to now that only structures situated caudal of the facial nucleus area are responsible for the genesis of the R2 response, it is assumed on the basis of our own observations that pontomesencephalic structures rostral to the facial nuclei are also important for the genesis of R2. Registration of BR and BAEP in patients with acute diffuse brain stem damage shows that both methods have a high diagnostic and prognostic value. Isolated damage and combined brain stem lesion can be demonstrated and the course can be followed up. Normalization of pathological findings reflects clinical recovery, and conversely a secondary deterioration indicates the presence of complications.(ABSTRACT TRUNCATED AT 400 WORDS)

The diagnosis of multiple sclerosis. Contribution of non-clinical tests

A group of 89 patients in whom multiple sclerosis (MS) has been clinically diagnosed with varying degrees of certainty, and 25 patients with optic neuritis (ON), were subjected to the following electrophysiological tests: visual evoked response (VER), auditory brainstem-evoked response (ABER), somatosensory-evoked response (SSER), blink reflex and electronystagmography (ENG). All these patients also underwent computerized tomography (CT scan) and analysis of cerebrospinal fluid (CSF). A new diagnostic procedure is proposed, combining optimum detection of definite MS with optimally economical use of the above-mentioned non-clinical tests. The results for the MS patients show that definite MS can be diagnosed much more frequently (72%) if abnormal results in the above-mentioned tests are accepted as evidence of a (subclinical) CNS lesion. Application of the clinical diagnostic criteria of McAlpine yielded "definite MS" only in 27% of our patient material. Our diagnostic criteria showed evidence for MS in 36% of the patients clinically diagnosed as having ON. The test results were inconclusive as regards the possibility of the remaining ON patients developing MS in the future.

Jaw, blink and corneal reflex latencies in multiple sclerosis

Jaw, blink and corneal reflexes, which all involve the trigeminal system, were recorded in 54 patients with multiple sclerosis; thirty-seven of these patients were classified as having definite multiple sclerosis and 17 as indefinite multiple sclerosis, according to Schumacher's criteria. The jaw reflex was abnormal less frequently than either of the other two reflexes, but in four cases it was the only abnormal reflex found. Testing a combination of two or three trigeminal reflexes did not yield a higher incidence of abnormalities than testing the blink or corneal reflex alone. Nine patients showed abnormal reflexes which were unexpected on the basis of clinical symptoms. The combined recordings demonstrate at least one abnormal reflex in 74% of the patients. The various types of reflex abnormalities reflect major damage to different parts of the trigeminal system and may therefore make an important contribution to the diagnosis of multiple sclerosis.

Electrophysiological disorders in multiple sclerosis and optic neuritis

Visual evoked response (VER), auditory brainstem evoked response (ABER), somatosensory evoked response (SSER), blink reflex and electronystagmographic (ENG) investigative methods were applied to a group of 89 patients with Multiple Sclerosis (MS) and Optic Neuritis (ON). The MS patients were classified as definite (n = 31), probable (n = 31) and possible (n = 27). The aim of this study was to determine the diagnostic value of the five electrophysiological tests in MS. VER and ABER recordings were found to reveal the highest number of asymptomatic abnormalities (33 and 31 percent respectively). The combination of VER, ABER and ENG revealed all possible electrophysiological disorders. As these tests are completely non-invasive it is proposed, that a combination of two of these three tests is useful for the detection of a second silent lesion in patients with suspected MS showing purely spinal signs (VER, ENG, ABER) and/or a history of uncomplicated ON (ABER, ENG).

Brain stem auditory evoked potentials and blink reflexes in multiple sclerosis

Brain stem auditory evoked potentials (BAEP) and the blink reflex (BR) were recorded from 50 patients with a wide spectrum of multiple sclerosis, to determine whether the combination of the two tests of brain stem function would yield a higher rate of abnormality than each test performed alone. Sixty-four per cent of patients had a BAEP abnormality and fifty-two per cent had an abnormal BR, but when the results were combined, seventy-six per cent were abnormal. The blink reflex was abnormal in all patients with symptoms suggestive of trigemino-facial pathology.

Brainstem involvement in multiple sclerosis: a clinical and electrophysiological study

A major aim of this study was to determine the diagnostic value of 4 electrophysiological tests in MS, and particularly their effectiveness in detecting signs of brainstem involvement. Therefore, auditory brainstem evoked response (ABER), somatosensory evoked response (SSER), blink reflex and electronystagmographic (ENG) investigative methods were applied to a group of 89 patients with definite, probable or possible multiple sclerosis (MS). The 4 methods yielded interdependent data, especially where the brainstem function was concerned, thus it can be concluded that a single demyelinating lesion may cause a combination of electrophysiological disorders within a small structure such as the brainstem. ENG recordings were found to reveal the highest number of asymptomatic abnormalities. The combination of ABER and ENG tests revealed electrophysiological disorders in 81% of all patients. The blink reflex and the SSER tests gave hardly supplementary information.

Brain-stem auditory evoked responses (BAERs) in patients with chronic renal failure

Brain-stem auditory evoked responses have been investigated in 28 patients suffering from chronic renal failure (17 on diet, 11 on chronic dialysis) during monaural stimulation with 70 dB HL clicks. These responses were abnormal in 32.15% of cases. In 13 out of 15 years with altered BAERs a normal response morphology was present, with progressively more significant latency delays involving all peaks following wave I, while in the remaining two ears some of the components always found in healthy controls were not identifiable. The most prominent abnormality in patients with symptoms referable to peripheral neuropathy was the presence of a prolonged I-II interpeak latency, while in those without symptomatology the I-V and III-V interpeak times and the peak V latency were the most strikingly altered parameters. The incidence of altered BAERs was higher in the group of patients treated with diet than in the dialysed group. When BAERs were followed-up in the hours preceding and following the first dialysis in two patients not included in the previous group, the I-V interpeak time significantly decreased after 26 h from the end of dialysis.

Evoked potentials. With special reference to the diagnostic value in multiple sclerosis

A survey is given of my studies of evoked potentials in patients with multiple sclerosis (MS) and in control subjects. Potentials were recorded following random low-rate auditory stimulation (BAEP), checker-board pattern-reversal stimulation (VEP), somatosensory stimulation (SEP); blink reflexes (BR) were recorded following electrical stimulation of the supraorbital nerve. Normal data had to be related to age and sex in evaluating BAEPs and VEPs. In 160 MS patients, a total of 421 recordings were obtained. Changes by repeated BAEP and VEP tests might reflect changes in the clinical state, but they also did occur in clinically stable patients. In patients with definite MS, high incidences of abnormality were shown, supporting the clinical findings. The diagnostic value was greatest when clinically silent lesions were demonstrated in patients with suspected or possible MS. In these patients, either BAEP or VEP gave evidence of subclinical lesions in about 50%, and when combined, in 71% of the patients, thus making a transfer to a more certain diagnostic classification possible and invasive examinations unnecessary. When SEP and BR tests were added, subclinical lesions were found in 74% of the patients. The SEP recordings did show a high incidence of abnormality, but only few silent lesions; the BR test was the least sensitive. The VEP was abnormal in all patients with signs of optic neuritis and in all but one with a history of optic neuritis. The present results are compared to those obtained in other laboratories and with other types of examinations in MS patients. It is concluded that although the tests are not specific for MS, they give valuable information in the majority of patients with a clinically uncertain diagnosis. This information will most often not be given by other types of examination. The combination of VEP and BAEP is recommended, but it should be supplemented by SEP recording in patients without spinal signs.

Diagnostic features of the auditory brainstem response in identifying cerebellopontine angle tumours

This report concerns the diagnostic features of the ABR which are most effective in identifying patients with cerebellopontine angle tumours. The conclusions are based on the results of 40 normal subjects, 35 patients without a cerebellopontine angle tumour and 68 patients without a tumour. One hundred per cent of the tumour patients and ten per cent of the non-tumour patients had abnormal ABR results.

Brain stem auditory evoked potentials: a comparative study of monaural versus binaural stimulation in the detection of multiple sclerosis

As the latency of these responses is the most stable measure in normal subjects, the present study examines the latency of the BAEP wave forms in multiple sclerosis (MS) with a view to comparing a monaural stimulation with binaural. In previous studies binaural stimulation has been used to detect MS in clinically 'definite' cases. In this study both clinically definite and possible MS cases were examined and it was shown that in the clinically definite MS category the detection rate improved from 70% to 90% with ipsilateral/contralateral stimulation. In the possible multiple sclerosis group the detection rate was negligible with binaural stimulation compared to 67% with monaural stimulation. Both inter-wave latency and the repeatability of the response in the different groups are discussed in detail.

Evaluation of various brain structures in multiple sclerosis with multimodality evoked potentials, blink reflex and nystagmography

Pattern reversal visual evoked potentials (VEP), blink reflexes, auditory brainstem evoked potentials (ABEP), spinal and scalp recorded somatosensory evoked potentials (SSEP), and nystagmographic records were investigated in 55 patients with multiple sclerosis (MS), who were separated in different categories of probability according to the clinical history, symptoms, and signs. The combined use of different electrophysiological methods forms a sensitive battery for investigating clinically uncertain cases of MS. It was stressed that care should be taken in the interpretation of the electrophysiological findings, since a single lesion in the central nervous system, particularly in the brainstem, may affect different functional systems simultaneously and therefore mimic a disseminated disease.