Selective unilateral absence or attenuation of wave V of brain-stem auditory evoked potentials with intrinsic brain-stem lesions

The contribution of ipsilateral and contralateral auditory brain-stem structures to the generation of wave V of brain-stem auditory evoked potentials is a controversial subject. We describe two cases with an intrinsic brain-stem lesion that involved the lateral lemniscus unilaterally in the middle and upper pons. The focal nature of the auditory structures was confirmed by detailed neuropathologic data in one case and by magnetic resonance scans in the other one. In both cases, brain-stem auditory evoked potentials revealed the unilateral absence (case 1) or marked attenuation (case 2) of wave V on stimulation of the ear contralateral to the intrinsic pontine lesion. Findings in both cases strongly suggest that wave V is predominantly generated by pontine structures contralateral to the stimulated ear and that the integrity of the contralateral lateral lemniscus is essential.     

Brainstem auditory and somatosensory evoked potentials in neuro-Beh?et's syndrome

Brainstem auditory evoked potentials (BAEPs) and somatosensory evoked potentials after median nerve stimulation (MN-SEPs) and after posterior tibial nerve stimulation (PTN-SEPs) were studied in 17 patients with neuro-Beh?et's syndrome (NB). Eleven patients (64.7%) showed an absence of wave I, III or V or a prolongation of the interpeak latency I-III, or III-V in BAEPs. Six patients (37.4%) showed a prolongation in the latency of cortical P37 of PTN-SEPs and/or the interpeak latency EP-N13 or N13-N18 of MN-SEPs. The BAEP and SEP abnormalities indicated a conduction failure of the acoustic lateral lemniscus pathway and the medial lemniscus pathway in the brainstem of the patients with NB. Abnormal EPs can provide sensitive information which shows the presence of subclinical lesions in the central nervous system.     

Brainstem Auditory and Somatosensory Evoked Potentials in Neuro-Behqet's Syndrome

Abstract: Brainstem auditory evoked potentials (BAEPs) and somatosensory evoked potentials after median nerve stimulation (MN-SEPs) and after posterior tibial nerve stimulation (PTN-SEPs) were studied in 17 patients with neurolehget's syndrome (NB). Eleven patients (64.7%) showed an absence of wave I, III or V or a prolongation of the interpeak latency 1–111, or 111-V in BAEPs. Six patients (37.4%) showed a prolongation in the latency of cortical P37 of PTN-SEPs and/, or the interpeak latency EP-N13 or N13–N18 of MN-SEPs. The BAEP and SEP abnormalities indicated a conduction failure of the acoustic lateral lemniscus pathway and the medial lemniscus pathway in the brainstem of the patients with NB. Abnormal EPs can provide sensitive information which shows the presence of subclinical lesions in the central nervous system.     

Clinical evidence supporting a subthalamic origin of the P15 wave of the somatosensory evoked potentials to median nerve stimulation

Both somatosensory (SSEPs) and brain-stem auditory evoked potentials (BAEPs) were recorded in 3 patients with localized lesions in the thalamus or brain-stem. In one patient with a right thalamic cystic tumour there was a significant interhemispheric difference in the central conduction time (CCT), but the N14-P15 interval was not affected on either side and BAEPs showed normal wave latencies and interpeak latencies (IPLs). The second patient had a colloid cyst of the third ventricle in which central herniation had occurred resulting in 'locked-in' syndrome. The P15 peak was absent on one side and markedly prolonged in latency on the other. BAEPs showed neither wave IV nor V on either side. The third patient had compression of the right posterior rostral pons by a metastatic tumour, resulting in significant prolongation of the CCT on the side of the tumour because of increase in the N14-P15 interval. Both I-V and III-V interpeak latencies were significantly prolonged bilaterally without prolongation in I-III IPL in this case. There was a correlation between the electrophysiological abnormalities of P15 and of BAEP wave V. These results suggest that the origin of the P15, which is usually recorded as a far-field potential, may be in the subthalamus or the upper part of the brain-stem.     

Magnetic resonance imaging and brain-stem auditory evoked potentials in neuro-Behcet's disease

We studied central nervous system lesions in patients with neuro-Behcet's disease using magnetic resonance imaging (MRI) of the brain and recording of brain-stem auditory evoked potentials (BAEPs). MRI revealed abnormal findings in seven of eight patients. MRI studies demonstrated extensive regions with high intensity signal in the brain stem and/or basal ganglia on T2-weighted images obtained during the acute stage of the disease in three patients. One of these patients had a strongly gadolinum-enhanced round lesion in the lower pons. In four of the other five patients with chronic disease, brain-stem atrophy was observed on T1-weighted images. Atrophic changes were more severe in the brain stem than in the cerebellum. Abnormal BAEPs were observed in three patients and consisted of prolongation of interpeak latency of waves III-V and defects of wave III or V. Abnormal BAEPs were recorded in patients with severe inflammatory changes or progression of atrophic changes in the brain stem. Our findings show that MRI and BAEPs are useful in detecting the presence and assessing the degree of neurological involvement in patients with neuro-Behcet's disease.     

Brainstem auditory evoked potential in Japanese encephalitis.

Japanese encephalitis (JE) is associated with varying degrees of coma and brainstem involvement is frequent which can be evaluated and monitored by brainstem auditory evoked potential (BAEP). The present study has been undertaken to evaluate the BAEP changes and their role in predicting the outcome. Twelve adult patients with JE were subjected to CT scan, MRI and BAEP studies after detailed neurological evaluation. The severity of coma was assessed by Glasgow coma scale and outcome was defined at the end of 3 months into good and poor recovery on the basis of Barthel Index score (BI). The mean age of the patients was 28.3 years (range 14-50), and four of them were females. Most of the patients were comatose. The mean Glasgow coma scale (GCS) score was 7 (range 4-11). There were no brainstem signs or cranial nerve palsy. Cranial CT scan revealed thalamic hypodensity in four, whitematter oedema in three and left putaminal hypodensity in one patient. Cranial MRI was carried out in eight patients which revealed bilateral thalamic lesions in all, basal ganglia and midbrain lesions in three each and pontine and cerebellar lesions in one patient each. Brainstem auditory evoked potentials were recordable bilaterally. The absolute latency of wave I, II, III, IV and V and interpeak latencies (IPL) of I-V, III-V, and I-III were normal. The V/I amplitude ratio were significantly reduced in five patients. The BAEP abnormalities correlated with brainstem lesions on CT or MRI but not with severity of coma or outcome. The reduced amplitude ratio of wave V/I may be due to raised intracranial tension or brainstem involvement in JE.     

Evoked potentials in basilar artery thrombosis: correlation with clinical and angiographic findings

In 28 patients with vertebro-basilar or basilar artery thrombosis brain-stem auditory evoked potentials (BAEPs) and somatosensory evoked potentials (SEPs) have been recorded. Visual evoked potentials (VEPs) were recorded in 7 of these 28 patients. In 24 patients the diagnosis was angiographically proven and in 4 patients Doppler sonography and computerized tomography suggested this diagnosis. The BAEP and SEP findings were correlated to clinical and angiographical signs. BAEPs could be classified into 6 different patterns. In more than half of the patients different BAEP patterns from the two ears could be found. A pathological IV/V complex was most often found in comatose patients and in patients with a basilar artery occlusion distal to the anterior inferior cerebellar artery. Prolonged interpeak latency of I-III was mainly found in alert or drowsy patients with caudal occlusions. The frequent occurrence of a BAEP with only wave I preserved, or with no waves preserved, in patients with brain-stem functions suggests that BAEPs are not useful in the diagnosis of brain death when basilar artery thrombosis is suspected. SEPs were either absent bilaterally or else severely altered on one side in all comatose patients. In alert patients, including those with 'locked-in' syndrome, SEPs were never absent bilaterally. Increased N13-N20 interpeak latency was an uncommon finding in this series. There was no correlation between the SEP and the angiographically proven location of the occlusion. In the 'locked-in' syndrome both SEP and BAEP findings were non-uniform. Normal SEPs were sometimes found in combination with severely altered BAEPs, suggesting partial deafferentation. Since basilar artery thrombosis is now a treatable condition, early diagnosis and documentation of functional deficits moves into a more important clinical area than heretofore.     

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.     

Evoked potentials and EEG in multiple sclerosis

Thirteen patients with clinically definite multiple sclerosis (MS) were studied with electroencephalogram (EEG), magnetic resonance imaging (MRI), evoked potentials and cerebrospinal fluid (CSF) analysis. We attempted to correlate the findings with physical disability as defined by Kurtzke score and presence of dementia or seizures. More severe plaque disease on MRI and increased physical disability correlated significantly with abnormality on brain-stem auditory evoked potentials (BAEPs) while visual evoked potential (VEP) abnormality correlated only with MRI findings. No such correlation was found with the EEG. The close relationship between BAEP and MRI abnormalities probably reflects frequent involvement of brain-stem corticospinal pathways.     

Absence of rate-dependent BAEP P5 latency changes in patients with definite multiple sclerosis: possible physiological mechanisms

Brain-stem auditory evoked potential (BAEP) rate studies have been incorporated into evoked potential protocols in an attempt to identify demyelinating lesions. A group of 9 patients with clinically definite MS are described who showed abnormal BAEP P1-P5 interwave latencies at slow repetition rates and failed to demonstrate a significant enhancement of this abnormality following rapid click presentation rates. The lack of rate-dependent P5 latency changes has been hypothesized to represent a less severe form of axonal demyelination. Thus, it may be possible to subclassify or subgroup patients with evidence of brain-stem demyelination based on the presence or absence of BAEP rate-dependent abnormalities.     

The interaction between sex and click polarity in brain-stem auditory potentials evoked from control subjects of Oriental and Caucasian origin

Brain-stem auditory evoked potentials (BAEPs) were performed on 30 male and 30 female young normal Oriental subjects, using both condensation and rarefaction stimulation. The effects of sex and click polarity on the BAEP latencies and amplitudes were studied. Females had shorter absolute and interpeak latencies and higher absolute amplitudes than the males. These sex-related BAEP differences were independent of the click polarity. Rarefaction clicks produced shorter wave I latency and longer I-III interpeak latency, but the differences were significant in the female only. The polarity-related BAEP amplitude differences were essentially independent of the sex. BAEPs performed on 60 sex- and age-matched young Caucasian subjects produced similar results. The importance of establishing control BAEP values according to the sex and click polarity is emphasised.     

Brain-stem tuberculoma. An analysis of 11 patients

The clinical and radiologic findings in 11 patients with brain-stem tuberculoma were reviewed. Clinical manifestations included various combinations of focal signs and symptoms of subacute onset, similar to those produced by other space-occupying lesions of the brain stem. Evidence of systemic tuberculosis was found in six cases (55%). Computed tomography (CT) usually showed an isodense or hyperdense brain-stem mass with abnormal contrast enhancement; associated supratentorial granulomas were found in four cases, and hydrocephalus was found in two cases. Magnetic resonance imaging showed irregular brain-stem lesions with long T1 and short T2 relaxation times. Cerebrospinal fluid findings were also nonspecific, as smears for acid-fast bacilli were most often negative. An incorrect diagnosis of pontine glioma was made in one patient. In contrast, proper integration of data from CT and magnetic resonance imaging findings, cerebrospinal fluid analysis, and x-ray films of the chest permitted an accurate diagnosis in ten cases. Prompt therapy with antituberculous drugs resulted in clinical improvement, documented by CT, in most patients. Brain-stem tuberculoma should be suspected in patients with space-occupying lesions of the brain stem who live in geographic areas where tuberculosis is endemic. Early diagnosis and prompt medical therapy are important in preventing mortality and reducing morbidity.     

Behavioral manifestations of central pontine myelinolysis

A young woman with a clinical history and magnetic resonance imaging scan consistent with central pontine myelinolysis came to medical attention because of prominent behavioral symptoms. Marked clinical recovery occurred despite persistent radiologic abnormalities. Rapid correction of hyponatremia was probably related to the development of the central pontine myelinolysis. A normal computed tomographic scan and the absence of brain-stem signs delayed accurate diagnosis.     

Correlation between blink reflex abnormalities and magnetic resonance imaging findings in patients with multiple sclerosis

This study investigates the correlation between brain magnetic resonance imaging findings and blink reflex abnormalities in patients with relapsing remitting multiple sclerosis. Twenty-six patients and 17 healthy subjects were included in this study. Blink reflex test (BRT) results were obtained using right and left stimulations; thus, 52 BRT results were recorded for the patient group, and 34 BRT results were recorded for the control group. The magnetic resonance imaging (MRI) findings were classified based on the existence of brainstem lesions (hyperintense lesion on T2 weighted (W) and fast fluid-attenuated inversion recovery MRI or contrast-enhancing lesion on T1W MRI). Correlation analysis was performed for the BRT and MRI findings. The percentage of individuals with abnormal BRT results (including R1 latency, ipsilateral R2 latency, and contralateral R2 latency) was significantly higher in the patient group as compared to the control group (p values: 0.015, 0.001, and 0.002, respectively). Correlation analysis revealed significant correlations between contralateral R2 latency abnormalities and brainstem lesions (p value: 0.011). Our results showed significant correlation correlations between contralateral R2 latency abnormalities and brainstem lesions and these results may be explained the effects of multiple demyelinating lesions of the brain stem of patients with relapsing remitting multiple sclerosis.     

Short latency somatosensory evoked potentials: studies in patients with focal neurological disease

In non-cephalic reference recordings, the scalp recorded short latency evoked potentials to median nerve stimulation in normal subjects consist of 3 positive potentials followed by a negative potential. The sources of these potentials have not been precisely defined. Therefore, these potentials were recorded in 31 patients with focal lesions of the nervous system. Recordings were evaluated for (a) the presence or absence of these potentials and (b) peak latency differences between components. The results were compared with similar data obtained on 25 normal control subjects. Only the first positive potential was recorded with stimulation ipsilateral to the lesion in one patient with unilateral C5-T1 root avulsion. This indicates that this potential arises in stimulated peripheral nerve fibers. The second potential, although not consistently recorded in normal subjects, had an abnormally prolonged interpeak latency in 2 patients with cervical cord and medullary lesions. Therefore, it seems that it arises in the central nervous system, either in spinal cord or lower brain stem. The third potential was absent in 2 patients with medullary lesions and its interpeak latency was prolonged in 2 patients with brain stem lesions. It was recorded in 3 patients with thalamic lesions in whom subsequent potentials were absent. This suggests that this potential arises primarily in brain stem pathways. The negative potential was absent in 2 patients with cerebral lesions which did not appear to involve the thalamus which suggests that it arises in the thalamocortical radiations or cerebral cortex. Short latency evoked potential abnormalities correlated more with impairment of proprioception than with disturbances in appreciation of pain and temperature.     

Paresis of contralateral smooth pursuit and normal vestibular smooth eye movements after unilateral brainstem lesions.

Pursuit and vestibular smooth eye movements were measured in patients with lesions of the caudal brainstem tegmentum identified by magnetic resonance imaging (MRI) and computed tomography (CT), with neuropathological correlation in 1 patient. Contralateral smooth pursuit gain was significantly lower than ipsilateral gain in each patient. Ipsilateral smooth pursuit gain was also subnormal in patients with unilateral pontine damage that caused slowing of ipsilateral saccades. Horizontal vestibulo-ocular reflex gain and phase were normal. These quantitative correlations indicate that lesions of the pontine tegmentum that paralyze ipsilateral saccades can spare the vestibulo-ocular reflex, and that smooth pursuit movement and the vestibulo-ocular reflex can be impaired independently by pontine or medullary lesions. In contrast to lesions at other sites, unilateral lesions of the pontine or medullary tegmentum impair contralateral smooth pursuit more than ipsilateral pursuit movements. These findings provide evidence that a double decussating pathway mediates smooth pursuit; the first decussation is from the pons to the cerebellum, and the second decussation is from the vestibular nucleus to the contralateral abducens nucleus.     

Visual and auditory evoked potentials during long-term vigabatrin treatment in children and adolescents with epilepsy.

OBJECTIVES: The aim of the study was to estimate the effects of Vigabatrin (VGB) as add-on therapy on visual (VEP) and brain-stem (BAEP) evoked potentials. METHOD: The investigation covered 100 epileptic patients from 8 to 18 years of age. The treatment included therapy with carbamazepine (CBZ) or valproate acid (VPA) using slow release formulations of these AEDs. Combination therapy was administered using add-on VGB in the recommended dose 57.4+/-26.5 mg/kg body mass/day. VEP and BAEP evoked potentials were recorded by means of Multiliner (Toennies, Germany). The obtained values were compared with age matched control group. RESULTS: Compared to control groups, significant differences in epileptic groups emerged in latencies of the peak III, V along with the interpeak intervals I-III of BAEP. Also VEP studies showed the reduction of N75/P100 and P100/N145 amplitudes. CONCLUSIONS: Adding VGB did not significantly increase the percentage of pathological abnormalities observed from EPs. Our electrophysiological studies demonstrate abnormalities in EPs parameters due to subclinical toxicity induced by AEDs. Major alterations produced bitherapy of VPA-SR + VGB and minor SR formulations of CBZ or VPA.     

Isolated cranial nerve palsies due to brainstem lesions.

Isolated cranial nerve palsies are often attributed to lesions of the respective nerves along their extraaxial courses. There are a significant number of reports of individual patients with cranial nerve palsies, mostly of the 3rd and 6th nerves, as the sole manifestation of brainstem lesions proven by magnetic resonance imaging (MRI) or computer-assisted tomography (CT). An intraaxial basis may still be underestimated if based on MRI only, as electrophysiological abnormalities indicating brainstem lesions (masseter reflex, blink reflex, DC electrooculography) may be independent from MRI-documented morphological lesions. This article reviews the evidence that ischemic and demyelinating brainstem lesions are an important and underestimated cause of clinically isolated cranial nerve palsies. Especially in middle-aged and elderly people with 3rd and 6th nerve palsies, small pontine and mesencephalic infarctions seem to be more frequent than small-vessel ischemic infarctions of the extraaxial nerves.     

Brainstem auditory evoked potential abnormalities and magnetic resonance imaging in posterior fossa lesions

Brainstem auditory evoked potentials (BAEPs) were evaluated in a series of 15 patients with extra-axial cerebello-pontine angle tumors (3 cases), demyelinating plaques (11 cases), and intra-axial tumor (1 case), verified by magnetic resonance imaging (MRI). A satisfactory correlation between the location of the lesions and the type of BAEP abnormalities was found in 11 cases. In 2 other cases, definite MRI brainstem lesions located outside the acoustic pathways were associated with normal BAEPs. In the opposite situation (2 cases of BAEP abnormalities with normal MRI), the inability of MRI to detect demyelinating lesions may be due to the temporal evolution of the lesions themselves. The results of this BAEP-MRI comparative study confirm that BAEP is a sensitive diagnostic tool in revealing brainstem dysfunction, although its localizing power appears to be debatable. The most satisfactory MRI/BAEP topodiagnostic correlation was found with lesions involving the acoustic nerve in its intracranial tract or the caudal pons and bulbopontine junctions.     

Evaluation of ipsilateral and contralateral brainstem auditory evoked potentials in multiple sclerosis patients

Brainstem auditory evoked potentials (BAEP) were recorded simultaneously between the vertex and the mastoid ipsilateral and contralateral to the ear stimulated in 30 patients with multiple sclerosis (MS) and compared with the responses in a control group of 30 normal hearing adults. The control group showed that significant latency differences exist between ipsilateral and contralateral recording. Definitions of abnormalities were based on interwave separation and the wave V amplitude ratio. No case was found among the MS patients with an abnormal contralateral but normal ipsilateral response.