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 assessment of severe head injury by short-latency somatosensory and brain-stem auditory evoked potentials

The relative prognostic value of short-latency somatosensory evoked potentials (SEPs) and brain-stem auditory evoked potentials (BAEPs) was assessed in 35 patients with post-traumatic coma. Analysis of the evoked potentials was restricted to those recorded within the first 4 days following head injury. Abnormal SEPs were defined as an increase in central somatosensory conduction time or an absence of the initial cortical potential following stimulation of either median nerve. Abnormal BAEPs were classified as an increase in the wave I–V interval or the loss of any or all of its 3 most stable components (waves I, III and V) following stimulation of either ear. SEPs reliably both good and bad outcomes. All 17 patients in whom SEPs were graded as normal had a favourable outcome and 15 of 18 patients in whom SEPs were abnormal had an unfavourable outcome. Although abnormal BAEPs were associated with an unfavourable outcome in almost all patients (6 of 7), only 19 of 28 patients with normal BAEPs had a favourable outcome. The finding of normal BAEPs was therefore of little prognostic significance. These results confirm the superiority and greater sensitivity of the SEP in detecting abnormalities of brain function shortly after severe head trauma.     

Chronic effects of phenytoin on brain-stem auditory evoked potentials in man

The effects of phenytoin (PHT) on brain-stem auditory evoked potentials (BAEPs) were studied in 65 epileptic patients who received long-term PHT monotherapy at therapeutic and supra-therapeutic levels with no clinical evidence of brain-stem toxicity. Abnormal BAEPs were found in 7.5% and 33.3% of patients with therapeutic and supra-therapeutic PHT levels respectively. Serum PHT levels had a trend towards a positive relationship with the I–V interpeak latency (IPL), and a significant negative relationship with the amplitudes of waves I and V. at supra-therapeutic levels, both I–V and I–III IPLs were significantly prolonged while at therapeutic evels onl I–III IPLs were prolonged. The absolute latency of wave I was prolonged in both the therapeutic and the supra-therapeutic groups. These results suggest that PHT acts both peripherally on either the auditory nerve or the cochlea, and centrally on brain-stem conduction.     

Evoked potential findings in Behçet's disease. Brain-stem auditory,visual, and somatosensory evoked potentials in 44 patients

We studied 54 patients with Behçet's disease, 41 males and 13 females, mean age 28 years. Forty-four patients had auditory brain-stem evoked potential (BAEP) recordings, 39 had pattern reversal visual evoked potentials (VEP), 27 had median nerve somatosensory evoked potential (SEP) recordings, and 25 tibial nerve SEPs. BAEPs were abnormal in 16 patients (52%) with neurological manifestations and in 4 (31%) without, because of decreased amplitude of wave V, prolonged I–III or III–V interpeak latencies, or uncertain/absent waves III and/or V. Eleven patients (40%) with neurological symptoms and 3 patients (25%) without, had abnormal VEPs. Absent potentials, decreased amplitude, with or without prolonged P100 latency, were found in 75% of the cases, the rest had prolonged P100 latency only. Median SEPs were abnormal in 8 patients (38%) with neurological manifestations. Four patients (21%) had abnormal tibial SEPs. Decreased amplitude with or without mild slowing in central conduction was the predominant SEP abnormality. SEPs were normal in all patients without neurological symptoms. In total, 84% of patients with, and 38% of patients without, neurological symptoms had abnormalities of one or more EP modality.When used cautiously, EP studies in Behçet's disease might be helpful to separate neuro-Behçet from other disorders with similar symptomatology, to disclose subclinical CNS involvement, to evaluate and monitor CNS disease activity, and to provide objective measures of treatment response.     

Correlation between a unilateral midbrain-pontine lesion and abnormalities of brain-stem auditory evoked potential

Brain-stem auditory evoked potentials (BAEPs) were evaluated over a 39 day period in a patient with a unilateral pontine-midbrain lesion verified by CAT scan and autopsy. Waves I, II and III were present on the side of lesion, whereas all 5 waves were present on the side opposite the lesion. The findings suggest that the BAEPs may be obtained with only an intact ipsilateral auditory pathway. Crossing fibers in the trapezoid body also appear to make contributions to the normal generation of wave V.     

Age- and sex-related differences in brainstem auditory evoked potentials in secondary school students living in Northern European Russia

Brainstem auditory evoked potentials (BAEPs) were studied in 46 1st- to 11th-year students (22 boys and 24 girls) of a rural secondary school in Arkhangel’sk oblast. The objective of this work was to study age- and sex-related differences in BAEP characteristics in children and adolescents, living in the North and assess the BAEP characteristics as compared to reference values. In all three age groups of students, interpeak intervals I–III, III–V, and I–V characterizing the peripheral and central conduction times were shorter in girls than in boys. Interpeak interval III–V tended to increase with age only in boys (at puberty), with a significant increase in the latencies of waves I, III, and V. The BAEP characteristics in the subjects examined included a shorter peak latency and a greater amplitude of wave I (except senior students), relatively prolonged interpeak interval I–III, and more pronounced sex-related differences in BAEPs, especially at puberty. These findings show that it is necessary to revise regional reference values for BAEPs, differentiated by sex and age, including at puberty.     

Brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 10 common marmosets (Callithrix jacchus) to investigate the effects of recording electrode configurations, stimulus rate, and stimulus frequency on BAEP wave forms and peak latencies. Tone burst stimulations were used to evaluate the effects of pure tone on BAEP wave forms. Five positive peaks superimposed on positive and negative slow potentials were identified in the BAEP recorded at the linkage between the vertex and the dorsal base of the ear ipsilateral to a monaural stimulus. When the reference electrode was placed at the ipsilateral mastoid or the neck, the amplitudes of positive and negative slow potentials and the incidence of wave I increased. There were no significant changes in peak latencies of BAEP waves with changes in stimulus rate from 5 to 20/s. It was possible to record the BAEPs in response to tone burst stimulations at frequencies extending from 0.5 to 99 kHz. Wave I appeared apparently at high stimulus frequencies; while waves III to V, at low frequencies. Wave II was recorded at frequencies ranging from 0.5 to 99 kHz and comprised a superposition of 2 or 3 potentials.     

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 auditory evoked potentials (BAEPs) from basal surface of temporal lobe recorded from chronic subdural electrodes

BAEPs were recorded from the basal surface of the temporal lobe by subdural electrodes chronically implanted in 6 patients who were evaluated for surgical management of intractable partial seizures. Near-field recordings were obtained by recording between the subdural electrode closet and most distant to the brain-stem. Far-field recordings were obtained by recording between the subdural electrodes and an indifferent electrode over the spinal process of the seventh cervical vertebrae. The recordings were compared with standard ear-vertex recordings.After ipsilateral ear stimulation, the subdural electrode closet to the brain-stem recorded large amplitude waves I and II, followed by less well-defined waves of longer latencies. Recordings to contralateral stimulation showed no clearly defined waves I and II and a large amplitude wave Vn. Waves III, IV, V, Vn and VI were of opposite polarity after ipsi- and contralateral stimulation. These findings indicate that waves I and II are generated ipsilaterally to the stimulation side, whereas wave Vn has a contralateral origin. Wave Vn may be generated in the brachium of the inferior colliculus, as suggested from latency and from dipole configuration studies. This conclusion is consistent with the classical anatomical observations that the supracollicular auditory pathways are predominantly crossed.     

Brain-stem monitoring. II. Preterminal BAEP changes observed until brain death in deeply comatose patients

Preterminal BAEP changes were studied until brain death in 8 head-injured patients out of a series of 38 comas monitored by means of a system allowing high-rate sequential recording. Two different modalities of BAEP degradation were disclosed: (1) simultaneous latency increase of all components associated with a decrease of cerebral perfusion pressure (CPP), consistent with ongoing ischaemia of the posterior fossa; (2) deterioration of brain-stem components (waves III–V) with preserved or even enhanced wave I. The latter pattern was not consistently associated with any haemodynamic change and might be related to mechanical factors causing rostro-caudal deterioration of brain-stem function. The time course of BAEP degradation ranged from a few minutes to more than 10 h. In the case of slow preterminal evolution definitely pathological trends were identified even when individual BAEPs were still within normal limits. Such trends would have remained unnoticed in single BAEP records. Hypothermia and anaesthetic drugs were found to induce falsely alarming BAEP changes very similar to those seen during preterminal evolution. Our results suggest that continuous brain-stem monitoring could be helpful for management of comatose head-injured patients.     

Brainstem auditory evoked potentials (BAEPs), pathology of wave IV

In a group of 134 consecutive patients with brainstem symptomatology wave IV was bilaterally absent in 69%. Bilateral absence of this wave can be considered as a normal state. Only absence of wave IV on one side with its presence on the other side was appraised as pathologic. Asymmetries of the latency and amplitude could not be taken into consideration because of the lack of normative data for this wave. Computer tomography showed in our pathologic cases lesions in the pons, oblongata and cerebellum. The clinical semiology was extensive and multiform pointing in 84% to a pontine origin, in 16% to a lesion of the midbrain or oblongata. A possible lesion of the pons was in accordance with its functional anatomy as well as with the supposed origin of wave IV (superior olivar complex, lateral lemniscal nucleus). In 62% of cases the pathology of wave IV was present without impairment of auditory functions. The pathology of wave IV was considered as little sensitive and little specific.     

BAEP subcomponents and wave form — relation to click phase and stimulus rate

The latency distributions of normal brain-stem auditory evoked potential (BAEP) components elicited by condensation (C) and rarefaction (R) clicks at 10 and 50 Hz were found to be double- or multi-peaked for II (10 and 50 Hz), III (50 Hz), IV (10 and 50 Hz) and V (10 Hz). A bifid component III was found in 3.5% (10 Hz) and 7.4% (50 Hz) of BAEPs. A bifid II and triple IV/V configuration were occasionally noted. The prevalences of the different IV/V complex configurations were significantly dependent upon click phase and rate. These results suggest that several subcomponent might participate in the generation of the single BAEP components and that a single generator may contribute to different BAEP components in different subjects.Early subcomponents between I and II (Ib) were found in 13% of 10 Hz BAEPs and 27% of 50 Hz BAEPs (P = 0.002) and the latency distribution of Ib seemed to be bimodal. Ib/I relative amplitude frequently increased with 50 Hz stimulation.We suggest that the generator of Ib is partially cochlear (CM) and partially neural (equivalent to N2 of the ECochG-AP) in origin.The existence of subcomponents must be recognized in clinical use of BAEPs both to avoid misinterpretation and to decrease the normal variability in monophasic click evoked BAEP studies.     

Brain-stem auditory evoked potentials (BAEPs) and magnetic resonance imaging (MRI) in a case of facial myokymia

The case of a 37-year-old woman with facial myokymia is reported. Magnetic resonance imaging (MRI), electromyography (EMG) and brain-stem auditory evoked potentials (BAEPs) supported the clinical diagnosis of suspected multiple sclerosis (MS). MRI showed a single area of abnormal signal in the pontine region. The authors discuss the possible relationship between the brain-stem lesion and the electrophysiological abnormalities demonstrated by BAEPs and the EMG of facial muscles.     

Sex and ear differences of brain-stem acoustic evoked potentials in a sample of normal full-term newborns. Normative study

The present paper reports a normative study of the BAEPs recorded from 80 normal full-term newborns by using a rarefaction click at 70, 60, 40, 20 dB HL.Positive, negative peaks and the relative amplitudes were measured. Means, standard deviations and 95% and 99% confidence limits were calculated for each component, for positive and negative IPLs and amplitude ratios. A normality test distribution showed that each component had normal distribution except for wave PIII at 70 dB and at 60 dB HL beacause of its index of kurtosis and for IPLs PII-PIII and NII-NIII at 70 and 60 dB HL. MLRA was performed and significant statistical differences were found for sex, ears and intensities. Females had the latencies of waves PIII, PIV, PV, NII and NIV shorter than males. The BAEPs obtained from the left ear had shorter latencies for positive and negative peaks. Latencies, amplitude and morphology of the BAEPs vary with variations of the intensity. The IPLs PII-PV, PIII-PV and PIV-PV were not affected by changes of intensity.     

Brainstem auditory evoked potentials in the fetal sheep, in utero

We studied brainstem auditory evoked potentials (BAEPs) in 8 fetal sheep in utero, ranging in gestational age from 105 to 142 days gestation (normal term 147 days). We could not elicit BAEPs prior to 117 days of gestation. After this age rapid maturation was seen, with three discernible peaks observed prior to 120 days and five peaks after 120 days. A significant (P less than 0.05) gestational age related fall in peak latencies and interpeak latencies was observed. The rate of stimulus presentation that could be tolerated without significant changes in wavepeak latency or amplitude also increased with advancing gestational age. In older fetuses (greater than 125 days), where a differentiated electrocorticogram (ECOG) was observed, differences were seen in latency and amplitude of several of the BAEP wavepeaks dependent upon the state. In high voltage ECOG states the amplitudes of wave IV and V were significantly (P less than 0.05) greater than in the low voltage ECOG state and the latencies of wave I, II and V were significantly (P less than 0.05) longer in low as compared to high voltage ECOG state. The BAEP, being obtainable over very short periods of time, appears to provide a useful indice of neural maturation for the sheep fetus in utero.     

Neuroanatomic correlations with the late waves of the brain-stem auditory evoked potential

The goal of this study was to investigate the neuroanatomic correlations of the late waves (VI–VIII) of the BAEP. Patients (N = 55) with clinical evidence of a CVA were compared to a normal control group (N = 85). Latencies of > 3 S.D. from the means of the normal group were considered abnormal. CT and MRI scans provided evidence of the lesions. For the 14 patients who had normal BAEPs, the sizes of lesions were significantly smaller than for those with abnormal tests. Evidence shows that an abnormal wave VI was related to an ipsilateral cortical lesion and an abnormal wave VIII was related to a lesion in the internal capsule-corpus striatum.     

Reappearance of brain-stem auditory evoked potentials after surgical treatment of a brain-stem hemorrhage: contributions to the question of wave generation

We report on a patient suffering a spontaneous hemorrhage primarily located in the right brain-stem; surgical correction of this led to a substantial improvement in clinical deficits. Brain-stem auditory evoked potentials (BAEPs) were recorded on postoperative days 18, 30, 55 and 205. Waves II through V were initially undetectable on stimulation of the damaged side, whereas the absence of peak V was the only abnormality seen on left-side stimulation. With the regression of the right lower mid-pontine deficits, the right waves gradually reappeared and normalized progressively. On the last recording, only a left wave V abnormality persisted. At that time, the patient had a moderate left hemisyndrome due to a circumscribed right upper pontine-midbrain lesion. Therefore, it can be suggested that the first 4 waves of BAEPs mainly originate in the ipsilateral pons, and the Vth in the contralateral higher regions.     

Dynamics of MLAEP changes in midazolam-induced sedation

This study aimed at assessing the effects of midazolam (MDZ) sedation on auditory brainstem (BAEP) and middle latency (MLAEP) evoked potentials in intensive care conditions. Ten ventilated comatose patients were receiving an intravenous MDZ bolus dose (0.2 mg/kg) followed by a 2 h continuous infusion (0.1 mg/kg/h). MLAEPs and BAEPs elicited by clicks (90 dB HL+masking) were simultaneously and continuously monitored during the first 6 h and for 30 min the next morning. We found no effect of MDZ sedation on BAEPs. Only MLAEP components were modified. However, none of the patients presented any total abolition of the MLAEPs. Bolus injection led to very early alteration of cortical responses, beginning after 5 min and lasting almost 1 h (maximum Pa latency increase, 3.1 ms; maximum Pa-Nb amplitude decrease, 46%). During continuous infusion, MLAEPs remained slightly, although significantly, altered (Pa latency, +1.3 ms; Pa-Nb amplitude, 27%). The Nb wave seemed to be modified earlier and to return to normality later than the Pa wave. These findings incite a careful interpretation of MLAEP tracings acquired during the first hour following MDZ bolus injection. If possible, MDZ should be administered as continuous infusion for reliable interpretation of evoked potential changes in intensive care unit, or during surgery.     

Brain-stem auditory evoked potentials and brain death

BAEP records were obtained from 30 brain-dead patients. Three BAEP patterns were observed: (1) no identifiable waves (73.34%), (2) an isolated bilateral wave I (16.66%) and (3) an isolated unilateral wave I (10%). When wave I was present, it was always significantly delayed. Significant augmentation of wave I amplitude was present bilaterally in one case and unilaterally in another. On the other hand, in serial records from 3 cases wave I latency tended to increase progressively until this component disappeared. During the same period. wave I amplitude fluctuations were observed. A significant negative correlation was found for wave I latency with heart rate and body temperature in 1 case. Two facts might explain the progressive delay and disappearance of wave I in brain-dead patients: a progressive hypoxic-ischaemic dysfunction of the cochlea and the eight nnerve plus hypothermia, often present in brain-dead patients. Then the incidence of wave I preservation reported by different authors in single BAEP records from brain-dead patients might depend on the moment at which the evoked potential study was done in relation to the onset of the clinical state. It is suggested that, although BAEPs provide an objective electrophysiological assessment of brain-stem function, essential for BD diagnosis, this technique could be of no value for this purpose when used in isolation.     

Monitoring therapeutic efficacy of decompressive craniotomy in space occupying cerebellar infarcts using brain-stem auditory evoked potentials

Brain-stem auditory evoked potentials (BAEPs) have been used to gauge effects of brain-stem dysfunction in humans and animal models. The purpose of this study was to evaluate the usefulness of BAEP in monitoring patients undergoing decompressive surgery of the posterior fossa for space occupying cerebellar infarcts.We report on serial BAEP recordings in 11 comatose patients with space occupying cerebellar infarcts undergoing decompressive craniotomy. BAEP studies were performed within 12 h after admission, 24 h following surgery and prior to extubation. BAEP signals were analyzed using latency determination and cross-correlation.Following surgery, 9 patients regained consciousness; 2 patients persisted in a comatose state and died subsequently.BAEP interpeak latency (IPL) I-V assessed prior to surgery exceeded normal values in all patients in whom it could be reliably measured (N = 9). Following decompressive surgery BAEP wave I-V IPL normalized in 5 patients, but remained prolonged despite dramtic clinical improvement in 4 patients. We prospectively computed the coefficient of cross-correlation (MCC) of combined ipsilateral BAEP trials after right and left ear stimulation. In all patients increasing MCC was associated with clinical improvement. Unchanging or decreasing MCC indicated poor outcome.We conclude that serial BAEP studies are an appropriate perioperative monitoring modality in patients with space occupying cerebellar infarcts undergoing decompressive surgery of the posterior fossa.Our study suggests advantages of cross-correlation analysis as an objective signal processing strategy; relevant information can be extracted even if BAEP wave discrimination is impossible due to severe brain-stem dysfunction.