Somatosensory evoked potentials and electromyography in spinal cord intraoperative monitoring

Intraoperative monitoring can be defined as an application of several electroneurophysiological techniques for nervous system monitoring throughout the surgery. The principal goal of monitoring is to identify new neurologic impairment early enough to find the cause and to prevent permanent deficits. This paper reviews monitoring techniques during surgery for spinal deformity.     

Somatosensory evoked potentials with a unilateral migration disorder of the cerebrum

Transcranial electrical stimulation can be used for clinical investigations of the central nervous system and for monitoring of motor nerve tracts during surgical operations. We wished to reduce the pain involved with the transcranial electrical stimulation and to improve the usefulness of the method for monitoring during surgical operations. A dedicated transcranial electrical stimulator was designed having special features to reduce the pain sensation and the nerve blocking effect of anaesthetics. It provides constant current and constant voltage stimulation pulses with very short duration and high amplitude. The pulse length is adjustable in the range of 15 to 125 microseconds, while the maximum amplitude is 100 V and 1 A for voltage and current stimulation modes, respectively. Special features included high-repetition-rate pulse trains (50-2000 pulses s-1) and a three-electrode stimulation configuration. We suggest that the electrical transcranial stimulation has the potential to be a relatively painless method for routine clinical investigations and a reliable method for monitoring during surgery.     

Somatosensory evoked potentials in rheumatoid polyarthritis with radiologic involvement of the cervical spine

Somatosensory evoked potentials (SEP) have been recorded in 11 patients with cervical spine involvement, with or without signs of myelopathy due to rheumatoid arthritis (RA). In three patients, SEP have been recorded both before and after cervical spine surgery. In seven cases, the P14 (particularly the P9/P14 amplitude ratio) or P30 potentials were abnormal, whereas other potentials and conduction times were less often modified. Vertebral luxation sites that were predominantly observed at the upper cervical level account for these findings, thus supporting the diagnostic utility of P14 and P30 potentials which respectively take origin in the lower brain stem, close to or into the nuclei cuneatus and gracilis. Postoperative SEP were strongly correlated with the surgical outcome. SEP could be abnormal in the absence of overt clinical myelopathy or vertebral luxations, thus revealing infraclinical damage to the somatosensory pathways. This suggests that SEP recording is useful to discriminate RA patients with upper cervical cord dysfunction from those in whom vertebral lesion proves to have no direct impact on somatosensory conduction.     

Somatosensory evoked potentials: a simple neurophysiological monitoring technique in supra-aortal balloon test occlusions

The aim of this study was to evaluate somatosensory evoked potentials (SEP) as a simple neurophysiological monitoring method in supra-aortal balloon test occlusions (BTO). The 13 patients examined had carcinoma of the larynx (n = 6), nasopharyngeal malignancy (n = 3), sphenoid meningioma (n = 2), mycotic aneurysm (n = 1), and a tumor of the carotid body (n = 1). Transfemoral balloon occlusion of the internal carotid artery was maintained for 30 min and monitored both clinically and by SEP. None of the 13 patients showed neurological deficits or pathological changes in the SEP. No thromboembolic complications occurred during BTO. In 11 cases the cervical vessels could be spared or reconstructed during surgery. No neurological symptoms occurred during the clinical follow-up. One patient died the day after BTO due to cardiac arrest. Neurophysiological monitoring of preoperative BTO using SEP is a technically simple method. A similar method has been shown to have a high sensitivity and reliability in carotid surgery.     

Somatosensory trigeminal evoked potentials after gingival stimulation of the mental nerve. Normal values

OBJECTIVE: Somatosensory evoked potentials were recorded following unilateral stimulation of the mental nerve in the gum of 100 healthy volunteers aged between 17 and 22 years. METHODS AND RESULTS: Responses were recorded until 100 ms with electrodes placed over the scalp (C5/C6) referenced to central frontal (Fz). In 10 subjects, simultaneous recordings were made in masticatory and facial muscles to detect possible muscle artefacts. Stimulation was effected using a specially-designed stimulator adaptable to each individual. Contralateral responses consisted of four very constant deflexions (N12, P19, N26 and P35) forming a W-shaped complex of mean duration 31.27 ms. Tables of normality were compiled for latencies and amplitudes with confidence intervals of 99.8% reliability. Constancy of deflexions, stability of response (by serial studies), and possible sexual differences were also studied. Muscle artefacts were ruled out, and the participation of the mental nerve in the genesis of the responses was confirmed. CONCLUSION: We consider the proposed method a reliable alternative to other procedures used to obtain TEPs.     

Brainstem auditory evoked potentials and visually evoked potentials in young patients with IDDM

OBJECTIVE: To investigate whether young IDDM patients develop central nervous dysfunction and to establish a possible relationship with various disease parameters. RESEARCH DESIGN AND METHODS: Thirty-two patients, aged 13.5 +/- 2 years, with disease duration of 6 +/- 2.6 years and age of onset of 7.7 +/- 3.2 years (group 1), and 21 patients with short-term disease, age 9.7 +/- 3.5 years, duration of disease < 2 years and age of onset of 9.4 +/- 3.3 years (group 2) were compared with age- and sex-matched control subjects. Exclusion criteria were clinical signs of neuropathy, retinopathy, nephropathy, or hearing impairment. Neurophysiological studies included auditory and visually evoked potentials (EPs). RESULTS: Patients in group 1 revealed increased P100 latencies of visually EPs (103.4 +/- 4.5 vs. 96.8 +/- 3.7 ms) and interpeak latencies I-V of auditory EPs (4.16 +/- 0.10 vs. 3.99 +/- 0.09 ms) and had abnormal latencies (values outside 2.5 SD) in 37%. However, short-term patients (group 2) had results within normal limits compared with control subjects. In group 1, longer disease duration and younger age at onset correlated with an increase of P100 latency (P < 0.001) and IPL I-V (P < 0.001). Patients with a history of severe hypoglycemic episodes had increased latencies compared with patients without hypoglycemia (P < 0.05). Furthermore, metabolic control during the last 2 years was related to P100 latencies (P < 0.05). CONCLUSIONS: EPs noninvasively detect subclinical central nervous system involvement in children and adolescents with IDDM. Most important risk factors are duration of disease and frequency of severe hypoglycemia.     

Somatosensory evoked magnetic fields following passive finger movement

RATIONALE AND OBJECTIVES: The author introduces a number of techniques well known in exploratory pattern recognition that can be used for the analysis of the shape of metacarpophalangeal profiles. It is shown that the classic Q-scores must be adapted for such techniques to be applicable. METHODS: A new set of scores (P-scores) describing the shape of metacarpophalangeal profiles is derived. The application of various pattern-recognition techniques that use P-scores is described, using a collection of metacarpophalangeal length measurements in patients with various pathologic conditions. RESULTS: Different pattern-recognition techniques highlight different aspects of the profiles, which, when interpreted together, yield a consistent understanding of the data set and insight in individual patients' peculiarities. CONCLUSIONS: The use of scale-invariant scores is imperative when the shape of profiles is to be analyzed, especially in data sets with large variations in the scale factor. Methods of pattern recognition using such scores are of potential clinical interest.     

Visual evoked potentials in multiple sclerosis

A study was carried out of 32 patients suffering from multiple sclerosis the diagnois of which was quite definite according to Mac Alpine's criteria and which had developed over more than two years. Comparison was made with patient suffering from optic neuritis of a different aetiology and with normal subjects. The method of investigation was dynamic electroretinoencephalography : the visual evoked potentials were investigated after stimulation by white and coloured light before and after adapatation to darkness. The specificity of the results was tested by, firstly, electro-retinogram recording for control of the visual system, and secondly, by the recording of auditory evoked potentials for control cerebral function. Abnormalities in visual evoked potentials were found in 77 percent of the cases. In particular, there was delayed latency, that is, a slowing of retino-cortical conduction. The significance of these abnormalities is discussed, by analyzing the electroclinical correlationships according to whether there was obvious or subclinical optic neuritis, and the dissemination, activity or duration of the disease. The incidence of visual evoked potential abnormalities was considerably greater than that in optic neuritis (35 percent). The links between abnormalities in nervous conduction and demyelinisation are emphasized. The role and specificity of electrophysiological investigation in diagnosis of multiple sclerosis are discussed.     

Brainstem evoked potentials in panic disorder

Three hundred and one clinical medical students in four universities took the same 50 question MCQ dermatology examination after their dermatology teaching. In one centre, half the students had had additional teaching; these students performed better (mean score 47.5%, n = 29) than those who had no extra teaching (mean score 40.9%, n = 29). In another centre, the students' mean score improved from 24.1 (SD = 6.7) before to 41.6 (SD = 7) (n = 46, P < 0.001) after their dermatology teaching. The different subject areas covered by the examination were analysed separately. In the lowest scoring centre (mean score 34.0, SD = 9.4) the students scored lowest in 9 of the 14 subject areas. In the highest scoring centre (mean score 47.5, SD = 9.9) students scored highest in 7 of these 14 subject areas. This study enabled questions of high discriminatory value to be identified for future use. The use of the same examination in different centres provides feedback for the centres concerning strengths and weaknesses of their teaching.     

Somatosensory evoked potential studies in internal capsule and corona radiata infarction

To document the somatosensory evoked potential (SEP) changes in capsular and corona radiata infarction and correlate these with clinical and radiological findings, 15 patients with corona radiata and 16 with internal capsular infarction were studied. The mean age of the patients was 55 years (range 26-80), and 6 of them were female. In the patients with corona radiata infarction, median N9-N20 conduction time was abnormal in 4 cases, which correlated with sensory abnormalities in 1. In 3 of these patients, infarction was located in the anterior two-thirds and in 1 there was total corona radiata infarction. The amplitude of N20 potential on the affected side was reduced in 1 patient. In the capsular infarction group, N9-N20 conduction time was abnormal in 1 patient only who had total involvement of the posterior limb of the internal capsule. The amplitude of N20 was reduced in another patient. There were 4 patients who had abnormal sensory findings, but their SEPs were normal. At 3 months, the SEP changes remained stable in all of the patients who were followed up. The SEP changes did not correlate with changes in sensation or 3-month outcome as assessed by the Barthel index score. The lack of clinicoradiological and SEP correlation may be owing to variation on the organisation of sensory pathways in the corona radiata and internal capsule.     

Acupuncture and cortical evoked potentials

Research works for the effects of acupuncture on cortical evoked potentials were reviewed since 1970 in this article. As a result of the acupuncture anesthesia being applied widely in clinical operation, most of the studies were focused on the evoked potential of somatosensory cortex for elucidating the principle of the analgesic effect of acupuncture, while less observations were reported on the aspects of auditory and visual cortex. The amplitude of the evoked potential was often used as an index in assessing the excitability of the cerebral cortex in the studies of the effect of acupuncture in the past. An increase in the amplitude of evoked potential means an excitory process of the cortex and a decrease means depression. Based on their work, the authors consider that whether the change in the amplitude of cortical evoked potential could be served as an optional index in reflecting the excitability of the cortex is still a problem in neurophysiology remained for further investigation.     

Middle latency auditory evoked potentials in epilepsy

Heparin (HE) exhibited a protective effect on liposome peroxidation induced by Fe2+ and Cu2+, decreasing the formation of both conjugated dienes and thiobarbituric acid reactive substances (TBARS) in a dose-dependent manner. The antioxidant activity was more relevant in the oxidizing system employing Fe2+ and H2O2 and generating the highly reactive OH radical. The analysis of liposome size distribution by quasielastic laser light scattering showed that: (1) the native structure of the particles was completely lost after exposure to Fenton reagent; (2) the presence of HE in the reaction mixture completely prevented the peroxidative damage on liposomes. Thus, HE acts as an antioxidant factor on membrane lipid bilayer. This suggests that HE, released from mast-cell granules during inflammatory processes, might locally protect the cell membrane from the oxidative injuries.     

Hypnotic hallucination alters evoked potentials.

Studied whether the amplitude of the visual EP is reduced during hypnotic hallucination in which the S is instructed to perceive visual stimuli as diminished in brightness or obstructed from view. The visual EP responses of 6 high- and 6 low-hypnotizable Ss (aged 18–33 yrs) and of 6 undergraduate controls were compared in 3 hypnotic conditions: stimulus enhancement, stimulus diminution, and stimulus elimination (obstructive hallucination). ANOVA revealed that high-hypnotizable Ss demonstrated significant suppression of the later components of the EP response (N? and P?) while experiencing obstructive hallucinations, indicating a change in information processing. This effect was significantly greater in the right, as compared to the left, occipital region. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cerebral evoked potentials and semantic categorization

INTRODUCTION: Cerebral evoked potentials represent variations in the electrical activity of the nervous system, excited by a sensory stimulus and which are recorded on the surface. They may be classified as endogenous or exogenous. Amongst the late endogenous evoked potentials (EEP) we may emphasize N400 which seems to represent the linguistic management wave, particularly for semantics. OBJECTIVE: To observe the EEP recorded throughout the process of carrying out a task involving sequential semantic categorization. PATIENTS AND METHODS: Nine healthy subjects carried out a task based on a paradigm of sequential reaction time (RT), similar to that designed by us in 1994. The data recorded were the RT and EEP at the level of the electrodes Fz, Cz and Pz in five lots of stimuli (in the first four lots the same list of words were repeated and in the fifth and final lot a different, new list appeared). CONCLUSIONS: It was seen that only N400 varied during the procedure. This variation was related to familiarity with the task. That is to say that the amplitude of N400 was reduced when the same words were repeated and increased when new words appeared for semantic classification. The reduction in parallel, although not significant for RT, allowed the reduction in N400 alone to be followed whilst the task was carried out. It may be the electrophysiological marker of the process of learning semantic categorization.     

Memory processes and evoked potentials.

Reviews research on memory and evoked potentials (EPs) and presents new experimental data in which a storage component of the EP was identified. In Exp I, Ss performed information-processing operations on number and letter comparison tasks under 16 conditions varying stimulus, position, and relevance while EEGs were taken. In Exp II, 52 Ss were tested for short-term recall under the same 16 conditions. From Exp I, an EP storage component with a poststimulus maximum about 250 msec was found to be related to the storage of stimulus information in short-term memory. The storage component results led to a memory prediction that was substantiated in Exp II. Recall was not as closely related to 2 other, orthogonal EP components (P??? and CNV). Retrieval from and storage in short-term memory are discussed. Memory scanning rate derived from P??? latency changes with memory set size are faster than, but comparable to, RT estimates. An EP experiment dealing with levels of processing and memory is discussed, and a schematic model of some aspects of EPs that may be related to memory processes is presented. (French abstract) (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brainstem auditory evoked potentials in liver transplant candidates

BAEPs were recorded on 18 patients before, and/or after liver transplantation. Clinical assessment included 5 standardized scales. Data were divided by stringent criteria into 2 groups: clinical hepatic encephalopathy present (HE) or absent (nonHE). Dependent variables were BAEP configuration and I-V, I-III and III-V IPLs. The following comparisons were made: all patients vs. controls; HE vs. controls; nonHE vs. controls; HE vs. nonHE. BAEP configuration changes were not significantly associated with HE. I-V and III-V IPLs were prolonged for all patients, nonHE patients, and HE patients vs. controls; I-III IPL differences were not significant. There were no correlations between BAEP variables and EEG grade or grades on any single clinical scale. The results suggest that BAEP IPLs (especially the I-V IPL) are a sensitive, although not specific, measure of HE and may be sensitive enough to detect incipient HE.