Comparative study of visual evoked potentials in spinocerebellar ataxias and multiple sclerosis

Visual evoked potentials (VEPs) were delayed in 11 out of 18 patients with Friedreich's ataxia, in 1 out of 8 patients with Strumpell's hereditary spastic ataxia, in 2 out of 5 cases with cerebellar atrophy and in 42 out of 50 patients with multiple sclerosis (MS). Responses were normal in 5 cases with Pierre Marie's disease. Amplitude and temporal dispersion were statistically analyzed in the above-mentioned groups of patients with respect to controls. An abnormal temporal dispersion, also considered as interpeak N1P2, was frequently found in MS but only occasionally in spinocerebellar ataxias. Amplitude was statistically reduced in Friedreich's ataxia group, where an inverse relationship between latency and amplitude was found. No relation was found between VEP delay and duration of the disease, in any group considered.     

Evoked potentials in multiple system atrophy (MSA)

OBJECTIVES: To study the involvement of pyramidal tracts and sensory pathways in multiple system atrophy (MSA). MATERIALS AND METHODS: Evoked potential studies were performed in 45 MSA patients suffering from either MSA of cerebellar type (MSA-C) or MSA of parkinsonian type (MSA-P). RESULTS: Motor evoked potentials were normal in all MSA patients, whereas visual and somatosensory evoked potential abnormalities were found in about 40% of the MSA patients with no significant difference between the cerebellar (MSA-C) and parkinsonian (MSA-P) subgroup. Abnormal latencies of wave III in brainstem auditory evoked potentials were significantly more frequent in MSA-C. CONCLUSIONS: Abnormalities of somatosensory, visual and auditory evoked potentials are frequent findings in MSA, whereas abnormal motor evoked potentials are not a characteristic feature of the disease.     

Evoked potentials

ABSTRACT- 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), checkerboard 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.     

遗传性小脑共济失调的多形式诱发电位研究

研究遗传性小脑共济失调的诱发电位变化。方法采用多种形式诱发电位，对３６例此类疾病的患者进行检测，并与３０～４０名健康者作对比。结果全部患者至少存在１种以上的诱发电位异常。磁刺激运动诱发电位（ＭＥＰ）、脑干听觉诱发电位（ＢＡＥＰ）及胫后神经与正中神经体感诱发电位（ｔＳＥＰ、ｍＳＥＰ）的异常率分别为８３．３％、８８．９％、８０．０％和６２．５％。不同类型小脑共济失调的诱发电位异常率不同，各型ＢＡＥＰ的异常率普遍较高，橄榄－桥脑－小脑萎缩患者的ＭＥＰ与遗传性痉挛性共济失调的ｔＳＥＰ异常率也很高。ＭＥＰ测试时，刺激皮质在患者中所记录到的双峰波、多相波以及波宽增加，表明皮质运动神经元的异常放电。结论多形式诱发电位改变应列为慢性小脑变性分类学上的诊断依据     

Magnetically evoked motor potentials in demyelinating and axonal polyneuropathy: a comparative study

We investigated the value of magnetically evoked motor potentials (MEPs) for the differentiation of demyelinating and axonal polyneuropathies. The study population comprised 107 patients, with polyneuropathy verified by electromyography (EMG) and nerve conduction study (NCS), who had also been examined by means of MEP. MEPs were evoked by magnetic stimulation of the cortex and the spinal roots and were recorded from three upper limb muscles and two lower limb muscles bilaterally. From the EMG/NCS results 53 patients were characterized as having primary demyelination (demyelinating patients) and 54 as having axonal involvement (axonal patients). Demyelinating patients were classified as acute (acute inflammatory demyelinating polyradiculoneuropathy: AIDP) or chronic (chronic inflammatory demyelinating polyradiculoneuropathy: CIDP) according to the duration of illness. A series of indices were calculated from MEP results. One demyelinating patient and two axonal patients had normal MEPs. The MEPs of the demyelinating patients showed significantly longer peripheral conduction times, larger interside differences and lower amplitudes than the axonal patients. The central conduction index and the amplitudes upon cortical stimulation were significantly higher in patients with CIDP than in those with AIDP. Peripheral conduction time prolonged by more than 85% in at least one of the 10 muscles studied or a peripheral conduction index of above 9.4 were pathognomonic for demyelination. By combining all criteria 75% of the patients could be categorized as CIDP vs. AIDP in accordance with the EMG/NCS diagnosis. Likewise, 83% were categorized correctly as demyelinating versus axonal according to the EMG/NCS data.     

帕金森病患者运动皮质兴奋性的经颅磁刺激研究

目的:本研究拟应用低频重复性经颅磁刺激(rTMS)分别刺激帕金森病(PD)患者M1手代表区(M1Hand)及运动前区(PMC),探讨不同干预手段对运动皮质兴奋性的影响,以及M1与PMC间的联系。方法:对18名确诊PD患者先后进行4种不同干预,即口服美多芭、低频rTMS刺激M1Hand(0.5Hz,100%静息阈值,共1600次脉冲)、低频rTMS刺激PMC(0.5Hz,100%静息阈值,共1600次脉冲)以及假刺激。于每次干预前后各进行临床评价并测定运动诱发电位(MEP)相关指标。结果:①口服美多芭后UPDRSⅢ(P=0.001)以及其中有关僵直(P=0.001)、运动迟缓(P<0.001)的评分均较服药前显著改善。三种不同磁刺激干预产生结果不同,M1Hand组UPDRSⅢ减低(P=0.015),僵直(P=0.010)、运动迟缓(P=0.004)亦有所改善;PMC组UPDRSⅢ较干预前减低(P=0.046),僵直评分亦减低,但无显著性意义(P=0.163);②口服美多芭1h后MEP120减低(P=0.002),CSP延长(P=0.006);M1Hand组MEP120无著变,而CSP延长(P=0.015);PMC组MEP120减低(P=0.004),而CSP无著变;假刺激组则均无显著性改变。结论:低频rTMS对不同脑区产生的效应不同:刺激M1可使CSP延长;而刺激PMC可使MEP波幅减低。     

脑血管病患者的经颅磁刺激运动诱发电位和短潜伏期体感诱发电位的对比研究

采用经颅磁刺激运动诱发电位（MEP）对72名脑血管病患者进行检测，其中57例还同时测定短潜伏期体感诱发电位（SSEP），并和50例正常人进行对比研究．结果发现脑血管病患者瘫痪侧上肢MEP异常表现为刺激无反应或皮层潜伏期延长和中枢传导时间延长，与正常对照组和健侧比较差异有极高度显著性（P＜0．001），瘫痪侧下肢MEP异常表现为刺激无反应或中枢传导时间延长，与正常对照组和健侧比较，差异有显著性（P＜0．05）．MEP和SSEP异常率在脑出血与脑梗塞之间无显著性差异（P＞0．05），而与临床表现和病变部位密切相关。本文提示MEP和SSEP分别能客观地反映脑血管病愈者中枢运动传导通路和中枢感觉通路功能受损的情况．     

Motor Evoked Potentials Improve Targeting in Deep Brain Stimulation Surgery

ObjectivesOne of the main challenges posed by the surgical deep brain stimulation (DBS) procedure is the successful targeting of the structures of interest and avoidance of side effects, especially in asleep surgery. Here, intraoperative motor evoked potentials (MEPs) might serve as tool to identify the pyramidal tract. We hypothesized that intraoperative MEPs are useful to define the distance to the pyramidal tract and reduce the occurrence of postoperative capsular side effects.Materials and MethodsMotor potentials were evoked through both microelectrode and DBS-electrode stimulation during stereotactic DBS surgery on 25 subthalamic nuclei and 3 ventral intermediate thalamic nuclei. Internal capsule proximity was calculated for contacts on microelectrode trajectories, as well as for DBS-electrodes, and correlated with the corresponding MEP thresholds. Moreover, the predictivity of intraoperative MEP thresholds on the probability of postoperative capsular side effects was calculated.ResultsIntraoperative MEPs thresholds correlated significantly with internal capsule proximity, regardless of the stimulation source. Furthermore, MEPs thresholds were highly accurate to exclude the occurrence of postoperative capsular side effects.ConclusionsIntraoperative MEPs provide additional targeting guidance, especially in asleep DBS surgery, where clinical value of microelectrode recordings and test stimulation may be limited. As this technique can exclude future capsular side effects, it can directly be translated into clinical practice.     

Comparison of Rossini–Rothwell and adaptive threshold‐hunting methods on the stability of TMS induced motor evoked potentials amplitudes

Several methods can be used to determine the resting motor threshold (RMT) and by that recording transcranial magnetic stimulation (TMS) induced motor evoked potentials (MEPs). However, no research has compared the test retest reliability of these methods. Thus, the aim of this study was to determine intra‐ and inter‐session reliability of Rossini–Rothwell (R–R) and parameter estimation by sequential testing (PEST) methods on TMS‐induced MEPs and comparison of these two methods on RMT. Twelve healthy individuals participated in this study three times (T1, T2 and T3) over two days. TMS was applied using both R–R and PEST to estimate RMT and average of 25 MEPs were acquired at each of the three time points. The intra‐class correlation coefficient indicated high intra‐session reliability in the MEP amplitudes for both methods (0.79 and 0.88, R–R and PEST respectively). The RMT and MEP amplitudes had higher inter‐session reliability in both methods (0.99 and 0.998, R–R and PEST respectively; 0.84 and 0.76, R–R and PEST respectively). There was no significant difference between methods for RMT at both T1 (maximum stimulator output of R–R vs. PEST, 33.7% ± 7.7% vs. 33.8% ± 7.6%, p = 0.75) and T3 (maximum stimulator output of R–R vs. PEST, 33.5% ± 7.3% vs. 33.7% ± 7.3%, p = 0.19). There was a significant positive correlation between the methods' estimates of RMT, with PEST requiring significantly fewer stimuli. This study shows that the R–R and PEST methods have high intra‐and inter‐session reliability and the same precision, with PEST having the advantage over R–R in speed of estimation of RMT.     

脑血管病患者经颅磁刺激运动诱发电位的研究

采用经颅磁刺激运动诱发电位（ＭＥＰ）对７２例脑血管病（ＣＶＤ）患者和５０例正常人进行检测。结果：ＣＶＤ患者瘫痪侧上肢磁刺激无反应或皮层潜伏期和中枢传导时间（ＣＭＣＴ）较正常对照组和健侧显著延长（Ｐ＜０．００１）；瘫痪侧下肢磁刺激无反应或ＣＭＣＴ较正常对照组和健侧显著延长（Ｐ＜０．０５）。脑出血与脑梗塞患者ＭＥＰ异常率无显著差异（Ｐ＞０．０５），而与临床病情轻重和病变部位密切相关。提示ＭＥＰ能客观反映ＣＶＤ患者中枢运动传导通路功能受损的情况。     

Focal enhancement of motor cortex excitability during motor imagery: a transcranial magnetic stimulation study

OBJECTIVES: In order to learn more about the physiology of the motor cortex during motor imagery, we evaluated the changes in excitability of two different hand muscle representations in the primary motor cortex (M1) of both hemispheres during two imagery conditions. MATERIALS AND METHODS: We applied focal transcranial magnetic stimulation (TMS) over each M1, recording motor evoked potentials (MEPs) from the contralateral abductor pollicis brevis (APB) and first dorsal interosseus (FDI) muscles during rest, imagery of contralateral thumb abduction (C-APB), and imagery of ipsilateral thumb abduction (I-APB). We obtained measures of motor threshold (MT), MEP recruitment curve (MEP-rc) and F waves. RESULTS: Motor imagery compared with rest significantly decreased the MT and increased MEPs amplitude at stimulation intensities clearly above MT in condition C-APB, but not in condition I-APB. These effects were not significantly different between right and left hemisphere. MEPs simultaneously recorded from the FDI, which was not involved in the task, did not show facilitatory effects. There were no significant changes in F wave amplitude during motor imagery compared with rest. CONCLUSIONS: Imagery of unilateral simple movements is associated with increased excitability only of a highly specific representation in the contralateral M1 and does not differ between hemispheres.     

直接皮质刺激运动诱发电位在累及运动区胶质瘤切除术中运动通路保护研究

目的在累及运动区的胶质瘤切除术中．利用直接皮质刺激产生的运动诱发电位（MEP）去判断运动传导通路纤维的数量和功能，并分析其变化和术后病人四肢运动功能的关系。方法对42例累及运动区的胶质瘤病人．术中利用微弱电流直接刺激运动区皮质并记录产生的运动诱发电位，比较肿瘤切除前、中、后MEP的变化，分析肿瘤切除后MEP下降程度和术后3个月四肢运动功能的关系。结果切瘤后MEP较切瘤前波幅下降50％以上26例，其中出现严重运动功能障碍17例（65．4％）．轻度运动功能障碍9例（34．5％）；MEP下降50％以下16例，其中出现严重运动功能障碍2例（1.3％），轻度运动功能障碍10例（62．5％）．基本正常4例（25．0％）。两组严重运动功能障碍经Х^2检验，P〈0．05，差异有统计学意义。结论术中行直接皮质刺激运动诱发电位监测可直接反映运动传导纤维的数量和功能，预测术后肢体运动情况。MEP波幅下降50％可作为将发生严重运动功能障碍的临界警戒点．     

Etomidate dose-response on somatosensory and transcranial magnetic induced spinal motor evoked potentials in primates

Abstract

There is growing interest and need to monitor reliably both motor (MEP) and somatosensory (SEP) evoked potentials under anesthesia. On a pre-established primate model, the present study examined the effect of incremental etomidate (ET) dosages on spinal neural MEPs to transcranial magnetic stimulation (TMS) and posterior tibial rate (PTN) SEPs. Through a small thoracic Tl 1-T12 laminotomy, an insulated double bipolar electrode was inserted epidurally in seven cynomolgus monkeys. Spinal TMS-MEPs, PTN-SEPs, and frontal EEC were tested against graded increase of ET doses. Etomidate 0.5 mg kg-1 i.v. was initially given and followed by 30 min continuous infusion of 0.01 mg kg^1 min~1, 0.018, 0.032, 0.056, 0.1, and 0.18 mg kg'1 min"1 in that order. Measurable spinal MEPs and SEPs were recorded under deep ET anesthesia (total 12.38 mg kg-1 cumulative dose over 180 min). The EEC showed marked slow wave and graded burst suppression at cumulative dose of ^3.14 mg kg~'. The direct (D) and subsequent initial indirect (I) waves (Ij, l2,13) were reproducible at doses <0.18 mg kg~7 min~1 infusion. The latter l-waves (l4 and l5) showed graded loss at infusion dosage 0.056 mg kg'1 min~1. Etomidate remains an anesthetic of attractive features in neuroanesthesia. In the primate model, neural MEPs-SEPs were reproducible despite the exceedingly high dose of ET and markedly depressed EEC. Moreover, MEP-SEP can be monitored during ET burst-suppressive neuroprotective state. The study may set a model in humans for intra-operative multi-modality neurophysiologic recording under ET-based anesthesia. [Neurol Res 1999; 21: 714-7201     

Megnetic motor evoked potentials (MEP) in diseases of the spinal cord

Transcranial magnetic stimulation (TMS) is a non-invasive diagnostic method particularly suited to investigation of the long motor tracts. The clinical value of this method in many cortical and subcortical diseases has been well established, but comparable studies for most spinal cord diseases have still to be made. Forty patients in whom spinal cord disease was established by clinical examination, cerebrospinal fluid examination, and magnetic resonance imaging (MRI) were studied by means of somatosensory evoked potentials (SEP, median and tibial nerve stimulation) and magnetic motor evoked potentials (MEP, first dorsal interosseus and tibialis anterior muscle recordings after transcranial and spinal stimulation). The underlying pathology was neoplastic (n= 16), inflammatory (n= 15) or ischemic (n = 9). Clinical signs and symptoms ranged from slight sensory disturbances to complete paraplegia and had developed within minutes (ischemia) or over many years (benign neoplastic disease). The overall frequency of pathological SEP was slightly higher than that of MEP (78% vs 68%) which was statistically not significant (p > 0.05). This was also true for the subgroups, except for pure motor disorders, which gave the same yield for both methods. Decreased amplitudes or absence of MEP were more frequent in neoplastic than in inflammatory lesions (75% vs 33%, p < 0.05). In the latter, however, MEP more often occurred with increased latencies (40% vs 31%, p > 0.05, n. s.). Pathological SEP were found in 75% of patients presenting with pure motor abnormalities, while pathological MEP were found in 30% of patients with pure sensory disturbances. We conclude, in common with the SEP, the MEP are helpful in the examination of spinal cord diseases, even in subclinical disturbances, although the SEP would seem to yield a larger percentage of pathological results.     

Facilitation of motor evoked potentials: Timing of jendrassik maneuver effects

Remote voluntary contraction, such as the classical Jendrassik maneuver (JM), is a procedure routinely used to increase the amplitude of tendon reflexes in the lower limb. In 8 healthy subjects we studied the effects of JM on the motor evoked potentials (MEP) recorded from tibialis anterior muscle, produced by transcranial magnetic stimulation (stimulus output of 5–10% over motor threshold). In this study, JM consisted here of a bilateral violent handgrip, preceding magnetic stimulation from 100 to 50 ms (steps of 100 ms). Compared to the control test, latencies remained unchanged. MEP amplitudes were greatly enhanced with a JM test interval from 200 to 400 ms (170% of control amplitude at 300 ms). We also studied 6 patients with severe alterations of MEPs from tibialis anterior muscle. In each case, JM preceding magnetic stimulation (stimulus output 100%) from 300 ms induced reappearance of response or marked enhancement of amplitude, allowing calculation of central conduction time. Such a technique, which is easy to perform, may be useful in clinical practice to calculate central motor conduction time, where it would otherwise be difficult or impossible. © 1995 John Wiley & Sons, Inc.     

Conditioning effect on the long latency potentials in the lower limb to transcranial magnetic stimulation

Objectives – We used an electrical conditioning stimulation followed by transcranial magnetic stimulation (TMS) to facilitate the occurrence of long latency potentials (LLPs) in order to study the relationship between primary motor evoked potentials (MEPs) and LLPs in the lower limbs. Materials and methods – The study group included 6 healthy subjects, 1 patient with right thalamic infarction, and 3 patients with spinal cord injuries. The subjects were subjected to electrical conditioning (C) stimulation delivered to the left big toe at 250 Hz in a train of pulses of 20 ms duration prior to TMS (T) from 0 to 150 ms at an increment of 10 ms. The surface electromyographic signals were recorded at the tibialis anterior and gastrocnemius medialis for 400 ms. Results – The C-T test facilitated both primary MEPs and LLPs with a pattern similar to the primary MEPs of its antagonist. There was no facilitation of the primary MEPs or LLPs in the affected limb of patients with thalamic or spinal cord lesions. Conclusion – At appropriate C-T interval, LLPs could be consistently provoked by TMS. The LLPs were absent in the patients with thalamic infarction and spinal cord injuries. It suggests that LLPs might be provoked through a supraspinal control.     

Neurodegeneration in friedreich's ataxia is associated with a mixed activation pattern of the brain. A fMRI study

Friedreich's ataxia (FRDA) is associated with a distributed pattern of neurodegeneration in the spinal cord and the brain secondary to selective neuronal loss. We used functional MR Imaging (fMRI) to explore brain activation in FRDA patients during two motor-sensory tasks of different complexity, i.e. continuous hand tapping and writing of "8" figure, with the right dominant hand and without visual feedback. Seventeen FRDA patients and two groups of age-matched healthy controls were recruited. Task execution was monitored and recorded using MR-compatible devices. Hand tapping was correctly performed by 11 (65%) patients and writing of the "8" by 7 (41%) patients. After correction for behavioral variables, FRDA patients showed in both tasks areas of significantly lower activation in the left primary sensory-motor cortex and right cerebellum. Also left thalamus and right dorsolateral prefrontal cortex showed hypo-activation during hand tapping. During writing of the "8" task FRDA patients showed areas of higher activation in the right parietal and precentral cortex, globus pallidus, and putamen. Activation of right parietal cortex, anterior cingulum, globus pallidus, and putamen during writing of the "8" increased with severity of the neurological deficit. In conclusion fMRI demonstrates in FRDA a mixed pattern constituted by areas of decreased activation and areas of increased activation. The decreased activation in the primary motor cortex and cerebellum presumably reflects a regional neuronal damage, the decreased activation of the left thalamus and primary sensory cortex could be secondary to deafferentation phenomena, and the increased activation of right parietal cortex and striatum might have a possible compensatory significance.     

重复经颅磁刺激对帕金森病运动功能及运动诱发电位的影响

目的:探讨低频重复经颅磁刺激(rTMS)对PD患者运动皮质兴奋性影响的持续效应。方法:对38例PD患者,予0.5Hz rTMS刺激其主要受累肢体对侧的M1Hand(20×80,100%RMT),连续7d。于首次干预前及末次干预后20min、1周及1个月分别评价其临床运动功能和运动诱发电位。结果:低频rTMS干预后,PD患者UPDRS Ⅲ、僵直、运动迟缓评分、计时运动试验及CSP均存在显著时间效应(P<0.001)。结论:低频rTMS可改善PD患者运动迟缓症状,其对运动功能的影响可持续到刺激停止后1个月,与运动皮质兴奋性的改变一致。