Neurophysiological evaluation of the central nervous impulse propagation in patients with sensorimotor disturbances

Motor evoked potentials (MEPs) to transcranial stimulation (TCS) and somatosensory evoked potentials to median nerve stimulation (MN-SEPs) were examined in 74 patients affected by multiple sclerosis (MS = 49 cases), amyotrophic lateral sclerosis (ALS = 9 cases), cervical cord lesions (7 cases), Parkinson's disease (PD = 5 cases), Huntington's chorea (HC = 2 cases), Wilson's disease (WD = 1 case), subacute combined degeneration (SCD = 1 case). MN-SEPs were altered in 38% of arms in MS with a higher incidence in clinically affected than in clinically 'silent' arms (= 77.8% vs. 27.5%). MEP alterations were found in 54% of examined arms, mostly because of a prolongation of the motor CCT. This index was invariably altered in the affected arms, whilst it was involved in 40% of the 'silent' ones. Twelve out of 18 arms displayed abnormal MEPs in ALS. These were mainly due to an absent response, even if moderate motor CCT prolongation and 'giant' MEPs were also encountered. MN-SEPs were altered in 3/18 arms. By recording MEPs from proximal and distal upper limb muscles, cues on the level of abnormal propagation were obtained in patients suffering from 'focal' lesions of the spinal cord. Combining SEP records enhanced the diagnostic yield in this field. Both MEPs and SEPs were normal in patients with PD and HC, whilst abnormally prolonged CCTs were found in the case with WD. MEP and SEP recording revealed central propagation abnormalities coupled to a severe clinical picture of the peripheral nerve involvement (as in the case of SCD).     

Evoked potentials in HIV infection]

The study of the literature data on the multimodal evoked potentials in HIV infected patients shows many abnormalities as well in asymptomatic subjects without AIDS as in AIDS subjects with or without neurological signs. Visual evoked potentials (VEPs) reveal prolonged P100 wave latency in 22% of HIV asymptomatic subjects and in 26% of HIV symptomatic subjects; brainstem auditory evoked potentials (BAEPs) reveal an increase of the interpeak latency I-V in 16% of asymptomatic subjects and in 32% of symptomatic subjects; somatosensory evoked potentials (SEPs) by median nerve stimulation reveal prolonged central conduction time in 6% of asymptomatic subjects and in 11% of symptomatic subjects; somatosensory evoked potentials (SEPs) by tibial nerve stimulation reveal prolonged central conduction time in 4% of asymptomatic subjects and in 45% of symptomatic subjects; motor evoked potentials (MEPs) by magnetic stimulation reveal prolonged central motor conduction time in 46% of asymptomatic subjects.     

Familial paroxysmal exercise-induced dyskinesia and benign epilepsy: a clinical and neurophysiological study of an uncommon disorder

We report a family with 6 members affected by a long-lasting paroxysmal exertion-induced dyskinesia. Fasting and stress were precipitating factors. All the patients of this family had also epileptic seizures mainly of generalised type with a favourable outcome. All patients were submitted to a neurophysiological study which included somatosensory evoked potentials by median nerve stimulation (MN-SEPs), somatosensory evoked potentials by posterior tibial nerve stimulation (PTN-SEPs), brainstem auditory evoked potentials (BAEPs), visual evoked potentials (VEPs), motor evoked potentials (MEPs) by magnetic transcranial cortical stimulation (TCS) and electromyography (EMG). The neurophysiological findings suggest a hyperexcitability at the muscular and brain membrane levels, probably due to an ion channel disorder. Received: 2 February 2000 / Accepted in revised form: 16 June 2000     

Neurophysiological study in Pelizaeus-Merzbacher disease

The neurophysiological characteristics of Pelizaeus-Marzbacher disease (PMD) were studied in four Japanese patients aged between 5 and 13 years. Pendular spontaneous nystagmus was always recorded with a frequency between 2.5 and 4 Hz, and abnormal saccades with an almost twofold prolongation in onset time and 50% decrease in velocity were noted. Brainstem auditory evoked potentials consistently demonstrated severely altered waves II to V, following a normal wave I, despite normal hearing acuity. Somatosensory evoked potentials (SEPs) were always absent between brainstem components and early cortical responses. Late cortical components of SEPs and visual evoked potentials with significantly prolonged latencies were recorded in the three younger cases having normal sensory and visual acuity (N35 of SEP, 73.1 ± 2.1 ms; N75 of VEP, 129.0 ± 12.7 ms; mean ± S.D.), while these peaks were absent in the oldest case having the most severe handicap. In motor evoked potentials (MEPs), R1 of blink reflex with significantly prolonged latency (14.9 ± 1.48 ms) was always obtained, and no subsequent R2 was elicited. Magnetic transcortical stimulation elicited no MEPs of the thenar even in the facilitating condition on voluntary contraction despite mild weakness of the thenar, while normal MEPs were always elicited on cervical stimulation. These electrophysiological findings were consistent with extensive conduction slowing involving the brainstem to the cerebrum, which seemed to be accompanied by conduction block in motor systems rather than sensory systems. Although each of the results was not specific, in combination they suggested the characteristics of diffuse brain dysmyelination in PMD.     

Motor and somatosensory evoked potentials in hereditary spastic paraplegia.

Motor evoked potentials (MEPs) from the arms and legs to transcranial stimulation of the motor cortex and somatosensory evoked potentials (SSEPs) from stimulation of the nerves of the arms and legs, were recorded in 11 patients with hereditary spastic paraplegia. Electrophysiological abnormalities were found to be distributed differently among the systems examined; the longer the pathway, the higher the incidence and severity of impairment. MEPs from the leg were either absent or clearly reduced or prolonged in all patients. Eight patients showed abnormal cortical SSEPs on stimulation of the leg (absent or reduced responses in four, slowed central conduction velocity in seven), but only two of these patients had abnormal MEPs from the arm (absent responses). Cortical SSEPs on stimulation of the median nerve were reduced in two patients. Mean values of amplitude and central conduction velocity for MEPs and SSEPs from the leg were significantly different between patients and controls. Such differences were not found for either MEPs or SSEPs from the arm. This distribution of abnormalities, which suggests a differential involvement of the spinal pathways, parallels the reported pathological pattern in which degeneration of axons is more common and severe in the motor and sensory fibres supplying the leg.     

Motor evoked potentials (MEPs) in lacunar syndromes.

Motor evoked potentials (MEPs) evoked in the biceps, thenar and tibialis anterior muscles by electrical stimulation of the scalp and of the spinal regions were recorded in 32 patients with focal deficits due to minor cerebral ischemia of the lacunar type and in a control group. Somatosensory evoked potentials (SEPs) to median nerve stimulation were also recorded. The central motor conduction times (CMCTs) and the threshold intensities for eliciting MEPs in the relaxed muscles were significantly increased on the affected side. Central motor conduction, for at least one muscle, was altered in 18 patients. MEP abnormalities were related to pyramidal signs (though they could be observed also in a patient without any motor impairment) and occurred independently of a specific clinical picture or a radiologically confirmed lacunar lesion. SEPs were less frequently altered than MEPs.     

A new neurophysiological approach to assess central motor conduction damage to proximal and distal muscles of lower limbs

ObjectiveTo develop a neurophysiological method to explore central motor pathways to proximal and distal muscles of lower limbs.MethodsMEPs to transcranial magnetic stimulation using the double cone coil were bilaterally and simultaneously recorded from vastus medialis, tibialis anterior and flexor hallucis brevis. Voluntary facilitation was controlled using a predefined sequence of movements of constant amplitude. Compound motor action potentials elicited by maximal high voltage electrical stimulation of lumbosacral roots (root-CMAPs) were recorded from the same muscles to obtain the corresponding peripheral conduction times. We studied 28 healthy subjects and 28 multiple sclerosis (MS) patients with no or mild motor impairment.ResultsThe described facilitation procedure and the averaging of 5 MEPs reduced area variability to about 10%. In MS patients conduction slowing and/or MEP area reduction in at least one muscle was found in 91.7% of cases, with significant correlation with individual motor impairment.ConclusionsCombined use of stable MEPs and maximal root-CMAPs was able to detect both conduction slowing and conduction failure in central motor pathways to proximal and distal districts of lower limbs in MS patients.SignificanceThe proposed method provides an extensive electrophysiological mapping of central motor impairment of lower limbs in clinical application.     

脊髓型颈椎病病人经颅磁电刺激运动诱发电位的对比研究

目的探讨磁电刺激运动诱发电位（ＭＥＰ）在脊髓型颈椎病（ＣＳＭ）的应用价值，并对其临床相关性进行分析。方法采用经颅磁、电刺激对３０例脊髓型颈椎病病人以及年龄性别等相配匹的３０名健康成人分别于外展小指肌、肱二头肌及下肢展短肌表面进行ＭＥＰ的检测。结果全部病人的ＭＥＰ都出现异常，表现为潜伏期、中枢传导时间（ＣＭＣＴ）延长，时限增宽，波辐降低或不能引出。磁刺激ＭＥＰ的ＣＭＣＴ和皮层刺激潜伏期与脊髓型颈椎病临床日本整形外科协会（ＪＯＡ）评分间有密切相关性，能较好地反映ＣＳＭ病人的病情。结论ＭＥＰ在检测ＣＳＭ病人运动功能方面具有定量评价作用。与电刺激相比，磁刺激ＭＥＰ能更好地反映ＣＳＭ病人的病情。     

Serial changes in motor and somatosensory evoked potentials in putaminal haemorrhage

Little is known about evoked potential changes in putaminal haemorrhage. In this study, somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) have been serially evaluated and their role in the prognosis of putaminal haemorrhage is now reported. Nineteen patients with CT- or MRI-proven putaminal haemorrhage were examined after a mean duration of 13 days (range 2–30); there were 4 females and 9 males, ranging in age between 25 and 70 years. The haematomas were of medium size in 13 and large or small in 3 patients each. The changes in the clinical picture and the SEPs and MEPs were evaluated on admission, and after 30 and 90 days. Central motor conduction time (CMCT) could not be recorded in 13, but was prolonged in 2 and normal in 4 patients. Median SEPs revealed the absence of near field potentials in 11 and prolongation of N9–N20 conduction time in 1 patient. In the follow-up period MEP and SEP abnormalities only changed in 5 patients; MEPs changed in 4 and SEPs in 2. The period of normalisation of MEPs ranged between 1 and 6 months. CMCT correlated with motor and N9–N20 conduction time with sensory impairment. Eight patients had poor, 6 partial and 5 complete recovery. Power, sensation, CMCT, and size and location of haematoma made positive contributions to recovery.     

SEPs and CNS magnetic stimulation in syringomyelia.

Somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) to transcranial and spinal stimulation from upper and lower limb muscles were elicited in 13 patients with syringomyelia. Seven had an associated Chiari type I anomaly. Diagnosis was confirmed by MRI. In 5 cases, SEPs and MEPs were performed before and after surgical treatment. Prolonged central motor conduction times or absent motor responses in upper or lower limbs were found in most patients. The greatest number of abnormalities was disclosed by measurement of CMCT followed by SEPs after tibial nerve stimulation. Two of 5 cases undergoing surgery improved clinically and showed reduction in CMCT after surgical treatment. Our study shows that MEPs were useful in the evaluation of neurophysiological status in syringomyelia patients, helping to estimate anterolateral spinal cord function.     

Dissociation of somatosensory and motor evoked potentials in non-comatose patients after head injury.

OBJECTIVES: This study was performed to evaluate the clinical value of combined use of somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in patients with different brain lesions after head trauma. METHODS: A total of 64 patients with minor and moderate head injury were investigated by means of SEPs recorded over the parietal and frontal areas and MEPs following single-pulse transcranial magnetic stimulation (sTMS) and slow-rate repetitive transcranial magnetic stimulation (rTMS). RESULTS: In almost 50% of the patients, a dissociated impairment of somatosensory and motor evoked potentials was found. This dissociation was related to different distribution of SEP and MEP abnormalities in head injury subgroups. The higher threshold to sTMS and increased variability of the MEP amplitude during slow-rate rTMS were the most prominent features in patients with focal brain contusions, suggesting impairment of the cortical excitability. SEP abnormalities, as well as central conduction impairments, were more noticeable in patients with diffuse brain injury. CONCLUSIONS: A combined analysis of SEPs and MEPs may improve the assessment of cortical dysfunctions and central conduction abnormalities in non-comatose patients with head injury. A slow-rate rTMS may be considered as a complementary technique to the evaluation of the threshold in assessment of the excitability of the motor cortex in minor and moderate head injury.     

Motor evoked potentials from the pelvic floor in patients with multiple sclerosis

The use of motor evoked potentials (MEPs) to study the integrity of pelvic floor motor innervation is poorly described in the literature. This study evaluated the clinical use of pelvic floor MEPs in 16 women with multiple sclerosis. Lower urinary tract dysfunction was assessed with urodynamic investigations. Transcutaneous magnetic stimulation was applied over the motor cortex and spinal roots, and MEPs were recorded from the puborectalis, the external urethral sphincter, and the abductor hallucis muscles. In many patients, responses from the pelvic floor muscles could not be evoked, and central motor conduction times for the puborectalis motor pathways could only be calculated in 56%. There was a poor correlation of abnormal conduction to lower urinary tract dysfunction. It is concluded, that unevokable responses from pelvic floor muscles in a patient with multiple sclerosis should be interpreted with care, and that pelvic floor MEPs have a limited clinical value in the investigation of suspected demyelinating disease.     

AAEM minimonograph #35: Clinical experience with transcranial magnetic stimulation

We elicited motor evoked potentials (MEPs) using transcortical magnetic stimulation in 150 control subjects aged 14 to 85 years and 275 patients with a variety of diseases. There were no significant side effects. Cortex-to-target muscle latencies measured 20.2 +/- 1.6 ms (thenar), 14.2 +/- 1.7 ms (extensor digitorum communis), 9.4 +/- 1.7 ms (biceps), and 27.2 +/- 2.9 ms (tibialis anterior). Central motor delay between the cortex and the C-7 and L-5 measured 6.7 +/- 1.2 ms and 13.1 +/- 3.8 ms, respectively. Mean spinal cord motor conduction velocity measured 65.4 m/s. MEP amplitude expressed as a percentage of the maximum M wave was never less than 20% of the M wave. A value of less than 10% is considered abnormal. MEP latency increases linearly with age and central motor delay is longer in older subjects. Compound muscle action potentials and absolute MEP amplitudes decreased linearly with age. In multiple sclerosis (MS), MEP latency and central delay were often very prolonged. The MEP was more sensitive than the SEP in MS. In amyotrophic lateral sclerosis, MEP latencies were only modestly prolonged; the characteristic abnormality was reduced amplitude. When pseudobulbar features predominated MEPs were often absent. The MEP was of normal latency in Parkinson's disease, but age-related amplitude was often increased. MEP latency and amplitude were normal in Huntington's disease. Abnormal MEPs persisted several months after stroke despite good functional recovery. The MEP could be used to advantage to demonstrate proximal conduction slowing and block in demyelinating neuropathies. In plexopathy, ability to elicit an MEP several days after onset of paresis was good evidence of neuronal continuity in motor fibers.     

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.     

Preservation of central motor conduction in patients with spinal muscular atrophy type II

We evaluated the central (motor cortex to C8 motoneuron) and peripheral (C8 motoneuron to the muscle) motor conduction in 14 limbs of 7 patients with the intermediate form of spinal muscular atrophy (SMA II). The central motor conduction time (CMCT) was calculated using motor evoked potentials (MEPs) by transcranial magnetic stimulation and the results of a conventional F wave study. Peripheral conduction abnormality was found in 6 median nerves (43%) and 10 ulnar nerves (71%). Even in these patients with peripheral conduction abnormalities, the CMCT was consistently normal whenever the MEP was recorded. These results indicate that the motor conduction of the corticospinal fibers remains normal in SMA II.     

Neurophysiological evaluation of central-peripheral sensory and motor pudendal fibres

Extensive neurophysiological investigations were carried out in 18 healthy volunteer subjects, and 6 patients with neurological disease. The tests consisted of spinal and scalp somatosensory evoked potentials (SEPs) to stimulation of the dorsal nerve of penis/clitoris, motor evoked potentials (MEPs) from the bulbocavernosus muscle (BC) and anal sphincter (AS) in response to scalp and sacral root stimulation, and measurement of sacral reflex latency (SRL) from BC and AS. In the control subjects, the mean sensory total conduction time (sensory TCT), as measured at the peak of the scalp P40 wave was 40.9 msec (range: 37.8-44.2). The mean sensory central conduction time (sensory CCT = spine-to-scalp conduction time) was 27.0 msec (range: 23.5-30.4). Transcranial brain stimulation was performed by using a magnetic stimulator both at rest and during voluntary contraction of the examined muscle. Sacral root stimulation was performed at rest. Motor total conduction times (motor TCT) to BC and AS muscles were respectively 28.8 and 30.0 msec at rest, and 22.5 and 22.8 msec during contraction. Motor central conduction times (motor CCT) to sacral cord segments controlling BC and AS muscles were respectively 22.4 and 21.2 msec at rest, and 15.1 and 12.4 msec during contraction. The mean latencies of SRL were respectively 31.4 msec in the bulbocavernosus muscle and 35.9 msec in the anal sphincter. Combined or isolated abnormalities of SEPs, MEPs and SRL were found in a small group of patients with neurological disorders primarily or secondarily affecting the genito-urinary tract.     

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.     

Amyotrophic lateral sclerosis versus cervical spondylotic myelopathy: a study using transcranial magnetic stimulation with recordings from the trapezius and limb muscles.

OBJECTIVE: We report an electrophysiological method to differentiate amyotrophic lateral sclerosis (ALS) from cervical spondylotic myelopathy (CSM). METHODS: Motor evoked potentials (MEPs) by transcranial magnetic stimulation were investigated in patients with ALS (n=10) and CSM (n=9). In addition to limb MEPs using the triple stimulation technique (TST) at upper limbs, MEPs recorded from trapezius muscles were compared with those obtained from 23 normal subjects. The parameters studied were: central motor conduction time, amplitude ratio and, for the trapezius, the interside asymmetry. RESULTS: Whereas limb MEPs were abnormal in most ALS and CSM patients (17/19), trapezius MEPs were abnormal in all ALS patients, and normal in 8 out of 9 CSM patients. CONCLUSION: Recording of trapezius MEPs is a valuable addition to the limb MEPs study, since it distinguishes ALS from SCM in most patients.     

The F wave disappears due to impaired excitability of motor neurons or proximal axons in inflammatory demyelinating neuropathies.

OBJECTIVES--Investigation of pathophysiology of F wave disappearance in demyelinating neuropathies. METHODS--The peripheral motor nerve conduction was studied by motor evoked potential (MEP) on transcranial magnetic stimulation as well as conventional nerve conduction studies before and after the treatment in 26 patients with inflammatory demyelinating neuropathies. In addition, serum antiganglioside antibodies in the acute or active stage were examined. RESULTS--The F wave was abolished in 10 patients. Seven of the 10 patients showed motor evoked potentials (MEPs) on transcranial magnetic stimulation that ranged from 1-4 mV. In six of them the F wave reappeared in the recovery stage, but the MEP size did not change. This may be caused by humoral factors, because the F wave reappeared immediately after plasma exchange or intravenous immunoglobulin treatment. A correlation of F wave disappearance with the presence of serum antiganglioside antibodies was found. CONCLUSIONS--The major pathophysiology of F wave disappearance in demyelinating neuropathies is impairment of motor neuron excitability or prolonged refractoriness of the most proximal axon for backfiring. The conventional interpretation that absent F waves suggest a conduction block at the proximal site is often inadequate.     

Long-term nervous system damage from radiation of the spinal cord: An electrophysiological study

Summary A group of 13 patients suffering from Hodgkin's disease who had undergone chemotherapy and radiotherapy (above and below the diaphragm) approximately 10 years earlier was studied. The total chemotherapeutic dose was similar for all patients; the radiotherapy dose, however, was standard for 7 patients, while the other 6 received much higher dosages over limited regions of the spinal cord. Although most of these patients appeared normal both clinically and on magnetic resonance imaging, a neurophysiological study was performed to determine whether there was any involvement of the central or peripheral nervous system. Motor conduction velocity and sensory conduction velocity were measured in the lower limbs as well as spinal- and scalprecorded somatosensory evoked potentials (SEPs) in response to stimulation of the posterior tibial and sural nerves at the ankle. In addition, motor evoked potentials were recorded from the upper and lower limbs during cortical stimulation. All neurophysiological data were normal in patients who had received a standard radiation dose, while most of those who had been exposed to higher doses showed altered cortical SEPs and a slowing of central conduction time (D10-P1). Thus even though they were asymptomatic, these patients appeared to have sustained CNS damage, mainly at the level of the spinal cord.