Duration Of Motor Evoked Potentials Research Articles

A Novel Sensory Wave (P25) in Myelin Oligodendrocyte Glycoprotein-induced Experimental Autoimmune Encephalomyelitis Murine Model

Myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) is a murine model for multiple sclerosis. This model is characterized by chronic and progressive demyelination, leading to impairment of motor function and paralysis. While the outcomes of the disease, including impaired motor function and immunological changes, are well-characterized, little is known about the impact of EAE on the electrophysiology of the motor and sensory systems. In this study, we assessed evoked potentials as a quantitative marker for in vivo monitoring of nervous system damage. Motor-evoked potentials (MEPs) and sensory-evoked potentials (SEPs) were first standardized in naïve C57BL mice and studied thoroughly in EAE mice. The duration of MEPs and the number of connotative potentials increased significantly alongside an increase in temporal SEP amplitudes. Moreover, a new SEP wave was identified in naïve animals, which significantly increased in MOG-induced EAE animals with no or mild symptoms (clinical score 0–2, 0–5 scale). This wave occurred ∼25 milliseconds poststimulation, thus named p25. P25 was correlated with increased vocalization and was also reduced in amplitude following treatment with morphine. As the EAE score progressed (clinical score 3–4, 0–5 scale), the amplitude of MEPs and SEPs decreased drastically. Our results demonstrate that desynchronized neural motor activity, along with hypersensitivity in the early stages of EAE, leads to a complete loss of motor and sensory functions in the late stages of the disease. The findings also suggest an increase in p25 amplitude before motor deficits appear, indicating SEP as a predictive marker for disease progression. PerspectiveThis article assesses p25, a new sensory electrophysiology wave that correlates with pain-related behavior in MOG-induced EAE mice and appears prior to the clinical symptoms. Motor electrophysiology correlates with traditional motor behavior scoring and histology.

Developmental models of motor-evoked potential features by transcranial magnetic stimulation across age groups from childhood to adulthood

To derive the maturation of neurophysiological processes from childhood to adulthood reflected by the change of motor-evoked potential (MEP) features. 38 participants were recruited from four groups (age mean in years [SD in months], number (males)): children (7.3 [4.2], 7(4)), preadolescents (10.3 [6.9], 10(5)), adolescents (15.3 [9.8], 11(5)), and adults (26.9 [46.2], 10(5)). The navigated transcranial magnetic stimulation was performed on both hemispheres at seven stimulation intensity (SI) levels from sub- to supra-threshold and targeted to the representative cortical area of abductor pollicis brevis muscle. MEPs were measured from three hand- and two forearm-muscles. The input–output (I/O) curves of MEP features across age groups were constructed using linear mixed-effect models. Age and SI significantly affected MEP features, whereas the stimulated side had a minor impact. MEP size and duration increased from childhood to adulthood. MEP onset- and peak-latency dropped in adolescence, particularly in hand muscles. Children had the smallest MEPs with the highest polyphasia, whereas I/O curves were similar among preadolescents, adolescents, and adults. This study illustrates some of the changing patterns of MEP features across the ages, suggesting developing patterns of neurophysiological processes activated by TMS, and to motivate studies with larger sample size.

Motor Evoked Potential-A Pilot Study Looking at Reliability and Clinical Correlations in Multiple Sclerosis.

Multiple sclerosis (MS) is a clinically heterogeneous disease. Biomarkers that can assess pathological processes that are unseen with conventional imaging remain an unmet need in MS disease management. Motor evoked potentials (MEPs) could be such a biomarker. To determine and follow longitudinal MEP reliability and correlations with clinical measures in MS patients. This is a single-center study in alemtuzumab-treated MS patients to evaluate temporal reliability of MEPs, identify MEP minimum detectible differences, and explore correlations with existing clinical scales. Ten MS patients recently treated with alemtuzumab were evaluated every 6 months over 3 years. Clinical evaluations consisted of expanded disability status scale, timed 25-foot walk, 6-minute walk, and nine-hole peg test. MEPs were measured twice, 2 weeks apart, every 6 months. Eight patients completed all 3 years of study. The intraclass correlation coefficient for MEP parameters ranged from 0.76 to 0.98. TA latency and amplitude with facilitation significantly and strongly correlated with all clinical measures, whereas the MEP duration modestly correlated. Biceps latency with facilitation significantly and moderately correlated with 9-hole peg test. Longitudinal correlations demonstrated good predictive values for either clinical deterioration or improvement. MEPs have excellent intrapatient and intrarater reliability, and TA MEPs significantly and strongly correlated with expanded disability status scale, 6-minute walk, and timed 25-foot walk, whereas biceps MEPs significantly and moderately correlated with nine-hole peg test. Further studies using larger cohorts of MS patients are indicated. ClinicalTrials.gov, Identifier: NCT02623946.

Diagnostic value of motor evoked potential parameters in patients with Parkinson’s disease stage II

The aim of our study was to identify the most informative parameters of motor evoked potential (MEP) based on clinical and neurophysiological comparisons in patients with Parkinson’s disease (PD) stage II. Materials and methods. The study included 90 patients aged 45 to 75 years with stage II PD according to Hoehn–Yahr. Examination of patients was performed according to the following scheme: clinical and neurological examination with MDS UPDRS scale and neurophysiological examination to determine the latency, amplitude and duration of MEP after 4 tests with a gradual increase of magnetic field induction. Our study involved patients with predominantly right and left-sided motor symptoms, so for correct statistical analysis, the dominant side was considered as the debut side or the side with more pronounced motor symptoms, the subdominant side was considered as the opposite one. Results. In cases of patients with stage II PD the MEP latency significantly decreased, and the amplitude and duration of MEP significantly increased in samples with increasing magnetic field induction in the right and left hemispheres of the brain. It was found significant positive moderate correlation between UPDRS part III total score and MEP latency in the ipsilateral premotor cortex to the dominant side of motor symptoms with samples of magnetic induction (1.1 Tl – r = 0.34, P < 0.05; 1.32 Tl – r = 0.32, P < 0.05; 1.76 Tl – r = 0.31, P < 0.05). Also positive mild correlation was found between MEP latency in the ipsilateral premotor cortex to the subdominant side of motor symptoms and UPDRS part III total score (1.54 Tl – r = 0.22, P < 0.05; 1.76 Tl – r = 0.29, P < 0.05). Mild positive correlation (r = 0.29, P < 0.05) was found between MEP duration of ipsilateral premotor cortex to the subdominant side of motor symptoms and UPDRS part III total score in sample with 1.54 Tl magnetic induction. No significant correlations were found to the amplitude parameter and the severity of clinical symptoms in investigated patients with PD stage II. Conclusions. The most informative neurophysiological indicators in patients with PD stage II are the MEP latencies. The MEP latencies of the premotor cortex, which is ipsilateral to the side with more pronounced motor symptoms, have a particularly close relationship with UPDRS part III total score in the samples with 1.10–1.76 Tl magnetic inductions (r = 0.31–0.34, P ˂ 0.05). The MEP duration of premotor cortex, which is ipsilateral to the side with less pronounced motor symptoms, is most closely associated with the severity of motor manifestations on the subdominant side in patients with PD stage II (r = 0.27, P ˂ 0.05).

Evaluating the Effects of 5-Hz Repetitive Transcranial Magnetic Stimulation With and Without Wrist-Ankle Acupuncture on Improving Spasticity and Motor Function in Children With Cerebral Palsy: A Randomized Controlled Trial.

Objective: The goal of this study is to explore the effect of wrist-ankle acupuncture combined with 5-Hz repetitive transcranial magnetic stimulation (rTMS) on improving spastic state and motor function of children with spastic cerebral palsy by measuring electrophysiological parameters and behaviors.Methods: Twenty-five children with spastic cerebral palsy were enrolled in a single-blind and randomized controlled trial. The control group received 20 sessions of 5-Hz rTMS over the affected hemisphere with 1,000 pulses. The experimental group was given wrist-ankle acupuncture on the basis of the control group. Gross motor function measure (GMFM-66), muscle tension, and electrophysiological parameters of the two groups were assessed at baseline and after intervention.Results: After treatment, the GMFM-66 scores in the same groups were significantly improved (p < 0.001). Besides, the R-value of soleus, gastrocnemius, and hamstring muscle decreased (p < 0.05), and the results showed a trend of shortening MEP latency, increasing amplitude and duration (p < 0.05). Compared to the controlled group, the experimental group displayed more excellent changes in the GMFM-66 scores and motor evoked potential (MEP) latency. The statistical results showed that the increase of GMFM-66 score and the shortening of MEP latency in the experimental group were greater than that in the control group (p < 0.05). However, no significant differences were found in the assessment of muscle tension, amplitude, and duration of MEPs between two groups (p > 0.05).Conclusion: Wrist-ankle acupuncture combined with 5-Hz rTMS is optimal to improve gross motor function and enhance the conductivity of corticospinal tract in children with cerebral palsy but cannot highlight its clinical superiority in improving spasticity.Clinical Trial Registration: [http://www.chictr.org.cn/index.aspx], identifier [chictr2000039495].

Motor evoked potential latency and duration from tibialis anterior in individuals with chronic stroke.

Ipsilateral motor pathways from the contralesional hemisphere to the paretic limbs may be upregulated to compensate for impaired function after stroke. Onset latency and duration of motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS) provide insight into compensatory pathways but have been understudied in the lower limb. This study assessed MEP onset latency and duration in the lower limb after stroke, and compared ipsilateral and contralateral MEPs in the paretic and non-paretic limb. We hypothesized that: (1) onset latency would be longer for ipsilateral than contralateral MEPs and longer for the paretic than the non-paretic limb, and (2) duration would be shorter for ipsilateral than contralateral MEPs and longer for the paretic than the non-paretic limb. Data were collected as a part of a pre-test of a randomized controlled trial. TMS was applied to the ipsilateral and contralateral hemisphere of the paretic and non-paretic limb. MEP onset latency and duration were calculated from the tibialis anterior. Thirty-five participants with chronic stroke were included in the final analysis. Onset latency was longer in the paretic than the non-paretic limb (~ 6.0ms) and longer after ipsilateral than contralateral stimulation (~ 1.8ms). Duration was longer in the paretic than the non-paretic limb (~ 9.2ms) and longer after contralateral than ipsilateral stimulation (~ 5.2ms). Ipsilateral MEPs may be elicited through ipsilateral pathways with fewer fibers with a higher activation threshold and/or greater spinal branching. MEPs from the paretic limb may reflect slower central motor conduction, peripheral changes, or changes in motor pathway.

Neck rotation modulates motor-evoked potential duration of proximal muscle cortical representations in healthy adults

Transcranial magnetic stimulation (TMS) produces motor-evoked potentials (MEP) used to infer changes in corticomotor excitability. In humans, neck rotation can probe reticulospinal input on corticomotor output. This study investigated the effect of neck rotation on MEP duration in a proximal and distal upper limb muscle and compared responses between rest and preactivation. Single-pulse TMS to motor cortex was used to evoke MEPs at two stimulus intensities in 18 healthy adults (20-40years). Surface electromyography recorded MEPs from the non-dominant biceps brachii (BB) and first dorsal interosseous (FDI). Participants were seated with the target muscle at rest or 10% preactivated, and head rotated ipsilateral, contralateral, or in neutral position. The primary outcome was MEP tail, defined as the mean difference in MEP duration between active and rest trials. Secondary outcomes were MEP duration and amplitude. MEP tail was modulated by neck rotation in the proximal BB (P = 0.03) but not distal FDI (P > 0.19), with shorter duration during ipsilateral or contralateral rotation relative to neutral. In a neutral neck position, MEP duration was prolonged by muscle preactivation and higher TMS intensities in the FDI and BB (P < 0.03). Neck rotation attenuated the prolongation of MEP duration during preactivation in the BB, but not the FDI. Neck rotation had no effect on MEP amplitude for either muscle (P > 0.05). Modulation of the late portion of the MEP by rotation of the neck could indicate subcortical projections to alpha-motoneuron pools are stronger in proximal than distal upper limb muscles. These findings may have relevance for using MEP duration as a neural biomarker in neurological diseases.

Motor corticospinal excitability: a novel facet of pain modulation?

Introduction:Increase in excitability of the primary motor cortex (M1) is associated with pain inhibition by analgesics, which is, in turn, associated with the psychophysical antinociceptive pain modulation profile. However, the relationship between neurophysiological M1 excitability and psychophysical pain modulation has not yet been explored.Objectives:We aim to study these relationships in healthy subjects.Methods:Forty-one young healthy subjects (22 women) underwent a wide battery of psychophysical testing that included conditioned pain modulation (CPM) and pain temporal summation, and a transcranial magnetic stimulation neurophysiological assessment of the motor corticospinal excitability, including resting motor threshold, motor-evoked potentials (MEPs), and cortical silent period.Results:Increased motor corticospinal excitability in 2 parameters was associated with more efficient CPM: (1) higher MEP amplitude (r = −0.574; P_Bonferroni = 0.02) and (2) longer MEP duration (r = −0.543; P_Bonferroni = 0.02). The latter also correlated with the lower temporal summation magnitude (r = −0.421; P = 0.007); however, on multiplicity adjustment, significance was lost.Conclusions:Increased corticospinal excitability of the primary motor cortex is associated with more efficient inhibitory pain modulation as assessed by CPM, in healthy subjects. Motor-evoked potential amplitude and duration may be considered as an additional, objective and easy to measure parameter to allow for better individual assessment of pain modulation profile.

Physiological processes influencing motor-evoked potential duration with voluntary contraction.

Voluntary contraction leads to facilitation of motor-evoked potentials (MEPs) producing greater amplitude, shorter onset latency, and prolonged duration of the electromyography potential. Whereas hyperexcitability of spinal motoneurons and changes in descending corticospinal volleys have been proposed as putative mechanisms for changes in MEP amplitude and onset latency, a contribution of propriospinal interneurons, exerting modulatory effects on α-motoneurons, has been proposed as a potential explanation for prolongation of MEP duration. The aim of the present study is to gain further insight into the physiological processes underlying changes in MEP duration. Transcranial magnetic stimulation (TMS) studies were undertaken on 30 healthy controls, using a 90-mm circular coil, with MEPs recorded at rest and during facilitation, produced by contraction of abductor pollicis brevis. In the same experiment, short interval-intracortical inhibition (SICI) was recorded at rest. Facilitation resulted in a significant prolongation of MEP duration, which increased with stimulus intensity and was accompanied by an increase in MEP amplitude. The main effect (TMS intensity × activation state) was correlated with MEP duration (F = 10.9, P < 0.001), whereas TMS intensity (F = 30.5, P < 0.001) and activation state (F = 125.8, P < 0.001) in isolation were correlated with MEP amplitude. There was a significant inverse relationship between SICI and MEP duration at rest (R2 = 0.141, P = 0.041) and during facilitation (R2 = 0.340, P = 0.001). The present findings suggest that similar physiological processes mediate changes in the facilitated MEP duration and amplitude and that both cortical and nonpropriospinal spinal mechanisms contribute to changes in MEP duration.NEW & NOTEWORTHY Muscle contraction is associated with a significant increase in motor-evoked potential (MEP) duration and amplitude. Whereas the increase in MEP duration was linear, the amplitude increase exhibited a ceiling effect. Importantly, the MEP duration increase strongly correlated with short interval-intracortical inhibition, a biomarker of motor cortical function. This suggests that whereas similar physiological processes contribute to changes in facilitated MEP duration and amplitude, cortical mechanisms appear to contribute to MEP duration changes.

Evaluation of the Predictive Value of Intraoperative Changes in Motor-Evoked Potentials of Caudal Cranial Nerves for the Postoperative Functional Outcome

The predictive value of changes in intraoperatively acquired motor-evoked potentials (MEPs) of the lower cranial nerves (LCN) IX-X (glossopharyngeal-vagus nerve) and CN XII (hypoglossal nerve) on operative outcomes was investigated. MEPs of CN IX-X and CN XII were recorded intraoperatively in 63 patients undergoing surgery of the posterior cranial fossa. We correlated the changes of the MEPs with postoperative nerve function. For CN IX-X, we found a correlation between the amplitude of the MEP ratio and uvula deviation (P= 0.028) and the amplitude duration of the MEP and gag reflex function (P= 0.027). Patients with an MEP ratio of the glossopharyngeal-vagus amplitude ≤1.47 μV had a 3.4 times increased risk of developing a uvula deviation. Patients with a final MEP duration of the CN IX-X ≤11.6 milliseconds had a 3.6 times increased risk for their gag reflex to become extinct. Our study greatly contributes to the current knowledge of intraoperative MEPs as a predictor for postoperative cranial nerve function. We were able to extent previous findings on MEP values of the facial nerve on postoperative nerve function to 3 additional cranial nerves. Finding reliable predictors for postoperative nerve function is of great importance to the overall quality of life for a patient undergoing surgery of the posterior cranial fossa.

ID 317 – On the clinical value of measuring the increase in duration of the motor evoked potential with contraction-induced facilitation

Objective Contraction-induced facilitation of the motor evoked potential (MEP) to transcranial magnetic stimulation (TMS) consists in three main changes: shortening of onset latency, enhancement of peak-to-peak amplitude and increase in duration. We hypothesized that the latter can be of clinical utility and retrospectively investigated how it is affected by disease. Methods We revised data obtained in 50 patients with different neurological disorders who, as part of their clinical assessment, received focal TMS at rest and during contraction, with recording on the 1st interossesous (INT) and/or tibialis anterior (TA). We measured the MEP duration difference between facilitation and rest. Results Healthy subjects increased the MEP duration during a mild contraction by 8.1 ± 1.1 ms in INT and by 9.8 ± 1.7 ms in TA. Patients with spastic paraparesis and a number of those with multiple sclerosis had polyphasic long duration MEPs in TA already at rest, with little increase during contraction. Patients with stroke, if they had the possibility to contract, increased duration up to normal levels. Patients with psychogenic weakness did not increase MEP duration. Conclusion Duration of the MEP during facilitation may reveal the engagement of excitatory spinal cord premotoneuronal interneurons and may be useful for the assessment of weakness.

Clinical Value of the Assessment of Changes in MEP Duration with Voluntary Contraction.

Transcranial magnetic stimulation (TMS) gives rise to muscle responses, known as motor evoked potentials (MEP), through activation of the motor pathways. Voluntary contraction causes facilitation of MEPs, which consists of shortening MEP latency, increasing MEP amplitude and widening MEP duration. While an increase in excitability of alpha motorneurons and the corticospinal tract can easily explain latency shortening and amplitude increase, other mechanisms have to be accounted for to explain the increase in duration. We measured the increase in duration of the MEP during contraction with respect to rest in a group of healthy volunteers and retrospectively assessed this parameter in patients who were examined in a standardized fashion during the past 5 years. We included 25 healthy subjects, 21 patients with multiple sclerosis, 33 patients with acute stroke, 5 patients with hereditary spastic paraparesis, and 5 patients with signs suggesting psychogenic paresis. We found already significant differences among groups in the MEP duration at rest, patients with MS had a significantly longer duration, and patients with stroke had significantly shorter duration, than the other two groups. The increase in MEP duration during voluntary contraction was different in patients and in healthy subjects. It was significantly shorter in MS and significantly longer in stroke patients. It was absent in the five patients with suspected psychogenic weakness. In patients with HSP, an abnormally increase in duration occurred only in leg muscles. Our results suggest that the increase in duration of the MEP during contraction may reveal the contribution of propriospinal interneurons to the activation of alpha motorneurons. This mechanism may be altered in some diseases and, therefore, the assessment proposed in this work may have clinical applicability for the differential diagnosis of weakness.

Effects of dexmedetomidine on intraoperative motor and somatosensory evoked potential monitoring during spinal surgery in adolescents

Dexmedetomidine may be a useful agent as an adjunct to an opioid-propofol total intravenous anesthesia (TIVA) technique during posterior spinal fusion (PSF) surgery. There are limited data regarding its effects on somatosensory (SSEPs) and motor evoked potentials (MEPs). The data presented represent a retrospective review of prospectively collected quality assurance data. When the decision was made to incorporate dexmedetomidine into the anesthetic regimen for intraoperative care of patients undergoing PSF, a prospective evaluation of its effects on SSEPs and MEPs was undertaken. SSEPs and MEPs were measured before and after the administration of dexmedetomidine in a cohort of pediatric patients undergoing PSF. Dexmedetomidine (1 microg x kg(-1) over 20 min followed by an infusion of 0.5 microg x kg(-1) x h(-1)) was administered at the completion of the surgical procedure, but prior to wound closure as an adjunct to TIVA which included propofol and remifentanil, adjusted to maintain a constant depth of anesthesia as measured by a BIS of 45-60. The cohort for the study included nine patients, ranging in age from 12 to 17 years, anesthetized with remifentanil and propofol. In the first patient, dexmedetomidine was administered in conjunction with propofol at 110 microg x kg(-1) x min(-1) which resulted in a decrease in the bispectral index from 58 to 31. Although no significant effect was noted on the SSEPs (amplitude or latency) or the MEP duration, there was a decrease in the MEP amplitude. The protocol was modified so that the propofol infusion was incrementally decreased during the dexmedetomidine infusion to achieve the same depth of anesthesia. In the remaining eight patients, the bispectral index was 52 +/- 6 at the start of the dexmedetomidine loading dose and 49 +/- 4 at its completion (P = NS). There was no statistically significant difference in the MEPs and SSEPs obtained before and at completion of the dexmedetomidine loading dose. Using the above-mentioned protocol, dexmedetomidine can be used as a component of TIVA during PSF without affecting neurophysiological monitoring.

Motor and somatosensory evoked potentials in Autosomal Dominant Hereditary Spastic Paraparesis (ADHSP) linked to chromosome 2p, SPG4

The aim of our study was to evaluate Motor Evoked Potentials (MEPs) and cortical excitability, using Transcranial Magnetic Stimulation (TMS) as well as short latency Somatosensory Evoked Potentials (SEPs) in Autosomal Dominant Hereditary Spastic Paraparesis (ADHSP) patients. MEPs were recorded from upper and lower limb muscles in 12 patients (7 m and 5 f) affected by ADHSP with spastin mutation (SPG4). We measured: (i) motor threshold (MTh); (ii) total motor conduction time (TMCT); (iii) direct and indirect central motor conduction time (d-CMCT and i-CMCT) calculated by subtracting from the cortical latency those obtained on magnetic spinal stimulation (d-PMCT) and via the F-wave method (i-PMCT); (iv) MEP amplitude (MEP/Mmax ratio%) and (v) duration of the cortical silent period (CSP). Latency, amplitude and persistence of the F-wave obtained with electrical nerve stimulation were also considered; H reflex was also tested from lower extremities. SEPs were recorded from spine and scalp sites following median and posterior tibial nerve stimulation; conventional latency and amplitude measurements were performed. In a comparison with the control group, the MTh recording from lower limbs was significantly higher (67.5 ± 7.7% versus 52.5 ± 6.9%), MEPs were absent in one case and showed reduced amplitude in the remainders (22.9 ± 12.6% versus 66.3 ± 25.9% of M wave); TMCT resulted to be abnormal (36.5 ± 3.9 ms versus 27.1 ± 1.4 ms) and d-CMCT as well as i-CMCT were significantly prolonged (23.1 ± 3.5 ms versus 13.8 ± 1.3 ms; and 20.1 ± 3.4 ms versus 10.6 ± 1.3 ms, respectively). The CSP, which was normal from the hands, was significantly shortened from the legs and correlated with spasticity scoring (Ashworth scale). Cortical SEPs from lower limbs were abnormal in all cases, whereas SEPs by stimulation of median nerves were normal; F-wave parameters from upper limbs showed no abnormalities, whereas an increased persistence was detected from lower limbs; H reflex amplitudes resulted larger compared with controls. Moreover, shortening of the CSP, being correlated with the Ashworth scale, can be considered an electrophysiological marker of spasticity that seems to arise from impairment of the supraspinal or intracortical inhibitory pathways with an additional contribution of increased segmental motor neuron excitability. These data prove the existence of comparable neurophysiological abnormalities in ADHSP with spastin mutation (SPG4) when long ascending and descending pathways are involved.

Abnormal parameters of magnetically evoked motor-evoked potentials in patients with cervical spondylotic myelopathy

Background context Magnetic stimulation (MS), which is used to evaluate motor pathways, is helpful in evaluating cervical spinal cord compression (cervical myelopathy [CM]). Previous studies have shown that the central motor conduction time (CMCT), which is the time taken for the nerve impulses to reach the cervical spinal roots after the stimulation of the motor cortex, is prolonged in CM. However, the duration of motor-evoked potentials (MEPs) in CM has not been studied in detail. Purpose To compare the duration, CMCT and amplitude of MEPs by MS between patients with clinical and magnetic resonance imaging (MRI) features of CM and a control group. Study design/setting A cross-sectional study done at Teaching Hospital, Peradeniya, Sri Lanka. Patient sample Consecutive patients with clinical features of cervical spondylotic myelopathy, without coexisting neurological abnormality. Methods Transcranial and cervical spinal magnetic stimulation were performed on 21 patients with clinical and MRI features of spondylotic CM (mean age, 43.5years; range, 36–63 years; 9 men) and 17 healthy volunteers (mean age, 39.05 years; range, 23–54yrs; 6 males) using a circular coil with a Magstim 200 stimulator. MEPs were recorded over abductor digiti minimi muscle on both hands. Results Seventeen patients had upper motor neuron (UMN) features in all four limbs; in the others, both lower limbs and one upper limb were affected. The upper limbs with UMN features had shorter duration MEPs compared with the control group. The CMCT and the total motor conduction time were also delayed in the CM group. All three differences were very highly significant (t=5.75, −3.76, 5.27; p<.001). The amplitudes showed no significant difference between the two groups (t=1.27, p=.208). Conclusion This study shows that in addition to the CMCT, the duration of MEPs is also useful in evaluating patients with CM using MS.

Corticospinal Excitability in Patients With Chronic Low Back Pain

This study was designed to investigate corticospinal excitability of lumbar muscles using transcranial magnetic stimulation (TMS) in patients with chronic low back pain and correlate this with self-rated measures of disability and pain. Twenty-four patients with chronic low back pain and 11 healthy control subjects were used in this study. TMS was delivered through an angled double-cone coil, with its cross-over on the vertex and a posterior-to-anterior current flow in the brain. Electromyographic (EMG) recordings were made from erector spinae (ES) muscles at the fourth lumbar level. Motor cortical excitability was assessed using motor threshold (MTh) for motor evoked potentials (MEPs) and threshold for silent period (SP) during facilitation of the back muscles. Latency, duration, and area of MEPs and SPs were also measured. The latency, duration, and size of MEPs and SPs did not differ between the left and right ES muscles in either the patients or the control subjects and also did not differ between the patients and the control subjects. However, there was a significantly higher MTh and threshold for the SP in the patients as compared with the control subjects; the full significance of this requires further investigation. Interestingly, there was a positive correlation between the self-rated measure of disability (the Oswestry Disability Index score) and both the MTh and the threshold for the SP in the patients. There was also a positive correlation between the self-rated index of back pain and the threshold for the SP in the patients. This finding of an association between clinical and neurophysiologic measures reinforces the need for further research to establish the clinical relevance of these rises in MTh and SP threshold. In summary, this study has revealed that corticospinal excitability, driving ES muscles close to the site of pain, is lowered in patients with chronic low back pain.

Magnetic stimulation of motor cortex in children: maturity of corticospinal pathway and problem of clinical application

The developmental profile of the electromyographic responses to transcranial magnetic stimulation (TMS) was studied in 46 neurologically normal children aged from one to 14 years, compared with data in 10 normal control adults. To obtain motor evoked potentials (MEPs) from the first dorsal interosseous muscle in the resting state, the motor cortex was stimulated through a circular coil with the stimulus intensity set at 10% above the threshold intensity for eliciting MEPs. Reproducible MEPs were obtained in all but the children aged below 2 years, and the threshold intensity and central motor conduction time (CMCT) showed a linear decrease with maturation. The MEP amplitude changed little until 9 years of age, but it tended to increase between 10 years and adulthood. The MEP duration, which was not influenced by age, was less than 16 ms over the ages studied. The present data suggest that maturity of the corticospinal motor pathway that controls the intrinsic hand muscles is electrophysiologically complete at 13 years of age. Among the parameters of MEPs, CMCT and MEP duration may be useful for evaluating impairment of the corticospinal tracts in children aged 2 years and older.

Transcranial magnetic stimulation in benign childhood epilepsy with centro-temporal spikes

Motor cortical excitability was studied using transcranial magnetic stimulation (TMS) in 10 age-matched controls, and 13 children with benign childhood epilepsy with centro-temporal spikes (BECT), with a mean age of 11.2 ± 2.0 years (five untreated, and eight treated with sodium valproate (VPA) and well controlled). Motor evoked potentials (MEPs) elicited by TMS through a circular coil were recorded from the first dorsal interosseous muscle (17131) while relaxed. There was no significant difference in latency or duration of MEPs, or central motor conduction time among controls, untreated and treated patients. The threshold intensity for TMS in the untreated patients (63.0 ± 14.8%, mean ± SD) was similar to that in controls (63.0 ± 12.5%), while the threshold intensity in the treated patients (79.4 ± 11.8%) was significantly higher than that in the other groups. A significant increase in threshold intensity (15 ± 4.1%) was also observed in the untreated patients retested after starting VPA treatment. No adverse effects occurred during TMS in any subjects. Thus, motor cortical hyperexcitability in BECT was not recognized in the present TMS study, while VPA was confirmed to have an effect on the threshold intensity for TMS.

Abnormal facilitation of the response to transcranial magnetic stimulation in patients with Parkinson's disease.

We studied the facilitation of the motor evoked potential (MEP) elicited with transcranial magnetic stimulation by increasing the stimulus intensity and the degree of voluntary activation of the target muscle in patients with Parkinson's disease (PD) and in normal volunteers. The threshold intensity for eliciting MEPs with the muscle at rest did not differ in PD patients and normal subjects. At rest, stimuli of similar intensity, related to the individual's threshold, elicited MEPs with amplitudes consistently larger in patients than in normal subjects, although when we compared the averaged MEP amplitude across all stimulus intensities, the differences reached only borderline statistical significance. Voluntary muscle activation elicited a smaller increase in the MEP area in PD patients than in normal subjects. Increasing the degree of voluntary muscle activation at fixed stimulus intensities elicited a smaller increase of MEP amplitude, duration, and area in PD patients than in normal subjects. These results suggest that control of the excitability of the motor system is abnormal in PD patients, with enhancement of excitability at rest and weak energization during voluntary muscle activation.