Neurophysiological testing in anorectal disorders

The neurophysiological techniques currently available to evaluate anorectal disorders include concentric needle electromyography (EMG) of the external anal sphincter, anal nerve terminal motor latency (TML) measurement in response to transrectal electrical stimulation or sacral magnetic stimulation, motor evoked potentials (MEPs) of the anal sphincter to transcranial magnetic cortical stimulation, cortical recording of somatosensory evoked potentials (SEPs) to anal nerve stimulation, quantification of electrical or thermal sensory thresholds (QSTs) within the anal canal, sacral anal reflex (SAR) latency measurement in response to pudendal nerve or perianal stimulation, and perianal recording of sympathetic skin responses (SSRs). In most cases, a comprehensive approach using several tests is helpful for diagnosis: needle EMG signs of sphincter denervation or prolonged TML give evidence for anal motor nerve lesion; SEP/QST or SSR abnormalities can suggest sensory or autonomic neuropathy; and in the absence of peripheral nerve disorder, MEPs, SEPs, SSRs, and SARs can assist in demonstrating and localizing spinal or supraspinal disease. Such techniques are complementary to other methods of investigation, such as pelvic floor imaging and anorectal manometry, to establish the diagnosis and guide therapeutic management of neurogenic anorectal disorders.     

Effects of Translumbosacral Neuromodulation Therapy on Gut and Brain Interactions and Anorectal Neuropathy in Fecal Incontinence: A Randomized Study

ObjectivesTranslumbosacral neuromodulation therapy (TNT) improves symptoms of fecal incontinence (FI), but its mechanism of action is unknown. We tested the hypothesis that TNT at one or more frequency will significantly improve underlying pathophysiology of FI through modulation of ascending and/or descending signaling pathways in the gut and brain axis and anorectal sensorimotor function.Materials and MethodsWe assessed afferent anorectal-cortical evoked potentials (CEP) following electrical stimulation of anorectum, efferent cortico-anorectal and lumbo-anorectal and sacro-anorectal motor evoked potentials (MEP) after transcranial and lumbosacral magnetic stimulations, and anorectal manometry before and after six weekly TNT sessions in FI subjects, randomized to 1, 5, or 15 Hz repetitive magnetic stimulations. Neurophysiology, anorectal sensorimotor function, and symptoms were compared to examine mechanistic effects. Co-primary measures were ano-cortical CEPs, cortico-anal MEPs, and lumbosacral-anal MEPs. Baseline and post-treatment data were compared with Wilcoxon signed-rank test and changes between the three frequencies with one-way ANOVA.ResultsThirty-three FI patients participated. After TNT, the afferent anal CEP latencies significantly decreased in the 1 Hz group compared to baseline (p = 0.0029) and 5 Hz or 15 Hz groups (p = 0.032). Cortico-anal MEPs were unchanged in all three groups. Bilateral lumbo-anal and sacro-anal MEP latencies significantly decreased with 1 Hz, lumbo-anal with 15 Hz, and sacro-anal with 5 Hz compared to baseline but without group differences. The 1 Hz group showed significant increase in anal squeeze sphincter pressure (p < 0.005) and maximum tolerable volume (p < 0.019) and demonstrated higher FI responder rate (p < 0.04) compared to the other two groups. The MEP responders were significantly correlated with FI responders (p = 0.006) in 1 Hz group.ConclusionsTNT significantly improves afferent ano-cortical signaling, efferent lumbo-anal and sacro-anal neuropathy and anorectal sensorimotor function. These neurobiologic effects were most prominent with 1 Hz frequency. TNT improves FI by modifying the underlying pathophysiology possibly through neuromodulation.     

Intrarectal ground electrode improves the reliability of motor evoked potentials recorded in the anal sphincter

Motor evoked potentials (MEPs) can be recorded in the external anal sphincter in response to magnetic stimulation of the cerebral cortex or sacral roots. However, the magnitude of the stimulus artifact may alter the reliability of anal MEP recording. An intrarectal ground electrode substantially reduces stimulus artifact and technical failure, improving MEP latency determination to sacral root stimulation in particular.     

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。     

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.     

Systematic assessment of duration and intensity of anodal transcranial direct current stimulation on primary motor cortex excitability

Since the initial demonstration of linear effects of stimulation duration and intensity on the strength of after‐effects associated with transcranial direct current stimulation (tDCS), few studies have systematically assessed how varying these parameters modulates corticospinal excitability. Therefore, the objective of this study was to systematically evaluate the effects of anodal tDCS on corticospinal excitability at two stimulation intensities (1 mA, 2 mA) and durations (10 min, 20 min), and determine the value of several variables in predicting response. Two groups of 20 individuals received, in two separate sessions, 1 and 2 mA anodal tDCS (left primary motor cortex (M1)‐right supra‐orbital montage) for either 10‐ or 20‐min. Transcranial magnetic stimulation was delivered over left M1 and motor evoked potentials (MEPs) of the contralateral hand were recorded prior to tDCS and every 5 min for 20‐min post‐tDCS. The following predictive variables were evaluated: I‐wave recruitment, stimulation intensity, baseline M1 excitability and inter‐trial MEP variability. Results show that anodal tDCS failed to significantly modulate corticospinal excitability in all conditions. Furthermore, low response rates were identified across all parameter combinations. No baseline measure was significantly correlated with increases in MEP amplitude. However, a decrease in inter‐trial MEP variability was linked to response to anodal tDCS. In conclusion, the present findings are consistent with recent reports showing high levels of inter‐subject variability in the neurophysiological response to tDCS, which may partly explain inconsistent group results. Furthermore, the level of variability in the neurophysiological outcome measure, i.e. MEPs, appears to be related to response.     

Motor and somatosensory evoked potentials in asymptomatic spondylotic cord compression.

To assess whether electrophysiological tests are of use in differentiating between patients with asymptomatic cervical stenosis and patients with clinical evidence of myelopathy, we studied motor evoked potentials (MEPs) to magnetic brain stimulation and somatosensory evoked potentials (SEPs) in patients with asymptomatic cervical cord compression and compared the results to healthy age-matched controls. The MEPs were normal in 23 of 25 patients and SEPs in 22 of 23 patients. Thus, MEPs and SEPs are normal in most cases of asymptomatic cervical stenosis. As previous studies have shown MEPs, and to a lesser extent SEPs, to be sensitive in the detection of spondylotic myelopathy, our data indicate that MEP and SEP may be clinically useful for differentiating patients with cervical stenosis who have myelopathy from those who have not.     

磁刺激运动诱发肌电位对运动机能评价的临床应用

目的：观察磁刺激运动诱发肌电位对运动机能的评价。方法：用磁刺激装置对正常人１２例，运动障碍患者３１例进行了经颅脑刺激，记录运动诱发肌电位。结果：受检测的４３例，无一例引起头痛和感觉异常，也无癫痫及意识障碍等副作用。正常人中，诱发肌电位的潜伏期相对恒定，振幅在个体间虽存有差异，但同一例左右侧几乎相同。对２０例单侧肢体功能障碍的肌力按体征分级，比较患侧和健侧的诱发肌电位，发现患侧振幅较健侧明显减低。对肌力０～２级的病例，不能诱发出肌电位。结论：磁刺激运动诱发肌电位，在临床上可在数量上正确评价肢体的运动机能，并且经颅磁刺激法是安全的。     

Poisson distribution to analyze near-threshold motor evoked potentials

Motor unit action potentials (MUAPs) evoked by repetitive, low-intensity transcranial magnetic stimulation can be modeled as a Poisson process. A mathematical consequence of such a model is that the ratio of the variance to the mean of the amplitudes of motor evoked potentials (MEPs) should provide an estimate of the mean size of the individual MUAPs that summate to generate each MEP. We found that this is, in fact, the case. Our finding thus supports the use of the Poisson distribution to model MEP generation and indicates that this model enables characterization of the motor unit population that contributes to near-threshold MEPs.     

Motor potentials evoked by magnetic stimulation of the motor cortex in normal subjects and patients with motor disorders.

Motor evoked potentials (MEPs) elicited by magnetic coil stimulation of motor cortex were studied at rest and during maximum voluntary muscle contraction in 20 normal subjects and 42 patients with motor disorders. MEP parameters employed in this study included: onset latency, amplitude, MEP/M wave amplitude ratio and background EMG/MEP area ratio. Maximum voluntary contraction increased the amplitude of MEPs compared to the size of M waves elicited by peripheral nerve stimulation. A reduced MEP/M wave amplitude ratio had a higher correlation with pyramidal tract involvement than did a prolonged MEP onset latency. Analysis of MEP parameters may help in the differential diagnosis of cerebral infarction, ALS and cervical spondylotic radiculomyelopathy. The inhibitory period which follows MEPs during voluntary contraction was observed in all subjects; the mean duration in normal subjects was 126.6 +/- 29.5 msec. The mean duration of the inhibitory period in patients with cerebral infarction, ALS and cervical spondylotic radiculomyelopathy was 73.9 +/- 41.7 msec, 79.5 +/- 54.5 msec and 85.1 +/- 36.5 msec, respectively. These values were significantly shorter than in normal subjects.     

Insights on the neural basis of motor plasticity induced by theta burst stimulation from TMS–EEG

Transcranial magnetic stimulation (TMS) is a useful tool to induce and measure plasticity in the human brain. However, the cortical effects are generally indirectly evaluated with motor‐evoked potentials (MEPs) reflective of modulation of cortico‐spinal excitability. In this study, we aim to provide direct measures of cortical plasticity by combining TMS with electroencephalography (EEG). Continuous theta‐burst stimulation (cTBS) was applied over the primary motor cortex (M1) of young healthy adults, and we measured modulation of (i) MEPs, (ii) TMS‐induced EEG evoked potentials (TEPs), (iii) TMS‐induced EEG synchronization and (iv) eyes‐closed resting EEG. Our results show the expected cTBS‐induced decrease in MEP size, which we found to be paralleled by a modulation of a combination of TEPs. Furthermore, we found that cTBS increased the power in the theta band of eyes‐closed resting EEG, whereas it decreased single‐pulse TMS‐induced power in the theta and alpha bands. In addition, cTBS decreased the power in the beta band of eyes‐closed resting EEG, whereas it increased single‐pulse TMS‐induced power in the beta band. We suggest that cTBS acts by modulating the phase alignment between already active oscillators; it synchronizes low‐frequency (theta and/or alpha) oscillators and desynchronizes high‐frequency (beta) oscillators. These results provide novel insight into the cortical effects of cTBS and could be useful for exploring cTBS‐induced plasticity outside of the motor cortex.     

Investigating the effects of muscle contraction and conditioning stimulus intensity on short‐interval intracortical inhibition

A reduction in short‐interval intracortical inhibition (SICI) has been shown to accompany acute or chronic resistance exercise; however, little is known about how SICI is modulated under different contraction intensities. Therefore, the purpose of this study was to assess the effect of muscle contraction and conditioning stimulus intensity on the modulation of SICI. Single‐ and paired‐pulse transcranial magnetic stimulation was applied to the primary motor cortex (M1), and motor evoked potentials (MEPs) were recorded from the biceps brachii in 16 adults (10M/6F). A conditioning‐test stimulus paradigm (3 ms inter‐stimulus intervals) was delivered during 10%, 20%, 40% and 75% of maximal voluntary isometric contraction (MVIC). At each force level, conditioning stimulus intensities of 60%, 70% and 80% of active motor threshold (AMT) were tested. Single‐pulse MEPs were expressed as a proportion of the maximal muscle compound action potential, while SICI was quantified as a ratio of the unconditioned MEP. MEP amplitude increased with force output, with the greatest increase at 75% of MVIC. A reduction in SICI was observed from 40% to 75% of MVIC, but not 10%–40% of MVIC. There was no significant interaction between conditioning stimulus intensity and force level. The conditioning stimulus intensity (60%, 70% or 80% of AMT) did not alter the modulation of SICI. SICI was reduced at 75% of MVIC compared with the lower force outputs, and the magnitude of SICI in individual participants at different force outputs was not related. The findings suggest that strong muscle contractions are accompanied by less inhibition, which may have implications for neuroplasticity in exercise interventions.     

Effects of sex, height and age on motor evoked potentials with magnetic stimulation

Magnetic stimulation of the brain and cervical and lumbar spinal roots was performed on 48 healthy subjects in order to investigate the effects of sex, height and age on motor evoked potentials (MEPs). The compound muscle action potentials were recorded from the abductor pollicis brevis and abductor hallucis muscles. The central motor conduction time (CMCT) was measured between the cerebral cortex and the cervical root and also between the cerebral cortex and the lumbar root. A multiple regression analysis was used to determine which of the physical variables, namely sex, height and age, were significant. A significant gender difference was observed in the MEP latencies and CMCT of the leg, but not in those of the hand. Both height and age had a significant effect on the leg MEP latencies with a lesser effect on the hand MEP latencies. The leg CMCT was also significantly influenced by height and age, while the hand CMCT was not. These results thus suggest that physical variables are very important in defining normal MEPs, especially in the lower limbs. Therefore, when we assess motor function in patients with neurological disorders, both the patients and control groups should be matched for sex, height and age distribution. Received: 8 May 1997 Received in revised form: 1 December 1997 Accepted: 31 December 1997     

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.     

The spontaneous fluctuation of the excitability of a single node modulates the internodes connectivity: A TMS‐EEG study

Brain effective connectivity can be tracked by cerebral recruitments evoked by transcranial magnetic stimulation (TMS), as measured by simultaneous electroencephalography (TMS‐EEG). When TMS is targeting the primary motor area, motor evoked potentials (MEPs) can be collected from the “target” muscles. The aim of this study was to measure whether or not effective brain connectivity changes with the excitability level of the corticospinal motor pathway (CSMP) as parameterized by MEP amplitude. After averaging two subgroups of EEG‐evoked responses corresponding to high and low MEP amplitudes, we calculated the individual differences between them and submitted the grand average to sLORETA algorithm obtaining localized regions of interest (RoIs). Statistical differences of RoI recruitment strength between low and high CSMP excitation was assessed in single subjects. Preceding the feedback arrival, neural recruitment for stronger CSMP activation were weaker at 6–10 ms of homotopic sensorimotor areas BA3/4/5 of the right nonstimulated hemisphere (trend), weaker at 18–25 ms of left parietal BA2/3/40, and stronger at 26–32 ms of bilateral frontal motor areas BA6/8. The proposed method enables the tracking of brain network connectivity during stimulation of one node by measuring the strength of the connected recruited node activations. Spontaneous increases of the excitation of the node originating the transmission within the hand control network gave rise to dynamic recruitment patterns with opposite behaviors, weaker in homotopic and parietal circuits, stronger in frontal ones. The effective connectivity within bilateral circuits orchestrating hand control appeared dynamically modulated in time even in resting state as probed by TMS. Hum Brain Mapp 35:1740–1749, 2014. © 2013 Wiley Periodicals, Inc.     

Non-invasive evaluation of central motor tract excitability changes following peripheral nerve stimulation in healthy humans.

The interval between muscle stretch and the onset of the long latency electromyographic responses (LLRs) has been theoretically fragmented into an afferent time (AT), taken at the peak of wave N20 of somatosensory evoked potentials and an efferent time (ET), calculated by means of magnetic transcranial stimulation (TCS), the two being separated by a cortical interval (CI). If this were the case, the afferent input should progressively 'energize' the sensorimotor cortex during the CI and change the excitability of cortico-spinal tracts. To investigate this, motor evoked potentials (MEPs) from thumb flexor muscles were recorded, whilst a conditioning stimulation of median or ulnar nerve randomly preceded (10-48 msec intervals) magnetic brain TCS. Nerve stimulation was adjusted to motor threshold and amplitudes of conditioned and test MEPs at different nerve-TCS interstimulus intervals were evaluated. Conditioned MEPs were significantly attenuated with nerve-TCS intervals between 16 and 20 msec for elbow and 20 and 22 msec for wrist stimulation. This was followed by MEP potentiation with nerve-TCS intervals corresponding to the sum of AT + CI (mean 23.2 msec, range 21.7-24.8). The onset latency of facilitated conditioned MEPs was about 1 msec briefer than that of test MEPs, but invariably longer than the latency of MEPs facilitated by a voluntary contraction. This protocol did not demonstrate amplitude facilitation of the segmental H reflex, corroborating the idea that the facilitated part of the conditioning nerve-TCS curve receives a transcortical loop contribution.     

Motor imagery in a locked-in patient: evidence from transcranial magnetic stimulation

Motor evoked potentials (MEPs) to transcranial magnetic stimulation were evaluated in a case of locked-in syndrome due to a large pontine infarction. In this patient, magnetic resonance imaging (MRI) and somatosensory evoked potentials demonstrated a tegmental involvement. One month after the attack, no MEP could be recorded from the right abductor digiti minimi (ADM) or either tibialis anterior muscle. On the contrary, MEPs were obtained from the left ADM, although with a prolonged latency and a reduced amplitude. When the patient was requested to think about the abduction of her paralyzed left little finger, the latency and the elicitability of these responses improved as compared with the relaxed condition. These severe MEP alterations correctly predicted a poor recovery of motor function in the chronic stage. However, although the tegmental involvement raises the question of an insufficient cortical motor arousal, preserved motor imagery suggested a normal cortical motor area activation.     

Motor cortex plasticity induced by theta burst stimulation is impaired in patients with obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is a respiratory condition occurring during sleep characterised by repeated collapse of the upper airway. Patients with OSA show altered brain structure and function that may manifest as impaired neuroplasticity. We assessed this hypothesis in 13 patients with moderate‐to‐severe OSA and 11 healthy control subjects. Transcranial magnetic stimulation was used to induce and measure neuroplastic changes in the motor cortex by assessing changes in motor‐evoked potentials (MEPs) in a hand muscle. Baseline measurements of cortical excitability included active (AMT) and resting motor thresholds (RMT), and the maximal stimulator output producing a 1‐mV MEP. Intracortical inhibition (ICI) was investigated with short‐ and long‐interval ICI paradigms (SICI and LICI, respectively), and neuroplastic changes were induced using continuous theta burst stimulation (cTBS). At baseline, differences were found between groups for RMT (9.5% maximal stimulator output higher in OSA) and 1‐mV MEPs (10.3% maximal stimulator output higher in OSA), but not AMT. No differences were found between groups for SICI or LICI. The response to cTBS was different between groups, with control subjects showing an expected reduction in MEP amplitude after cTBS, whereas the MEPs in patients with OSA did not change. The lack of response to cTBS suggests impaired long‐term depression‐like neuroplasticity in patients with OSA, which may be a consequence of sleep fragmentation or chronic blood gas disturbance in sleep. This reduced neuroplastic capacity may have implications for the learning, retention or consolidation of motor skills in patients with OSA.     

Cortical mechanisms underlying variability in intermittent theta-burst stimulation-induced plasticity: A TMS-EEG study

ObjectiveTo test the hypothesis that intermittent theta burst stimulation (iTBS) variability depends on the ability to engage specific neurons in the primary motor cortex (M1).MethodsIn a sham-controlled interventional study on 31 healthy volunteers, we used concomitant transcranial magnetic stimulation (TMS) and electroencephalography (EEG). We compared baseline motor evoked potentials (MEPs), M1 iTBS-evoked EEG oscillations, and resting-state EEG (rsEEG) between subjects who did and did not show MEP facilitation following iTBS. We also investigated whether baseline MEP and iTBS-evoked EEG oscillations could explain inter and intraindividual variability in iTBS aftereffects.ResultsThe facilitation group had smaller baseline MEPs than the no-facilitation group and showed more iTBS-evoked EEG oscillation synchronization in the alpha and beta frequency bands. Resting-state EEG power was similar between groups and iTBS had a similar non-significant effect on rsEEG in both groups. Baseline MEP amplitude and beta iTBS-evoked EEG oscillation power explained both inter and intraindividual variability in MEP modulation following iTBS.ConclusionsThe results show that variability in iTBS-associated plasticity depends on baseline corticospinal excitability and on the ability of iTBS to engage M1 beta oscillations.SignificanceThese observations can be used to optimize iTBS investigational and therapeutic applications.     

Cortical motor neuron excitability during cutaneous silent period

Objective: To investigate cortical motor neuron excitability during cutaneous silent period (CSP), motor evoked potentials (MEPs) from abductor pollicis brevis following transcranial magnetic stimulation (TCM) were recorded with and without a conditioning of ipsilateral painful digital nerve electric stimulation.Methods: MEPs following TCM were recorded with and without a conditioning stimulation at an interstimulus interval (ISI) from 0 ms to 100ms in 6 controls and four patients who had reduced pain sensation in unilateral upper limbs associated with cervical syringomyelia. In addition MEPs and evoked spinal cord potentials (ESCPs) from cervical epidural space following TCM with and without a conditioning stimulation were recorded in four patients with thoracic myelopathy.Results: MEP amplitude was clearly attenuated by a conditioning stimulation at an ISI from 40 ms to 80 ms in controls (statistically significant at 60 ms). In patients with cervical syringomyelia, MEP amplitude was attenuated by a conditioning stimulation in asymptomatic hands similarly in controls but that was unchanged by a conditioning stimulation in the symptomatic hand with reduced pain sensation. In patients with thoracic myelopathy MEP amplitude was attenuated by conditioning stimulation similarly in controls, but ESCP amplitude was unchanged.Conclusions: We demonstrated that noxious cutaneous nerve stimulation suppressed spinal motor neurons but cortical motor neuron excitability was unchanged during CSP. In clinical practice, measurement of MEP suppression after noxious cutaneous nerve stimulation may provide useful information in patients with damaged pain related nerve fibers.