Muscle Motor Evoked Potentials Research Articles

Motor Evoked Potentials of Trunk Muscles in Traumatic Brain Injury Patients

ObjectiveTo evaluate the motor innervation of trunk muscles in traumatic brain injury patients.MethodTwenty patients (12 men and 8 women) with traumatic brain injury were enrolled in this study. Their mean age was 41 years. Motor evoked potentials (MEPs) were performed on the motor cortex. Electromyographic activities were recorded from the bilateral rectus abdominis muscles, the external oblique abdominal muscles, and the 4th and 9th thoracic erector spinae muscles. The onset latency and amplitude of contralateral and ipsilateral MEPs were measured. All patients were assessed by the Korean version of the Berg Balance Scale (K-BBS) to investigate the relationship between the frequency of MEPs in trunk muscles and gait ability.ResultsThe mean frequency of ipsilateral MEPs was 23.8% with more damaged hemisphere stimulation, while the contralateral MEPs showed a mean frequency of 47.5% with more damaged hemisphere stimulation in traumatic brain injury patients. The latencies and amplitudes of MEPs obtained from the more damaged hemisphere were not significantly different from those of the less damaged hemisphere. There was no correlation between the manifestation of MEPs in trunk muscles and gait ability.ConclusionThe ipsilateral and contralateral corticospinal pathways to trunk muscles are less likely to be activated in traumatic brain injury patients because of direct injury of the descending corticospinal motor tract or decreased excitability of the corticospinal tract from prefrontal contusion.

Motor Evoked Potentials of the Upper Extremities in Healthy Children

ObjectiveTo evaluate and compare the organization of descending motor pathways to upper extremity muscles among healthy children.MethodThe healthy children were 16 males and 7 females aged 1-19 years (average, 9 years), and eight healthy adults were enrolled as the control group. Transcranial magnetic stimulation was applied to bilateral motor cortices, and motor evoked potentials (MEPs) were recorded using surface electrodes from the first dorsal interossei (FDI), the biceps brachii (BIC), and the deltoid (DEL) muscles. The onset latency, central motor conduction time (CMCT), and amplitude were obtained during a relaxed state.ResultsMEPs of FDI were obtained from subjects aged 13 months. The frequency of obtaining MEPs in proximal and distal muscles increased with age, although there was a less frequent incidence of obtaining MEPs in the proximal BIC and DEL muscles compared with those in the distal FDI muscle. MEP amplitudes increased with age, whereas latencies were relatively constant. CMCTs showed a similar pattern of maturation, and adult values were obtained by 13-years-of-age.ConclusionThese results suggest that the proximal and distal muscles of the upper extremities show different maturation and organization patterns.

Evaluation of Combined Use of Transcranial and Direct Cortical Motor Evoked Potential Monitoring During Unruptured Aneurysm Surgery

The feasibility and reliability of combined use of transcranial and direct cortical motor evoked potential (MEP) monitoring during unruptured aneurysm surgery were evaluated. Forty-eight patients with unruptured cerebral aneurysms underwent craniotomy and neck clipping accompanied by muscle MEP monitoring. MEPs were elicited successfully by transcranial electrical stimulation in all patients. Direct cortical stimulation elicited MEPs in 44 patients. Reduction in MEP amplitude to less than 50% of baseline was considered significant. No postoperative motor paresis occurred in 39 patients in whom transcranial and direct MEPs remained unchanged. Four patients in whom direct MEPs could not be recorded had no intraoperative abnormality in transcranial MEPs and no postoperative motor dysfunction. Four of the other 5 patients manifested significant transient direct MEP changes without transcranial MEP changes. The transient MEP changes were observed in 3 patients during temporary clipping of the parent artery and in one patient with inadequate clipping of an middle cerebral artery aneurysm, and were considered due to insufficiency of blood flow. Decrease or disappearance of direct MEP waves recovered immediately after re-application of the clip and release of the temporary clip. Direct MEP waves disappeared and did not recover until the end of microsurgical procedures in one patient, although transcranial MEP amplitude remained at less than 50% of baseline. She developed hemiparesis postoperatively, which recovered within 6 hours. The duration of temporary occlusion in patients with direct MEP changes was significantly longer than that in patients without (p < 0.05). Direct MEP was sensitive in detecting ischemic stress to descending motor pathways during aneurysm surgery. Transcranial MEPs could be elicited in patients in whom direct MEPs could not be obtained, and during periods such as craniotomy or after dural closure, in which direct MEPs could not be recorded. These findings suggest that combined transcranial and direct cortical MEP recording may improve the feasibility and reliability of MEP monitoring during unruptured aneurysm surgery.

Fatiguing intermittent lower limb exercise influences corticospinal and corticocortical excitability in the nonexercised upper limb

It has recently been reported that unilateral fatiguing exercise affects not only the motor area innervating the exercising muscle but also the ipsilateral motor area innervating homologous nonexercised muscle. This study was designed to clarify the effects of fatiguing intermittent lower limb exercise on the excitability of the motor cortex representation of nonexercised muscles in the arm. Eight subjects performed an intermittent leg press exercise composed of three bouts of 5-minute leg press (T1, T2, and T3) at 50% of maximal voluntary contraction separated by a 2-minute rest. Motor-evoked potentials (MEP), short interval intracortical inhibition (SICI), and intracortical facilitation (ICF), using paired-pulse transcranial magnetic stimulation, were assessed in two nonexercised arm muscles (first dorsal interosseous muscle: FDI, n = 8; biceps brachii muscle: BB, n = 6) and one exercised leg muscle (quadriceps femoris muscle: QF, n = 6) before and immediately after each bout of exercise and for 30 minutes during recovery after the end of the third exercise bout (Experiment 1). Experiment 2 was the same as Experiment 1, except that the test pulse intensity was adjusted to produce a given amplitude of MEP(TEST) at each time point. MEPs and SICI in the exercised QF muscle were depressed at all time points during and after fatigue. In contrast, MEPs in nonexercised arm muscles were facilitated from T1-T3 (T3, only FDI), but were then depressed for up to 20 minutes in the recovery period. SICI was reduced in both muscles during T1-T3 and remained depressed until 20 minutes into recovery. ICF was unchanged in arm muscles but depressed in QF over T1-T3. The current study indicates that muscle fatigue induced by exercise of a large lower limb muscle group has powerful effects on the excitability of both SICI and the corticospinal projection to muscles of the nonexercised upper limb.

Transcranial motor evoked potential monitoring during the surgical clipping of unruptured intracranial aneurysms

ObjectiveThe aim of the present study was to evaluate the usefulness of transcranial motor evoked potential (MEP) monitoring and its impact on morbidity after surgical clipping of unruptured intracranial aneurysms. MethodsMotor outcomes were compared before and after the application of MEP monitoring for a one year period. A total intravenous anesthesia was induced and maintained with a continuous infusion of vecuronium. Muscle MEPs were elicited by constant voltage stimulation via subdermal needle electrodes placed at C3 and C4 positions. A more than 50% decrement of MEP amplitudes compared with baseline recordings was regarded as a warning sign and promptly indicated to the surgeon. ResultsBefore the application of MEP monitoring, a new motor deficit was observed in 3 of 66 patients. However, in 98 patients operated under MEP monitoring, no new motor deficit was found except for one patient who manifested delayed hemiparesis 30h after the operation owing to a cortical vein injury during craniotomy. MEPs deteriorated in 12 patients which were related to hypotension (n=1), temporary clipping (n=7), and permanent clipping (n=4), and recovered in all after prompt corrective measures. After surgical clipping of unruptured aneurysms, the absence of new motor deficits could be reliably anticipated by recovered MEPs as well as unchanged MEPs. ConclusionsTranscranial MEP monitoring is a simple, safe, and reliable tool for the prediction of postoperative motor functions. The ischemic complications can be reduced via prompt corrective measures taken on the basis of MEP changes during aneurysm surgery.

Ventral premotor to primary motor cortical interactions during object-driven grasp in humans

Interactions between the ventral premotor (PMv) and the primary motor cortex (M1) are crucial for transforming an object's geometrical properties, such as its size and shape, into a motor command suitable for grasp of the object. Recently, we showed that PMv interacts with M1 in a specific fashion, depending on the hand posture. However, the functional connectivity between PMv and M1 during the preparation of an actual grasp is still unknown.To address this issue, PMv–M1 interactions were tested while subjects were preparing to grasp different visible objects requiring either a precision grip or a whole hand grasp. A conditioning–test transcranial magnetic stimulation (TMS) paradigm was used: a test stimulus was applied over M1 either in isolation or after a conditioning stimulus delivered, at different delays, over the ipsilateral PMv. Motor evoked potentials (MEPs) were recorded in the first dorsal interosseus and abductor digiti minimi muscles, which show highly differentiated activity according to grasp.While subjects prepared to grasp, delivering a conditioning PMv pulse 6 or 8msec before a test pulse over M1 strikingly facilitated MEPs in the specific muscles that were used in the upcoming grasp. This degree of facilitation correlated with the amount of muscle activity used later in the trial to grasp the objects.The present results demonstrate that, during grasp preparation, the PMv–M1 interactions are muscle-specific. PMv appears to process the object geometrical properties relevant for the upcoming grasp, and transmits this information to M1, which in turn generates a motor command appropriate for the grasp. We also reveal that the grasp-specific facilitation resulting from PMv–M1 interactions is differently related to the upcoming grasp muscle activity than is that from paired-pulse stimulation over M1, suggesting that these two TMS paradigms assess the excitability of cortico-cortical pathways devoted to the control of grasp at two different levels.

Extraoperative functional mapping of motor areas in epileptic patients by high-frequency cortical stimulation

The aim of this study was to investigate the usefulness of a short train of high-frequency (500 Hz) cortical stimulation to delineate the primary motor cortex (MI), supplementary motor area (SMA), primary somatosensory cortex (SI), supplementary sensory area (SSA), negative motor area (NMA), and supplementary negative motor area (SNMA) in patients with epilepsy who were undergoing functional mapping. Seventeen patients were studied, all of whom underwent functional mapping using 50-Hz electrical stimulation. After these clinical evaluations, cortical stimulations with a short train of electrical pulses at 500 Hz were performed through subdural electrodes placed at the MI, SMA, SI, SSA, NMA, and SNMA, which had been identified by 50-Hz stimulation, and surrounding cortical areas, while surface electromyography readings were recorded. Stimulation of the MI elicited motor evoked potentials (MEPs) in contralateral muscles. Stimulation of the SMA also induced MEPs in contralateral muscles but with longer latencies compared with the MI stimulation. Stimulation of the SMA did not elicit MEPs in ipsilateral muscles. Stimulation of the SI, SSA, NMA, and SNMA did not induce MEPs in any muscle. In one patient, MEPs were elicited without seizure induction by 500-Hz stimulation of the electrodes, whereas a 50-Hz stimulation of the same electrodes induced his habitual seizures. Extraoperative high-frequency stimulation with MEP monitoring is a useful complementary method for cortical mapping without inducing seizure. Stimulation of SMA induces MEPs in contralateral muscles, with longer latencies compared with the stimulation of MI. This finding may be useful for the differentiation between MI and SMA, especially in the foot motor areas.

Experimental Model of Lacunar Infarction in the Gyrencephalic Brain of the Miniature Pig

Lacunar infarction accounts for 25% of ischemic strokes, but the pathological characteristics have not been investigated systematically. A new experimental model of lacunar infarction in the miniature pig was developed to investigate the pathophysiological changes in the corticospinal tract from the acute to chronic phases. Thirty-five miniature pigs underwent transcranial surgery for permanent anterior choroidal artery occlusion. Animals recovered for 24 hours (n=7), 2 (n=5), 3 (n=2), 4 (n=2), 6 (n=1), 7 (n=7), 8 (n=2), and 9 days (n=1), 2 weeks (n=2), 4 weeks (n=3), and more than 4 weeks (n=3). Neurology, electrophysiology, histology, and MRI were performed. Seven additional miniature pigs underwent transient anterior choroidal artery occlusion to study muscle motor-evoked potentials and evaluate corticospinal tract function during transient anterior choroidal artery occlusion. The protocol had a 91.4% success rate in induction of internal capsule infarction 286+/-153 mm(3) (mean+/-SD). Motor-evoked potentials revealed the presence of penumbral tissue in the internal capsule after 6 to 15 minutes anterior choroidal artery occlusion. Total neurological deficit scores of 15.0 (95% CI, 13.5 to 16.4) and 3.4 (0.3 to 6.4) were recorded for permanent anterior choroidal artery occlusion and sham groups, respectively (P<0.001, maximum score 25) with motor deficit scores of 3.4 (95% CI, 2.9 to 4.0) and 0.0 (CI, 0.0 to 0.0), respectively (P<0.001, maximum score 9). Histology revealed that the internal capsule lesion expands gradually from acute to chronic phases. This new model of lacunar infarction induces a reproducible infarct in subcortical white matter with a measurable functional deficit and evidence of penumbral tissue acutely.

Quadro-pulse stimulation is more effective than paired-pulse stimulation for plasticity induction of the human motor cortex

Objective Repetitive paired-pulse transcranial magnetic stimulation (TMS) at I-wave periodicity has been shown to induce a motor-evoked potential (MEP) facilitation. We hypothesized that a greater enhancement of motor cortical excitability is provoked by increasing the number of pulses per train beyond those by paired-pulse stimulation (PPS). Methods We explored motor cortical excitability changes induced by repetitive application of trains of four monophasic magnetic pulses (quadro-pulse stimulation: QPS) at 1.5-ms intervals, repeated every 5 s over the motor cortex projecting to the hand muscles. The aftereffects of QPS were evaluated with MEPs to a single-pulse TMS, motor threshold (MT), and responses to brain-stem stimulation. These effects were compared to those after PPS. To evaluate the QPS safety, we also studied the spread of excitation and after discharge using surface electromyograms (EMGs) of hand and arm muscles. Results Sizes of MEPs from the hand muscle were enhanced for longer than 75 min after QPS; they reverted to the baseline at 90 min. Responses to brain-stem stimulation from the hand muscle and cortical MEPs from the forearm muscle were unchanged after QPS over the hand motor area. MT was unaffected by QPS. No spreads of excitation were detected after QPS. The appearance rate of after discharges during QPS was not different from that during sham stimulation. Conclusions Results show that QPS can safely induce long-lasting, topographically specific enhancement of motor cortical excitability. Significance QPS is more effective than PPS for inducing motor cortical plasticity.

Monitoring of motor pathways during brain stem surgery: What we have achieved and what we still miss?

Intraoperative neurophysiological monitoring (IOM) has established itself as one of the paths by which modern neurosurgery can improve surgical results while minimizing morbidity. IOM consists of both monitoring (continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (functional identification and preservation of anatomically ambiguous nervous tissue) techniques. In posterior-fossa and brainstem surgery, mapping techniques can be used to identify - and therefore preserve - cranial nerves, their motor nuclei and corticospinal or corticobulbar pathways. Similarly, free-running electromyography (EMG) and muscle motor-evoked potential (mMEP) monitoring can continuously assess the functional integrity of these pathways during surgery. Mapping of the corticospinal tract, at the level of the cerebral peduncle as well as mapping of the VII, IX-X and XII cranial nerve motor nuclei on the floor of the fourth ventricle, is of great value to identify "safe entry-zones" into the brainstem. Mapping techniques allow recognizing anatomical landmarks such as the facial colliculus, the hypoglosseal and glossopharyngeal triangles on the floor of the fourth ventricle, even when normal anatomy is distorted by a tumor. On the basis of neurophysiological mapping, specific patterns of motor cranial nuclei displacement can be recognized. However, brainstem mapping cannot detect injury to the supranuclear tracts originating in the motor cortex and ending on the cranial nerve motor nuclei. Therefore, monitoring techniques should be used. Standard techniques for continuously assessing the functional integrity of motor cranial nerves traditionally rely on the evaluation of spontaneous free-running EMG in muscles innervated by motor cranial nerves. Although several criteria have been proposed to identify those EMG activity patterns that are suspicious for nerve injury, the terminology remains somewhat confusing and convincing data regarding a clinical correlation between EMG activity and clinical outcome are still lacking. Transcranial mMEPs are also currently used during posterior-fossa surgery and principles of MEP monitoring to assess the functional integrity of motor pathways are similar to those used in brain and spinal-cord surgery. Recently, current concepts in muscle MEP monitoring have been extended to the monitoring of motor cranial nerves. So-called "corticobulbar mMEPs" can be used to monitor the functional integrity of corticobulbar tracts from the cortex through the cranial motor nuclei and to the muscle innervated by cranial nerves. Methodology for this purpose has appeared in the literature only recently and mostly with regards to the VII cranial nerve monitoring. Nevertheless, this technique has not yet been standardized and some limitations still exist. In particular, with regards to the preservation of the swallowing and coughing reflexes, available intraoperative techniques are insufficient to provide reliable prognostic data since only the efferent arc of the reflex can be tested.

Transcranial and direct cortical stimulation for motor evoked potential monitoring in intracerebral aneurysm surgery

To analyse the parallel use of transcranial electrical stimulation (TES) and direct cortical stimulation (DCS) for eliciting muscle motor evoked potentials (MMEPs) in intracranial aneurysm surgery; to correlate permanent or transient TES- and/or DCS-MMEP changes with surgical maneuvers and clinical motor outcome. TES and DCS were intraoperatively performed in 108 patients (51.5+/-14.7 years); MMEPs were obtained in muscles belonging to the vascular territory of interest. Monopolar, anodal stimulation was achieved with a train of five stimuli consisting of an individual pulse width of 0.5ms, an interstimulus interval of 4ms, a train repetition rate of 0.5-2Hz, and maximum stimulation intensities up to 200mA (TES) versus 25mA (DCS). In 95/108 (88%) patients, no changes in MMEPs occurred and none of these patients suffered a permanent severe motor deficit. In 14/108 (12%) patients, we observed nine (64%) temporary changes, four (29%) permanent deteriorations and one (7%) permanent MMEP loss. Out of 14 MMEP changes, nine (64%) occurred with TES, compared to 13 (93%) with DCS (Fishers'p=0.165). Parallel changes in TES- and DCS-MMEPs occurred in 8/14 patients (57%), in which case a permanent loss was always followed by a permanent severe motor deficit. Sixty-seven percent of all permanent changes occurred with DCS-MMEPs, compared to 33% with TES-MMEPs (p=0.567, NS). In aneurysm surgery, provided that close-to-motor-threshold stimulation and the most focal stimulating electrode montage are used, TES- and DCS-MMEPs do not differ in their capacity to detect an impending lesion of the motor cortex or its efferent pathways. TES stimulation can cause significant muscular contraction during surgery, potentially disrupting the operating surgeon. DCS maintains the singular advantage of stimulating a very focal and superficial motor cortex stimulation that does not result in patient movement.

Surgery for intramedullary spinal cord tumors: the role of intraoperative (neurophysiological) monitoring

In spite of advancements in neuro-imaging and microsurgical techniques, surgery for intramedullary spinal cord tumors (ISCT) remains a challenging task. The rationale for using intraoperative neurophysiological monitoring (IOM) is in keeping with the goal of maximizing tumor resection and minimizing neurological morbidity. For many years, before the advent of motor evoked potentials (MEPs), only somatosensory evoked potentials (SEPs) were monitored. However, SEPs are not aimed to reflect the functional integrity of motor pathways and, nowadays, the combined used of SEPs and MEPs in ISCT surgery is almost mandatory because of the possibility to selectively injury either the somatosensory or the motor pathways. This paper is aimed to review our perspective in the field of IOM during ISCT surgery and to discuss it in the light of other intraoperative neurophysiologic strategies that have recently appeared in the literature with regards to ISCT surgery. Besides standard cortical SEP monitoring after peripheral stimulation, both muscle (mMEPs) and epidural MEPs (D-wave) are monitored after transcranial electrical stimulation (TES). Given the dorsal approach to the spinal cord, SEPs must be monitored continuously during the incision of the dorsal midline. When the surgeon starts to work on the cleavage plane between tumor and spinal cord, attention must be paid to MEPs. During tumor removal, we alternatively monitor D-wave and mMEPs, sustaining the stimulation during the most critical steps of the procedure. D-waves, obtained through a single pulse TES technique, allow a semi-quantitative assessment of the functional integrity of the cortico-spinal tracts and represent the strongest predictor of motor outcome. Whenever evoked potentials deteriorate, temporarily stop surgery, warm saline irrigation and improved blood perfusion have proved useful for promoting recovery, Most of intraoperative neurophysiological derangements are reversible and therefore IOM is able to prevent more than merely predict neurological injury. In our opinion combining mMEPs and D-wave monitoring, when available, is the gold standard for ISCT surgery because it supports a more aggressive surgery in the attempt to achieve a complete tumor removal. If quantitative (threshold or waveform dependent) mMEPs criteria only are used to stop surgery, this likely impacts unfavorably on the rate of tumor removal.

Four-limb muscle motor evoked potential and optimized somatosensory evoked potential monitoring with decussation assessment: results in 206 thoracolumbar spine surgeries

The objective of this study was to improve upon leg somatosensory-evoked potential (SEP) monitoring that halves paraplegia risk but can be slow, miss or falsely imply motor injury and omits arm and decussation assessment. We applied four-limb transcranial muscle motor-evoked potential (MEP) and optimized peripheral/cortical SEP monitoring with decussation assessment in 206 thoracolumbar spine surgeries under propofol/opioid anesthesia. SEPs were optimized to minimal averaging time that determined feedback intervals between MEP/SEP sets. Generalized changes defined systemic alterations. Focal decrements (MEP disappearance and/or clear SEP reduction) defined neural compromise and prompted intervention. They were transient (quickly resolved) or protracted (>40 min). Arm and leg MEP/SEP monitorability was 100% and 98/97% (due to neurological pathology). Decussation assessment disclosed sensorimotor non-decussation requiring ipsilateral monitoring in six scoliosis surgeries (2.9%). Feedback intervals were 1-3 min. Systemic changes never produced injury regardless of degree. They were gradual, commonly included MEP/SEP fade and sometimes required large stimulus increments to maintain MEPs or produced >50% SEP reductions. Focal decrements were abrupt; their positive predictive value for injury was 100% when protracted and 13% when transient. Six transient arm decrements predicted one temporary radial nerve injury; five suggested arm neural injury prevention (2.4%). There were 15 leg decrements: six MEP-only, four MEP before SEP, three simultaneous and two SEP-only. Five were protracted, predicting four temporary cord injuries (three motor, one Brown-Sequard) and one temporary radiculopathy. Ten were transient, predicting one temporary sensory cord injury; nine suggested cord injury prevention (4.4%). Two radiculopathies and one temporary delayed paraparesis were unpredicted. The methods are reliable, provide technical/systemic control, adapt to non-decussation and improve spinal cord and arm neural protection. SEP optimization speeds feedback and MEPs should further reduce paraplegia risk. Radiculopathy and delayed paraparesis can evade prediction.

Transcranial electric stimulation for intraoperative motor evoked potential monitoring: Stimulation parameters and electrode montages

Objective To evaluate the efficacy of constant current transcranial electric stimulation (TES) parameters for eliciting muscle motor evoked potentials (MEPs) in the abductor pollicis brevis muscles (APB) and the tibialis anterior muscles (TA). The following parameters were tested intraoperatively: interstimulus interval (ISI), individual stimulation pulse duration within a train of five stimuli. Different montages of stimulating electrodes were assessed for effectiveness and focality. Further, reference values for APB and TA motor thresholds in neurosurgical patients with normal motor status under total intravenous anesthesia were determined. Methods Motor thresholds of contralateral muscle MEPs were determined at 0.1, 0.2, 0.4, and 0.5 ms pulse duration and ISIs of 2, 3, 4, and 5 ms using a train of five monophasic constant current pulses with C3/C4 (27 patients). The stimulating electrodes were positioned at C1, C2, C3, C4, Cz, and Cz+6 cm. Different montages were used to determine the most effective and the most focal stimulation montages for the APB and TA muscles (30 patients). Eighty-six patients with clinically normal motor function were studied for motor threshold reference values. Results The prolongation of the pulse duration has the strongest effect to decrease the motor threshold, which proportionally increases the delivered charge. The lowest stimulation threshold to elicit muscle MEPs in the APB and TA muscles is achieved with a train of stimuli consisting of an individual stimulus pulse duration of 0.5 ms. An ISI of 4 ms gave the lowest motor thresholds, but did not reach statistical significance compared to 3 ms. The stimulating electrode montage C3/C4 (C4/C3) allows for the lowest stimulation thresholds, but the vigorous muscle contractions it has is a disadvantage. The most focal stimulating electrode montages for the contralateral APB muscles are C3/Cz and C4/Cz, respectively, and for the TA muscles Cz/Cz+6 cm. Conclusions In adult neurosurgical patients with a normal motor status under total intravenous anesthesia, an individual pulse duration of 0.5 ms and an ISI of 4 ms provide the lowest motor thresholds. Pragmatically, C1/C2, resp., C2/C1 montage provides monitorable responses in both APB and TA muscles at reasonable stimulation thresholds without inducing movements disturbing surgery and especially microdissection. If the most focal hemispheric stimulation for the distal upper extremity muscles is required, the use of C3 or C4 referenced to Cz is recommended. Significance The stimulation parameters within a train of five pulses with an individual pulse duration of 0.5 ms and an ISI of 4 ms provide the lowest motor threshold. These data confirm not only studies for D wave recovery but also provide optimal stimulation parameters for intraoperative near threshold stimulation.

Review of physiological motor outcome measures in spinal cord injury using transcranial magnetic stimulation and spinal reflexes

This article reviews methods that have been developed as part of a clinical initiative on improving outcome measures for motor function assessment in subjects with spinal cord injury (SCI). Physiological motor outcome measures originally developed for limbs-transcranial magnetic stimulation (TMS) of the motor cortex to elicit motor-evoked potentials (MEPs) and mechanical stimulation to elicit spinal reflexes-have been extended to muscles of the trunk. The impetus for this development is the lack of a motor component in the American Spinal Injury Association clinical assessment for the thoracic myotomes. The application of TMS to the assessment of limb muscles is reviewed, followed by consideration of its application to the assessment of paravertebral and intercostal muscles. Spinal reflex testing of paravertebral muscles is also described. The principal markers for the thoracic SCI motor level that have emerged from this clinical initiative are (1) the threshold of MEPs in paravertebral muscles in response to TMS of the motor cortex, (2) the facilitation pattern and latency of MEPs in intercostal muscles during voluntary expiratory effort, and (3) the absence of long-latency reflex responses and the exaggeration of short-latency reflex responses in paravertebral muscles.

Monitoring of muscle motor evoked potentials during cerebral aneurysm surgery: intraoperative changes and postoperative outcome

The authors in this study evaluated muscle motor evoked potentials (MMEPs) elicited by transcranial electrical stimulation (TES) and direct cortical stimulation as a means of monitoring during cerebral aneurysm surgery. The analysis focused on the value and frequencies of any intraoperative changes and their correlation to the postoperative motor status. One hundred nineteen patients undergoing surgery for 148 cerebral aneurysms were included in the study. Muscle motor evoked potentials were elicited by a train of five constant-current anodal stimuli with an individual pulse duration of 0.5 msec and a stimulation rate of 2 Hz. Stimulation intensity was up to 240 mA for TES and up to 33 mA for direct cortical stimulation. The MMEPs were continuously recorded from the abductor pollicis brevis and tibialis anterior muscles bilaterally and from the biceps brachii and extensor digitorum communis muscles contralateral to the surgical side. The motor status was evaluated immediately after surgery and 7 days later. In 97% of the patients MMEPs were recordable for continuous neurophysiological monitoring of the vascular territory of interest throughout the surgery. In 14 patients significant intraoperative MMEP changes occurred, resulting in a transient motor deficit in one patient and a permanent motor deficit in six. The permanent loss of MMEPs in three patients was followed by a permanent severe motor deficit in one patient and severe clinical deterioration in the other two. Data in this study demonstrated that MMEPs are a useful means of intraoperative neurophysiological monitoring of motor pathway integrity and predicting postoperative motor status. The intraoperative loss of MMEPs reliably predicts both severe and permanent postoperative motor deficits.

Correlation of motor evoked potentials with magnetic resonance imaging and neurologic findings in Doberman Pinschers with and without signs of cervical spondylomyelopathy

To establish the reference ranges for motor evoked potential (MEP) latency and amplitude in clinically normal Doberman Pinschers, compare the MEPs of Doberman Pinschers with and without clinical signs of cervical spondylomyelopathy (CSM; wobbler syndrome), and determine whether MEP data correlate with neurologic or magnetic resonance imaging (MRI) findings. 16 clinically normal and 16 CSM-affected Doberman Pinschers. Dogs were classified according to their neurologic deficits. After sedation with acepromazine and hydromorphone, transcranial magnetic MEPs were assessed in each dog; latencies and amplitudes were recorded from the extensor carpi radialis and cranial tibial muscles. Magnetic resonance imaging was performed to evaluate the presence and severity of spinal cord compression. Significant differences in cranial tibial muscle MEP latencies and amplitudes were detected between clinically normal and CSM-affected dogs. No differences in the extensor carpi radialis MEP were detected between groups. There was a significant correlation (r = 0.776) between the cranial tibial muscle MEP latencies and neurologic findings. Significant correlations were also found between MRI findings and the cranial tibial muscle MEP latencies (r = 0.757) and amplitudes (r = -0.453). Results provided a reference range for MEPs in clinically normal Doberman Pinschers and indicated that cranial tibial muscle MEP latencies correlated well with both MRI and neurologic findings. Because of the high correlation between cranial tibial muscle MEP data and neurologic and MRI findings, MEP assessment could be considered as a screening tool in the management of dogs with spinal cord disease.

BS3 How to preserve the functional integrity of the corticospinal tracts during spine and spinal cord surgeries

Up to the 1990’s, motor evoked potentials (MEPs) were not yet a part of intraoperative monitoring (IOM) methodologies. Therefore, conclusions about the integrity of the corticospinal tracts (CTs) within the spinal cord were indirectly drawn from monitoring the dorsal columns with somato sensory evoked potentials (SEPs). It is understandable that such a correlation cannot always be correct and discrepancies between the functional integrity of the dorsal columns and of the CTs was reported. These reports, together with the observation that the disappearance of SEPs during myelotomy for spinal cord tumor surgery is not necessarily followed by motor deficits, further questioned IOM’s usefulness. Furthermore, it was shown that ‘‘neurogenic MEPs’’ method, which electrically stimulates the spinal cord and records elicited activity from the peripheral nerves does not represent motor evoked potentials, but antidromic activity from the stimulated dorsal columns. Further development of motor evoked potentials recorded from the spinal cord as a D and I waves as well as from the limb muscle after eliciting them with a short train of transcranialy applied stimuli, has brought the full confidence of (neuro)surgeons in the ability of IOM to predict and prevent intraoperative injury to the spinal cord’s motor system. Combination that uses the D wave and muscle MEPs’ to monitor spinal cord surgeries has proven to be realiable tool for preventing intraoperative injury to the spinal cord’s motor system. By contrast, the D wave – but not muscle MEPs – has shown false positive data, but only during scoliosis surgeries. This is due to the new anatomical relationship between recording electrode and the spinal cord after correction of the scoliotic curvature. Further development of IOM techniques to neurophysiologically identify (map) dorsal and lateral columns of the exposed spinal cord, giving us a new tools to prevent injury to those structures.

W3 Intraoperative monitoring: Spinal cord

Surgery at and around the spinal cord places the cord at risk from ischemic, thermal or mechanical injury. The most feared injuries cause motor loss, e.g., paraplegia. Somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) are used for spinal cord intraoperative monitoring (IOM). SEPs are easiest to monitor and were first to gain widespread acceptance. SEP IOM reduced postoperative paraplegia by more than 60%. In the SEP technique, spinal cord pyramidal tract integrity is inferred from SEP posterior column monitoring. Correlations were good, yet some discrepancies occurred between posterior column function and motor outcome. SEPs during myelotomy for spinal cord tumors did not predict motor deficits well. In contrast, MEPs monitor pyramidal tracks directly. Transcranial or direct electrical cortical stimulation produces corticospinal (pyramidal) D and I waves recordable directly from the spinal cord. Limb muscle MEPs can and should bemonitored too. These techniquesmore confidently warn surgeons, and predict and prevent intraoperative injury to the spinal motor pathway. Combining D wave spinal recording with muscle MEPs is a reliable technique. D wave without muscle MEPs has shown false positive changes when assessed in scoliosis surgery, possibly due to recording electrode movement during spinal column distraction. Many users now combine SEP and types of MEP, tailored to the particular patient’s condition, surgery and anesthesia regimen. Further development of IOM techniques could map dorsal and lateral columns of the exposed spinal cord, new tools better to prevent intraoperative spinal injury.

Motor strategies and excitability changes of human hand motor area are dependent on different voluntary drives

The present study examined whether there were different voluntary drives between intended and non-intended muscle contractions. In experiment 1, during intended and non-intended muscle contractions, electromyograms (EMGs) were recorded from the first dorsal interosseous (FDI) and extensor carpi radialis (ECR) muscles when force levels were varied from 10% to 50% maximal voluntary contraction (MVC) in 10% MVC steps. In experiment 2, using transcranial magnetic stimulation, motor-evoked potentials (MEPs) were recorded from the FDI muscle when EMGs were varied from 10% to 40% EMGmax (EMG activities during MVC) in 10% EMGmax steps during intended and non-intended muscle contractions. In experiment 3, at 10% MVC force level MEPs were recorded before and after practice. The results showed that, in the FDI muscle, EMGs during intended muscle contractions were larger than those during non-intended ones at higher force levels (30-50% MVC). In the ECR muscle, reverse results were observed. At comparable EMG levels of the FDI muscle MEPs were the same during intended and non-intended muscle contractions. After practice, MEPs during intended muscle contraction became larger than those during non-intended at 10% MVC force level, while EMGs were the same between two muscle contractions. It is concluded that motor strategies and excitability changes of hand motor area are different during intended and non-intended muscle contractions, and these differences are due to the different voluntary drives of intended and non-intended. The present findings may contribute to the understanding of rehabilitation for patients suffering from damages of the central motor system.