Transcranial Electrical Motor Evoked Potentials Research Articles

Investigation of Segmental Motor Paralysis After Cervical Laminoplasty Using Intraoperative Spinal Cord Monitoring With Transcranial Electric Motor-evoked Potentials

A retrospective study of segmental motor paralysis after cervical laminoplasty for cervical myelopathy. The objective of this study was to use transcranial electric motor-evoked potentials during cervical laminoplasty, to monitor and investigate the intraoperative electrophysiologic change in patients with cervical myelopathy, who subsequently develop postoperative segmental motor paralysis potentials. There have been several reports about segmental motor paralysis after cervical laminoplasty for patients with cervical myelopathy. However, the pathogenesis of segmental motor paralysis of C5 myotome, so-called C5 palsy, remains unclear. The cases of 184 consecutive patients who underwent cervical laminoplasty were analyzed to clarify the incidence of postoperative segmental motor paralysis and to monitor intraoperative change. Postoperative C5 palsy was defined as development of postoperative motor palsy of the deltoid and biceps muscles in the upper extremity by at least 1 grade in the manual muscle test without sensory disturbance or impairment of the lower extremities. All patients underwent cervical laminoplasty under intraoperative spinal cord monitoring with transcranial electric motor-evoked potentials. The evoked potentials were recorded over the deltoid, biceps, and triceps muscles in the bilateral upper extremities. Postoperative C5 palsy developed in 6 patients (3.3%, 5 males and 1 female) but there were no abnormal changes monitored. The incidence of C5 palsy involved 4 of 124 (3.2%) cervical spondylotic myelopathy patients, 2 of 31 (6.5%) patients with cervical ossification of the posterior longitudinal ligament. No patients with cervical disc herniation or cervical spondylotic amyotrophy developed C5 palsy. There were no abnormal findings on transcranial electric motor-evoked potential monitoring even in those patients who developed postoperative C5 palsy. These results indicate that the development of postoperative segmental motor paralysis after cervical laminoplasty occurs even if there are no abnormal findings during intraoperative monitoring.

Comparison of the Effects of Etomidate and Propofol Combined With Remifentanil and Guided By Comparable BIS on Transcranial Electrical Motor-evoked Potentials During Spinal Surgery

Transcranial electrical motor-evoked potentials (TceMEPs) can provide early warning of possible motor compromise during surgery. There are fewer reports comparing the effects of etomidate and propofol infusion on TceMEPs when used for the maintenance of anesthesia and guided by comparable values of bispectral index (BIS) during spinal surgery. Thirty-three patients scheduled for spinal surgery were randomly divided into 2 groups: propofol (PR, n=18) and etomidate (ER, n=15). Anesthesia was maintained with either propofol or etomidate combined with remifentanil. The infusion rates for propofol or etomidate were guided by the BIS value, which was maintained between 40 and 45. TceMEPs were conducted by stimulating needles placed at C1 and C2; recordings were made by measuring myogenic responses from the upper extremity abductor pollicis brevis muscles using needle electrodes. The threshold for eliciting a response, amplitudes, and latencies of TceMEPs, were recorded at 30, 60, 90, and 120 minutes after the induction of anesthesia. The cortisol levels were measured at 2 and 24 hours after induction. The voltage threshold needed to enlist TceMEPs in the ER group was significantly lower than that in the PR group (142±20 vs. 172±23 V, P=0.005). The amplitudes of TceMEPs were higher in the ER group than those in the PR group (P<0.05), whereas the latencies were shorter in the ER group than those in the PR group (P<0.05) at all study time points. Cortisol levels at all study time points were within the normal range. Etomidate has more favorable effects than propofol during the monitoring of TceMEPs under comparable BIS levels.

Effects of Intrathecal Morphine on Transcranial Electric Motor-Evoked Potentials in Adolescents Undergoing Posterior Spinal Fusion

Intrathecal morphine (ITM) provides effective analgesia after posterior spinal fusion (PSF). Although most anesthetic drugs have well-characterized effects on evoked potentials, there is little data on the effects of ITM on transcranial electric motor-evoked potentials (tceMEPs). We performed this study to assess the effects of ITM on tceMEPs in the first 30 minutes after administration. We hypothesized that administration of ITM in doses currently used at our institution would not significantly affect mean tceMEP amplitudes and latencies of an ITM study group relative to control patients who did not receive the drug. tceMEPs were recorded before ITM injection and 5, 10, 20, and 30 minutes after injection in 14 subjects ages 11 through 18 years undergoing PSF. These recordings were compared to an age-matched control group undergoing PSF in which ITM was not injected. The effects of ITM on tceMEP amplitude and latency were compared between the 2 groups. Fourteen subjects were enrolled in the ITM group and 16 served as controls. There were no significant differences in the baseline mean response amplitudes of the 2 groups for any of the 8 muscles studied. Mean response amplitudes over the 30-minute posttreatment period in the ITM group did not differ significantly from those of the control subjects. Average response amplitudes collapsed across all muscles for each subject were not significantly different during the baseline period (95% CI = -38% to 45%; P = 0.783), nor were they significantly different between the 2 groups during the posttreatment period (95% CI = -30% to 78%; P = 0.640). There also were no significant differences in the mean response latencies of the 2 groups in either the baseline or posttreatment periods. Average response latencies collapsed across all muscles for each subject were 4% larger for the ITM group than for controls during the baseline period (95% CI = -5% to 13%; P = 0.377), and 3% larger for the ITM group than for controls during the posttreatment period (95% CI = -4% to 12%; P = 0.359). Administration of ITM in doses currently used at our institution did not cause more than a 70% attenuation of mean tceMEP amplitudes or latency changes of an ITM study group relative to control subjects during the 30-minute period after injection. Further studies are required to determine if there are delayed effects after this initial time period.

Transcranial Motor Evoked Potential Changes Induced by Provocative Testing during Embolization of Cerebral Arteriovenous Malformations in Patients under Total Intravenous Anesthesia

ABSTRACT.Cerebral motor evoked potential (MEP) monitoring during arteriovenous malformation (AVM) embolization is not well studied (Söderman et al. 2003). Alterations of cerebral blood flow (CBF) during cerebral embolization could cause ischemia/infarction to the cerebral cortex. Permanent loss of MEPs is correlated with a permanent motor deficit. We report a case of a patient undergoing AVM embolization during which transcranial electrical motor evoked potentials (TCeMEP) reliably predicted changes to CBF induced by selective methohexital testing. Our finding demonstrated that MEPs are a useful means of intraoperative monitoring of motor pathway integrity and predicting changes. The loss of MEP predicted and prevented severe postoperative motor deficits. Intraoperative neuromonitoring with SSEP, TCeMEP, and continuous EEG revealed no changes until the posterior cerebral artery (PCA), but not the anterior cerebral artery (ACA), was injected. TCeMEP may be superior to somatosensory evoked potential (SSEP) and EEG monitoring in predicting motor impairment during AVM surgery.

Intraoperative Neurophysiological Monitoring (IONM): Lessons Learned from 32 Case Events in 2069 Spine Cases

ABSTRACT.Intraoperative neurophysiological monitoring (IONM) is becoming the standard of care for many spinal surgeries, especially those with deformity correction and instrumentation. We reviewed 2069 spine cases with multimodality IONM including somatosensory evoked potentials (SSEP), transcranial electrical motor evoked potentials (TCeMEP), and spontaneous and triggered electromyography (s-EMG and t-EMG) in a University setting over a period of four years to examine perioperative clinical findings when an IONM event was noted and to ascertain how IONM has affected our ability to avoid potential neurological injury during spine surgery.We performed a retrospective analysis of cases from 2006 to 2010 to study the frequency and cause of intraoperative events detected via IONM and the clinical outcome of the patient. There were 32 cases (1.5%) with possible intraoperative events. There were 17 (53%) cases where IONM changes affected the course of the surgery and prevented possible postoperative neurological deficits. Seven cases (41%) were due to deformity correction, five (29%) due to hypotension, four (24%) due to patient positioning, and one (6%) due to a screw requiring repositioning. None of the 17 patients had postoperative motor or sensory deficits. There were four cases with false-positive IONM findings due to correctible technical issues. Three cases required surgical revision due to pedicle screw malposition. In each case, s-EMGs failed to exhibit intraoperative changes but the patient presented with postoperative radiculopathy. We believe that the use of t-EMGs may have prevented these complications.This review reinforces the importance of multimodality IONM for spinal surgery. The incidence of possible events in our series was 1.5%, and several likely postoperative neurologic deficits were avoided by intraoperative intervention.

Preventing Position-Related Brachial Plexus Injury with Intraoperative Somatosensory Evoked Potentials and Transcranial Electrical Motor Evoked Potentials during Anterior Cervical Spine Surgery

ABSTRACT.The use of somatosensory evoked potentials (SSEPs) to monitor upper extremity nerves during surgery is becoming more accepted as a valid and useful technique to minimize intraoperative nerve injuries. We present a case illustrating the benefit of utilizing both SSEPs and transcranial electrical motor evoked potentials (TCeMEPs) for preventing position-related injury during surgery.The patient was a 43-year-old male with a history of neck pain, along with numbness and tingling of the upper extremities. While the patient was being draped, upper extremity SSEPs diminished significantly. TCeMEP responses in the hands (abductor pollicus brevis-abductor digiti minimi; APB-ADM) vanished shortly after that, followed by the biceps and left deltoid. The surgeons were notified, and the tape on the shoulders was loosened. No improvements were noted in SSEPs nor TCeMEPs due to this intervention, so all tape was removed and the patient's arms were allowed to rest naturally upon the arm boards. Upper extremity TCeMEP responses could then be elicited and SSEPs improved shortly afterward. Surgery was completed with the arms on the arm boards. All signals remained stable for the remaining three hours of the procedure. At two months follow-up, the patient was well with total pain relief and normal upper extremity function when neurological examination was performed.This report demonstrates a case in which intraoperative neurophysiological monitoring was useful in identifying and reversing impending nerve injury during cervical spine surgery. Significant changes were seen in SSEPs as well as TCeMEPs, so we recommend that TCeMEP monitoring be considered as an adjunct to SSEPs for prevention of injury to the brachial plexus.

Improving successful rate of transcranial electrical motor-evoked potentials monitoring during spinal surgery in young children

This prospective study was to investigate the successful rate of intraoperative motor evoked potentials (MEP) monitoring for children (<12 years old) with congenital scoliosis. A consecutive series of 27 young children (7 girls and 20 boys; from 1 to 11 years old) between September 2007 and November 2009, were enrolled to this study. 12 patients received general anesthesia based on TIVA, induced with propofol 2-4 mg/kg and fentanyl 3-5 µg/kg followed by a continuous infusion of propofol (20-150 µg/kg/min, at mean of 71.7 µg/kg/min). The other 15 patients received combined inhalation and intravenous anesthesia, induced with sevoflurane and fentanyl 3-5 µg/kg and maintained by sevoflurane (0.5-1%). The maintenance of anaesthesia management was performed with stable physiological parameters during surgery. Intraoperative MEP monitoring was successfully performed in all patients, while SEP was successfully performed in 26 of 27 patients. There was no significant difference of successful rates between SEP and MEP monitoring (P > 0.05). As well, no difference in MEP successful rates was observed in two groups with different anesthetic techniques. No wake-up test and no post-operative neurological deficits occurred in this series of patients. Low dose anesthesia by either TIVA with propofol or sevoflurane-based mixture anesthesia protocol can help the intraoperative spinal cord monitoring to successfully elicit MEP and perform reliable monitoring for patients below 12 years of age.

Influences of partial muscle relax and depth of anesthesia on transcranial electrical motor evoked potential

Objective To explore the influences of partial muscle relax and depth of anesthesia on transcranial electrical motor evoked potential (TceMEP).Methods 12 patients undergoing neurosurgical operation were enrolled.Anesthesia was maintained with sevoflurane , propofol and remifentanil.The level of muscle relax and anesthesia depth were monitored by train of five stimulation (TOF) and burst -suppressed rate (BSR).After the baseline recording when T4 equal tn T1 and there was no burst suppression wave on EEG( BSR =0), then BSR was increased to 0.25 ～0.5 and above 0.75 by regulating dosage of propofol and TceMEP was recorded respectively .At the state of disapperance of burst suppression wave and cisatracurium (40～ 80)μg/(kg/h) was administered simultaneously, when T4 / T1 was equal to 25% TceMEP was elicited again.The movements of patients were also assessed during monitoring.Results The incidence of patient's movement at baseline was high(9/10).At the state of recovery of muscle relax,movement incidence was decreased and the amplitude of TceMEP was attenuated greatly when 0.25 ＜ BSR ＜0.5 and BSR ＞0.75 comparing to baseline( ＜0.05 and ＜0.01 respectively).When BSR =0 and T4 /T1 was equal to 25% , a similar intensity stimulation could almost maintain the amplitude of TceMEP as well as baseline( P ＞0.05) ,but there was only 1 patient showing movement.The latency of TceMEPs was not significantly different comparing to baseline.Conclusions Monitoring of TceMEP need to avoid the presence of burst suppression waves EEG by deepening anaesthesia.TceMEP could be recorded at the state of partial muscle relax by T4 / T1 equal to 25% and without burst suppression wave EEG, in which the risk of movement of patients responsed to transcranial stimulation is decreased and the effect on TceMEP is reduced. Key words: Evoked potentials,motor; Muscle relax; EEG

Transcranial Electric Motor Evoked Potential Monitoring During Spine Surgery

Retrospective review. To report on the safety of repetitive transcranial electric stimulation (RTES) for eliciting motor-evoked potentials during spine surgery. Theoretical concerns over the safety of RTES have hindered broader acceptance of transcranial electric motor-evoked potentials (tceMEP), despite successful implementation of spinal cord monitoring with tceMEPs in many large spine centers, as well as their apparent superiority over mixed-nerve somatosensory-evoked potentials (SSEP) for detection of spinal cord injury. The records of 18,862 consecutive patients who met inclusion criteria and underwent spine surgery with tceMEP monitoring were reviewed for RTES-related complications. This large retrospective review identified only 26 (0.14%) cases with RTES-related complications; all but one of these were tongue lacerations, most of which were self-limiting. The results demonstrate that RTES is a highly safe modality for monitoring spinal cord motor tract function intraoperatively.

Nerve Monitoring During Proximal Humeral Fracture Fixation: What Have We Learned?

The incidence of neurologic injury after proximal humerus fractures is variable, ranging from 6.2% to as much as 67%. However, it is unclear what factors might contribute to these injuries or whether they can be prevented by intraoperative nerve monitoring. Therefore, using intraoperative nerve monitoring, we assessed the incidence, pattern of nerve involvement, and predisposing factors for nerve injury before and during shoulder fracture fixation. We used continuous intraoperative monitoring of the brachial plexus in 37 patients undergoing open operative treatment of proximal humerus fractures. Impending intraoperative compromise of nerve function was signaled by sustained neurotonic EMG activity or greater than 50% amplitude attenuation of transcranial electrical motor evoked potentials (MEPs) (or both). When a nerve alert occurred, current surgical activity and arm and retractor position were recorded and adjustments were made to relieve tension. The intraoperative affected nerves included axillary (46%), combined (mixed plexopathy) (23%), radial (23%), musculocutaneous (4%), and ulnar (4%). Postoperatively, three patients had transient nerve palsies, which fully resolved within 3 weeks of surgery. Low body mass index (BMI) (22.7 ± 2.8), history of cervical spine disease, diabetes mellitus, and delay in surgical treatment (14 ± 2.9 days from time of injury) were associated with an increased incidence of nerve dysfunction. Our observations suggest transcranial electrical MEPs are sensitive indicators of impending iatrogenic injury to the brachial plexus or peripheral nerves (or both) during open operative treatment of proximal humerus fractures. The use of intraoperative nerve monitoring during these procedures may be considered for the prevention of nerve injury, particularly in patients with underlying cervical spine disease, low BMI, diabetes mellitus, and/or delay in surgical treatment greater than approximately 14 days. Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Successful Monitoring of Transcranial Electrical Motor Evoked Potentials With Isoflurane and Nitrous Oxide in Scoliosis Surgeries

This is a case series studying the efficacy of concomitant inhalational anesthesia and transcranial electrical motor-evoked potential (tceMEP) monitoring in spinal deformity surgery. To determine the affects of inhalational anesthesia on the efficacy of tceMEP monitoring. Inhalational agents inhibit transmission of evoked potentials from the motor cortex. Consequently, many authors have recommended using total intravenous anesthesia during motor-evoked potential monitoring. A total of 247 consecutive patients, aged 1 to 83 years (156 patients <22 years), undergoing spinal fusion for scoliosis, excluding those with history of seizure or myelopathy, were monitored with tceMEP intraoperatively. Isoflurane with or without nitrous oxide (per anesthesiologist preference) was administered with vecuronium and i.v. agents including propofol and/or narcotic. Vecuronium was titrated for a goal of 2/4 twitches, and isoflurane was decreased (if necessary) to a maximum level at which tceMEP responses were monitorable (patient specific). Patients were grouped according to whether they received nitrous oxide and the anesthetic depth at which responses were monitored (<0.5, 0.5-0.9, 1-1.4, and >1.5 MAC). A total of 232 (94%) patients received nitrous oxide. Of these patients, responses were obtained throughout the case in 20 (8.6%) at <0.5 MAC, 118 (50.9%) at 0.5 to 0.9 MAC, 85 (36.6%) at 1 to 1.4 MAC, and 9 (3.9%) at >1.5 MAC. Of the remaining 15 (6%) who received no nitrous oxide, responses were monitored in 3 (20%) at <0.5 MAC, 10 (66.7%) at 0.5 to 0.9 MAC, 2 (13.3%) at 1 to 1.5 MAC, and 0 at >1.5 MAC. No false-positive and 1 true-positive (transient) loss of responses occurred. No operations resulted in postoperative motor deficit. Although isoflurane and nitrous oxide diminish tceMEP responses, reliable monitoring can still be accomplished while using significant levels of inhalational anesthetic agents.

A Report of Two Cases of Lip and Tongue Bite Injury Associated with Transcranial Motor Evoked Potentials

ABSTRACT.Transcranial electric motor evoked potentials (TCeMEPs) are routinely used intraoperatively to detect and prevent iatrogenic injury to the spinal cord, specifically the corticospinal tract. Complications related to TCeMEP testing include the potential for seizure induction, cardiac arrhythmia, scalp burns, infection, and tongue or lip laceration. Among this list of potential complications, tongue and lip lacerations are the most common and most directly attributable to transcranial stimulation. The technique of low voltage stimulation and the correct placement of oral bite blocks is successful in preventing patient bite injuries. We report two cases of patient bite injuries following TCeMEPs and discuss potential mechanisms of injury and prevention.

Validity and Reliability of Intraoperative Monitoring in Pediatric Spinal Deformity Surgery

This was a 23-year retrospective study of 3436 consecutive pediatric orthopedic spinal surgery patients between 1995 and 2008. To demonstrate the effectiveness of multimodality electrophysiologic monitoring in reducing the incidence of iatrogenic neurologic deficit in a pediatric spinal surgery population. The elective nature of many pediatric spinal surgery procedures continues to drive the need for minimizing risk to each individual patient. Electrophysiologic monitoring has been proposed as an effective means of decreasing permanent neurologic injury in this population. A total of 3436 consecutive monitored pediatric spinal procedures at a single institution between January 1985 and September 2008 were reviewed. Monitoring included somatosensory-evoked potentials, descending neurogenic-evoked potentials, transcranial electric motor-evoked potentials, and various nerve root monitoring techniques. Patients were divided into 10 diagnostic categories. True-positive and false-negative monitoring outcomes were analyzed for each category. Neurologic deficits were classified as transient or permanent. Seven of 10 diagnostic groups demonstrated true positive findings resulting in surgical intervention. Seventy-four (2.2%) potential neurologic deficits were identified in 3436 pediatric surgical cases. Seven patients (0.2%) had false-negative monitoring outcomes. These patients awoke with neurologic deficits undetected by neuromonitoring. Intervention reduced permanent neurologic deficits to 6 (0.17%) patients. Monitoring data were able to detect permanent neurologic status in 99.6% of this population. The ratio of intraoperative events to total monitored cases was 1 event every 42 surgical cases and 1 permanent neurologic deficit every 573 cases. The combined use of somatosensory-evoked potentials, transcranial electric motor-evoked potentials, descending neurogenic-evoked potentials, and electromyography monitoring allowed accurate detection of permanent neurologic status in 99.6% of 3436 patients and reduced the total number of permanent neurologic injuries to 6.

Effects of Anesthetic Regimens and Other Confounding Factors Affecting the Interpretation of Motor Evoked Potentials During Pediatric Spine Surgery

ABSTRACT.Children undergoing corrective spine surgery are at risk of serious neurologic injury. Monitoring transcranial electric motor evoked potentials (TCeMEPs) during these procedures may identify and help prevent injury to motor pathways. The difficulty in obtaining consistent motor evoked potential (MEP) responses during pediatric spine surgery can result in part to the suppression of evoked responses caused by volatile inhalational anesthetics, elevated levels of propofol, and/or physiologic variables. Data obtained from 140 pediatric patients who underwent spine surgery with MEP monitoring were retrospectively analyzed and evaluated for age and anesthetic effects on stimulation variables. MEPs acquired under inhalational anesthetic agents required greater stimulation compared to intravenous propofol anesthesia. Additionally, the responses were more variable when inhalational agents were used. These effects were more prominent in younger age patients. The number of alerts of MEP loss or reduction related to anesthetic levels or blood pressure changes was higher under inhalational agents.

Predicting Surgical Outcome Using Somatosensory Evoked Potentials and Transcranial Electric Motor Evoked Potentials in a Cervical-Medullary Junction Hemangioblastoma

ABSTRACT.A 38-year-old female with a history of nausea, vomiting, headache, and neck pain underwent suboccipital craniectomy and Cl laminectomy for resection of a cervical-medullary junction hemangioblastoma. Posterior tibial nerve somatosensory evoked potentials (SSEPs), median nerve SSEPs, and transcranial electrical motor evoked potentials (TCeMEPs) from arm and leg muscles were recorded bilaterally during the surgical procedure. Total intravenous anesthesia (TIVA) was used for anesthesia. Neuromuscular blockade levels were monitored with train of four (TOF). At the end of resection, left upper median nerve SSEP responses were lost. Postoperative sensory exam revealed a profound lack of fine touch and proprioception in the left arm, with intact motor strength. Magnetic resonance imaging (MRI) revealed no evidence of hemorrhage or edema. The patient slowly regained some sensory function over the next several days before being discharged home. At the time of discharge the patient continued to have markedly decreased sensation in the left arm, but was otherwise intact. In this case, SSEP was an effective method to predict sensory loss in one extremity in the presence of intact TCeMEP responses.

Susceptibility of Transcranial Electric Motor-evoked Potentials to Varying Targeted Blood Levels of Dexmedetomidine during Spine Surgery

Dexmedetomidine has been increasingly used as an adjunct to opioid-propofol total intravenous anesthesia (TIVA). The authors tested the hypothesis and found that clinically relevant blood levels of dexmedetomidine do not produce significant attenuation of the amplitude of transcranial electric motor-evoked potentials either independently or by interaction with propofol in a dose-dependent manner. The authors planned to recruit 72 patients with idiopathic scoliosis who had posterior spine fusion surgery during propofol and remifentanil TIVA with dexmedetomidine as an adjunct. However, the authors terminated the study after enrolling 44 patients because of change in surgical technique. Before administering dexmedetomidine, baseline transcranial electric motor-evoked potentials were acquired during TIVA with remifentanil and propofol. Patients were randomized to varying targeted blood levels of dexmedetomidine (0.4, 0.6, and 0.8 ng/ml) and propofol (2.5, 3.75, and 5 microg/ml) using a factorial design. The primary outcome variable was amplitude of transcranial electric motor-evoked potential. The secondary outcome was amplitude of cortical somatosensory-evoked potentials. Of the 44 recruited patients, 40 completed the study, and their data were analyzed. The administration of dexmedetomidine in increasing doses as an adjunct to propofol-based TIVA caused a clinically and statistically significant attenuation of amplitudes of transcranial electric motor-evoked potentials. The authors conclude that under the stimulation conditions used, dexmedetomidine as an anesthetic adjunct to propofol-based TIVA at clinically relevant target plasma concentrations (0.6-0.8 ng/ml) can significantly attenuate the amplitude of transcranial electric motor-evoked potentials.

Postoperative Segmental C5 Palsy After Cervical Laminoplasty May Occur Without Intraoperative Nerve Injury: A Prospective Study With Transcranial Electric Motor-Evoked Potentials

Intraoperative neurophysiologic monitoring with transcranial electric motor-evoked potentials was performed on patients who underwent cervical laminoplasty at a university hospital in a prospective study. To evaluate the usefulness of intraoperative spinal cord monitoring with transcranial electric motor-evoked potentials for prediction of the occurrence of segmental motor paralysis after cervical laminoplasty. Segmental motor paralysis occasionally occurs among patients who undergo expansive laminoplasty for cervical myelopathy, and it has been attributed to nerve root lesions caused by either a traumatic surgical technique or a tethering effect after decompression. Sixty-two consecutive patients (47 men and 15 women; mean age 64 years [range 32-89]) who were scheduled to undergo cervical laminoplasty under intraoperative spinal cord monitoring with transcranial electric motor-evoked potentials were included in this study. Transcranial electrical stimulations were delivered through pin-type electrodes, and the evoked potentials were recorded over the deltoid, biceps, and triceps muscles in the bilateral upper extremities and thoracic spinal cord. Intraoperative evoked potentials were successfully recorded in all muscles in 57 patients (92%), and incomplete evoked potentials were recorded in the remaining 5 patients. No critical decrease in the amplitude of the evoked potentials was observed in any of the 62 patients. All patients showed sufficient postoperative recovery from their clinical symptoms; however, postoperative transient C5 palsy occurred in 3 patients. No abnormalities were observed on transcranial electric motor-evoked potential monitoring, even in those patients who developed postoperative transient C5 palsy. These results suggest that the development of postoperative C5 palsy after cervical laminoplasty is not associated with intraoperative injury of the nerve root or the spinal cord, although the precise mechanism of its development is still unclear. Surgeons should be aware that C5 palsy is a possible complication of cervical laminoplasty, even in the absence of intraoperative nerve injury.

Characterization of Neurophysiologic Alerts During Anterior Cervical Spine Surgery

A retrospective review of neurophysiologic alerts during anterior cervical surgery. To examine incidence and types of neurophysiologic alerts and their correlation with new postoperative neurologic deficits after anterior cervical discectomy or corpectomy procedures. Although multimodality neurophysiologic monitoring has been shown to predict iatrogenic neurologic injuries in scoliosis surgeries, their role in degenerative or trauma-related anterior cervical spine surgery is still unclear. We retrospectively reviewed 1,445 patients who underwent anterior cervical discectomy or corpectomy and arthrodesis with neurophysiologic monitoring that included transcranial electrical motor-evoked potentials (tceMEP), somatosensory-evoked potentials (SSEP), and spontaneous electromyography (EMG). Intraoperative alerts were analyzed for type, perceived cause, actions taken to reverse or minimize the possible spinal cord injury, and any new postoperative neurologic deficits. There were 267 (18.4%) procedures that had either minor (spontaneous, sustained EMG) or major (tceMEP/SSEP amplitude reduction) alerts. Patients who underwent corpectomies had 28% increased risk of having a major neurophysiologic alert compared with those who had discectomies. Diagnosis of cervical spondylotic myelopathy or trauma increased the risk of having a major neurophysiologic alert 30% and 76%, respectively, compared with cervical radiculopathy. Eight surgeries were aborted due to persistent tceMEP/SSEP amplitude loss, but none resulted in new postoperative neurologic deficits. Two patients had halo-vest applied due to early termination of surgery. One of these patients ultimately could not receive definitive surgical stabilization. Diagnosis of cervical spondylotic myelopathy or trauma and cervical corpectomy procedures increase the risk for having major intraoperative alerts. In case of persistent tceMEP/SSEP amplitude loss, consider delaying potentially harmful interventions, such as premature termination of the procedure or methylprednisolone infusion, until a new neurologic deficit is verified with an awake-clinical examination.

A Guide to the Performance of Transcranial Electrical Motor Evoked Potentials. Part 1. Basic Concepts, Recording Parameters, Special Considerations, and Application

ABSTRACT.In August 2002, the Food and Drug Administration (FDA) approved the use of a high-intensity multipulse stimulator to perform transcranial electrical motor evoked potentials (TCeMEPs) to monitor motor pathways in the brain and spinal cord. Since that time, this technique for monitoring pure motor pathways during surgeries that place these neural structures at risk has proceeded rapidly toward becoming the standard of care. This article is meant to be an introduction to the performance and use of this exciting new tool in the field of intraoperative neurophysiologic monitoring. Basic concepts regarding the need for this modality of monitoring, the anatomy of the pathways involved, and the mechanisms of waveform propagation are addressed. Stimulating and recording protocols are suggested for myogenic recordings, and illustrations of waveforms are provided. Special considerations specific to utilizing TCeMEPs, such as anesthetic requirements, risk factors, and other intraoperative considerations are reviewed. Lastly, alarm criteria are discussed and illustrative cases are presented. Appendices of electrode placements, case studies, sample forms, and other information are provided.

Plasticity in the descending motor pathways after spinal cord hemisection

The present study evaluates the motor functional recovery after C2 spinal cord hemisection combined with contralateral brachial root transection, which causes a condition that is similar to the crossed phrenic phenomenon (CPP). Descending motor pathways, including the reticulospinal extrapyramidal tract and corticospinal pyramidal tracts, were evaluated by transcranial magnetic motor-evoked potentials (mMEPs) and direct cortical electrical motor-evoked potentials (eMEP), respectively. All MEPs recorded from the left forelimb were abolished immediately after the left C2 hemisection. Left mMEPs recovered dramatically immediately after contralateral right brachial root transection. Corticospinal eMEPs never recovered, regardless of transection. The facilitation of mMEPs in animals that had undergone combined contralateral root transection was well correlated with open-field behavioral motor performance.