Surface electromyography activity in the upper limbs of patients following surgery for compressive cervical myelopathy.

BACKGROUND: Surface electromyography (EMG) is a noninvasive, accurate method to measure electrical activity produced in muscles. AIM: To assess the improvement of spasticity after decompressive surgery for compressive myelopathy using surface EMG. SETTING AND DESIGN: Neurophysiology laboratory of a tertiary care center. Before-after trial. Both EMG and Modified Modified Ashworth Scale (MMAS) were utilized. MATERIALS AND METHODS: Thirty-one nonconsecutive patients (28 males; age 25-72 years) with compressive cervical myelopathy and spasticity (MMAS score ≥1) were recruited. Patients with lower motor neuron findings, Nurick grade 5, and those with joint deformities, contractures, or thrombophlebitis of the upper limbs were excluded. EMG activity was measured from the pronator teres and biceps brachii for 31 age-related controls (25 males) as well as for the patients both pre- and post-operatively. STATISTICAL ANALYSIS: Student's t-test for comparison of continuous variables and Pearson correlation co-efficient for assessing the significance of associations. RESULTS: EMG recording done 1-week postoperatively showed a reduction in baseline activity in the pronators and supinators by 21% and 36%, respectively. There was a decrease in co-activation of the pronators during active supination by almost 62% and of the supinators during active pronation by around 33% (P < 0.05). On passive movement, there was a decrease in co-activation of the pronators during supination by approximately 23%, and the supinators during pronation by 35% (P < 0.05). EMG activity was significantly reduced in the pronators during supination in all patients, including those in whom the MMAS scores remained the same postoperatively. CONCLUSION: Surface EMG is an objective tool to detect improvement in spasticity following decompressive surgery for compressive cervical myelopathy even in those patients who showed no improvement on the MMAS.

Improvement in intraoperative transcranial electrical motor-evoked potentials in tethered cord surgery: an analysis of 45 cases.

BACKGROUND: Improvement of transcranial electrical motor-evoked potentials (TeMEPs) following untethering during tethered cord surgery (TCS) and its clinical significance have not been analyzed in the literature. METHODS: Forty-five consecutive cases of tethered cord were operated on with multimodality intraoperative neurophysiological monitoring (IONM) between February 2005 and January 2012. Intraoperative TeMEP change was classified as improvement, worsening or no change. Motor, sensory, bladder and bowel symptoms and signs were evaluated preoperatively, in the first week post-surgery and at the last follow-up (maximum of 2 years). RESULTS: Patient age ranged from 5 to 44 years (mean, 16 ± 10 years), with 30 children. Intraoperative MEPs improved in 23 (51 %), remained the same in 21 (46.7 %) and worsened in 1 (2 %) patient. Motor improvement occurred in 7 patients and clinical improvement in 17 patients in the immediate postoperative period. Postoperative neurological worsening occurred in one patient (2.2 %). Improved and stable MEPs correlated with the motor (p = 0.002) and clinical improvement (p = 0.02) in the immediate postoperative period. Follow-up was available in 35 patients (77.7 %), ranging from 5 to 24 months (median, 21 months; mean, 17.7 ± 6.8 months). There was late clinical improvement in 73.5 % of the patients in whom the intraoperative MEP had remained the same or improved. However, there was no statistically significant correlation between MEP change and long-term outcome. CONCLUSIONS: Intraoperative MEP improvement occurs in about 50 % of the patients following successful untethering. This finding probably provides support to the ischemic theory of tethered cord syndrome.

The effects of anaesthetic agents on cortical mapping during neurosurgical procedures involving eloquent areas of the brain.

BACKGROUND: In patients presenting for surgical resection of lesions involving, or adjacent to, the functionally important eloquent cortical areas, it is vital to achieve complete or near complete resection of the pathology without damaging the healthy surrounding tissues.The eloquent areas that the surgeons are concerned with are the primary motor, premotor cortex, supplementary motor cortex and speech areas. If the lesions are within these regions surgeons could either take a biopsy or do a intracapsular decompression without damaging the mentioned areas to avoid postoperative dysfunction. If the lesions are adjacent to the above mentioned areas, the normal anatomy would get distorted. However, proper identification of the above mentioned areas would enable the surgeon to radically remove the tumours. Intraoperative mapping of the cortex with stimulating and recording electrodes is termed as electrophysiological (EP) mapping.The EP mapping of motor, sensory and language cortex is widely employed in the resection of lesions involving or adjacent to the eloquent areas. Both intravenous and inhalational agents are known to affect these EP mapping techniques. OBJECTIVES: The aim of this review was to evaluate the effect of anaesthetic agents on intra-operative EP mapping in patients undergoing neurosurgical procedures involving, or adjacent to, the functional areas of the cortex under general anaesthesia. SEARCH METHODS: We searched the Cochrane Epilepsy Group Specialized Register (7 March 2011), The Cochrane Central Register of Controlled Trials (CENTRAL issue 1 of 4, The Cochrane Library 2011), MEDLINE (Ovid, 1948 to February week 4, 2011), PsycINFO (EBSCOhost, 7 March 2011), and the National Research Register Archive and UK Clinical Research Network (7 March 2011). We also contacted other researchers in the field in an attempt to ascertain unpublished studies. SELECTION CRITERIA: We planned to include randomised and quasi randomised controlled trials irrespective of blinding in patients of any age or gender undergoing neurosurgery under general anaesthesia where cortical mapping was attempted to identify eloquent areas using either somatosensory evoked potentials (SSEPs), or direct cortical stimulation (DCS) triggered muscle motor evoked potentials (mMEPs), or both. We excluded patients from trials where the anaesthetic effects were evaluated during spinal cord surgery or where MEPs were recorded from modes other than direct cortical stimulation such as transcranial electrical stimulation (TcMEPs), MEPs derived from epidural electrodes (D waves) and magnetic stimulation and trials involving awake craniotomies or the asleep-awake-asleep technique during cortical mapping. DATA COLLECTION AND ANALYSIS: Two review authors planned to independently apply the inclusion criteria and extract data. MAIN RESULTS: No RCTs were found for this study population. AUTHORS' CONCLUSIONS: This review highlights the need for well-designed randomised controlled trials to assess the effect of anaesthetic agents on cortical mapping during neurosurgical procedures involving eloquent areas of the brain.

Sensory monitoring of prehension in the parietal lobe: a study using digital video.

Digital video provides technological tools for monitoring hand kinematics during prehension, and for correlating motor behavior with the simultaneously recorded firing patterns of neurons in parietal cortex of monkeys. The constancy of the hand action in the task allowed us to derive population responses of neurons in both S-I and posterior parietal cortex (PPC) from serial single unit recordings. Activity of PPC neurons preceded that in S-I, and was often shape-selective for particular objects, suggesting that they play an important role in motor planning of prehension. Detailed sensory monitoring of hand-object interactions occurred in S-I, where distinct groups of neurons responded to specific behaviors such as grasping, lifting, holding or releasing objects.

Awake craniotomy and electrophysiological mapping for eloquent area tumours.

OBJECTIVE: An awake craniotomy facilitates radical excision of eloquent area gliomas and ensures neural integrity during the excision. The study describes our experience with 67 consecutive awake craniotomies for the excision of such tumours. METHODS: Sixty-seven patients with gliomas in or adjacent to eloquent areas were included in this study. The patient was awake during the procedure and intraoperative cortical and white matter stimulation was performed to safely maximize the extent of surgical resection. RESULTS: Of the 883 patients who underwent craniotomies for supratentorial intraaxial tumours during the study period, 84 were chosen for an awake craniotomy. Sixty-seven with a histological diagnosis of glioma were included in this study. There were 55 men and 12 women with a median age of 34.6 years. Forty-two (62.6%) patients had positive localization on cortical stimulation. In 6 (8.9%) patients white matter stimulation was positive, five of whom had responses at the end of a radical excision. In 3 patients who developed a neurological deficit during tumour removal, white matter stimulation was negative and cessation of the surgery did not result in neurological improvement. Sixteen patients (24.6%) had intraoperative neurological deficits at the time of wound closure, 9 (13.4%) of whom had persistent mild neurological deficits at discharge, while the remaining 7 improved to normal. At a mean follow-up of 40.8 months, only 4 (5.9%) of these 9 patients had persistent neurological deficits. CONCLUSION: Awake craniotomy for excision of eloquent area gliomas enable accurate mapping of motor and language areas as well as continuous neurological monitoring during tumour removal. Furthermore, positive responses on white matter stimulation indicate close proximity of eloquent cortex and projection fibres. This should alert the surgeon to the possibility of postoperative deficits to change the surgical strategy. Thus the surgeon can resect tumour safely, with the knowledge that he has not damaged neurological function up to that point in time thus maximizing the tumour resection and minimizing neurological deficits.

Outcomes of disconnective surgery in intractable pediatric hemispheric and subhemispheric epilepsy.

OBJECTIVES: To study the outcome of disconnective epilepsy surgery for intractable hemispheric and sub-hemispheric pediatric epilepsy. METHODS: A retrospective analysis of the epilepsy surgery database was done in all children (age <18 years) who underwent a peri-insular hemispherotomy (PIH) or a peri-insular posterior quadrantectomy (PIPQ) from April 2000 to March 2011. All patients underwent a detailed pre surgical evaluation. Seizure outcome was assessed by the Engel's classification and cognitive skills by appropriate measures of intelligence that were repeated annually. RESULTS: There were 34 patients in all. Epilepsy was due to Rasmussen's encephalitis (RE), Infantile hemiplegia seizure syndrome (IHSS), Hemimegalencephaly (HM), Sturge Weber syndrome (SWS) and due to post encephalitic sequelae (PES). Twenty seven (79.4%) patients underwent PIH and seven (20.6%) underwent PIPQ. The mean follow up was 30.5 months. At the last follow up, 31 (91.1%) were seizure free. The age of seizure onset and etiology of the disease causing epilepsy were predictors of a Class I seizure outcome. CONCLUSIONS: There is an excellent seizure outcome following disconnective epilepsy surgery for intractable hemispheric and subhemispheric pediatric epilepsy. An older age of seizure onset, RE, SWS and PES were good predictors of a Class I seizure outcome.

Factors predicting the feasibility of monitoring lower-limb muscle motor evoked potentials in patients undergoing excision of spinal cord tumors.

OBJECT: This prospective study on intraoperative muscle motor evoked potentials (MMEPs) from lower-limb muscles in patients undergoing surgery for spinal cord tumors was performed to: 1) determine preoperative clinical features that could predict successful recording of lower-limb MMEPs; 2) determine the muscle in the lower limb from which MMEPs could be most consistently obtained; 3) assess the need to monitor more than 1 muscle per limb; and 4) determine the effect of a successful baseline MMEP recording on early postoperative motor outcome. METHODS: Of 115 consecutive patients undergoing surgery for spinal cord tumors, 110 were included in this study (44 intramedullary and 66 intradural extramedullary tumors). Muscle MEPs were generated using transcranial electrical stimulation under controlled anesthesia and were recorded from the tibialis anterior, quadriceps, soleus, and external anal sphincter muscles bilaterally. The effect of age (≤ 20 or > 20 years old), location of the tumor (intramedullary or extramedullary), segmental location of the tumor (cervical, thoracic, or lumbar), duration of symptoms (≤ 12 or > 12 months), preoperative functional grade (Nurick Grades 0-3 or 4-5), and muscle power (Medical Research Council Grades 0/5-3/5 or 4/5-5/5) on the success rate of obtaining MMEPs was studied using multiple regression analysis. The effect of the ability to monitor MMEPs on motor outcome at discharge from the hospital was also analyzed. RESULTS: The overall success rate for obtaining baseline lower-limb MMEPs was 68.2% (75 of 110 patients). Eighty-nine percent of patients with Nurick Grades 0-3 had successful MMEP recordings. Muscle MEPs could not be obtained in any patient in whom muscle power was 2/5 or less, but were obtained from 91.4% of patients with muscle power of 4/5 or more. Analysis showed that only preoperative Nurick grade (p ≤ 0.0001) and muscle power (p < 0.0001) were significant predictors of the likelihood of obtaining MMEPs. Responses were most consistently obtained from the tibialis anterior muscle (68%), but in the other 32% MMEPs could not be recorded from the tibialis anterior but could be recorded from another muscle. The ability to monitor MMEPs was associated with better motor outcome at discharge from the hospital (p = 0.052). CONCLUSIONS: The likelihood of obtaining lower-limb MMEPs is significantly greater in patients with better functional grades and higher motor power. Muscle MEPs are most consistently obtained from the tibialis anterior muscle but other muscles should also be monitored to optimize the chances of obtaining MMEP responses from the lower limbs.

Neurophysiology of prehension. II. Response diversity in primary somatosensory (S-I) and motor (M-I) cortices.

Prehension responses of 76 neurons in primary somatosensory (S-I) and motor (M-I) cortices were analyzed in three macaques during performance of a grasp and lift task. Digital video recordings of hand kinematics synchronized to neuronal spike trains were compared with responses in posterior parietal areas 5 and AIP/7b (PPC) of the same monkeys during seven task stages: 1) approach, 2) contact, 3) grasp, 4) lift, 5) hold, 6) lower, and 7) relax. S-I and M-I firing patterns signaled particular hand actions, rather than overall task goals. S-I responses were more diverse than those in PPC, occurred later in time, and focused primarily on grasping. Sixty-three percent of S-I neurons fired at peak rates during contact and/or grasping. Lift, hold, and lowering excited fewer S-I cells. Only 8% of S-I cells fired at peak rates before contact, compared with 27% in PPC. M-I responses were also diverse, forming functional groups for hand preshaping, object acquisition, and grip force application. M-I activity began < or =500 ms before contact, coinciding with the earliest activity in PPC. Activation of specific muscle groups in the hand was paralleled by matching patterns of somatosensory feedback from S-I needed for efficient performance. These findings support hypotheses that predictive and planning components of prehension are represented in PPC and premotor cortex, whereas performance and feedback circuits dominate activity in M-I and S-I. Somatosensory feedback from the hand to S-I enables real-time adjustments of grasping by connections to M-I and updates future prehension plans through projections to PPC.

Neurophysiology of prehension. III. Representation of object features in posterior parietal cortex of the macaque monkey.

Neurons in posterior parietal cortex (PPC) may serve both proprioceptive and exteroceptive functions during prehension, signaling hand actions and object properties. To assess these roles, we used digital video recordings to analyze responses of 83 hand-manipulation neurons in area 5 as monkeys grasped and lifted objects that differed in shape (round and rectangular), size (large and small spheres), and location (identical rectangular blocks placed lateral and medial to the shoulder). The task contained seven stages -- approach, contact, grasp, lift, hold, lower, relax -- plus a pretrial interval. The four test objects evoked similar spike trains and mean rate profiles that rose significantly above baseline from approach through lift, with peak activity at contact. Although representation by the spike train of specific hand actions was stronger than distinctions between grasped objects, 34% of these neurons showed statistically significant effects of object properties or hand postures on firing rates. Somatosensory input from the hand played an important role as firing rates diverged most prominently on contact as grasp was secured. The small sphere -- grasped with the most flexed hand posture -- evoked the highest firing rates in 43% of the population. Twenty-one percent distinguished spheres that differed in size and weight, and 14% discriminated spheres from rectangular blocks. Location in the workspace modulated response amplitude as objects placed across the midline evoked higher firing rates than positions lateral to the shoulder. We conclude that area 5 neurons, like those in area AIP, integrate object features, hand actions, and grasp postures during prehension.

Neurophysiology of prehension. I. Posterior parietal cortex and object-oriented hand behaviors.

Hand manipulation neurons in areas 5 and 7b/anterior intraparietal area (AIP) of posterior parietal cortex were analyzed in three macaque monkeys during a trained prehension task. Digital video recordings of hand kinematics synchronized to neuronal spike trains were used to correlate firing rates of 128 neurons with hand actions as the animals grasped and lifted rectangular and round objects. We distinguished seven task stages: approach, contact, grasp, lift, hold, lower, and relax. Posterior parietal cortex (PPC) firing rates were highest during object acquisition; 88% of task-related area 5 neurons and 77% in AIP/7b fired maximally during stages 1, 2, or 3. Firing rates rose 200-500 ms before contact, peaked at contact, and declined after grasp was secured. 83% of area 5 neurons and 72% in AIP/7b showed significant increases in mean rates during approach as the fingers were preshaped for grasp. Somatosensory signals at contact provided feedback concerning the accuracy of reach and helped guide the hand to grasp sites. In error trials, tactile information was used to abort grasp, or to initiate corrective actions to achieve task goals. Firing rates declined as lift began. 41% of area 5 neurons and 38% in AIP/7b were inhibited during holding, and returned to baseline when grasp was relaxed. Anatomical connections suggest that area 5 provides somesthetic information to circuits linking AIP/7b to frontal motor areas involved in grasping. Area 5 may also participate in sensorimotor transformations coordinating reach and grasp behaviors and provide on-line feedback needed for goal-directed hand movements.

Intraoperative mapping of sacral nervous system (S2-4).

Electrophysiological mapping of the sacral nervous system was used during operations on 80 patients with conus and cauda equina lesions. At surgery, under controlled muscle relaxation, the sacral neural elements (S2-4) were mapped using direct mono-polar stimulation and recording of compound muscle action potentials (CMAPs) from the external anal sphincter (EAS). Responses were obtained in 86.25% (69/80) of the patients. In 33 (82.5%) out of 40 patients with preoperative deficits involving the S2-4 segments, CMAPs could be elicited. Identification of nerve roots was useful in dissection of lipomyelomeningocoeles, tumour excisions and untethering of filum terminale. In three patients, stimulation of the filum terminale elicited motor responses and, hence, it was not sectioned. Intraoperative mapping of the S2-4 nerve roots under controlled muscle relaxation is feasible in a majority of patients, including those with deficits involving S2-4. This method was useful in sparing viable nerve roots during surgery in conus and cauda equina regions, and identification of 'functional' filum terminale.