The hypoglossal nerve (CN XII) may be placed at risk during posterior fossa surgeries. The use of intraoperative monitoring (IOM), including the utilization of spontaneous and triggered electromyography (EMG), from tongue muscles innervated by CN XII has been used to reduce these risks. However, there were few reports regarding the intraoperative transcranial motor evoked potential (MEP) of hypoglossal nerve from the tongue muscles. For this reason, we report here two cases of intraoperative hypoglossal MEP monitoring in brain surgery as an indicator of hypoglossal deficits. Although the amplitude of the MEP was reduced in both patients, only in the case 1 whose MEP was disappeared demonstrated the neurological deficits of the hypoglossal nerve. Therefore, the disappearance of the hypoglossal MEP recorded from the tongue, could be considered a predictor of the postoperative hypoglossal nerve deficits.
Citations
To identify which combination of motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) is most reliable for postoperative motor deterioration during spinal cord tumor surgery, according to anatomical and pathologic type.
MEPs and SEPs were monitored in patients who underwent spinal cord tumor surgery between November 2012 and August 2016. Muscle strength was examined in all patients before surgery, within 48 hours postoperatively and 4 weeks later. We analyzed sensitivity, specificity, positive and negative predictive values of each significant change in SEPs and MEPs.
The overall sensitivity and specificity of SEPs or MEPs were 100% and 61.3%, respectively. The intraoperative MEP monitoring alone showed both higher sensitivity (67.9%) and specificity (83.2%) than SEP monitoring alone for postoperative motor deterioration. Two patients with persistent motor deterioration had significant changes only in SEPs. There are no significant differences in reliabilities between anatomical types, except with hemangioma, where SEPs were more specific than MEPs for postoperative motor deterioration. Both overall positive and negative predictive values of MEPs were higher than the predictive values of SEPs. However, the positive predictive value was higher by the dual monitoring of MEPs and SEPs, compared to MEPs alone.
For spinal cord tumor surgery, combined MEP and SEP monitoring showed the highest sensitivity for the postoperative motor deterioration. Although MEPs are more specific than SEPs in most types of spinal cord tumor surgery, SEPs should still be monitored, especially in hemangioma surgery.
Citations
To investigate the relationship between motor evoked potential (MEP) response and the severity of motor paralysis, evaluated according to the Korean disability evaluation system in patients with spinal cord injury (SCI).
We analyzed 192 lower limbs of 96 SCI patients. Lower limbs were classified according to their motor scores, as determined by the International Standards for Neurological Classification of Spinal Cord Injury: motor score <10 (group 1); ≥10 and <15 (group 2); ≥15 and <20 (group 3); and ≥20 (group 4). MEP responses were classified as ‘normal’, ‘delayed’ or ‘absent’, based on their onset latency, which was compared between the different motor score groups.
MEP responses and limb motor scores were highly correlated (p<0.001). There was a significant difference of MEP responses between the motor score groups (p<0.001). MEP response was markedly poorer in motor group 1 (limb motor score <10) than in the other three groups (p<0.0001). However, there were no differences between the three groups with motor scores of 10 or above.
Clinical utility of MEP as a complimentary tool to manual muscle tests could be limited to discriminating motor score groups with severe paralysis, i.e., single lower limb motor power grades of 0 or 1, and from grade 2, 3, and 4, or above, in the Korean disability evaluation system.
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To investigate the clinical significance of quantitative parameters in transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEP) which can be adopted to predict functional recovery of the upper limb in stroke patients in the early subacute phase.
One hundred thirteen patients (61 men, 52 women; mean age 57.8±12.2 years) who suffered faiarst-ever stroke were included in this study. All participants underwent TMS-induced MEP session to assess the corticospinal excitability of both hand motor cortices within 3 weeks after stroke onset. After the resting motor threshold (rMT) was assessed, five sweeps of MEP were performed, and the mean amplitude of the MEP was measured. Latency of MEP, volume of the MEP output curve, recruitment ratios, and intracortical inhibition and facilitation were also measured. Motor function was assessed using the Fugl-Meyer Assessment scale (FMA) within 3 weeks and at 3 months after stroke onset. Correlation analysis was performed between TMS-induced MEP derived measures and FMA scores.
In the MEP response group, rMT and rMT ratio measures within 3 weeks after stroke onset showed a significant negative correlation with the total and upper limb FMA scores at 3 months after stroke (p<0.001). Multiple regression analysis revealed that FMA score and rMT ratio, but not rMT within 3 weeks were independent prognostic factors for FMA scores at 3 months after stroke.
These results indicated that the quantitative parameter of TMS-induced MEP, especially rMT ratio in the early subacute phase, could be used as a parameter to predict motor function in patients with stroke.
Citations
To evaluate whether the combination of muscle motor evoked potentials (mMEPs) and somatosensory evoked potentials (SEPs) measured during spinal surgery can predict immediate and permanent postoperative motor deficits.
mMEP and SEP was monitored in patients undergoing spinal surgery between November 2012 and July 2014. mMEPs were elicited by a train of transcranial electrical stimulation over the motor cortex and recorded from the upper/lower limbs. SEPs were recorded by stimulating the tibial and median nerves.
Combined mMEP/SEP recording was successfully achieved in 190 operations. In 117 of these, mMEPs and SEPs were stable and 73 showed significant changes. In 20 cases, motor deficits in the first 48 postoperative hours were observed and 6 patients manifested permanent neurological deficits. The two potentials were monitored in a number of spinal surgeries. For surgery on spinal deformities, the sensitivity and specificity of combined mMEP/SEP monitoring were 100% and 92.4%, respectively. In the case of spinal cord tumor surgeries, sensitivity was only 50% but SEP changes were observed preceding permanent motor deficits in some cases.
Intraoperative monitoring is a useful tool in spinal surgery. For spinal deformity surgery, combined mMEP/SEP monitoring showed high sensitivity and specificity; in spinal tumor surgery, only SEP changes predicted permanent motor deficits. Therefore, mMEP, SEP, and joint monitoring may all be appropriate and beneficial for the intraoperative monitoring of spinal surgery.
Citations
To examine the association between motor evoked potentials (MEPs) in lower limbs and ambulatory outcomes of hemiplegic stroke patients.
Medical records of hemiplegic patients with the first ever stroke who received inpatient rehabilitation from January 2013 to May 2014 were reviewed. Patient who had diabetes, quadriplegia, bilateral lesion, brainstem lesion, severe musculoskeletal problem, and old age over 80 years were excluded. MEPs in lower limbs were measured when they were transferred to the Department of Rehabilitation Medicine. Subjects were categorized into three groups (normal, abnormal, and absent response) according to MEPs findings. Berg Balance Scale (BBS) and Functional Ambulation Category (FAC) at initial and discharge were compared among the three groups by one-way analysis of variance (ANOVA). Correlation was determined using a linear regression model.
Fifty-eight hemiplegic patients were included. BBS and FAC at discharge were significantly (ANOVA, p<0.001) different according to MEPs findings. In linear regression model of BBS and FAC using stepwise selection, patients' age (p<0.01), BBS at admission (p<0.01), and MEPs (p<0.01) remained significant covariates. In regression assumption model of BBS and FAC at admission, MEPs and gender were significant covariates.
Initial MEPs of lower limbs can prognosticate the ambulatory outcomes of hemiplegic patients.
Citations
To investigate the clinical significance of upper and lower extremity transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) in patients with parkinsonism.
Twenty patients (14 men, 6 women; mean age 70.5±9.1 years) suffering from parkinsonism were included in this study. All participants underwent single-pulse TMS session to assess the corticospinal excitability of the upper and lower extremity motor cortex. The resting motor threshold (RMT) was defined as the lowest stimulus intensity able to evoke MEPs of an at least 50 µV peak-to-peak amplitude in 5 of 10 consecutive trials. Five sweeps of MEPs at 120% of the RMT were performed, and the mean amplitude and latency of the MEPs were calculated. Patients were also assessed using the Unified Parkinson's Disease Rating Scale part III (UPDRS-III) and the 5-meter Timed Up and Go (5m-TUG) test.
There was a significant positive correlation between the RMTs of MEPs in the upper and lower extremities (r=0.612, p=0.004) and between the amplitude of MEPs in the upper and lower extremities (r=0.579, p=0.007). The RMT of upper extremity MEPs showed a significant negative relationship with the UPDRS-III score (r=–0.516, p=0.020). In addition, RMTs of lower extremity MEPs exhibited a negative relationship with the UPDRS-III score, but the association was not statistically significant (r=–406, p=0.075).
These results indicated that the RMT of MEPs reflect the severity of motor dysfunction in patients with parkinsonism. MEP is a potential quantitative, electrodiagnostic method to assess motor function in patients with parkinsonism.
Citations
To compare diffusion tensor tractography (DTT) and motor evoked potentials (MEPs) for estimation of clinical status in patients in the subacute stage of stroke.
Patients with hemiplegia due to stroke who were evaluated using both DTT and MEPs between May 2012 and April 2015 were recruited. Clinical assessments investigated upper extremity motor and functional status. Motor status was evaluated using Medical Research Council grading and the Fugl-Meyer Assessment of upper limb and hand (FMA-U and FMA-H). Functional status was measured using the Modified Barthel Index (MBI). Patients were classified into subgroups according to DTT findings, MEP presence, fractional anisotropy (FA) value, FA ratio (rFA), and central motor conduction time (CMCT). Correlations of clinical assessments with DTT parameters and MEPs were estimated.
Fifty-five patients with hemiplegia were recruited. In motor assessments (FMA-U), MEPs had the highest sensitivity and negative predictive value (NPV) as well as the second highest specificity and positive predictive value (PPV). CMCT showed the highest specificity and PPV. Regarding functional status (MBI), FA showed the highest sensitivity and NPV, whereas CMCT had the highest specificity and PPV. Correlation analysis showed that the resting motor threshold (RMT) ratio was strongly associated with motor status of the upper limb, and MEP parameters were not associated with MBI.
DTT and MEPs could be suitable complementary modalities for analyzing the motor and functional status of patients in the subacute stage of stroke. The RMT ratio was strongly correlated with motor status.
Citations
To determine the predictability of motor evoked potentials (MEP) in patients with putaminal hemorrhage (PH) according to the time of MEP from the onset of stroke.
Sixty consecutive patients with PH from January 2006 to November 2013 were retrospectively reviewed. Motor function of affected extremities was measured at onset time and at six months after the onset. Patients were classified into two groups according to the time of MEP from the onset of stroke: early MEP group (within 15 days from onset) and late MEP group (16-30 days from onset). Patients were also classified into two groups according to the presence of MEP on the affected abductor pollicis brevis (APB): MEP (+) group-patients (showing MEP in the affected APB) and MEP (-) group-patients (no MEP in the affected APB). Motor outcome was compared between the two early and late MEP groups or between the presence and absence of MEP in the affected APB groups.
For patients with MEP (+), a larger portion in the late MEP group showed good prognosis compared to the early MEP group (late MEP, 94.4%; early MEP, 80%). In contrast, in patients with MEP (-), a larger portion of patients in the late MEP group showed bad prognosis compared to the early MEP group (late MEP, 80%; early MEP, 71.4%). No significant improvement of MI between MEP (+) and MEP (-) was observed when MEP was performed early or late.
Our results revealed that the predictability of motor outcome might be better if MEP is performed late compared to that when MEP is performed early in patients with PH.
Citations
To investigate whether motor evoked potential (MEP) amplitude ratio measurements are sufficiently objective to assess functional activities of the extremities. We also delineated the distribution between the presence or absence of MEPs and the Medical Research Council (MRC) scale for muscle strength of the extremities.
We enrolled 183 patients with first-ever unilateral hemiplegia after stroke. The MEP parameters were amplitude ratio (amplitude of affected side/amplitude of unaffected side) recorded at the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles. We performed frequency analyses using the MRC scale for muscle strength and the presence or absence of evoked MEPs. Change on the MRC scale, hand function tests (HFTs), and the Modified Barthel Index (MBI) subscore were compared between the evoked MEP and absent MEP groups using the independent t-test. Receiver operating characteristic curves were used to determine the optimal cutoff scores for the MEP amplitude ratio using the HFT results and MBI subscores. Correlations between the MEP amplitude ratio and the MRC scale, HFTs, and MBI subscore were analyzed.
About 10% of patients with MRC scale grades 0-2 showed evoked MEPs at the FDI muscle, and 4% of patients with MRC scale grades 3-5 did not show MEPs. About 18% of patients with MRC scale grades 0-2 showed evoked MEPs at the TA muscle, and 4% of patients with MRC scale grades 3-5 did not show MEPs. MEP amplitude increased with increasing MRC scale grade. The evoked MEP group had more significant changes on the MRC scale, HFT, and the climbing stair score on the MBI than those in the group without MEPs. Larger MEP amplitude ratios were observed in patients who had more difficulty with the HFTs and ambulation. The MEP amplitude ratio was significantly correlated with the MRC scale, HFT, and MBI subscore.
We conclude that the MEP amplitude ratio may be useful to predict functional status of the extremities in patients who suffered stroke.
Citations
To investigate neuroradiological and neurophysiological characteristics of patients with dyskinetic cerebral palsy (CP), by using magnetic resonance imaging (MRI), voxel-based morphometry (VBM), diffusion tensor tractography (DTT), and motor evoked potential (MEP).
Twenty-three patients with dyskinetic CP (13 males, 10 females; mean age 34 years, range 16-50 years) were participated in this study. Functional evaluation was assessed by the Gross Motor Functional Classification System (GMFCS) and Barry-Albright Dystonia Scale (BADS). Brain imaging was performed on 3.0 Tesla MRI, and volume change of the grey matter was assessed using VBM. The corticospinal tract (CST) and superior longitudinal fasciculus (SLF) were analyzed by DTT. MEPs were recorded in the first dorsal interossei, the biceps brachii and the deltoid muscles.
Mean BADS was 16.4±5.0 in ambulatory group (GMFCS levels I, II, and III; n=11) and 21.3±3.9 in non-ambulatory group (GMFCS levels IV and V; n=12). Twelve patients showed normal MRI findings, and eleven patients showed abnormal MRI findings (grade I, n=5; grade II, n=2; grade III, n=4). About half of patients with dyskinetic CP showed putamen and thalamus lesions on MRI. Mean BADS was 20.3±5.7 in normal MRI group and 17.5±4.0 in abnormal MRI group. VBM showed reduced volume of the hippocampus and parahippocampal gyrus. In DTT, no abnormality was observed in CST, but not in SLF. In MEPs, most patients showed normal central motor conduction time.
These results support that extrapyramidal tract, related with basal ganglia circuitry, may be responsible for the pathophysiology of dyskinetic CP rather than CST abnormality.
Citations
To investigate the factors which affect the motor evoked potential (MEP) responsiveness and parameters and to find the correlation between the function of the upper extremities and the combined study of MEP with a diffusion tensor tractography (DTT) in patients with stroke.
A retrospective study design was used by analyzing medical records and neuroimaging data of 70 stroke patients who underwent a MEP test between June 2011 and March 2013. MEP parameters which were recorded from the abductor pollicis brevis muscle were the resting motor threshold, latency, amplitude, and their ratios. Functional variables, Brunnstrom stage of hand, upper extremity subscore of Fugl-Meyer assessment, Manual Function Test, and the Korean version of Modified Barthel Index (K-MBI) were collected together with the biographical and neurological data. The DTT parameters were fiber number, fractional anisotropy value and their ratios of affected corticospinal tract. The data were compared between two groups, built up according to the presence (MEP-P) or absence (MEP-N) of MEP on the affected hand.
Functional and DTT variables were significantly different between MEP-P and MEP-N groups (p<0.001). Among the MEP-P group, the amplitude ratio (unaffected/affected) was significantly correlated with the Brunnstrom stage of hand (r=-0.427, p=0.013), K-MBI (r=-0.380, p=0.029) and the time post-onset (r=-0.401, p=0.021). The functional scores were significantly better when both MEP response and DTT were present and decreased if one or both of the two studies were absent.
This study indicates MEP responsiveness and amplitude ratio are significantly associated with the upper extremity function and the activities of daily living performance, and the combined study of MEP and DTT provides useful information.
Citations
To investigate the predictive index of functional recovery after primary pontine hemorrhage (PPH) using the combined motor evoked potential (MEP) and somatosensory evoked potential (SEP) in comparison to the hematoma volume and transverse diameter measured with computerized tomography.
Patients (n=14) with PPH were divided into good- and poor-outcome groups according to the modified Rankin Score (mRS). We evaluated clinical manifestations, radiological characteristics, and the combined MEP and SEP responses. The summed MEP and SEP (EP sum) was compared to the hematoma volume and transverse diameter predictive index of global disability, gait ability, and trunk stability in sitting posture.
All measures of functional status and radiological parameters of the good-outcome group were significantly better than those of the poor-outcome group. The EP sum showed the highest value for the mRS and functional ambulatory category, and transverse diameter showed the highest value for "sitting-unsupported" of Berg Balance Scale.
The combined MEP and SEP is a reliable and useful tool for functional recovery after PPH.
Citations
To investigate the effectiveness of the daily living activity and motor evoked potential (MEP) in the subacute stroke patients.
Nineteen subjects with subacute ischaemic/hemorrhagic stroke developed in the last three months were enrolled, and MEP was measured with transcranial magnetic stimulation. Functional Independence Measure (FIM) score were evaluated in both groups before and 4 weeks after comprehensive rehabilitative management. According to the presence of MEP response in the affected hemisphere, subjects were divided into MEP positive and negative group.
There was no significant difference between the two groups in age, sex, and post-onset duration. Four weeks later, the change in total FIM and self-care score improved significantly in the MEP-positive group, when compared to the MEP-negative group (p<0.05). However, cognitive improvement had no relationship with MEP responsiveness.
We concluded that initial measurement of MEP is a useful assessment tool in predicting functional outcome of subacute stroke patients.
Citations
To evaluate and compare the organization of descending motor pathways to upper extremity muscles among healthy children.
The 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.
MEPs 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.
These results suggest that the proximal and distal muscles of the upper extremities show different maturation and organization patterns.
Citations
To evaluate the motor innervation of trunk muscles in traumatic brain injury patients.
Twenty 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.
The 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.
The 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.
Citations
Method: Thirty-six post-stroke hemiplegic patients with a lesion in the internal capsule were included in this study. Diffusion tensor imaging (DTI) was performed with a 3.0 tesla MR at about 1 month after stroke. FA ratio was measured in posterior limb of the internal capsule of the patients. Motor evoked potential (MEP) was obtained by magnetic stimulation of the motor cortex and recorded from the abductor pollicis muscle. Somatosensory evoked potential (SSEP) was obtained by electrical stimulation of the median nerve at the wrist and recorded from the somatosensory cortex. Hand movement scale was obtained at about 1 month and 3 months after stroke. Results: Hand movement scale at about 1 month and 3 months after stroke and FA ratio were reduced significantly in patients who showed no response on MEP. However, no significant differences were observed between the patients who showed SSEP response and those who did not. FA ratio and hand movement scale were highly correlated to each other. Conclusion: MEP and FA ratio can be helpful in assessing the hand function at about 1 month and 3 months in post-stroke hemiplegic patients. (J Korean Acad Rehab Med 2008; 32: 182-188)
Method: MEPs induced by cortical stimulation were obtained at both thenar muscles in 28 post-stroke patients. Motor cortex was stimulated with 110% and 130% intensity of threshold during rest, minimal and moderate voluntary muscle contraction. We analyzed the MEP amplitude or area in 130% threshold intensity at rest (Rmax) and on moderate contraction (Fmax). The ratio of Fmax in both hemispheres (interhemispheric facilitation ratio, FR) and the ratio of Fmax to Rmax (facilitation index, FI) were also analyzed. Pinch strength, Brunnstrom stage, and Jebsen hand function test were included evaluating their motor functions.
Results: MEPs could not be evoked in cases whose Brunnstrom stage of hand was under 3. In response group, amplitude and area of Fmax of unaffected side were significantly larger than those of affected side (p＜0.05). FR showed good correlation with clinical findings evaluating motor functions (p＜0.05). In cases of FR ＞ 0.5, FI of unaffected side was significantly greater than that of affected side (p＜0.05).
Conclusion: We suggest to use FR and FI as useful parameters for evaluation of hand function in post-stroke patients. (J Korean Acad Rehab Med 2003; 27: 314-319)
Objective: To determine the effects of the voluntary contraction of muscles and magnetic stimulation intensity on the motor evoked potential (MEP) and the silent period (SP).
Method: We studied MEPs and SPs in opponens pollicis muscle in 30 healthy adults (male: 16, female: 14) while varying the amount of the voluntary contraction and the stimulation intensity. We analyzed MEPs and SPs in relation to sex, recording site, opposition power and height.
Results: 1) During the contraction, the latencies of MEP were significantly shorter than during the relaxation. 2) The amplitudes of MEP reached plateau at 30% of maximal voluntary
contraction and increased with increment of stimulation intensity without limitation. The amplitudes of MEP of right hand were bigger than left hand. There were no significant differences according to sex and recording site. 3) The durations of SP were directly proportional to the degrees of voluntary contraction and the stimulation intensity.
Conclusion: Transcranial magnetic stimulation should be performed under the same voluntary contraction and magnetic stimulation intensity. (J Korean Acad Rehab Med 2002; 26: 140-146)
Objective: The purpose of this study is to evaluate the relationship between cognitive function and findings of evoked potential study in chronic renal failure patients.
Method: Thirty chronic renal failure patients with cognitive dysfunction were recruited, whose mini-mental state examination (MMSE) scores were less than 24 points. According to the underlying diseases of chronic renal failure, we categorized thirty patients into diabetic group (11 patients) and non-diabetic group (19 patients), and the control-group was composed of 15 normal volunteers. Somatosensory evoked potential (SEP) on stimulating median and posterior tibial nerves, and cortical and spinal conduction time of the motor pathways were valuated.
Results: In tibial nerve SEP, N22-P38 interpeak latencies (IPL) were 18.1⁑4.2 msec in the patient group and 15.7⁑1.9 msec in the control group, respectively. In MEP, cortico-lumbar central motor conduction times (CMCT) were 19.5⁑2.7 and 16.5⁑3.0 msec, respectively. CMCT were prolonged in patients than controls (p＜0.05). There was significant correlation between serum creatinine concentration and N22-P38 IPL (r=0.64, p＜0.05), but, there were no correlations between the underlying diseases of chronic renal failure, duration of disease, MMSE score and cortico-lumbar CMCT, N22-P38 IPL (p＞0.05).
Conclusion: Evoked potentials will be helpful in evaluating the patients with cognitive dysfunction in chronic renal failure.
Objective: The aim of this study is to identify the ipsilateral motor evoked potentials (iMEPs) from unaffected cerebral hemisphere after stroke via transcranial magnetic stimulation, especially in acute stage (within 1 week from attack), and to evaluate the characteristics of iMEPs compared with the crossed contralateral motor evoked potentials (cMEPs).
Method: Thirty patients were recruited, who had suffered their first ischemic stroke and consequent motor deficits and mean duration from attack to examination was 6.0⁑3.3 days. They were tested with round coil stimulator in order to record motor evoked potentials from both contralateral and ipsilateral abductor pollicis brevis (APB) muscles. For the purpose of hand motor cortex mapping, we designed specialized cap, which was marked using international 10∼20 systems by 1 cm interval. In addition, we observed the changes in onset latency and amplitude of MEPs during the isometric contraction of thenar muscle guided by visual and auditory feedback.
Results: iMEPs were generally absent in normal subjects, but they were obtained in 17 (56.7%) of 30 patients by stimulating the unaffected hemisphere. Different from contralateral MEPs, ipsilateral MEPs were obtained with higher stimulation intensity, significantly delayed latencies and lower amplitudes. And we noticed shorter latencies and larger amplitudes of MEPs by the isometric contraction of thenar muscle.
Conclusion: Our results will reflect the compensatory role by the unaffected cerebral hemisphere with respect to motor recovery, if contralateral route is damaged. We provided neurophysiologic evidences of cerebral neuroplasticity, proven by the ipsilateral unaffected hemispheric activation in early phase stroke patients.
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