Motor evoked potentials (MEPs) in lacunar syndromes

Functional Mechanisms of Recovery after Chronic Stroke: Modeling with the Virtual Brain

We have seen important strides in our understanding of mechanisms underlying stroke recovery, yet effective translational links between basic and applied sciences, as well as from big data to individualized therapies, are needed to truly develop a cure for stroke. We present such an approach using The Virtual Brain (TVB), a neuroinformatics platform that uses empirical neuroimaging data to create dynamic models of an individual’s human brain; specifically, we simulate fMRI signals by modeling parameters associated with brain dynamics after stroke.

In 20 individuals with stroke and 11 controls, we obtained rest fMRI, T1w, and diffusion tensor imaging (DTI) data. Motor performance was assessed pre-therapy, post-therapy, and 6–12 months post-therapy. Based on individual structural connectomes derived from DTI, the following steps were performed in the TVB platform: (1) optimization of local and global parameters (conduction velocity, global coupling); (2) simulation of BOLD signal using optimized parameter values; (3) validation of simulated time series by comparing frequency, amplitude, and phase of the simulated signal with empirical time series; and (4) multivariate linear regression of model parameters with clinical phenotype. Compared with controls, individuals with stroke demonstrated a consistent reduction in conduction velocity, increased local dynamics, and reduced local inhibitory coupling. A negative relationship between local excitation and motor recovery, and a positive correlation between local dynamics and motor recovery were seen.

TVB reveals a disrupted post-stroke system favoring excitation-over-inhibition and local-over-global dynamics, consistent with existing mammal literature on stroke mechanisms. Our results point to the potential of TVB to determine individualized biomarkers of stroke recovery.

[Effects of electro-acupuncture at Shuigou (DU26) point on motor evoked potential in rats with cerebral infarction]

OBJECTIVE

To investigate the effects of electro-acupuncture at Shuigou (DU26) on latency and amplitude of motor evoked potential (MEP) in rats after cerebral infarction.

METHODS

Fifty healthy male Wistar rats were randomly divided into five groups as normal group, untreated group, sham-operated group, non-acupoint group and Shuigou group, with 10 rats in each group. By using a modification of the technique of middle cerebral artery occlusion, focal cerebral ischemia injury was induced in rats except normal and sham-operated groups. Rats in the normal group received no treatment. Rats in the sham-operated group underwent identical experimental procedures as the other groups, except that the nylon suture was inserted into the internal carotid artery. After the behavioral deficit was evaluated by using Zausinger 6-point neurological function score, rats in the Shuigou group and non-acupoint group were separately acupunctured and stimulated by continuous-wave with 2 Hz frequency, 1 mA intensity, for 10 minutes, twice a day for 3 days. Non-acupoint was located at the left side 0.5 cm of the Shuigou point. No intervention was given to the other groups. Zausinger 6-point neurological function and MEP were measured after 72-hour treatment.

RESULTS

The latency at the affected side in the untreated group was significantly longer than that in the normal group (P<0.05), and the amplitude at the affected side was significantly reduced (P<0.01). After 3-day electro-acupuncture, the latency at the affected side of rats in the Shuigou group was obviously shortened as compared with the untreated group (P<0.05), and the amplitude was significantly increased (P<0.05). The latency at the affected side in the Shuigou group was shorter than that in the non-acupoint group (P<0.05), and the amplitude tended to increase as compared with the non-acupoint group, but there were no significant differences (P>0.05). There were no significant differences on the latency and amplitude between the untreated group and non-acupoint group (P>0.05). The neurobehavioral score of the Shuigou group was significantly higher than those of the untreated group and non-acupoint group (P<0.05), and there were no significant differences between the untreated group and non-acupoint group (P>0.05).

CONCLUSION

Electro-acupuncture at Shuigou can increase the latency and amplitude of MEP in rats after cerebral infarction.

Arm function after stroke: Neurophysiological correlates and recovery mechanisms assessed by transcranial magnetic stimulation

Transcranial Magnetic Stimulation has been used for over 20 years to investigate recovery of motor function in stroke patients. In particular, it has been used to quantify the extent of damage to the corticospinal output, reorganisation of the cortical representation of the affected body parts and excitability of intracortical and cortico-cortical circuitries in both hemispheres. In this review, we provide a detailed account of most of the published data with particular reference to methodological issues that affect their interpretation.

Transcranial Motor Evoked Potential Recording in a Case of Kernohan's Notch Syndrome: Case Report

OBJECTIVE AND IMPORTANCE

Compression of the cerebral peduncle against the tentorial incisura contralateral to a supratentorial mass lesion, the so-called Kernohan-Woltman notch phenomenon, can be an important cause of false localizing motor signs. Here, we demonstrate a case in which clinical, radiological, and electrophysiological findings were used together to define this syndrome.

CLINICAL PRESENTATION

A 21-year-old man sustained a left temporal depressed cranial fracture from a motor vehicle accident. Serial computed tomographic examinations demonstrated no evolution of hematomas or contusions, and he was managed nonsurgically with ventriculostomy for intracranial pressure control. Throughout his course in the neurosurgical intensive care unit, he displayed persistent left hemiparesis.

INTERVENTION

Further radiological and electrophysiological studies were undertaken in an attempt to explain his left hemiparesis. Brain magnetic resonance imaging demonstrated T2 prolongation in the central portion of the right cerebral peduncle extending to the right internal capsule. Electrophysiological studies using transcranial electrical motor evoked potentials revealed both a marked increase in voltage threshold, as well as a reduction in the complexity of the motor evoked potential waveform on the hemiparetic left side. This contrasted to significantly lower voltage threshold as well as a highly complex motor evoked potential waveform recorded on the relatively intact contralateral side.

CONCLUSION

This is the first time that clinical, radiological, and electrophysiological findings have been correlated in a case of Kernohan's notch syndrome. Compression of the contralateral cerebral peduncle against the tentorial incisura can lead to damage and ipsilateral hemiparesis. The anatomic extent of the lesion can be defined by magnetic resonance imaging and the physiological extent by electrophysiological techniques.

Motor recovery following stroke: a transcranial magnetic stimulation study

OBJECTIVES

To verify the usefulness of early recording of motor evoked potentials (MEPs) in predicting motor outcome after stroke and to investigate the neural mechanisms underlying functional recovery following stroke.

METHODS

We performed a comparative analysis of the behaviour of motor responses evoked by transcranial magnetic stimulation (TMS) of the ipsilateral and contralateral motor cortex in the affected and unaffected thenar muscles of 21 consecutive patients with acute stroke.

RESULTS

According to the behaviour of MEPs in the affected muscles, patients could be divided into 3 groups: (a) 10 subjects with absent responses to TMS of both the damaged and undamaged hemisphere, whose motor recovery was poor and related to the size of MEPs on the normal side; (b) 5 subjects with larger MEPs upon TMS of the ipsilateral (undamaged) than of the contralateral (damaged) cortex, whose good recovery possibly resulted from the emergence of ipsilateral pathways; (c) 6 subjects with larger MEPs in the affected than in the unaffected muscles, whose good recovery was possibly subserved by alternative circuits taking over cortical deafferentation.

CONCLUSIONS

Early MEP recording in acute stroke provides useful information on the clinical prognosis and the different mechanisms of motor recovery.

Magnetic evoked potentials in neurocritical care patients with acute brainstem lesions

OBJECTIVES

Motor evoked potentials (MEPs) are widely used in various neurological diseases, but have not been systematically employed in neurocritical care patients. We evaluated the clinical and predictive value of MEPs by magnetic transcranial stimulation in intensive care patients with acute brainstem lesions of predominantly vascular origin.

METHODS

In a prospective trial, a total of 30 patients with acute brainstem lesions were studied. Diagnoses were brainstem infarction (n=15), brainstem hemorrhage (n=3), encephalitis (n=1), basilar artery aneurysm (n=1), and space-occupying cerebellar infarct (n=5), cerebellar hemorrhage (n=3), and brainstem contusion (n=2). We performed MEP tests by transcranial stimulation to the abductor pollicis brevis bilaterally, bilateral somatosensory (SEPs) and auditory evoked (BAEPs) potentials. We determined motor function at the time of electrophysiological testing and after 3 months, the presence of radiologically confirmed lesions, and clinical outcome after 3 months. At the time of MEP recordings, ten patients were comatose, twelve stuporous, seven somnolent and one awake.

RESULTS

MEPs were present bilaterally in seventeen, absent unilaterally in eight and bilateral absent in five patients. Absent MEP highly correlated with the presence of persisting motor deficit 3 months later (P<0.0001). Absent MEPs predicted motor deficit after 3 months with a high specificity and more precisely than the clinical examination at the time of MEP testing. MEP findings correlated with the presence of radiologically confirmed lesions within the brainstem (P<0.0001). Combined with SEP and BAEP data, MEPs predicted the presence of unilateral brainstem lesions with high accuracy.

CONCLUSIONS

MEP recordings can be safely performed in neurointensive care patients and yield utilizable results. In patients with brainstem lesions, MEPs correlate with radiological findings and predict final motor function more accurately than clinical findings. MEPs are a reliable diagnostic tool for assessing motor function in otherwise unresponsive patients.

Effects of spontaneous recanalization on functional and electrophysiological recovery in acute ischemic stroke

BACKGROUND AND PURPOSE

Transcranial Doppler ultrasound (TCD) studies have shown that spontaneous recanalization results in a better clinical improvement after the onset of stroke. However, its effect on electrophysiological recovery is still unknown. The aim of this study was to determine the effects of spontaneous recanalization on the change in central motor conduction time (CMCT) in acute ischemic stroke.

METHODS

Seventeen healthy subjects and 38 consecutive patients with a first acute ischemic stroke involving the middle cerebral artery territory were included. TCD was used to detect spontaneous recanalization. Transcranial magnetic stimulation was used to determine the change in CMCT on days 1 and 14. Improvement of the CMCT at day 14 was indicated if it decreased in comparison with previous data recorded at day 1 or when a nonrecordable motor response at day 1 reappeared at day 14. No CMCT improvement was indicated when there was no recordable motor response at day 1 and day 14 or the CMCT at day 14 worsened, becoming absent or more delayed. The Pearson chi(2) test was used to assess the statistical significance of the results in this study.

RESULTS

Spontaneous recanalization was observed in 62% of the patients: 24% before 24 hours and 38% after this period. No recanalization was observed in 14 patients. The CMCT improved in 87% of the patients who had recanalized before 24 hours and 62% in the recanalized after 24 hours group (P=0.005). In contrast, CMCT improved in only 17% of the patients in the non-recanalized group

CONCLUSIONS

These data show that spontaneous recanalization results in a better recovery of the central motor pathway leading to a better CMCT improvement in acute ischemic stroke.

Correlation between functional and electrophysiological recovery in acute ischemic stroke

BACKGROUND AND PURPOSE

There is still controversy about the prognostic value of motor evoked potentials (MEPs) in the assessment of hemiplegia. The aims of this study are to determine the relationship between functional and electrophysiological recovery and thus the value of MEP as a prognostic indicator of clinical outcome in acute ischemic stroke.

METHODS

Seventeen healthy subjects and 38 stroke patients were included in this study. Functional recovery was assessed with the Modified Canadian Neurological Scale (MCNS), the Barthel Activities of Daily Living Index (BI), and the Rankin scale. Transcranial magnetic stimulation was used to determine the change in central motor conduction time (CMCT). Stroke outcome was assessed at the end of 2 weeks. One-way ANOVA with post hoc comparisons using the Scheffé procedure as well as t tests were used to assess the significance of the results in this study.

RESULTS

Unpaired t test showed significantly higher mean scores of the MCNS (2P=0.001), BI (2P=0.002), and Rankin scale (P<0.001) at day 14 in the group of patients with recordable MEP at day 1. A better clinical improvement with a higher mean score of the MCNS (2P<0.001), BI (2P<0.001), and the Rankin scale (2P<0.001) was also observed in the patients in whom the CMCT improved.

CONCLUSIONS

These data show that there is a close relationship between clinical and electrophysiological improvement and that MEP is a useful prognostic indicator of clinical outcome.

Isolated dysarthria due to extracerebellar lacunar stroke: a central monoparesis of the tongue

OBJECTIVES

The pathophysiology of dysarthria can preferentially be studied in patients with the rare lacunar stroke syndrome of "isolated dysarthria".

METHODS

A single study was carried out on seven consecutive patients with sudden onset of isolated dysarthria due to single ischaemic lesion. The localisation of the lesion was identified using MRI. The corticolingual, cortico-orofacial, and corticospinal tract functions were investigated using transcranial magnetic stimulation. Corticopontocerebellar tract function was assessed using 99mTc hexamethylpropylene amine oxime-single photon emission computerised tomography (HMPAO-SPECT) in six patients. Sensory functions were evaluated clinically and by somatosensory evoked potentials.

RESULTS

Brain MRI showed the lesions to be located in the corona radiata (n=4) and the internal capsule (n=2). No morphological lesion was identified in one patient. Corticolingual tract function was impaired in all patients. In four patients with additional cortico-orofacial tract dysfunction, dysarthria did not differ from that in patients with isolated corticolingual tract dysfunction. Corticospinal tract functions were normal in all patients. HMPAO-SPECT showed no cerebellar diaschisis, suggesting unimpaired corticopontocerebellar tract function. Sensory functions were not affected.

CONCLUSION

Interruption of the corticolingual pathways to the tongue is crucial in the pathogenesis of isolated dysarthria after extracerebellar lacunar stroke.

Physiological studies of the corticomotor projection to the hand after subcortical stroke

OBJECTIVE

The mechanisms which lead to recovery of motor function after a stroke are poorly understood. Functional reorganization of cortical motor centres is thought to be one of the factors which may contribute to recovery. We have investigated the extent of reorganization which occurs at the level of the primary motor cortex after a lesion of the corticospinal pathway.

METHODS

Transcranial magnetic stimulation was used to map the topography of the primary corticomotor projection to the abductor pollicis brevis muscle and study changes in cortical motor thresholds and corticospinal conduction in a group of 20 subjects with subcortical infarcts of varying duration (1 week to 15 years) and varying degrees of motor deficit.

RESULTS

There was a broad correlation between motor evoked potential (MEP) amplitude and motor thresholds on the one hand and the severity of motor deficit and site and extent of the lesion on the other. Shifts in the cortical motor maps were found in both early and late cases, irrespective of the site of the lesion, but were more frequent in the longer standing cases. Shifts were usually along the mediolateral axis but anteroposterior shifts were found in some late cases.

CONCLUSION

Our findings indicate that there is functional reorganization of the corticomotor projection in subjects who regain a degree of motor control following a subcortical lesion sparing the motor cortex.

The effect of benzodiazepines and flumazenil on motor cortical excitability in the human brain

In the present study, the effects of benzodiazepines (diazepam) were evaluated in terms of cortical excitability changes, as tested with transcranial magnetic simulation (TMS). In particular, analyzed were drug-induced changes regarding two selected parameters of TMS: (1) the cortical excitability threshold and (2) the silent period duration (SP). For this purpose, we evaluated the effects of long-term therapy with diazepam in the patients affected by anxiety disorders and the changes induced by single oral doses of diazepam in both healthy controls and patients. In addition, we tested cortical excitability changes in two 'extreme conditions' where a considerable concentration of serum benzodiazepine-like activity was reached, as represented by diazepam overdose and idiopathic recurrent stupor (IRS). In both groups of patients, a significant increment of motor threshold was found, while in the overdose patients, the SP was also increased. The administration of flumazenil in these two conditions was followed by a prompt reversal effect, consisting of a return to normal cortical excitability parameters. The long-term usage of diazepam in patients with anxiety disorders is associated with significantly increased threshold; the increased value of these parameters was temporarily further enhanced by the administration of a single oral dose of diazepam, which, in normal control subjects, is not associated with changes of cortical excitability. The results of this study reveal that different physio-pathological conditions induced by the influence of benzodiazepine and its antagonist are reflected in excitability changes which attest to the involvement and modification of cortical GABAergic activity.

Preserved motor evoked potentials fail to predict functional outcome in quadriplegia because of bilateral lesions of the supplementary motor areas: a brief report

We present a patient with a lesion of the mesial frontal cortex, including the supplementary motor areas bilaterally, who on clinical examination revealed no spontaneous movements, although neurophysiological examination indicated integrity of the corticospinal tract to thenar and tibialis anterior muscles bilaterally. The patient was alert, speech was hesitant, and he was able to move his hands only on command. The role of the supplementary motor areas in planning, setting, and execution of skillful voluntary movements has been previously established by direct cortical electrical stimulation and studies of regional cerebral blood flow. The findings in our patient support the role of the supplementary motor areas in initiating movements. The presence of motor evoked potentials after acute insults to the brain is considered to be associated with a good functional outcome. This is in contrast to our patient who did not show improvement in motor performance, despite preserved motor evoked potentials. Hence, in the case of bilateral lesions to the supplementary motor areas sparing the corticospinal tract, the presence of motor evoked potentials may not predict functional recovery.

Clinical applications of motor evoked potentials

Magnetic stimulation of brain and spinal roots provides a non-invasive evaluation of nervous propagation as well as of motor cortex excitability in healthy subjects and in patients affected by neurological diseases (i.e. multiple sclerosis, stroke, Parkinson's disease, myelopathies etc.). Motor areas can be reliably mapped and short- and long-term 'plastic' changes of neural connections can be studied and monitored over time. By evaluating excitatory and inhibitory phenomena following transcranial stimuli, the mechanisms of action of different drugs, including antiepileptics, can be studied. Moreover, transcranial stimulation of non-motor brain areas represents a probe for the evaluation of lateralized hemispheric properties connected with higher cortical functions. Recent studies suggest a therapeutic role of repetitive magnetic stimulation in psychiatric disorders.

[Alterations of various parameters of evoked motor potentials in amyotrophic lateral sclerosis]

To assess their interest, we studied different motor evoked potentials (MEP) parameters in 18 amyotrophic lateral sclerosis (ALS) patients and compared them to those obtained in 20 subjects unaffected by neurological diseases: cortical threshold (CT), latency and amplitude of primary responses (PR), central conduction time (CCT), silent period (SP) contralateral to the stimulated cortex and late muscular responses (LMR). In normal subjects MEP parameters were in agreement with those described in the literature, except for LMR. These were only recorded in upper limbs with latencies around 200 ms in 9 out of 20 subjects. In ALS patients, LMR were not modified as compared to normal subjects. Except for mean CCT, in upper and lower limbs, all parameters were altered. We conclude that all MEP parameters are useful in ALS and disclose the involvement of the entire pyramidal tract in this disease.

Contralateral and ipsilateral EMG responses to transcranial magnetic stimulation during recovery of arm and hand function after stroke

We examined the relationship between the recovery of hand and arm function in a group of hemiplegic stroke patients and the presence of short-latency EMG responses to transcranial magnetic stimulation (TMS) in 4 different upper limb muscles (deltoid, biceps, extensor digitorum communis and the first dorsal interosseous). Twenty-one patients were examined within 5 weeks of stroke (median 2 weeks), and then at regular intervals over the next 12 months. Some patients recovered rapidly (Group A); in others, recovery was slow and incomplete (Group B). Even at the first test, Group A patients had responses to TMS in all muscles. Most Group B patients initially lacked responses in all tested upper limb muscles; in those that later were able to activate hand muscles, responses returned at or just before this stage of recovery. No such clear correlation between the presence of responses to TMS and ability to activate more proximal arm muscles was evident. Response latency was initially long and declined in a manner that was highly correlated with muscle strength and hand function test scores. Ipsilateral responses were elicited from both the affected and unaffected hemispheres. Ipsilateral responses from the latter were most common in the proximal muscles of the affected limb, and had latencies that were longer than those elicited in the contralateral (unaffected) arm. Nine cases of ipsilateral responses in hand muscles were found; such responses are not found in healthy subjects. Ipsilateral responses from the undamaged hemisphere were more prevalent in the poorly recovered patients; the underlying mechanisms may not be beneficial for recovery.

Prognostic value of transcranial magnetic stimulation in acute stroke

BACKGROUND AND PURPOSE

The aim of this study is to evaluate the role of motor-evoked potentials (MEPs) in predicting functional recovery of hemiparesis and hemiplegia in acute stroke patients.

METHODS

Twenty-seven acute stroke patients were evaluated clinically and electrophysiologically within the first week and 3 to 6 months after the event. Clinical assessment included a quantitative evaluation of motor ability and activities of daily living. MEPs were recorded from the abductor pollicis brevis and tibialis anterior muscles bilaterally. Correlations between clinical parameters and MEPs were assessed.

RESULTS

In the acute period, no MEP could be detected in 17 of 27 patients. In these 17 patients, the clinical scores were worse than in the patients whose MEPs could be elicited. However, in the follow-up period (3 to 6 months), no significant differences in motor function were observed between the two groups.

CONCLUSIONS

In the acute phase of stroke, neurophysiological parameters were correlated with the clinical findings, but MEPs had no value in predicting the outcome of hemiparesis and hemiplegia.