Prognostic value of motor evoked potential obtained by transcranial magnetic brain stimulation in motor function recovery in patients with acute ischemic stroke

Motor outcome according to diffusion tensor tractography findings in the early stage of intracerebral hemorrhage

We tried to investigate the motor outcome according to diffusion tensor tractography (DTT) findings for the corticospinal tract (CST) in the early stage for hemiparetic patients with intracerebral hemorrhage (ICH). Forty patients with severe paralysis of the affected side were enrolled. DTT was obtained in the early stage of the stroke (7-30 days) and was classified into four groups: type A, the CST originating from primary motor cortex was preserved around the hematoma; type B, the CST was similar to type A except the fiber originated from the adjacent areas to the primary motor cortex; type C, the CST was interrupted at or around the hematoma; and type D, the CST did not reach the hematoma due to degeneration (Fig. 1). Six months after onset, motor function was measured and the statistical influence of the DTT type was tested. Initially, none of the motor function scales of the affected side differed among the four DTT types. Six months after the onset of ICH, motor functions of the same side were significantly different according to DTT type (p<0.05). All motor scales were highest in the DTT type A group, and were lowest in the DTT type D group (p<0.0003). The early DTT findings for CST may be used to predict the motor outcome of the affected extremities in hemiparetic patients with ICH.

Outcome prediction in acute monohemispheric stroke via magnetoencephalography

BACKGROUND

Following an ischemic stroke a highly variable clinical outcome is commonly evident despite similar onset symptoms as well as lesion characteristics. The aim of this study was to identify indexes providing early prediction of functional recovery, in addition to clinical severity and lesion dimension at onset of stroke.

METHODS

In 32 patients, magnetoencephalographic (MEG) parameters collected in the acute phase (<10 days from symptoms onset, T0) from affected (AH) and unaffected (UH) hemispheres at rest and evoked by sensory stimuli were evaluated in association with the clinical outcome in a stabilized phase (T1, median 7.8 months) classified with three levels: worsening, partial and full recovery.

RESULTS

Multiple multinomial logistic regression indicated AH gamma and UH delta band powers able to prognosticate clinical outcome at T1. After inclusion in this analysis, lesion volume had the strongest predictive ability, and UH delta band power remained as a predictive factor with a measurable cut-off, maximizing both sensitivity and specificity of the prediction: a patient with UH delta below cut-off would recover to some extent; a patient with UH delta above cut-off would have a probability of about 70% to worsen.

CONCLUSIONS

MEG UH delta and AH gamma band powers were found to provide useful information about long-term outcome prognosis. Only the increase of delta band activity in the unaffected hemisphere contains information about the outcome in addition to the lesion volume.

Functional Imaging of Intervention Effects in Stroke Motor Rehabilitation

OBJECTIVE

To assess intervention-specific effects on cortical reorganization after stroke as shown by available functional neuroimaging studies.

DATA SOURCES

We searched Medline for clinical trials that contained the terms stroke, reorganization, and recovery, as well as either positron-emission tomography and PET, near-infrared spectroscopy and NIRS, single-photon emission tomography and SPECT, or functional magnetic resonance imaging and functional MRI; we reviewed primary and secondary references.

STUDY SELECTION

Articles that reported neuroimaging findings as a result of a specific treatment involving more than 1 subject were included.

DATA EXTRACTION

We included clinical trials that contained the terms stroke, reorganization, and recovery, as well as functional neuroimaging data findings as a result of a specific treatment involving more than 1 subject.

DATA SYNTHESIS

Included studies differed clearly from one another with regard to patient characteristics, intervention protocol, and outcome measures. Most studies used functional magnetic resonance imaging and a motor paradigm. Studies were limited in size.

CONCLUSIONS

Despite the methodologic differences, several common features can be identified based on the reviewed studies. Clinical improvements occurred even late after injury, after subjects were deemed to have reached a recovery plateau. This clinical improvement was accompanied by cortical reorganization that depended on the type of intervention as well as other factors. This review also suggests direction for future research studies.

Hand function improvement with low-frequency repetitive transcranial magnetic stimulation of the unaffected hemisphere in a severe case of stroke

Previous research has shown that low-frequency rTMS of the unaffected hemisphere can improve motor function in acute and chronic stroke patients. However, these studies only investigated patients with mild or moderate motor deficits. We report a case of a stroke patient with a severe motor impairment who underwent sham and active repetitive transcranial magnetic stimulation (rTMS) of the unaffected hemisphere and had significantly improved motor function after active, but not after sham, stimulation of the unaffected primary motor cortex. In an additional session of active rTMS, this patient maintained and further enhanced the initial motor improvement. This case report shows that inhibitory rTMS of the unaffected hemisphere can also be beneficial for stroke patients with severe motor deficits and suggests that this approach of noninvasive brain stimulation should be further investigated in this population of patients.

Imaging motor recovery after stroke

Most patients show improvement in the weeks or months after a stroke. Recovery is incomplete, however, leaving most with significant impairment and disability. Because the brain does not grow back to an appreciable extent, this recovery occurs on the basis of change in function of surviving tissues. Brain mapping studies have characterized a number of processes and principles relevant to recovery from stroke in humans. The findings have potential application to improving therapeutics that aim to restore function after stroke.

Stroke recovery can be enhanced by using repetitive transcranial magnetic stimulation (rTMS)

Post-stroke recovery is based on plastic changes in the central nervous system that can compensate the loss of activity in affected brain regions. In particular, monohemispheric stroke is thought to result in disinhibition of the contralesional unaffected hemisphere. Neurorehabilitation programs improve function partly by enhancing cortical reorganization. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive way of producing potent changes in cortical excitability. Therefore, the application of rTMS was recently proposed to promote functional recovery in stroke patients, owing to the induced neuroplasticity. This review discusses the first clinical results that were obtained by rTMS in patients with post-stroke motor deficit, visuospatial neglect, or aphasia. These results are promising and depend on the site and frequency of stimulation. In summary, functional recovery might be obtained either when rTMS is applied at low-frequency (around 1 Hz) over the disinhibited, unaffected hemisphere in order to restore defective inhibition or when rTMS is applied at high-frequency (5 Hz or more) over the affected hemisphere in order to reactivate hypoactive regions. The overall procedure remains to be optimized, in particular regarding the number of rTMS sessions and the time of rTMS application after stroke. Cortical stimulation is an exciting perspective for improving functional recovery from stroke. Transient application of non-invasive transcranial stimulation during the time of the rehabilitation process will be preferable to the temporary implantation of epidural cortical electrodes, as recently proposed. Therefore, in the future, acute or recent stroke might be a major indication of rTMS in neurological practice.

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.

Hand function and motor cortical output poststroke: are they related?

OBJECTIVES

To characterize hand function and cortical excitability in chronic and subacute stages of stroke recovery and to describe the relations between these measures.

DESIGN

Observational, case-control, and cohort pre-post inpatient rehabilitation.

SETTING

Motor performance laboratory.

PARTICIPANTS

Fourteen community-living chronic and 14 subacute inpatient stroke survivors volunteered. Fourteen similarly aged healthy subjects served as a control group.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Finger tapping, peg placing, and strength were measured as indicators of hand function. The amplitude and latency of motor-evoked potentials (MEPs) and the duration of the silent period in the first dorsal interosseous muscle elicited by transcranial magnetic stimulation (TMS) reflected the integrity of excitatory and inhibitory cortical circuits.

RESULTS

Diminished hand function, small MEPs, and prolonged silent-period durations were evident in stroke compared with control subjects. Longer MEP latencies and smaller amplitudes distinguished subacute from chronic stroke. Side-to-side asymmetries were greatest in the subacute group for all TMS outcomes, although this lessened over time based on the subsample retested at discharge. Greater side-to-side MEP amplitude symmetry and lower motor threshold (lesioned side) were associated with better hand function in subacute and chronic stroke, respectively.

CONCLUSIONS

Cortical excitability is an important determinant of hand function poststroke and evolves with the time elapsed since the stroke event. The unique neural correlates of hand function evident in subacute and chronic stroke may reflect different phases of neuromuscular recovery.

Transcranial magnetic stimulation and stroke: A computer-based human model study

This paper explores how transcranial magnetic stimulation (TMS) induced currents in the brain are perturbed by electrical and anatomical changes following a stroke in its chronic stage. Multiple MRI derived finite element head models were constructed and evaluated to address the effects that strokes can have on the induced stimulating TMS currents by comparing stroke models of various sizes and geometries to a healthy head model under a number of stimulation conditions. The TMS induced currents were significantly altered for stimulation proximal to the lesion site in all of the models analyzed. The current density distributions were modified in magnitude, location, and orientation such that the population of neural elements that are stimulated will be correspondingly altered. The current perturbations were minimized for conditions tested where the coil was far removed from the lesion site, including models of stimulation contralateral to the lesioned hemisphere. The present limitations of TMS to the peri-lesional cortex are explored, ultimately concluding that conventional clinical standards for stimulation are unreliable and potentially dangerous predictors of the site and degree of stimulation when TMS is applied proximal to infarction site.

Clinical Correlation Between Motor Evoked Potentials and Gait Recovery in Poststroke Patients

OBJECTIVE

To evaluate, in patients with a stroke in the area of the middle cerebral artery, whether transcranial magnetic stimulation values from the affected lower limb correlated with the degree of gait recovery.

DESIGN

The prognostic evaluation in subjects with complete lower-limb palsy, inability to walk, and dependence in the activities of daily living, 1 month after vascular injury.

SETTING

University-affiliated rehabilitation hospital.

PARTICIPANTS

Twenty consecutive patients (12 women, 8 men) were enrolled 1 month poststroke (30+/-5 d); all patients concluded the rehabilitation program, which lasted 6 months.

INTERVENTION

Barthel Index score, Hemiplegic Stroke Scale (HSS) score, and motor evoked potentials (MEPs) from the tibialis anterior muscle were performed 1, 4, and 7 months poststroke. The Wilcoxon signed-rank test, Mann-Whitney U test, and Spearman rank-order correlation coefficient were employed.

MAIN OUTCOME MEASURES

The independence of gait defined as an HSS gait score of 3 or less (ability to walk without assistance apart from a stick or cane).

RESULTS

Patients with no recordable MEPs 1 month poststroke never regained walking ability; patients with MEPs of 8% or more (13.11+/-5.95) regained independent gait at discharge. It was not possible to predict walking capacity in patients with MEPs less than 8% (4.0+/-1.41). Four months postinjury, walking capacity was achieved only by the patients with MEPs of 18% or more (23.1+/-6.2).

CONCLUSIONS

In the postacute phase of stroke, the lower-limb MEP amplitudes could be a supportive tool for prognosis of lower-limb motor outcome.

Protein ubiquitination in postsynaptic densities after transient cerebral ischemia

The mechanisms underlying neurologic deficits and delayed neuronal death after ischemia are not fully understood. In the present study, we report that transient cerebral ischemia induces accumulation of ubiquitinated proteins (ubi-proteins) in postsynaptic densities (PSDs). By immunoelectron microscopy, we demonstrated that ubi-proteins were highly accumulated in PSD structures after ischemia. On Western blots, ubi-proteins were markedly increased in purified PSDs at 30 minutes of reperfusion, and the increase persisted until cell death in the CA1 region after ischemia. In the resistant DG area, however, the changes were transient and significantly less pronounced. Deposition of ubi-proteins in PSDs after ischemia correlates well with PSD structural damage in the CA1 region as viewed by electron microscopy. These results suggest that the ubiquitin-proteasome system fails to repair and remove damaged proteins in PSDs. The changes may demolish synaptic neurotransmission, contribute to neurologic deficits, and eventually lead to delayed neuronal death after transient cerebral ischemia.

Motor outcome after subcortical stroke correlates with the degree of cortical reorganization

OBJECTIVE

The contribution of cortical reorganization to motor recovery after a subcortical stroke is uncertain. The purpose of the study was to investigate the relationship between changes in motor cortex organization, and the degree of motor function after a subcortical stroke.

METHODS

Transcranial magnetic stimulation mapping of the corticomotor projection to the hand was performed in 27 patients who had suffered a subcortical ischemic stroke resulting in an upper limb motor deficit up to 23 years previously. Corticospinal conduction was assessed by measurements of motor evoked potential latency, amplitude and threshold. Motor function in the upper limb was assessed using the Motor Assessment Scale for Stroke and measurements of grip strength.

RESULTS

Motor maps for the hand were displaced on the affected side relative to the unaffected side in 17 patients. In 10 of these patients in whom corticospinal conduction had normalized, there was a strong positive correlation between the magnitude of the map shift and grip strength in the affected hand (r=0.79; P=0.006). In the other seven patients with a map shift, in whom corticospinal conduction was still impaired, there was a tendency for a larger map area to be associated with better motor function, and in the group as a whole there was a correlation between map area and grip strength (r=0.52; P=0.005).

CONCLUSIONS

The present findings provide evidence that the cortical plasticity and reorganization that occurs after a subcortical stroke is functionally significant and contributes to motor outcome.

Early Motor Evoked Potentials in Acute Stroke: Adjunctive Measure to MRI for Assessment of Prognosis in Acute Stroke within 6 Hours

BACKGROUND

In acute stroke, a magnetic resonance (MR) perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) mismatch (PWI>DWI mismatch) may indicate tissue at risk for infarction and poor prognosis. However, different to early enthusiasm about this surrogate marker, its validity has shown several drawbacks in individual patients. Rather than relying on imaging, we evaluated motor evoked potentials (MEP) as a measure of cerebral function in the acute stroke setting.

METHODS

Thirteen patients with acute hemiparetic stroke underwent time to peak PWI and DWI within 6 h after onset as well as recordings of early MEP of first dorsal interosseous muscles. Outcome was assessed by the Unified Neurological Stroke Scale and Barthel Index at day 42.

RESULTS

Of 8 patients with PWI>DWI mismatch, 4 patients with normal MEP had a good clinical outcome and 4 patients with absent or pathological MEP had an unfavourable outcome (p < 0.05, Fisher's exact test). In all patients without PWI>DWI mismatch, MEP findings predicted clinical outcome. Normal MEP at day 0--but not PWI/DWI findings--significantly correlated with a good clinical outcome.

CONCLUSIONS

Early MEP recordings in acute stroke patients provide valid prognostic information; they may become more useful for specific treatment decisions than presently available MRI surrogate parameters.

Facilitation of motor evoked potentials in ischemic stroke patients: prognostic value and neurophysiologic correlations

OBJECTIVE

To investigate the predictive value of paired transcranial magnetic stimulation (TMS) at rest in stroke patients in comparison with the predictive value derived from data obtained by single TMS during facilitation.

METHODS

Fifty-six patients with a single ischemic lesion and no electromyographic responses from single TMS in the resting affected hand muscles participated in the study. TMS assessment was performed 32 days post-stroke. It consisted of a single stimulation at maximal output during facilitation (controlateral hand grip and elbow flexion) and a paired-pulse stimulation at rest with two stimuli at maximal output at interstimulus intervals ranging from 15 to 100 ms. Two blind clinical assessments using the 'motricity index' were carried out 26 and 76 days post-stroke.

RESULTS

Thirty-seven percent of patients were responsive to single TMS during facilitation, had better clinical scores at both evaluations and better clinical recovery. Fifty-four percent of patients responded to paired TMS, had better clinical scores at the second evaluation and better clinical recovery. All patients who responded to the single stimulation paradigm also responded to the paired one.

CONCLUSIONS

A positive correlation was found between the responsiveness to both the TMS paradigms (facilitation procedure and paired stimulation) and clinical recovery. This underlines the importance of facilitation during single TMS in stroke patients and suggests that paired TMS at rest might supplement this procedure in stroke studies.

Modern stroke unit

The modern stroke unit is making significant contributions to the care of stroke victims and is proving to be an effective, cost-saving enterprise. The precise factors that contribute to the efficacy of these units have yet to be identified, but a combination of protocolized approaches to patient care, critical paths, a focus of expertise, and heightened index of suspicion for comorbidities all probably play a role. This article outlines the basic features of a modern stroke unit and surveys the literature on stroke unit outcomes.

Motor evoked potentials of the lower extremity in predicting motor recovery and ambulation after stroke: a cohort study 11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated

OBJECTIVE

To assess the prognostic value of motor evoked potentials (MEPs) in the lower extremity with respect to motor recovery and functional recovery in stroke patients.

DESIGN

Cohort study.

SETTING

The department of neurology at a university hospital.

PARTICIPANTS

Thirty-eight acute-stroke patients with complete paralysis (paralysis subgroup) or severe paresis (paresis subgroup) of the lower extremity. MEPs of the vastus medialis and the tibialis anterior muscles were recorded between days 3 and 10 after stroke onset.

INTERVENTIONS

Not applicable. Main outcome measures A separate proximal leg motor score (maximum, 16 points) and crural motor score (maximum, 2 points) were defined within the lower-limb subset of the original Fugl-Meyer Motor Assessment to evaluate the motor performance at regular intervals until 6 months after stroke. The transfer item of the Barthel Index and the Functional Ambulation Categories scores were used to assess transfer and walking ability.

RESULTS

For the paralysis subgroup (n=30), the follow-up was complete in 27 patients (2 patients died, 1 patient underwent above-knee amputation). At 26 weeks, 20 patients experienced proximal motor recovery (mean score +/- standard deviation, 11.70+/-4.48), and 12 of them also showed crural motor recovery (mean score, 1.40+/-.51). Nine patients (33%) could perform an independent transfer safely, and 7 (26%) had learned to walk independently. Analysis revealed significant relationships for tibialis anterior muscle MEPs and motor recovery of crural leg muscles (odds ratio [OR]=18.00; 95% confidence interval [CI], 1.31-894.40), but not for vastus medialis muscle MEPs and proximal motor recovery (OR=6.00; 95% CI,.53-303.00). We found no association between vastus medialis muscle MEPs and recovery of ambulation. However, tibialis anterior muscle MEPs seemed to provide a test with prognostic value for the ability to perform independent transfers (OR=17.50; 95% CI, 1.36-267.00), but not for walking (OR=5.25; 95% CI,.40-77.57). Patients in the paresis subgroup experienced more favorable motor and functional recovery than did those in the paralysis subgroup.

CONCLUSIONS

Tibialis anterior muscle MEPs registered in subacute phase after stroke may provide important prognostic information, both for motor recovery of the crural muscles and for the ability to perform independent transfers in patients with initial complete paralysis of the lower extremity. Vastus medialis muscle MEPs were not predictive for motor and functional recovery.

Post-stroke reorganization of hand motor area: a 1-year prospective follow-up with focal transcranial magnetic stimulation

OBJECTIVE

Focal transcranial magnetic stimulation was used to test prospectively corticospinal excitability changes and reorganization of first dorsal interosseous (FDI) motor cortical representation in 31 patients who experienced a first ischemic stroke in the middle cerebral artery territory. All had severe hand palsy at onset.

METHODS

Patients were assessed clinically with the Medical Research Council, Rankin, the National Institutes of Health stroke scales and Barthel Index at days 1, 8, 30, 90, 180 and 360 after stroke. The following parameters of FDI motor evoked potential (MEPS) to focal transcranial magnetic stimulation were measured at the same delays: motor threshold, MEP amplitude, excitable cortical area, hot spot and center of gravity of FDI motor maps on affected and unaffected hemispheres. Correlations were sought between clinical and electrophysiological parameters.

RESULTS

In patients whose affected motor cortex remained excitable at day 1, motor thresholds were not significantly different between sides and were similar to those of controls. Persistence of MEP on the affected side at day 1 was a strong predictor of good recovery. If present at day 1, MEPs recorded in affected FDI were significantly smaller than of the opposite side or in normals and progressively recovered up to day 360. In these patients, area of excitable cortex remained stable throughout the entire study. At day 1, amplitudes of MEPs obtained in unaffected FDI were significantly larger than later. Between days 1 and 360, we observed a significant displacement of center of gravity of motor maps towards more frontal regions on the affected side while no change was noted on the unaffected side.

CONCLUSIONS

Our data confirm the early prognosis value of transcranial magnetic stimulation in stroke. They indicate that the brain insult induces a transient hyperexcitability of the unaffected motor cortex. The evolution of FDI motor maps along the course of recovery mostly reflect corticospinal excitability changes but might also reveal some degree of brain plasticity. Most modifications observed occurred within 3 months of stroke onset.

Transcranial magnetic stimulation: review of the technique, basic principles and applications

Transcranial magnetic stimulation is rapidly developing as a powerful, non-invasive tool for studying the descending motor tracts in humans. The applications of the test in animals are for the moment restricted to small animals. However, this non-invasive, sensitive and painless technique appears promising as a test of motor tract function in horses where the neurological examination is mainly restricted to clinical evaluation and some ancillary tests, such as radiography, cerebrospinal fluid analysis and electromyography. In this review, we want to discuss the history, basic principles, technique and applications of transcranial magnetic stimulation in humans and small animals and indicate the possibilities for its use in horses. Since the great portion of this review is based on human studies, it is worthwhile to mention that the reports being described are from humans unless otherwise specified.

Use of transcranial magnetic stimulation with measurement of motor evoked potentials in the acute period of hemispheric ischemic stroke

Functional derangements in the brain during the acute period of ischemic hemispheric stroke (IS) were assessed in terms of the severity of the motor neurological deficit in the acute period of IS and neurophysiological measures of motor evoked potentials (MEP) using transcranial magnetic stimulation (TCMS). A total of 52 patients (23 women, 29 men, mean age 58.5 +/- 8.7 years) were studied. Patients were divided into two subgroups: group 1 consisted of 29 patients with good functional outcomes from the acute period; group 2 consisted of 23 patients with poor functional outcomes. The use of TCMS for recording MEP demonstrated increases in the latency of the M response both after stimulation of the projection of the motor area of the cortex of the lesioned hemisphere and after stimulation of the spinal cord. There were increases in the central motor conduction time (CMCT) in the lesioned hemisphere of the brain and a negative correlation was seen between the severity of the neurological defect and CMCT on the one hand (r = -0.65 to -0.78; p < 0.001) and, on the other, the latency of the M response in TCMS of the motor zone of the cortex on the side of the hemispheric stroke (r = -0.65 to -0.79; p < 0.001). The increases in the latency of the M response and CMCT have prognostic significance for early assessment of the outcome of IS.

Analysis of recovery processes after stroke by means of transcranial magnetic stimulation

The objective of this study was to use motor evoked potentials (MEPs) to analyze the integrity of fast corticospinal functions as the neurophysiologic basis for motor recovery in stroke patients. This was a cohort study including 44 acute stroke patients with paralysis of the upper or the lower extremity. Motor evoked potentials of the abductor digiti minimi, the biceps brachii, the vastus medialis, and the tibialis anterior were performed within 10 days (mean, 6.9 days; range, 3 to 10 days) and 40 days (mean, 27.8 days; range, 14 to 40 days) after stroke onset. A separate score was defined for proximal and distal motor functions of the upper and lower extremity within the original Fugl-Meyer motor assessment. Motor performance was evaluated simultaneously with the MEP assessments and 26 weeks after stroke. For all the muscles in which a response was present during the first investigation, obvious recovery of the fast corticospinal functions occurred. For the abductor digiti minimi amplitude ratio and the vastus medialis MEP amplitude the differences between the two investigations were significant. An MEP response could be elicited in more cases at the second than on the first MEP assessment. A present MEP response during the first registration indicated nearly always subsequent motor recovery, both for proximal and distal motor functions of the upper and lower extremity. However, motor recovery was also observed in some patients for whom no MEP response could be elicited. Regression analysis showed significant relationships between the abductor digiti minimi (P = 0.020/0.004 [t1/t2])and biceps brachii (P = 0.020/0.004 [t1/t2]) MEP amplitude parameters and the 26-week hand and arm motor scores. No relationship existed between the tibialis anterior and the vastus medialis MEP parameters and the leg motor scores. Motor recovery manifests neurophysiologically often as the recovery of fast corticospinal functions. In many cases, assessment by MEPs is more sensitive than clinical examination to detect residual corticospinal functions, which forms the pathophysiologic basis for the predictive value of MEPs for motor recovery after stroke.

Transcranial magnetic stimulation in neurology

Transcranial magnetic stimulation (TMS) is a non-invasive tool for the electrical stimulation of neural tissue, including cerebral cortex, spinal roots, and cranial and peripheral nerves. TMS can be applied as single pulses of stimulation, pairs of stimuli separated by variable intervals to the same or different brain areas, or as trains of repetitive stimuli at various frequencies. Single stimuli can depolarise neurons and evoke measurable effects. Trains of stimuli (repetitive TMS) can modify excitability of the cerebral cortex at the stimulated site and also at remote areas along functional anatomical connections. TMS might provide novel insights into the pathophysiology of the neural circuitry underlying neurological and psychiatric disorders, be developed into clinically useful diagnostic and prognostic tests, and have therapeutic uses in various diseases. This potential is supported by the available studies, but more work is needed to establish the role of TMS in clinical neurology.

Functional magnetic resonance imaging in stroke recovery

A better understanding of brain reorganization following stroke may have value in predicting outcome defining the targets of restorative therapies, measuring the physiology of recovery, and in serving as a biologic marker in studies targeting stroke recovery. Measures of brain organization may provide insights as to which patients retain relevant substrate for therapies that target restorative events. Brain reorganization can be studied with many different methods that often have complementary value. Functional MR imaging provides insights into brain plasticity after stroke and remains a valuable tool in the study of motor recovery after stroke.

Motor outcome after subcortical stroke: MEPs correlate with hand strength but not dexterity

OBJECTIVE

Motor evoked potential (MEP) amplitude and threshold are predictors of functional outcome in the early stages after stroke, and improvement in these parameters usually accompanies motor recovery. The aim of this study in patients with subcortical stroke was to determine whether there is a correlation between MEP amplitude and threshold and the degree of recovery of strength and dexterity in the affected hand.

METHODS

MEP amplitude and threshold were measured on the affected and unaffected sides in 23 patients who had suffered a subcortical ischaemic stroke up to 23 years previously. Grip strength was measured using a hand-held dynamometer and dexterity was assessed using a modification of the McCarron test battery.

RESULTS

Grip strength correlated with both MEP amplitude and threshold (r=0.49 and r=-0.54, respectively, P<0.05), whereas the McCarron score for motor dexterity did not correlate significantly with either of these MEP parameters.

CONCLUSIONS

Grip strength and dexterity correlate differentially with MEP parameters of excitability and conduction in the corticospinal pathway after recovery in patients with subcortical stroke. Grip strength is dependent on restoration of corticospinal excitability and conduction whereas additional factors such as cortical reorganization may underlie recovery of motor dexterity.

Motor cortex activation is preserved in patients with chronic hemiplegic stroke

Many central nervous system conditions that cause weakness, including many strokes, injure corticospinal tract but leave motor cortex intact. Little is known about the functional properties of surviving cortical regions in this setting, in part because many studies have used probes reliant on the corticospinal tract. We hypothesized that many features of motor cortex function would be preserved when assessed independent of the stroke-affected corticospinal tract. Functional MRI was used to study 11 patients with chronic hemiplegia after unilateral stroke that spared regions of motor cortex. Activation in stroke-affected hemisphere was evaluated using 3 probes independent of affected corticospinal tract: passive finger movement, a hand-related visuomotor stimulus, and tapping by the nonstroke index finger. The site and magnitude of cortical activation were similar when comparing the stroke hemisphere to findings in 19 control subjects. Patients activated each of 8 cortical regions with similar frequency as compared to controls, generally with a smaller activation volume. In some cases, clinical measures correlated with the size or the site of stroke hemisphere activation. The results suggest that, despite stroke producing contralateral hemiplegia, surviving regions of motor cortex actively participate in the same proprioceptive, visuomotor, and bilateral movement control processes seen in control subjects.

Motor recovery after stroke: a systematic review of the literature

OBJECTIVE

To collect and integrate existing data concerning the occurrence, extent, time course, and prognostic determinants of motor recovery after stroke using a systematic methodologic approach.

DATA SOURCES

A computer-aided search in bibliographic databases was done of longitudinal cohort studies, original prognostic studies, and randomized controlled trials published in the period 1966 to November 2001, which was expanded by references from retrieved articles and narrative reviews.

STUDY SELECTION

After a preliminary screening, internal, external, and statistical validity was assessed by a priori methodologic criteria, with special emphasis on the internal validity.

DATA EXTRACTION

The studies finally selected were discussed, based on the quantitative analysis of the outcome measures and prognostic determinants. Meta-analysis was pursued, but was not possible because of substantial heterogeneity.

DATA SYNTHESIS

The search resulted in 174 potentially relevant studies, of which 80 passed the preliminary screening and were subjected to further methodologic assessment; 14 studies were finally selected. Approximately 65% of the hospitalized stroke survivors with initial motor deficits of the lower extremity showed some degree of motor recovery. In the case of paralysis, complete motor recovery occurred in less than 15% of the patients, both for the upper and lower extremities. Hospitalized patients with small lacunar strokes showed relatively good motor recovery. The recovery period in patients with severe stroke was twice as long as in patients with mild stroke. The initial grade of paresis was the most important predictor for motor recovery (odds ratios [OR], >4). Objective analysis of the motor pathways by motor-evoked potentials (MEPs) showed even higher ORs (ORs, >20).

CONCLUSIONS

Our knowledge of motor recovery after stroke in more accurate, quantitative, and qualitive terms is still limited. Nevertheless, our data synthesis and quantitative analysis comprises data from many methodologically robust studies, which may support the clinician in the management of stroke patients. With respect to early prognosis of motor recovery, our review confirms clinical experience that the initial grade of paresis (as measured on admission in the hospital) is the most important predictor, although the accuracy of prediction rapidly improves during the first few days after stroke. Initial paralysis implies the worst prognosis for subsequent motor recovery. Remarkably, the prognostic accuracy of MEPs appears much higher than that of clinical examination for different subgroups of patients.

Systematic review for the early prediction of motor and functional outcome after stroke by using motor-evoked potentials

OBJECTIVE

To clarify the prognostic value of motor-evoked potentials (MEPs) in predicting motor and functional outcomes after acute stroke.

DATA SOURCES

A computer-aided search to identify original prognostic studies published from 1988 through 2000; relevant references cited in the retrieved articles were also included.

STUDY SELECTION

A preliminary screening selected studies in which transcranial magnetic stimulation was assessed as a prognostic determinant for outcome at the level of impairments (motor recovery) and disabilities (functional recovery). The studies were then subjected to a critical review according to a priori methodologic criteria.

DATA EXTRACTION

Data from the studies were used to construct contingency tables with MEPs as a prognostic determinant. The distribution of cells was statistically assessed with the Fisher exact test. The prognostic test properties were expressed as sensitivity and specificity. The clinical significance was determined by odds ratios.

DATA SYNTHESIS

Of 85 potentially relevant studies, 20 met the criteria for the preliminary screening; after the critical review, 5 studies were included for analysis and discussion.

CONCLUSIONS

Analysis of the data from the 5 studies indicated obvious evidence for the prognostic value of MEPs for both motor and functional recovery. The prognostic test properties for subgroups of patients could be established. In predicting motor recovery of the upper extremity, the specificity was consistently very high for subgroups of patients with paralysis or severe paresis; this test property might be used in clinical practice. We discuss the prognostic value of MEPs and offer suggestions for further research.

Motor disinhibition in affected and unaffected hemisphere in the early period of recovery after stroke

OBJECTIVES

To investigate motor disinhibition in affected and unaffected motor areas in the acute stage after stroke and during the early period of recovery.

METHODS

Fifteen patients with moderate to severe hemiparesis after acute unilateral stroke were compared with 10 healthy age-matched controls. We used paired transcranial magnetic stimulation to study intracortical inhibition and facilitation from the thenar eminence muscles on both sides. F-wave from the median nerve on both sides were recorded. The recordings were performed 5-7 days (T1) and 30 days after stroke.

RESULTS

In 10 patients who showed the presence of reliable motor evoked potentials on the affected side, intracortical inhibition was significantly reduced. On the unaffected side intracortical inhibition (ICI) was significantly reduced in all patients. Patients who presented significant motor recovery after 30 days showed persistence of abnormal disinhibition in the affected hemisphere but a return to normal ICI in the unaffected hemisphere. Patients with poor motor recovery showed persistence of abnormal disinhibition on both sides. No significant changes were observed in F-wave amplitude.

CONCLUSIONS

Motor disinhibition occurs on both sides after stroke in all acute stage patients. Changes in motor disinhibition on unaffected side also are related to motor recovery.

Plasticity of the human motor cortex and recovery from stroke

By a variety of mechanisms, the human brain is constantly undergoing plastic changes. Plasticity can be studied with phenomena such as peripheral deafferentation and motor learning. Spontaneous recovery from stroke in the chronic stage likely comes about because of plasticity, and the best recovery seems to result from reorganization in the damaged hemisphere. Knowledge about the physiology of brain plasticity has led to the development of new techniques for rehabilitation.

Neurophysiological follow-up of motor cortical output in stroke patients

BACKGROUND AND PURPOSE

Transcranial magnetic stimulation (TMS) has been employed in following up a population of 20 stroke patients in a post-acute, apparently stabilized stage. Neurophysiological and clinical data were recorded in 5 different recording sessions, from the beginning of a neuro-rehabilitation treatment (T0, at about 5 weeks from the ictal event.), followed up for about 4 months (T4), with the purpose to study any modification of the cortical motor output in the course of a neuro-rehabilitation treatment.

METHODS

Motor evoked potentials (MEPs) were simultaneously recorded from 10 muscles of both upper limbs (affected and not-affected); meanwhile, clinical and functional scores were gathered. Spinal responsiveness was investigated via H-reflex and F-wave recordings.

RESULTS

We describe a pattern of improving changes still taking place four months after the stroke, even if the maximal amelioration burden was concentrated between T0 and T1 and T1 and T2 recording sessions (T0/admission to T2/42 days from T0=about 80 days from stroke occurrence). In particular, the excitability threshold (ETh) was progressively decreasing in the affected hemisphere (AH; P<0.001 between T0 and T4), while MEPs amplitude and latency tended toward normality, more in the resting state than during voluntary contraction. Slopes of neurophysiological and clinical data evolution were taken and trends of amelioration described.

CONCLUSIONS

These findings suggest that rearrangements of motor cortical neural circuitries are still operating after several months from an acute vascular monohemispheric insult, coupled with a clinical improvement in disability and neurological scores. The steepest part of the slopes were evident in the first 80 days, suggesting that this period is the one in which plastic changes of cortical motor areas are mainly active.

Altered mechanisms of motor-evoked potential generation after transient focal cerebral ischemia in the rat: implications for transcranial magnetic stimulation

We recently demonstrated that a long-lasting transmission defect in cortical synapses caused motor dysfunction after brief middle cerebral artery (MCA) occlusion in the rat despite rapid recovery of axons. In this experimental study, we have examined the impact of differential recovery of synapses and axons on generation of motor-evoked potentials (MEP) recorded from contralateral paralyzed and ipsilateral unaffected muscles, to gain insight into mechanisms of MEPs recorded from stroke patients by transcranial magnetic stimulation (TMS). MEPs generated by focal electrical stimulation of the forelimb area of motor cortex were simultaneously recorded from the brain stem, contra- and ipsilateral forelimb and contralateral hindlimb muscles in rats subjected to transient MCA occlusion. The effect of ischemia on cortical activity and axonal conduction was differentially studied by proximal or distal occlusion of the MCA. Regional cerebral blood flow changes in the forelimb area were monitored by laser-Doppler flowmetry during ischemia and reperfusion. In addition, synaptic transmission within the forelimb area of motor cortex was examined by intracellular and extracellular recording of potentials generated by stimulation of the premotor area. No MEP response was recorded during ischemia. Upon reperfusion: (i) motor axons readily regained their excitability and cortical stimulation caused successive pyramidal volleys (recorded as D waves from the brain stem) and a MEP from contralateral paralytic muscles although synaptic activation of motor pathways was not feasible; (ii) the amplitude of pyramidal volley was increased; (iii) MEPs with a longer latency were recorded from the ipsilateral forelimb. In conclusion, differential recovery of synapses and axons after ischemia may account for some previously unexplained findings (such as preserved MEPs in paralysed muscles) observed in cortical stimulation studies of stroke patients.

Magnetoelectric brain stimulation in the assessment of brain physiology and pathophysiology

OBJECTIVE

To review findings from transcranial magnetic stimulation (TMS)-induced motor evoked potentials in normal subjects, in various neurological diseases and with pharmacologic manipulation.

METHODS

MEDLINE was searched to identify pertinent articles and articles referenced therein were also reviewed.

RESULTS

TMS is a safe and non-invasive technique which has been used widely in the study of corticospinal and corticocortical connectivity as well as in the assessment of basal ganglia disorders, diffuse diseases, and neuropharmacology.

CONCLUSIONS

TMS motor measures have utility in examination of brain structure and function within and beyond the corticospinal tract. These measures have both research and clinical applications.

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.