Sensory and motor evoked potentials in multiple system atrophy: a comparative study with Parkinson's disease

Transcranial magnetic stimulation neurophysiology in patients with non-Alzheimer's neurodegenerative diseases: A systematic review and meta-analysis

Non-Alzheimer's dementia (NAD) accounts for 30% of all neurodegenerative conditions and is characterized by cognitive decline beyond mere memory dysfunction. Diagnosing NAD remains challenging due to the lack of established biomarkers. Transcranial magnetic stimulation (TMS) is a non-invasive neurophysiological tool that enables the investigation of cortical excitability in the human brain. Paired-pulse TMS paradigms include short- and long-interval intracortical inhibition (SICI/LICI), intracortical facilitation (ICF), and short-latency afferent inhibition (SAI), which can assess neurophysiological functions of GABAergic, glutamatergic, and cholinergic neural circuits, respectively. We conducted the first systematic review and meta-analysis to compare these TMS indices among patients with NAD and healthy controls. Our meta-analyses indicated that TMS neurophysiological examinations revealed decreased glutamatergic function in patients with frontotemporal dementia (FTD) and decreased GABAergic function in patients with FTD, progressive supranuclear palsy, Huntington's disease, cortico-basal syndrome, and multiple system atrophy-parkinsonian type. In addition, decreased cholinergic function was found in dementia with Lewy body and vascular dementia. These results suggest the potential of TMS as an additional diagnostic tool to differentiate NAD.

Neurophysiological differentiation of upper motor neuron damage in neurodegenerative disorders

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ALS and MSA presented with similar profiles of upper motor neuron signs.

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Central motor conduction time was more abnormal in ALS than in MSA.

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Different structures may be involved in ALS and MSA along the corticospinal tract.

Objective

Using transcranial magnetic stimulation (TMS) to delineate upper motor neuron (UMN) signs of two neurodegenerative disorders: amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA).

Methods

Medical records including clinical signs for UMN damage and TMS results were reviewed retrospectively. The UMN signs were classified into none, mild, and severe based on neurological examination of various reflexes. Then TMS-elicited motor evoked potentials (MEPs) were recorded from a hand and a leg muscle to calculate the central motor conduction time (CMCT), which represents fast, mono-synaptic conduction along the corticospinal tract. Relations between the UMN signs and CMCT were analysed for the two diseases.

Results

Prevalence and severity of the UMN signs for ALS and MSA were comparable for both upper and lower limbs. However, abnormality in CMCT was found more frequently in ALS: CMCT abnormalities were found in upper limbs for 44% in ALS patients but only for 7% in MSA patients; CMCT abnormalities in lower limbs were 55% in ALS and 20% in MSA. Some ALS patients showed abnormal CMCT in limbs without UMN signs, which was not true for most MSA patients.

Conclusions

The abnormalities of CMCT were different in ALS and MSA, even for those who clinically had similar UMN signs. Sometimes, CMCT can reveal UMN damage in the absence of clinical UMN signs. Differences presumably derive from selective degeneration of different fibres in the motor descending pathways. Longitudinal studies must be conducted to accumulate neuroimaging and pathological findings.

Significance

CMCT can be useful to differentiate ALS and MSA.

Effects of Non-invasive Brain Stimulation on Multiple System Atrophy: A Systematic Review

Background/Objective: Multiple system atrophy (MSA) refers to a progressive neurodegenerative disease characterized by autonomic dysfunction, parkinsonism, cerebellar ataxia, as well as cognitive deficits. Non-invasive brain stimulation (NIBS) has recently served as a therapeutic technique for MSA by personalized stimulation. The primary aim of this systematic review is to assess the effects of NIBS on two subtypes of MSA: parkinsonian-type MSA (MSA-P) and cerebellar-type MSA (MSA-C).

Methods: A literature search for English articles was conducted from PubMed, Embase, Web of Science, Cochrane Library, CENTRAL, CINAHL, and PsycINFO up to August 2021. Original articles investigating the therapeutics application of NIBS in MSA were screened and analyzed by two independent reviewers. Moreover, a customized form was adopted to extract data, and the quality of articles was assessed based on the PEDro scale for clinical articles.

Results: On the whole, nine articles were included, i.e., five for repetitive transcranial magnetic stimulation (rTMS), two for transcranial direct current stimulation (tDCS), one for paired associative stimulation, with 123 patients recruited. The mentioned articles comprised three randomized controlled trials, two controlled trials, two non-controlled trials, and two case reports which assessed NIBS effects on motor function, cognitive function, and brain modulatory effects. The majority of articles demonstrated significant motor symptoms improvement and increased cerebellar activation in the short term after active rTMS. Furthermore, short-term and long-term effects on improvement of motor performance were significant for tDCS. As opposed to the mentioned, no significant change of motor cortical excitability was reported after paired associative stimulation.

Conclusion: NIBS can serve as a useful neurorehabilitation strategy to improve motor and cognitive function in MSA-P and MSA-C patients. However, further high-quality articles are required to examine the underlying mechanisms and standardized protocol of rTMS as well as its long-term effect. Furthermore, the effects of other NIBS subtypes on MSA still need further investigation.

Early recognition and diagnosis of multiple system atrophy: best practice and emerging concepts

Introduction: Multiple system atrophy (MSA) is a progressive degenerative disorder of the central and autonomic nervous systems characterized by parkinsonism, cerebellar ataxia, dysautonomia, and pyramidal signs. The confirmatory diagnosis is pathological, but clinical-diagnostic criteria have been developed to help clinicians. To date, the early diagnosis of MSA is challenging due to the lack of reliable diagnostic biomarkers.Areas covered: The authors reappraised the main clinical, neurophysiological, imaging, genetic, and laboratory evidence to help in the early diagnosis of MSA in the clinical and in the research settings. They also addressed the practical clinical issues in the differential diagnosis between MSA and other parkinsonian and cerebellar syndromes. Finally, the authors summarized the unmet needs in the early diagnosis of MSA and proposed the next steps for future research efforts in this field.Expert opinion: In the last decade, many advances have been achieved to help the correct MSA diagnosis since early stages. In the next future, the early diagnosis and correct classification of MSA, together with a better knowledge of the causative mechanisms of the disease, will hopefully allow the identification of suitable candidates to enroll in clinical trials and select the most appropriate disease-modifying strategies to slow down disease progression.

On the Use of TMS to Investigate the Pathophysiology of Neurodegenerative Diseases

Neurodegenerative diseases are a collection of disorders that result in the progressive degeneration and death of neurons. They are clinically heterogenous and can present as deficits in movement, cognition, executive function, memory, visuospatial awareness and language. Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation tool that allows for the assessment of cortical function in vivo. We review how TMS has been used for the investigation of three neurodegenerative diseases that differ in their neuroanatomical axes: (1) Motor cortex-corticospinal tract (motor neuron diseases), (2) Non-motor cortical areas (dementias), and (3) Subcortical structures (parkinsonisms). We also make four recommendations that we hope will benefit the use of TMS in neurodegenerative diseases. Firstly, TMS has traditionally been limited by the lack of an objective output and so has been confined to stimulation of the motor cortex; this limitation can be overcome by the use of concurrent neuroimaging methods such as EEG. Given that neurodegenerative diseases progress over time, TMS measures should aim to track longitudinal changes, especially when the aim of the study is to look at disease progression and symptomatology. The lack of gold-standard diagnostic confirmation undermines the validity of findings in clinical populations. Consequently, diagnostic certainty should be maximized through a variety of methods including multiple, independent clinical assessments, imaging and fluids biomarkers, and post-mortem pathological confirmation where possible. There is great interest in understanding the mechanisms by which symptoms arise in neurodegenerative disorders. However, TMS assessments in patients are usually carried out during resting conditions, when the brain network engaged during these symptoms is not expressed. Rather, a context-appropriate form of TMS would be more suitable in probing the physiology driving clinical symptoms. In all, we hope that the recommendations made here will help to further understand the pathophysiology of neurodegenerative diseases.

Motor cortical circuits in Parkinson disease and dystonia

We review the motor cortical and basal ganglia involvement in two important movement disorders: Parkinson's disease (PD) and dystonia. Single and paired pulse transcranial magnetic stimulation studies showed altered excitability and cortical circuits in PD with decreased silent period, short interval intracortical inhibition, intracortical facilitation, long afferent inhibition, interhemispheric inhibition, and cerebellar inhibition, and increased long interval intracortical inhibition and short interval intracortical facilitation. In dystonia, there is decreased silent period, short interval intracortical inhibition, long afferent inhibition, interhemispheric inhibition, and increased intracortical facilitation. Plasticity induction protocols revealed deficient plasticity in PD and normal and exaggerated plasticity in dystonia. In the basal ganglia, there is increased β (14-30Hz) rhythm in PD and characteristic 5-18Hz band synchronization in dystonia. These motor cortical circuits, cortical plasticity, and oscillation profiles of the basal ganglia are altered with medications and deep brain stimulation treatment. There is considerable variability in these measures related to interindividual variations, different disease characteristics, and methodological considerations. Nevertheless, these pathophysiologic studies have expanded our knowledge of cortical excitability, plasticity, and oscillations in PD and dystonia, improved our understanding of disease pathophysiology, and helped to develop new treatments for these conditions.

Plasticity Induced in the Human Spinal Cord by Focal Muscle Vibration

The spinal cord spinal cord has in the past been considered a hardwired system which responds to inputs in a stereotyped way. A growing body of data have instead demonstrated its ability to retain information and modify its effector capabilities, showing activity-dependent plasticity. Whereas, plasticity in the spinal cord is well documented after different forms of physical exercise, whether exogenous stimulation can induce similar changes is still a matter of debate. This issue is both of scientific and clinical relevance, since at least one form of stimulation, i.e., focal muscle vibration (fMV), is currently used as a treatment for spasticity. The aim of the present study was to assess whether fMV can induce plasticity at the SC level when applied to different muscles of the upper limb. Changes in different electrophysiological measures, such as H-reflex testing homonymous and heteronymous pathways, reciprocal inhibition and somatosensory evoked potentials were used as outcomes. We found that fMV was able to induce long-term depression-like plasticity in specific spinal cord circuits depending on the muscle vibrated. These findings helped understand the basic mechanisms underlying the effects of fMV and might help to develop more advanced stimulation protocols.

Impaired nerve conduction velocity in MPTP-treated mouse model of Parkinson's disease

Electrophysiological examination can provide valuable information on functional abnormalities in patients with Parkinson's disease (PD). Although there are numerous reports on biochemical and molecular alterations in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced experimental parkinsonism in mice, the mode of electrophysiology in this animal model of PD is not clear. This study provides a comparative evaluation of corticomotor evoked potential (CMEP), compound muscle action potential (CMAP) and motor nerve conduction velocity (NCV) in mice treated with MPTP (30 mg/kg, ip, daily for 4 days) or saline (control group). Although the CMEP latencies were similar in both the groups, the CMEP amplitude was non-significantly decreased in MPTP-treated mice. There was a significant increase in the CMAP latency (1.37 ± 0.03 versus 1.20 ± 0.02 ms) and decrease in CMAP amplitude (4.50 ± 0.89 versus 8.31 ± 0.86 mV) in MPTP-treated mice as compared with control group. This prolonged conduction time resulted in a significant decrease in NCV in MPTP-treated mice (21.98 ± 0.54 m/s) as compared with control mice (24.47 ± 0.33 m/s). There was a significant depletion of striatal dopamine in MPTP-treated animals. These findings demonstrate that systemic administration of MPTP significantly impairs both the central and peripheral nervous systems in mice. However, the resemblance of this neurophysiological status with idiopathic PD or other animal models of PD is not clear and requires additional studies.

Prognostic Value of Evoked Responses and Event-Related Brain Potentials in

The behaviourally unresponsive patient, unable to exhibit the presence of cognition, constitutes a conundrum for health care specialists. Prognostic uncertainty impedes accurate management decisions and the application of ethical principles. An early, reliable prognosis is highly desirable. In this review investigations studying comatose patients with coma of different etiologies were selected. It is concluded that objective prognostication is enhanced by the use of electrophysiological tests. Persistent abnormalities of brainstem auditory evoked potentials and short-latency somatosensory evoked potentials reliably indicate the likelihood of irreversible neurological deficit or death. Meanwhile, the presence of “cognitive” event-related brain potentials (e.g., P300 and mismatch negativity) reflects the functional integrity of higher level information processing and, therefore, the likelihood of capacity for cognition. An approach that combines clinical and electrophysiological values provides optimal prediction of outcome and level of disability.

The contribution of transcranial magnetic stimulation in the diagnosis and in the management of dementia

Transcranial magnetic stimulation (TMS) is emerging as a promising tool to non-invasively assess specific cortical circuits in neurological diseases. A number of studies have reported the abnormalities in TMS assays of cortical function in dementias. A PubMed-based literature review on TMS studies targeting primary and secondary dementia has been conducted using the key words "transcranial magnetic stimulation" or "motor cortex excitability" and "dementia" or "cognitive impairment" or "memory impairment" or "memory decline". Cortical excitability is increased in Alzheimer's disease (AD) and in vascular dementia (VaD), generally reduced in secondary dementias. Short-latency afferent inhibition (SAI), a measure of central cholinergic circuitry, is normal in VaD and in frontotemporal dementia (FTD), but suppressed in AD. In mild cognitive impairment, abnormal SAI may predict the progression to AD. No change in cortical excitability has been observed in FTD, in Parkinson's dementia and in dementia with Lewy bodies. Short-interval intracortical inhibition and controlateral silent period (cSP), two measures of gabaergic cortical inhibition, are abnormal in most dementias associated with parkinsonian symptoms. Ipsilateral silent period (iSP), which is dependent on integrity of the corpus callosum is abnormal in AD. While single TMS measure owns low specificity, a panel of measures can support the clinical diagnosis, predict progression and possibly identify earlier the "brain at risk". In dementias, TMS can be also exploited to select and evaluate the responders to specific drugs and, it might become a rehabilitative tool, in the attempt to restore impaired brain plasticity.

EFNS/MDS-ES/ENS [corrected] recommendations for the diagnosis of Parkinson's disease

BACKGROUND

A Task Force was convened by the EFNS/MDS-ES Scientist Panel on Parkinson's disease (PD) and other movement disorders to systemically review relevant publications on the diagnosis of PD.

METHODS

Following the EFNS instruction for the preparation of neurological diagnostic guidelines, recommendation levels have been generated for diagnostic criteria and investigations.

RESULTS

For the clinical diagnosis, we recommend the use of the Queen Square Brain Bank criteria (Level B). Genetic testing for specific mutations is recommended on an individual basis (Level B), taking into account specific features (i.e. family history and age of onset). We recommend olfactory testing to differentiate PD from other parkinsonian disorders including recessive forms (Level A). Screening for pre-motor PD with olfactory testing requires additional tests due to limited specificity. Drug challenge tests are not recommended for the diagnosis in de novo parkinsonian patients. There is an insufficient evidence to support their role in the differential diagnosis between PD and other parkinsonian syndromes. We recommend an assessment of cognition and a screening for REM sleep behaviour disorder, psychotic manifestations and severe depression in the initial evaluation of suspected PD cases (Level A). Transcranial sonography is recommended for the differentiation of PD from atypical and secondary parkinsonian disorders (Level A), for the early diagnosis of PD and in the detection of subjects at risk for PD (Level A), although the technique is so far not universally used and requires some expertise. Because specificity of TCS for the development of PD is limited, TCS should be used in conjunction with other screening tests. Conventional magnetic resonance imaging and diffusion-weighted imaging at 1.5 T are recommended as neuroimaging tools that can support a diagnosis of multiple system atrophy (MSA) or progressive supranuclear palsy versus PD on the basis of regional atrophy and signal change as well as diffusivity patterns (Level A). DaTscan SPECT is registered in Europe and the United States for the differential diagnosis between degenerative parkinsonisms and essential tremor (Level A). More specifically, DaTscan is indicated in the presence of significant diagnostic uncertainty such as parkinsonism associated with neuroleptic exposure and atypical tremor manifestations such as isolated unilateral postural tremor. Studies of [(123) I]MIBG/SPECT cardiac uptake may be used to identify patients with PD versus controls and MSA patients (Level A). All other SPECT imaging studies do not fulfil registration standards and cannot be recommended for routine clinical use. At the moment, no conclusion can be drawn as to diagnostic efficacy of autonomic function tests, neurophysiological tests and positron emission tomography imaging in PD.

CONCLUSIONS

The diagnosis of PD is still largely based on the correct identification of its clinical features. Selected investigations (genetic, olfactory, and neuroimaging studies) have an ancillary role in confirming the diagnosis, and some of them could be possibly used in the near future to identify subjects in a pre-symptomatic phase of the disease.

Differences in dopaminergic modulation to motor cortical plasticity between Parkinson's disease and multiple system atrophy

Dopamine modulates the synaptic plasticity in the primary motor cortex (M1). To evaluate whether the functioning of the cortico-striatal circuit is necessary for this modulation, we applied a paired associative stimulation (PAS) protocol that comprised an electric stimulus to the right median nerve at the wrist and subsequent transcranial magnetic stimulation of the left M1, to 10 patients with Parkinson's disease (PD) and 10 with multiple system atrophy of the parkinsonian type (MSA-P) with and without dopamine replacement therapy (-on/off). To investigate the M1 function, motor-evoked potentials (MEPs) were measured before and after the PAS. In both patient groups without medication, the PAS protocol failed to increase the averaged amplitude of MEPs. The dopamine replacement therapy in PD, but not in MSA-P effectively restored the PAS-induced MEP increase. This suggests that not the existence of dopamine itself but the activation of cortico-striatal circuit might play an important role for cortical plasticity in the human M1.

Safety of transcranial magnetic stimulation in Parkinson's disease: a review of the literature

BACKGROUND

Transcranial magnetic stimulation (TMS) has been used in both physiological studies and, more recently, the therapy of Parkinson's disease (PD). Prior TMS studies in healthy subjects and other patient populations demonstrate a slight risk of seizures and other adverse events. Our goal was to estimate these risks and document other safety concerns specific to PD patients.

METHODS

We performed an English-Language literature search through PudMed to review all TMS studies involving PD patients. We documented any seizures or other adverse events associated with these studies. Crude risks were calculated per subject and per session of TMS.

RESULTS

We identified 84 single pulse (spTMS) and/or paired-pulse (ppTMS) TMS studies involving 1091 patients and 77 repetitive TMS (rTMS) studies involving 1137 patients. Risk of adverse events was low in all protocols. spTMS and ppTMS risk per patient for any adverse event was 0.0018 (95% CI: 0.0002-0.0066) per patient and no seizures were encountered. Risk of an adverse event from rTMS was 0.040 (95% CI: 0.029-0.053) per patient and no seizures were reported. Other adverse events included transient headaches, scalp pain, tinnitus, nausea, increase in pre-existing pain, and muscle jerks. Transient worsening of Parkinsonian symptoms was noted in one study involving rTMS of the supplementary motor area (SMA).

CONCLUSION

We conclude that current TMS and rTMS protocols do not pose significant risks to PD patients. We would recommend that TMS users in this population follow the most recent safety guidelines but do not warrant additional precautions.

Central motor conduction time

Central motor conduction time (CMCT) is the time taken for neural impulses to travel through the central nervous system on their way to the target muscles. When the motor cortex is stimulated with transcranial magnetic stimulation (TMS), CMCT is calculated by subtracting the peripheral conduction time from the motor evoked potential latency elicited by motor cortical TMS. CMCT in infants and children reaches adult level at about age of 6 years for the lower limbs. The alterations of CMCT in various neurological conditions are reviewed in this chapter. Prolongation of CMCT occurs due to slowing of conduction through rapidly conducting corticospinal fibers, as seen in various disorders such as demyelinating diseases (multiple sclerosis, MS), amyotrophic lateral sclerosis, structural lesions in the corticospinal tract such as stroke and compressive myelopathy, and neurodegenerative disorders including multiple system atrophy and progressive supranuclear palsy. As CMCT is prolonged in certain clinical conditions, it is of diagnostic value in some neurological disorders such as myelopathy, amyotrophic lateral sclerosis, and MS when used together with other clinical and electrophysiological measures. It could also be used as a prognostic marker in some of neurological conditions, such as myelopathy and MS.

Premovement facilitation of corticospinal excitability in patients with Parkinson's disease

The purpose of this study was to investigate the abnormality of premovement facilitation in patients with Parkinson's disease. Seven patients with Parkinson's disease and seven healthy subjects participated in this study. The subjects attempted abduction of the index finger in response to a visual start cue, and motor-evoked potentials were recorded from the first dorsal interosseous muscle before movement onset. The rate of premovement facilitation in patients with Parkinson's disease was slower than that in healthy subjects. Additionally, the rate of premovement facilitation as a function of delay from the start cue was positively correlated with the reaction time. These findings indicate that premovement facilitation is abnormal in patients with Parkinson's disease. This abnormality may be partially related to akinesia.

Anal sphincter EMG in the diagnosis of parkinsonian syndromes

BACKGROUND

The role of electromyography (EMG) recorded from the external anal sphincter (EAS) in the diagnosis of atypical parkinsonian syndromes is a matter for continuous debate. Most studies addressing this issue are retrospective.

METHODS

In this study, we prospectively investigated six patients with Parkinson's Disease (IPD), 14 patients with multiple system atrophy (MSA) and eight with progressive supranuclear palsy (PSP) using EMG of the EAS, motor-evoked potential (MEP) to the EAS and EMG of m. gastrocnemius and nerve conduction velocity measured at the sural nerve. Patients were followed up for 2 years to secure correct diagnosis.

RESULTS

The mean duration of motor unit potentials (MUPs) recorded from the EAS was significantly longer in patients with MSA and PSP compared with MUPs recorded from patients with PD (P < 0.005 for both). There were no signs of diffuse loss of motor neurons or peripheral neuropathy. MEP revealed signs of supranuclear affection in patients with MSA, whereas in patients with PSP the mechanism is a focal loss of motor neurons in Onuf's nucleus.

CONCLUSION

Abnormal EMG of the EAS is strongly suggestive of atypical parkinsonism and the pathophysiology may be different in patients with MSA and PSP.

Brain volume analyses and somatosensory evoked potentials in multiple system atrophy

We investigated a progression of brain atrophy and somatosensory system dysfunction in multiple system atrophy (MSA). Subjects were 21 MSA patients [12 MSA-C (cerebellar type) and 9 MSA-P (parkinsonism type)]. The relative volumes of cerebrum, brainstem and cerebellum to the intracranial volume were obtained from three-dimensional computed tomography (3D-CT) of the brain. The median nerve somatosensory evoked potentials (SEPs) were recorded, and the latencies and amplitudes of N9, N11, P13/14, N20 and P25 components were measured. We studied correlations between brain volumes, SEP and clinical features. The brainstem and cerebellar atrophies were aggravated with progression of the disease. The central sensory conduction time (CSCT) was progressively prolonged in parallel with the disease duration irrespective of the actual age of the patients. In MSA patients, the volume reductions of cerebellum and brainstem could be one of structural markers of disease progression, and the sensory pathway is progressively involved with the progression of disease processes.

Transcranial magnetic stimulation for differential diagnostics in patients with parkinsonism

OBJECTIVE

We investigated transcranial magnetic stimulation (TMS) parameters in patients with parkinsonism, particularly in the early stages of the disease.

SUBJECTS AND METHODS

We performed TMS in 48 patients with PD, progressive supranuclear palsy (PSP) and multiple system atrophy (MSA). We measured motor threshold (MT), latency (L), motor-evoked potential amplitude and central motor conduction time (CMCT) and cortical silent period (CSP). Furthermore, we selected and compared 27 patients with a disease duration of less than 3 years.

RESULTS

CMCT, MT, L and CSP were different among the three groups. Post hoc analyses revealed that CMCT and CSP were the shortest in PD, and that MT was significantly lower in PD than in MSA. In patients whose disease duration was less than 3 years, CMCT and CSP were different among the three groups. Post hoc analyses showed significantly shorter CMCT in PD.

CONCLUSIONS

TMS can detect the pathophysiological difference among the groups in the early stages of the disease.

Assessment of cortico-spinal tract impairment in multiple system atrophy using transcranial magnetic stimulation

OBJECTIVE

Among Parkinsonian syndromes, pyramidal signs suggesting cortico-spinal impairment are a hallmark of multiple system atrophy (MSA). Although it is crucial to diagnose correctly this disease to choose the appropriate treatment, the available diagnostic criteria lack sensitivity. Cortical excitability patterns assessed by transcranial magnetic stimulation (TMS) do not differentiate Parkinsonian disorders. TMS using triple stimulation technique (TST) accurately detects cortico-spinal impairment. We hypothesized that this technique could detect such impairment in MSA patients.

METHODS

The TST was applied along with single and paired-pulse TMS to 31 patients fulfilling the diagnostic criteria for MSA-P (n=10), MSA-C (n=4), progressive supranuclear palsy (PSP; n=6) and Idiopathic Parkinson's disease (IPD; n=11) and 11 control subjects.

RESULTS

Single and paired-pulse TMS patterns did not differ between any patient group. The TST pattern was abnormal in five MSA-P, one MSA-C and one PSP patients but not in IPD patients or controls. The mean TST ratio for MSA-P (86.6%) was significantly different from IPD (99.1%; p<0.05) whereas ratios for MSA-C (92.1%) and PSP (93.3%) were not different from IPD or controls (99.5%).

CONCLUSIONS

These results suggest that TST is effective to assess cortico-spinal impairment in MSA.

SIGNIFICANCE

TST might be useful for the diagnosis of atypical Parkinsonism.

Abnormal responses to repetitive transcranial magnetic stimulation in multiple system atrophy

We studied the response of the motor cortex to brief trains of suprathreshold repetitive transcranial magnetic stimulations (rTMS) in patients with the Parkinson-variant of multiple system atrophy (MSA-P) and compared it to patients with idiopathic Parkinson's disease (PD) and healthy controls. Eight subjects were studied in each group, and patients were matched for disease severity as assessed by Hoehn & Yahr stages. rTMS was delivered at rest and during low-level contractions in trains of 10 stimulations at 5 Hz, and stimulation intensity was set to result in an motor evoked potential (MEP) in the first dorsal interosseus muscle of 0.5 to 1.0 mV. In MSA-P, MEP amplitude at rest was already reduced after the second stimulus and remained so, while it did not change in PD and controls. During contraction, MEP size did not change during the train in any group. The silent period that followed the last stimulus was of similar duration as the first stimulus in MSA-P, but was increased in PD and controls. These findings indicate that abnormal inhibition occurs within the motor cortex in MSA-P, despite dopaminergic treatment and indicate differences in cortical dysfunction between MSA-P and PD. We suggest that these abnormalities reflect the motor cortex pathology found in MSA-P.

Predictive and reactive control of grasping forces: on the role of the basal ganglia and sensory feedback

We comparatively investigated predictive and reactive grip force behaviour in 12 subjects with basal ganglia dysfunction (six subjects with Parkinson's disease, six subjects with writer's cramp), two subjects chronically lacking all tactile and proprioceptive sensory feedback and 16 sex- and age-matched control subjects. Subjects held an instrumented receptacle between the index finger and thumb. A weight was dropped into the receptacle either unexpectedly from the experimenter's hand with the subject being blindfolded or expectedly from the subject's opposite hand. This paradigm allowed us to study predictive and reactive modes of grip force control. All patients generated an overshoot in grip force, irrespective of whether the weight was dropped expectedly or unexpectedly. When the weight was dropped from the experimenter's hand, a reactive grip force response lagged behind the load perturbation at impact in patients with basal ganglia dysfunction and healthy controls. When the weight was dropped expectedly from the subject's opposite hand, patients with basal ganglia dysfunction and healthy subjects started to increase grip force prior to the release of the weight, indicating a predictive mode of control. We interpret these data to support the notion that the motor dysfunction in basal ganglia disorders is associated with deficits of sensorimotor integration. Both deafferented subjects did not show a reactive mode of force control when the weight was dropped unexpectedly, underlining the importance of sensory feedback to initiate reactive force responses. Also in the predictive mode, grip force processing was severely impaired in deafferented subjects. Thus, at least intermittent sensory information is necessary to establish and update predictive modes of grasping force control.

Stimulation du cortex moteur, Parkinson et dystonie : que nous enseigne la stimulation magnétique transcrânienne? revue de la littérature

INTRODUCTION

Over the last few years, deep brain stimulation techniques, with targets such as the subthalamic nucleus or the pallidum, have bee found to be beneficial in the treatment of Parkinson's disease and dystonia. Conversely, therapeutic strategies of cortical stimulation have not yet been validated in these diseases, although they are known to be associated with various cortical dysfunctions. Transcranial magnetic stimulation (TMS) is a valuable tool for non-invasive study of the role played by the motor cortex in the pathophysiology of movement disorders, in particular by assessing various cortical excitability determinants using single or paired pulse paradigms. In addition, repetitive TMS (rTMS) trains can be used to study the effects of transient activity changes of a targeted cortical area.

BACKGROUND

Studies with TMS revealed significant motor cortex excitability changes, particularly regarding intracortical inhibitory pathways, both in Parkinson's disease and in dystonia, and these changes can be distinguished owing to the resting state or to the phases of movement preparation or execution. However, more specific correlation between electrophysiological features and clinical symptoms remains to be established. In addition, the stimulation of various cortical targets by rTMS protocols applied at low or high frequencies have induced some clear clinical effects.

PERSPECTIVES

The TMS effects are and will remain applied in movement disorders to better understand the role played by the motor cortex, to assess various types of treatment and appraise the therapeutic potential of cortical stimulation.

CONCLUSION

TMS provides evidence for motor cortex dysfunction in Parkinson's disease or dystonia. Moreover, rTMS results have opened new perspectives for therapeutic strategies of implanted cortical stimulation. By these both aspects, TMS techniques show their usefulness in the assessment of movement disorders.

Measurements of transcallosally mediated cortical inhibition for differentiating parkinsonian syndromes

Clinicopathologic evidence suggests differential involvement of cortex and corpus callosum (CC) in various disorders presenting with a parkinsonian syndrome. We tested the hypothesis of whether neurophysiologic and morphometric assessments of CC as surrogate parameters of cortical involvement could be helpful in differential diagnosis of parkinsonian disorders. The integrity of CC was assessed neurophysiologically by measuring the ipsilateral silent period (iSP) evoked by transcranial magnetic stimulation (TMS) in a total of 25 patients with idiopathic parkinsonian syndromes (IPS), corticobasal ganglionic degeneration (CBD), progressive supranuclear palsy (PSP), or multiple system atrophy (MSA). Additionally, morphometric analyses of magnetic resonance imaging (MRI) measurements of CC was carried out in all patients. iSP was abnormal in all 5 CBD and all 5 PSP patients, whereas it was intact in all 10 IPS patients and all 5 MSA patients. Among various MRI parameters of CC, testing between different groups revealed a significant difference only for measurements of the middle part of the truncus. CBD and PSP patients exhibited a significant atrophy as compared with control subjects. These data suggest impairment of callosal integrity in patients with CBD and PSP. iSP measurements may be a useful clinical neurophysiologic test in differential diagnosis of patients with parkinsonian syndromes.

Coordination of fingertip forces during precision grasping in multiple system atrophy

While the pathology and autonomic nervous system components of multiple system atrophy (MSA) have been well described, little is known about the associated motor dysfunction. One prominent feature of MSA is parkinsonism, although ataxias and pyramidal tract signs are frequently present. To investigate the nature of motor deficits in MSA, a natural grip-lift movement requiring a precision grasp was used to examine force coordination. Subjects were asked to grasp an instrumented object using the fingertips of the thumb and index finger and lift it 10 cm above the table surface. Subjects with MSA demonstrated a prolonged duration between object contact and initiation of the lifting drive that increased with the weight of the object. During this period these subjects produced large grasping forces generating a significant portion of the eventual grip force employed to hold the object. In contrast, control subjects generated grip and load forces in parallel after establishing contact with the object. Therefore, subjects with MSA showed a disrupted performance on both the sequential (grasp, then lift) and simultaneous (grip and load force development) portions of this task. Only after initiation of the vertical lifting drive did subjects with MSA generate forces in a similar manner to control subjects. These findings demonstrate that subjects with MSA exhibit a disrupted coordination of grasp and could suggest a general deficit in motor control resulting from multi-focal neural degeneration.

Sensorimotor integration in movement disorders

Although current knowledge attributes movement disorders to a dysfunction of the basal ganglia-motor cortex circuits, abnormalities in the peripheral afferent inputs or in their central processing may interfere with motor program execution. We review the abnormalities of sensorimotor integration described in the various types of movement disorders. Several observations, including those of parkinsonian patients' excessive reliance on ongoing visual information during movement tasks, suggest that proprioception is defective in Parkinson's disease (PD). The disturbance of proprioceptive regulation, possibly related to the occurrence of abnormal muscle-stretch reflexes, might be important for generating hypometric or bradykinetic movements. Studies with somatosensory evoked potentials (SEPs), prepulse inhibition, and event-related potentials support the hypothesis of central abnormalities of sensorimotor integration in PD. In Huntington's disease (HD), changes in SEPs and long-latency stretch reflexes suggest that a defective gating of peripheral afferent input to the brain might impair sensorimotor integration in cortical motor areas, thus interfering with the processing of motor programs. Defective motor programming might contribute to some features of motor impairment in HD. Sensory symptoms are frequent in focal dystonia and sensory manipulation can modify the dystonic movements. In addition, specific sensory functions (kinaesthesia, spatial-temporal discrimination) can be impaired in patients with focal hand dystonia, thus leading to a "sensory overflow." Sensory input may be abnormal and trigger focal dystonia, or defective "gating" may cause an input-output mismatch in specific motor programs. Altogether, several observations strongly support the idea that sensorimotor integration is impaired in focal dystonia. Although elemental sensation is normal in patients with tics, tics can be associated with sensory phenomena. Some neurophysiological studies suggest that an altered "gating" mechanism also underlies the development of tics. This review underlines the importance of abnormal sensorimotor integration in the pathophysiology of movement disorders. Although the physiological mechanism remains unclear, the defect is of special clinical relevance in determining the development of focal dystonia.

Applications of transcranial magnetic stimulation in movement disorders

The author reviews the applications of transcranial magnetic stimulation (TMS) in a series of movement disorders--namely, Parkinson's disease, corticobasal degeneration, multiple system atrophy, progressive supranuclear palsy, essential tremor, dystonia, Huntington's chorea, myoclonus, the ataxias, Tourette's syndrome, restless legs syndrome, Wilson's disease, Rett syndrome, and stiff-person syndrome. Single- and paired-pulse TMS studies have been done mainly for pathophysiologic purposes. Repetitive TMS has been used largely for therapy. Many TMS abnormalities are seen in the different diseases. They concur to show that motor cortical areas and their projections are the main target of the basal ganglia dysfunction typical of movement disorders. Interpretation has not always been clear, and sometimes there were discrepancies and contradictions. Largely, this may be the result of the extreme heterogeneity of the methods used and of the patients studied. It is premature to give repetitive TMS a role in treatment. Overall, however, TMS gives rise to a new, outstanding enthusiasm in the neurophysiology of movement disorders. There is reason to predict that TMS, with its continuous technical refinement, will prove even more helpful in the near future. Then, research achievements are reasonably expected to spill over into clinical practice.

Multiple system atrophy: pathophysiology and management

Multiple system atrophy (MSA) is a sporadic neurodegenerative disorder that usually manifests when an individual is in his/her early fifties and progresses relentlessly with a mean survival of 9 years. Clinically, MSA is dominated by autonomic/urogenital failure which may be associated with either parkinsonism (MSA-P subtype) in 80% of cases or with cerebellar ataxia (MSA-C subtype) in 20% of cases. Pathologically, MSA is characterised by a neuronal multisystem degeneration and abnormal glial cytoplasmic inclusions containing alpha-synuclein aggregates. Autonomic and urogenital features of MSA should be identified early on because they can be treated effectively in many instances. In contrast, pharmacological treatment of motor features is often disappointing, except for a minority of patients with MSA-P who derive transient benefit from levodopa treatment. In the future, neurotransplantation may extend or improve the treatment response in MSA-P, but further preclinical evidence is required prior to clinical application. Neuroprotection strategies may slow down disease progression in MSA and the results of the first double-blind trial of riluzole (an inhibitor of glutamate release) in patients with MSA will be available in 2004.

Abnormalities of sensorimotor integration in focal dystonia: a transcranial magnetic stimulation study

It has been postulated that sensorimotor integration is abnormal in dystonia. We investigated changes in motor cortical excitability induced by peripheral stimulation in patients with focal hand dystonia (12 patients with hand cramps) and with cervical dystonia (nine with spasmodic torticollis) compared with 16 age-matched normal controls. Motor evoked potentials (MEP) to focal (figure-of-eight coil) transcranial magnetic stimulation of the hand area were recorded from the right abductor pollicis brevis (APB), first dorsal interosseus (FDI), flexor carpi radialis and extensor carpi radialis muscles. Changes of test MEP size following conditioning stimulation of the right median nerve (or of the index finger) at conditioning-test (C-T) intervals of 50, 200, 600 and 1000 ms were analysed. Peripheral stimulation significantly reduced test MEP size in the APB and FDI muscles of normal control and spasmodic torticollis patients. The inhibitory effect was larger upon median nerve stimulation and reached a maximum at the C-T interval of 200 ms. On the contrary, hand cramp patients showed a significant facilitation of test MEP size. This study suggests that MEP suppression following peripheral stimulation is defective in patients with focal hand dystonia. Central processing of sensory input is abnormal in dystonia and may contribute to increased motor cortical excitability.

Abnormalities of motor cortical excitability are not correlated with clinical features in atypical parkinsonism

OBJECTIVE

To evaluate the specificity of motor cortical excitability changes in parkinsonian syndromes and their relevance to the pathophysiology of cardinal parkinsonian features.

METHODS

Paired transcranial magnetic stimulation (TMS) was used to assess cortico-cortical inhibition (CCI) and facilitation (CCF) in the opponens pollicis muscle of patients with atypical, non-L-dopa- (LD) responsive parkinsonism.

RESULTS

Compared with age-matched normal control subjects, CCI (interstimulus interval [ISI], 3 ms) was significantly reduced in 10 patients with predominantly parkinsonian multiple system atrophy (MSA-P) and in seven with vascular parkinsonism (VP), but not in four with predominantly cerebellar MSA. No significant change of CCF (ISI, 12 ms) was observed. No correlation was found between the amount of CCI and clinical status as evaluated with the Unified Parkinson's Disease Rating Scale (UPDRS). In 10 patients (5 MSA-P, 5 VP), CCI was significantly increased by LD acute administration without concurrent clinical changes.

CONCLUSIONS

Abnormalities of CCI are not peculiar to idiopathic Parkinson's disease and seem unlikely to underlie any specific parkinsonian feature, but rather possibly reflect a nonspecific imbalance of inhibitory and facilitatory motor cortical circuits.

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.

The diagnostic value of motor evoked potentials

OBJECTIVE

To assess the diagnostic usefulness of motor evoked potentials (MEPs) and to identify the optimal method for calculating the central conduction time. The test results were evaluated in a prospective study of 1023 neurological patients.

METHODS

We evaluated the correlation between clinical and electrophysiological findings, the accuracy, the sensitivity, the percentage of subclinical abnormalities and the false negative rates of MEPs in different neurological disorders. In patients with lower motor neuron involvement, we compared the central conduction time calculated as the difference between the latency of the cortical and magnetic root stimulation responses with that calculated using the F-wave method.

RESULTS

The agreement index between electrophysiological and clinical findings was 87%. The overall accuracy of the test was 0.97. The higher sensitivity values were demonstrated in spinal cord disorders (0.85), hereditary spastic paraplegia (0.80) and motor neuron diseases (0.74). The higher percentages of subclinical abnormalities were found in motor neuron disorders (26%) muscular diseases (24%), multiple sclerosis (13.5%) and spinal cord diseases (12.5%). The higher false negative rates were found in sylvian stroke (0.36) and hereditary spastic paraplegia (0.16). Central conduction study using magnetic paravertebral stimulation but not using the F-wave method, resulted in 12% and 10% of false positive values in lower limb multiradiculopathies and in neuropathies, respectively.

CONCLUSIONS

MEPs represent a highly accurate diagnostic test. MEP clinical value is maximum in motor neuron, muscle and spinal cord diseases. In patients with lower motor neuron involvement, the gold standard for central conduction determination is the F-wave method.

Multiple system atrophy

Multiple system atrophy (MSA) is a degenerative central nervous system disease of unclear origin. Patients affected typically show symptoms attributable to the combined involvement of the extrapyramidal, pyramidal, cerebellar and autonomic nervous systems. At onset patients mostly see a doctor because of extrapyramidal or--more rarely--cerebellar symptoms. Evidence of autonomic nervous system involvement is often not apparent, at least to the neurologist, before the history is taken. In later stages, by contrast, involvement of all of the above systems is clinically detectable.

Neurophysiological abnormalities in the Westphal variant of Huntington's disease

The Westphal variant of Huntington's disease (HD) is a distinct clinical entity of HD characterized by a rigid-hypokinetic syndrome and is often associated with a juvenile onset of disease. Definite genetic differences between the subtypes of HD have not been delineated so far. Here we present the results of a battery of neurophysiological tests including somatosensory-evoked potentials, blink reflexes, long-latency reflexes, and measurement of saccadic velocities in a Westphal HD patient. Although quantitative assessment of his motor performance showed a severe hypokinetic syndrome resembling Parkinson's disease, the results of somatosensory-evoked potentials and blink reflexes were indistinguishable from results obtained in hyperkinetic HD patients. Long-latency reflexes, however, which are typically absent in hyper-kinetic HD patients, were retained in this patient. It is concluded that neurophysiology in HD patients is not a mere reflection of the patient's symptomatology but can give insight into the underlying pathophysiological process.