Sensitivity of transcranial magnetic stimulation of cortico-bulbar vs. cortico-spinal tract involvement in Amyotrophic Lateral Sclerosis (ALS)

Abnormalities of cortical stimulation strength-duration time constant in amyotrophic lateral sclerosis

OBJECTIVES

Strength-duration time constant (SDTC) may now be determined for cortical motor neurones, with activity mediated by transient Na+ conductances. The present study determined whether cortical SDTC is abnormal and linked to the pathogenesis of amyotrophic lateral sclerosis.

METHODS

Cortical SDTC and rheobase were estimated from 17 ALS patients using a controllable pulse parameter transcranial magnetic stimulation (cTMS) device. Resting motor thresholds (RMTs) were determined at pulse widths (PW) of 30, 45, 60, 90 and 120 µs and M-ratio of 0.1, using a figure-of-eight coil applied to the primary motor cortex.

RESULTS

SDTC was significantly reduced in ALS patients (150.58 ± 9.98 µs; controls 205.94 ± 13.7 µs, P < 0.01). The reduced SDTC correlated with a rate of disease progression (Rho = -0.440, P < 0.05), ALS functional rating score (ALSFRS-R) score (Rho = 0.446, P < 0.05), and disease duration (R = 0.428, P < 0.05). The degree of change in SDTC was greater in patients with cognitive abnormalities as manifested by an abnormal total Edinburgh Cognitive ALS Screen score (140.5 ± 28.7 µs, P < 0.001) and ALS-specific subscore (141.7 ± 33.2 µs, P = 0.003).

CONCLUSIONS

Cortical SDTC reduction was associated with a more aggressive ALS phenotype, or with more prominent cognitive impairment.

SIGNIFICANCE

An increase in transient Na+ conductances may account for the reduction in SDTC, linked to the pathogenesis of ALS.

Reduction in short interval intracortical inhibition from the early stage reflects the pathophysiology in amyotrophic lateral sclerosis: A meta-analysis study

BACKGROUND AND PURPOSE

Cortical hyperexcitability has been identified as a diagnostic and pathogenic biomarker of amyotrophic lateral sclerosis (ALS). Cortical excitability is assessed by transcranial magnetic stimulation (TMS), a non-invasive neurophysiological technique. The TMS biomarkers exhibiting highest sensitivity for cortical hyperexcitability in ALS remain to be elucidated. A meta-analysis was performed to determine the TMS biomarkers exhibiting the highest sensitivity for cortical hyperexcitability in ALS.

METHODS

A systematic literature review was conducted of all relevant studies published in the English language by searching PubMed, MEDLINE, Embase and Scopus electronic databases from 1 January 2006 to 28 February 2023. Inclusion criteria included studies reporting the utility of threshold tracking TMS (serial ascending method) in ALS and controls.

RESULTS

In total, more than 2500 participants, incorporating 1530 ALS patients and 1102 controls (healthy, 907; neuromuscular, 195) were assessed with threshold tracking TMS across 25 studies. Significant reduction of mean short interval intracortical inhibition (interstimulus interval 1-7 ms) exhibited the highest standardized mean difference with moderate heterogeneity (-0.994, 95% confidence interval -1.12 to -0.873, p < 0.001; Q = 38.61, p < 0.05; I2 = 40%). The reduction of cortical silent period duration along with an increase in motor evoked potential amplitude and intracortical facilitation also exhibited significant, albeit smaller, standardized mean differences.

CONCLUSION

This large meta-analysis study disclosed that mean short interval intracortical inhibition reduction exhibited the highest sensitivity for cortical hyperexcitability in ALS. Combined findings from this meta-analysis suggest that research strategies aimed at understanding the cause of inhibitory interneuronal circuit dysfunction could enhance understanding of ALS pathogenesis.

Novel approaches to assessing upper motor neuron dysfunction in motor neuron disease/amyotrophic lateral sclerosis: IFCN handbook chapter

Identifying upper motor neuron (UMN) dysfunction is fundamental to the diagnosis and understanding of disease pathogenesis in motor neuron disease (MND). The clinical assessment of UMN dysfunction may be difficult, particularly in the setting of severe muscle weakness. From a physiological perspective, transcranial magnetic stimulation (TMS) techniques provide objective biomarkers of UMN dysfunction in MND and may also be useful to interrogate cortical and network function. Single, paired- and triple pulse TMS techniques have yielded novel diagnostic and prognostic biomarkers in MND, and have provided important pathogenic insights, particularly pertaining to site of disease onset. Cortical hyperexcitability, as heralded by reduced short interval intracortical inhibition (SICI) and increased short interval intracortical facilitation, has been associated with the onset of lower motor neuron degeneration, along with patterns of disease spread, development of specific clinical features such as the split hand phenomenon, and may provide an indication about the rate of disease progression. Additionally, reduction of SICI has emerged as a potential diagnostic aid in MND. The triple stimulation technique (TST) was shown to enhance the diagnostic utility of conventional TMS measures in detecting UMN dysfunction in MND. Separately, sophisticated brain imaging techniques have uncovered novel biomarkers of neurodegeneration that have bene associated with progression. The present review will discuss the utility of TMS and brain neuroimaging derived biomarkers of UMN dysfunction in MND, focusing on recently developed TMS techniques and advanced neuroimaging modalities that interrogate structural and functional integrity of the corticomotoneuronal system, with an emphasis on pathogenic, diagnostic, and prognostic utility.

Contribution of neurophysiology to the diagnosis and monitoring of ALS

This chapter describes the role of neurophysiological techniques in diagnosing and monitoring amyotrophic lateral sclerosis (ALS). Despite many advances, electromyography (EMG) remains a keystone investigation from which to build support for a diagnosis of ALS, demonstrating the pathophysiological processes of motor unit hyperexcitability, denervation and reinnervation. We consider development of the different diagnostic criteria and the role of EMG therein. While not formally recognised by established diagnostic criteria, we discuss the pioneering studies that have demonstrated the diagnostic potential of transcranial magnetic stimulation (TMS) of the motor cortex and highlight the growing evidence for TMS in the diagnostic process. Finally, accurately monitoring disease progression is crucial for the successful implementation of clinical trials. Neurophysiological measures of disease state have been incorporated into clinical trials for over 20 years and we review prominent techniques for assessing disease progression.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

Cortical hyperexcitability: Diagnostic and pathogenic biomarker of ALS

Cortical hyperexcitability is an early and intrinsic feature of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS).. Importantly, cortical hyperexcitability appears to be associated with motor neuron degeneration, possibly via an anterograde glutamate-mediated excitotoxic process, thereby forming a pathogenic basis for ALS. The presence of cortical hyperexcitability in ALS patients may be readily determined by transcranial magnetic stimulation (TMS), a neurophysiological tool that provides a non-invasive and painless method for assessing cortical function. Utilising the threshold tracking TMS technique, cortical hyperexcitability has been established as a robust diagnostic biomarker that distinguished ALS from mimicking disorders at early stages of the disease process. The present review discusses the pathophysiological and diagnostic utility of cortical hyperexcitability in ALS.

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.

Regional motor cortex dysfunction in amyotrophic lateral sclerosis

OBJECTIVE

The pathophysiological processes underlying amyotrophic lateral sclerosis (ALS) need to be better understood, although cortical dysfunction has been implicated. Previous transcranial magnetic stimulation (TMS) studies have assessed cortical dysfunction from the hand. The aim of the present study was to determine whether cortical dysfunction was evident across representations of three body regions, and to relate these changes to clinical features of ALS.

METHODS

In this cross-sectional study, threshold tracking TMS was undertaken in 60 sporadic ALS patients, with motor evoked potential (MEP) responses recorded over the hand (abductor pollicis brevis), lower limb (tibialis anterior), and bulbar (trapezius) regions. The cross-sectional findings were compared to 28 age- and gender-matched controls.

RESULTS

Cortical dysfunction was evident across the representation of the three body regions, although the degree and nature of the dysfunction varied. Cortical hyperexcitability, as heralded by reduced short interval intracortical inhibition (SICI), was evident in all cortical regions (hand, P < 0.01; leg, P < 0.05; bulbar, P < 0.05) in ALS patients when compared with healthy control subjects. Importantly, features of cortical hyperexcitability seemed more prominent in clinically affected body regions and correlated with functional disability and muscle weakness. Cortical inexcitability was more prominent in the leg (P < 0.001) and bulbar regions (P < 0.01) when compared with controls.

INTERPRETATION

The nature of cortical dysfunction varied across the body regions in ALS, with cortical hyperexcitability being more prominent in the upper limbs while cortical inexcitability was more evident in the lower limbs and bulbar regions. The findings suggest a heterogeneity of cortical pathophysiological processes in ALS.

Superconditioning TMS for examining upper motor neuron function in MND

We used transcranial magnetic stimulation (TMS) of motor cortex, including a novel four-pulse superconditioning (TMSsc) paradigm, in repeated examinations of motor-evoked potentials (MEPs) in eight subjects with motor neuron disease (MND), including seven with amyotrophic lateral sclerosis (ALS). The goals were: (1) to look for evidence of cortical hyperexcitability, including a reduction in short-interval intracortical inhibition (SICI); and (2) to examine the utility of using TMSsc for quantifying upper motor neuron function during MND progression. Testing of abductor pollicis brevis (APB) and tibialis anterior (TA) muscles bilaterally was carried out every 3 months in MND subjects for up to 2 years; results were compared to those from a cohort of 15 control subjects. Measures of SICI were not significantly different between control and MND subjects for either APB or TA muscles. Other measures of cortical excitability, including TMS threshold and MEP amplitude, were consistent with lowered cortical excitability in MND subjects. Certain combinations of superconditioning TMS were capable of causing stronger inhibition or facilitation of MEPs compared to dual-pulse TMS, for both APB and TA target muscles. Moreover, there were multiple cases in which target muscles unresponsive to strong single-pulse TMS, whether at rest or when tested with an active contraction, showed an MEP in response to TMSsc optimized for facilitation. Our findings suggest that a multi-faceted neurophysiologic protocol for examining upper motor neuron function in MND subjects might benefit from inclusion of TMSsc testing.

Utility of threshold tracking transcranial magnetic stimulation in ALS

Upper motor neuron [UMN] and lower motor neuron [LMN] dysfunction, in the absence of sensory features, is a pathognomonic feature of amyotrophic lateral sclerosis [ALS]. Although the precise mechanisms have yet to be elucidated, one leading hypothesis is that UMN precede LMN dysfunction, which is induced by anterograde glutamatergic excitotoxicity. Transcranial magnetic stimulation (TMS) is a neurophysiological tool that provides a non-invasive and painless assessment of cortical function. Threshold tracking methodologies have been recently adopted for TMS, whereby changes in threshold rather than motor evoked potential (MEP) amplitude serve as outcome measures. This technique is reliable and provides a rapid assessment of cortical function in ALS. Utilisng the threshold tracking TMS technique, cortical hyperexcitability was demonstrated as an early feature in sporadic ALS preceding the onset of LMN dysfunction and possibly contributing to disease spread. Separately, cortical hyperexcitability was reported to precede the clinical onset of familial ALS. Of further relevance, the threshold tracking TMS technique was proven to reliably distinguish ALS from mimicking disorders, even in the presence of a comparable degree of LMN dysfunction, suggesting a diagnostic utility of TMS. Taken in total, threshold tracking TMS has provided support for a cortical involvement at the earliest detectable stages of ALS, underscoring the utility of the technique for probing the underlying pathophysiology. The present review will discuss the physiological processes underlying TMS parameters, while further evaluating the pathophysiological and diagnostic utility of threshold tracking TMS in ALS.

Amyotrophic lateral sclerosis or not: Keys for the diagnosis

Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron disease (MND) which prognosis is poor. Early diagnosis permit to set up immediately adapted treatment and cares. Available diagnostic criteria are based on the detection of both central and peripheral motor neuron injury in bulbar, cervical, thoracic and lumbar regions. Electrodiagnostic (EDX) tests are the key tools to identify peripheral motor neuron involvement. Needle examination records abnormal activities at rest, and looks for neurogenic pattern during muscle contraction. Motor unit potentials morphology is modified primary to recruitment. Motor evoked potentials remain the test of choice to identify impairment of central motor neurons. In the absence of diagnostic biomarker of ALS and among essential investigations of suspected MND, a careful clinical and neurophysiological work-up is essential to rule out the differential diagnosis.

Transcranial Magnetic Stimulation for the Assessment of Neurodegenerative Disease

Transcranial magnetic stimulation (TMS) is a noninvasive technique that has provided important information about cortical function across an array of neurodegenerative disorders, including Alzheimer's disease, frontotemporal dementia, Parkinson's disease, and related extrapyramidal disorders. Application of TMS techniques in neurodegenerative diseases has provided important pathophysiological insights, leading to the development of pathogenic and diagnostic biomarkers that could be used in the clinical setting and therapeutic trials. Abnormalities of TMS outcome measures heralding cortical hyperexcitability, as evidenced by a reduction of short-interval intracortical inhibition and increased in motor-evoked potential amplitude, have been consistently identified as early and intrinsic features of amyotrophic lateral sclerosis (ALS), preceding and correlating with the ensuing neurodegeneration. Cortical hyperexcitability appears to form the pathogenic basis of ALS, mediated by trans-synaptic glutamate-mediated excitotoxic mechanisms. As a consequence of these research findings, TMS has been developed as a potential diagnostic biomarker, capable of identifying upper motor neuronal pathology, at earlier stages of the disease process, and thereby aiding in ALS diagnosis. Of further relevance, marked TMS abnormalities have been reported in other neurodegenerative diseases, which have varied from findings in ALS. With time and greater utilization by clinicians, TMS outcome measures may prove to be of utility in future therapeutic trial settings across the neurodegenerative disease spectrum, including the monitoring of neuroprotective, stem-cell, and genetic-based strategies, thereby enabling assessment of biological effectiveness at early stages of drug development.

Zebra sign of precentral gyri in amyotrophic lateral sclerosis: A novel finding using phase difference enhanced (PADRE) imaging-initial results

OBJECTIVE

We compared the precentral gyri (PG) on the PADRE of patients with amyotrophic lateral sclerosis (ALS) and healthy subjects (HSs) in order to determine whether it is possible to discriminate between ALS patients and HSs on an individual basis.

METHODS

First, two radiologists reviewed the appearance of the normal PG and that of ALS patients on PADRE in a non-blinded manner, and deviations from the appearance of the normal PG were recorded. Next, based on the presence of PG abnormalities on PADRE, we performed an observer performance study using 16 ALS patients and 16 HSs.

RESULTS

The radiologists were able to consensually define the PG as abnormal on PADRE when a low-signal-intensity layer was observed in the gray matter of the PG; a three- or four-layer organization (zebra sign) was characterized by the low-signal-intensity layer. The observer performance study demonstrated that the sensitivity, specificity, and accuracy of PG abnormalities on PADRE for discriminating ALS patients from HSs were 94 %, 94 %, and 94 %, respectively, for reviewers 1 and 2.

CONCLUSIONS

It was possible to discriminate between ALS patients and HSs based on the presence of PG abnormalities on PADRE, which may reflect upper motor neuron impairment in ALS.

KEY POINTS

• PADRE reveals low-signal-intensity layer in the PG of ALS • By PADRE findings on PG, we can discriminate ALS from HSs • PADRE may be a useful method for detecting UMN impairment in ALS.

Use of transcranial magnetic stimulation in the treatment of selected movement disorders

Transcranial magnetic stimulation (TMS) is a valuable technique for assessing the underlying neurophysiology associated with various neuropathologies, and is a unique tool for establishing potential neural mechanisms responsible for disease progression. Recently, repetitive TMS (rTMS) has been advanced as a potential therapeutic technique to treat selected neurologic disorders. In healthy individuals, rTMS can induce changes in cortical excitability. Therefore, targeting specific cortical areas affected by movement disorders theoretically may alter symptomology. This review discusses the evidence for the efficacy of rTMS in Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and multiple sclerosis. It is hoped that gaining a more thorough understanding of the timing and parameters of rTMS in individuals with neurodegenerative disorders may advance both clinical care and research into the most effective uses of this technology.

The facial motor system

Facial movements support a variety of functions in human behavior. They participate in automatic somatic and visceral motor programs, they are essential in producing communicative displays of affective states and they are also subject to voluntary control. The multiplicity of functions of facial muscles, compared to limb muscles, is reflected in the heterogeneity of their anatomical and histological characteristics that goes well beyond the conventional classification in single facial muscles. Such parcellation in different functional muscular units is maintained throughout the central representation of facial movements from the brainstem up to the neocortex. Facial movements peculiarly lack a conventional proprioceptive feedback system, which is only in part vicariated by cutaneous or auditory afferents. Facial motor activity is the main marker of endogenous affective states and of the affective valence of external stimuli. At the cortical level, a complex network of specialized motor areas supports voluntary facial movements and, differently from upper limb movements, in such network there does not seem to be a prime actor in the primary motor cortex.

Transcranial magnetic stimulation and amyotrophic lateral sclerosis: pathophysiological insights

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons in the motor cortex, brainstem and spinal cord. A combination of upper and lower motor neuron dysfunction comprises the clinical ALS phenotype. Although the ALS phenotype was first observed by Charcot over 100 years ago, the site of ALS onset and the pathophysiological mechanisms underlying the development of motor neuron degeneration remain to be elucidated. Transcranial magnetic stimulation (TMS) enables non-invasive assessment of the functional integrity of the motor cortex and its corticomotoneuronal projections. To date, TMS studies have established motor cortical and corticospinal dysfunction in ALS, with cortical hyperexcitability being an early feature in sporadic forms of ALS and preceding the clinical onset of familial ALS. Taken together, a central origin of ALS is supported by TMS studies, with an anterograde transsynaptic mechanism implicated in ALS pathogenesis. Of further relevance, TMS techniques reliably distinguish ALS from mimic disorders, despite a compatible peripheral disease burden, thereby suggesting a potential diagnostic utility of TMS in ALS. This review will focus on the mechanisms underlying the generation of TMS measures used in assessment of cortical excitability, the contribution of TMS in enhancing the understanding of ALS pathophysiology and the potential diagnostic utility of TMS techniques in ALS.

Rapidly progressive amyotrophic lateral sclerosis initially masquerading as a demyelinating neuropathy

Rare cases of demyelinating neuropathy have been described in association with amyotrophic lateral sclerosis (ALS). We report two patients with typical ALS whose initial electroneuromyographic (ENMG) presentation could suggest the existence of a process of motor nerve fiber demyelination. However, subsequent ENMG examinations and the fatal course of the disease in a few months rather supported severe ongoing axonal degeneration at the origin of motor nerve conduction abnormalities. Repeated examinations could be required to distinguish between ENMG features of concomitant demyelinating neuropathy and rapidly progressive motor neuron loss in ALS.

Utility of transcranial magnetic stimulation in delineating amyotrophic lateral sclerosis pathophysiology

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder of the motor neurons in the motor cortex, brainstem, and spinal cord. The clinical phenotype of ALS is underscored by a combination of upper and lower motor neuron dysfunction. Although this phenotype was observed over 100 years ago, the site of ALS onset and the pathophysiological mechanisms underlying the development of motor neuron degeneration remain to be elucidated. Transcranial magnetic stimulation (TMS) enables noninvasive assessment of the functional integrity of the motor cortex and its corticomotoneuronal projections. To date, TMS studies have established cortical dysfunction in ALS, with cortical hyperexcitability being an early feature in sporadic forms of ALS and preceding the clinical onset of familial ALS. Taken together, a central origin of ALS is supported by TMS studies, with an anterograde dying-forward mechanism implicated in ALS pathogenesis. Of further relevance, TMS techniques reliably distinguish ALS from mimic disorders, despite a compatible peripheral disease burden, thereby suggesting a potential diagnostic utility of TMS in ALS. This chapter reviews the mechanisms underlying the generation of TMS parameters utilized in assessment of cortical excitability, the contribution of TMS in enhancing the understanding of ALS pathophysiology, and the potential diagnostic utility of TMS techniques in ALS.

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.

Spinal cord markers in ALS: diagnostic and biomarker considerations

Despite considerable involvement of the spinal cord in amyotrophic lateral sclerosis (ALS), current biomarker research is primarily centred on brain imaging and CSF proteomics. In clinical practice, spinal cord imaging in ALS is performed primarily to rule out alternative conditions in the diagnostic phase of the disease. Quantitative spinal cord imaging has traditionally been regarded as challenging, as it requires high spatial resolution while minimizing partial volume effects, physiological motion and susceptibility distortions. In recent years however, as acquisition and post-processing methods have been perfected, a number of exciting and promising quantitative spinal imaging and electrophysiology techniques have been developed. We performed a systematic review of the trends, methodologies, limitations and conclusions of recent spinal cord studies in ALS to explore the diagnostic and prognostic potential of spinal markers. Novel corrective techniques for quantitative spinal cord imaging are systematically reviewed. Recent findings demonstrate that imaging techniques previously used in brain imaging, such as diffusion tensor, functional and metabolic imaging can now be successfully applied to the human spinal cord. Optimized electrophysiological approaches make the non-invasive assessment of corticospinal pathways possible, and multimodal spinal techniques are likely to increase the specificity and sensitivity of proposed spinal markers. In conclusion, spinal cord imaging is an emerging area of ALS biomarker research. Novel quantitative spinal modalities have already been successfully used in ALS animal models and have the potential for development into sensitive ALS biomarkers in humans.

Measures of bulbar and spinal motor function, muscle innervation, and mitochondrial function in ALS rats

Symptom onset in amyotrophic lateral sclerosis (ALS) may occur in the muscles of the limbs (spinal onset) or those of the head and neck (bulbar onset). Most preclinical studies have focused on spinal symptoms, despite the prevalence of and increased morbidity and mortality associated with bulbar disease. We measured lick rhythm and tongue force to evaluate bulbar disease in the SOD1-G93A rat model of familial ALS. Body weight and grip strength were measured concomitantly. Testing spanned the early (maturation), middle (pre-symptomatic), and late (symptomatic and end-stage) phases of the disease. We measured a persistent tongue motility deficit that became apparent in the early phase of the disease, providing behavioral evidence of bulbar pathology. At end-stage, however, cytochrome oxidase (CO) activity was normal in the hypoglossal nucleus, and in the tongue, neuromuscular innervation, citrate synthase (CS) protein levels and activity, and uncoupling protein 3 (UCP3) protein levels remained unchanged. Interestingly, significant denervation and atrophy were evident in the end-stage sternomastoid muscle, providing peripheral anatomical evidence of bulbar pathology. Changes in body weight and grip strength occurred in the late phase of the disease. Extensive atrophy and denervation were observed in the end-stage gastrocnemius muscle. In contrast to our findings in the tongue, CS protein levels were decreased in the extensor digitorum longus (EDL) and soleus, although CS activity was maintained or increased. UCP3 protein was decreased also in the EDL. These data provide evidence of differential effects in muscles that were more or less affected by disease.

Combined 3T diffusion tensor tractography and 1H-MR spectroscopy in motor neuron disease

BACKGROUND AND PURPOSE

Diagnostic confidence in motor neuron disease may be improved by the use of advanced MR imaging techniques. Our aim was to assess the accuracy (sensitivity/specificity) and agreement of combined (1)H-MR spectroscopy (proton MR spectroscopy) and diffusion tensor imaging (DTI) at 3T in patients with suspected motor neuron disease regarding detection of upper motor neuron (UMN) dysfunction.

MATERIALS AND METHODS

Eighteen patients with suspected motor neuron disease were studied with MR spectroscopy/DTI and clinically rated according to the El-Escorial and ALSFRS-R scales. For MR spectroscopy, absolute N-acetylaspartate (NAA), choline (Cho), and phosphocreatine (PCr) concentrations and relative NAA/Cho and NAA/PCr ratios of corresponding volumes of interest within the primary motor cortex were calculated. For DTI, fractional anisotropy (FA) and mean diffusivity (MD) were measured bilaterally at the level of the precentral gyrus, corona radiata, internal capsule, cerebral peduncles, pons, and pyramid. FA and MD statistics were averaged on the corticospinal tracts (CSTs) as a whole to account for a region-independent analysis.

RESULTS

MR spectroscopy indicated NAA reduction beyond the double SD of controls in 6 of 8 patients with clinical evidence for UMN involvement. Congruently, the mean FA of these patients was significantly lower in the upper 3 regions of measurements (P < .01). Overall, MR spectroscopy and DTI were concordant in all except 3 cases: 1 was correctly excluded from motor neuron disease by DTI (genetically proved Kennedy syndrome), whereas MR spectroscopy indicated CST involvement. MR spectroscopy and DTI each were false-positive for CST affection in 1 patient with lower motor neuron involvement only.

CONCLUSION

Combined MR spectroscopy/DTI at 3T effectively adds to the detection of motor neuron disease with a high degree of accordance.

Clinical utility of trapezius muscle studies in the evaluation of amyotrophic lateral sclerosis

Needle electromyography (EMG) and determining the motor evoked potential (MEP) of the genioglossus (tongue) are difficult to perform in evaluation of the craniobulbar region in patients with amyotrophic lateral sclerosis (ALS). Needle EMG and MEP determination in the upper trapezius were carried out in 17 consecutive ALS patients. The needle EMG parameters recorded included abnormal spontaneous activity and motor unit action potential morphology. An upper motor neuron lesion was presumed when either response to cortical stimulation was absent, or the central conduction time was delayed (>mean + 2 SD). Of the 12 patients with limb-onset ALS, using needle EMG, 11 were found to have abnormalities in the upper trapezius, and only five in the tongue. Three of the six patients with isolated limb involvement had abnormal MEP findings. In conclusion, electrophysiological studies of the upper trapezius are useful in ALS patients without bulbar symptoms.

Optimising the detection of upper motor neuron function dysfunction in amyotrophic lateral sclerosis?a transcranial magnetic stimulation study

Evidence of upper motor neuron (UMN) dysfunction is essential in making the diagnosis of amyotrophic lateral sclerosis (ALS). Central motor conduction (CMC) abnormalities detected using transcranial magnetic stimulation (TMS) are presumed to reflect UMN dysfunction. CMC is, however, often normal in patients with classical sporadic ALS. The aim of the study was to determine whether the utility of the CMC measure in ALS could be enhanced. We measured CMC to four pairs of muscles (abductor digiti minimi (ADM), biceps, vastus medialis (VM) and abductor hallucis (AH) in 20 controls and 25 ALS patients. The commonest abnormality detected in the ALS patients was an absent MEP, found in 11 patients (44 %) and in 25 of 200 muscles examined. Studying a minimum of three muscles increased the probability of detecting UMN dysfunction. Weakness in the muscle as well as selecting a distal rather than a proximal muscle was significantly associated with an abnormal CMC. Interside differences in CMC were significantly more pronounced in the patient group. In 30% of patients a significant interside difference in AH CMC time was the sole abnormality, suggesting mild UMN dysfunction on the side with the longer CMC.

Measures and markers in amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disorder characterized by loss of spinal and cortical motor neurons, leading to progressive weakness and ultimately, death. Clinically, there appears to be an anatomic focus at disease onset, from which the disease then spreads. Because the focus of initial symptoms and the subsequent direction of spread can vary from patient to patient, disease monitoring is difficult, especially in a clinical trial, in which outcome measures must be identical and able to capture progression of all types. Thus, the search for markers of disease progression is especially important in ALS. Many approaches have been taken, from voluntary strength assessment and functional rating scales to physiological and pathological sampling of affected portions of nervous system. No proposed marker has been demonstrated to meet the desired criteria of biological meaning, sensitivity to disease progression, clear relationship to overall prognosis and survival, and ease of measurement. However, progress is being made in all of these regards.

Turning heads: development of vertebrate branchiomotor neurons

The cranial motor neurons innervate muscles that control eye, jaw, and facial movements of the vertebrate head and parasympathetic neurons that innervate certain glands and organs. These efferent neurons develop at characteristic locations in the brainstem, and their axons exit the neural tube in well-defined trajectories to innervate target tissues. This review is focused on a subset of cranial motor neurons called the branchiomotor neurons, which innervate muscles derived from the branchial (pharyngeal) arches. First, the organization of the branchiomotor pathways in zebrafish, chick, and mouse embryos will be compared, and the underlying axon guidance mechanisms will be addressed. Next, the molecular mechanisms that generate branchiomotor neurons and specify their identities will be discussed. Finally, the caudally directed or tangential migration of facial branchiomotor neurons will be examined. Given the advances in the characterization and analysis of vertebrate genomes, we can expect rapid progress in elucidating the cellular and molecular mechanisms underlying the development of these vital neuronal networks. Developmental Dynamics 229:143-161, 2004.

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.