Spinal direct current stimulation (tsDCS) in hereditary spastic paraplegias (HSP): A sham-controlled crossover study

Emerging evidence on the effects of electrode arrangements and other parameters on the application of transcutaneous spinal direct current stimulation

Transcutaneous spinal direct current stimulation (TSDCS) has the potential to modulate spinal circuits and induce functional changes in humans. Nevertheless, differences across studies on basic parameters used and obtained metrics represent a confounding factor. Computer simulations are instrumental in improving the application of the TSDCS technique. Their findings allow a better interpretation of the tissue conductivities heterogeneity. Emerging findings indicate the electric field is maximal in the segments located between the electrodes, and that factors such as the depth of the targeted area, and location of the electrodes on low conductive points, such as the spinous processes, may impact the electric field generated in the spinal cord, with consequences for thoracic versus lumbar or cervical applications. Recently, growing attention has been directed toward the importance of the TSDCS reference electrode's position and its influence on the current field properties at the targeted site. This review highlights the influence of dosage, polarity, and electrode position on the variety of TSDCS results in healthy and some clinical populations. Based on the available evidence, we suggest that although the current dosage appears to have a negligible effect, the variety of electrode montages and configurations of TSDCS can significantly impact the electric field distributions and potentially explain the conflicting results of experimental studies. Future human trials should systematically and thoughtfully evaluate the location of TSDCS electrodes based on the targeted neural structures.

Frequency-Selective Suppression of Essential Tremor via Transcutaneous Spinal Cord Stimulation

BACKGROUND

Essential tremor (ET) is a common debilitating condition, yet current treatments often fail to provide satisfactory relief. Transcutaneous spinal cord electrical stimulation (tSCS) has emerged as a potential noninvasive neuromodulation technique capable of disrupting the oscillatory activity underlying tremors.

OBJECTIVE

This study aimed to investigate the potential of tSCS to disrupt tremor in a frequency-dependent manner in a cohort of patients with ET.

METHODS

Eighteen patients with ET completed the study. The experiment consisted of 60-s postural tremor recording, during tSCS at tremor frequency, at 1 Hz, at 21 Hz, no stimulation, and trapezius stimulation. Tremor frequency and amplitude were analyzed and compared across the conditions.

RESULTS

We found tremor amplitude reduction at tremor frequency stimulation significant only during the second half of the stimulation. The same stimulation resulted in the highest number of responders. tSCS at 1 Hz showed a trend toward decreased tremor amplitude in the latter half of stimulation. tSCS at 21 Hz did not produce any significant alterations in tremor, whereas trapezius stimulation exacerbated it. Notably, during tremor frequency stimulation, a subgroup of responders exhibited consistent synchronization between tremor phase and delivered stimulation, indicating tremor entrainment.

CONCLUSIONS

Cervical tSCS holds promise for alleviating postural tremor in patients with ET when delivered at the subject's tremor frequency. The observed changes in tremor amplitude likely result from the modulation of spinal cord circuits by tSCS, which disrupts the oscillatory drive to muscles by affecting afferent pathways or spinal reflexes. However, the possibility of an interplay between spinal and supraspinal centers cannot be discounted. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

A Pragmatic Review on Spinal Cord Stimulation Therapy for Parkinson's Disease Gait Related Disorders: Gaps and Controversies

BACKGROUND

Parkinson's Disease (PD) is a progressive neurological disorder that results in potentially debilitating mobility deficits. Recently, spinal cord stimulation (SCS) has been proposed as a novel therapy for PD gait disorders. The highest levels of evidence remain limited for SCS.

OBJECTIVES

In this systematic review and narrative synthesis, the literature was searched using combinations of key phrases indicating spinal cord stimulation and PD.

METHODS

We included pre-clinical studies and all published clinical trials, case reports, conference abstracts as well as protocols for ongoing clinical trials. Additionally, we included trials of SCS applied to atypical parkinsonism.

RESULTS

A total of 45 human studies and trials met the inclusion criteria. Based on the narrative synthesis, a number of knowledge gaps and future avenues of potential research were identified. This review demonstrated that evidence for SCS is currently not sufficient to recommend it as an evidence-based therapy for PD related gait disorders. There remain challenges and significant barriers to widespread implementation, including issues regarding patient selection, effective outcome selection, stimulation location and mode, and in programming parameter optimization. Results of early randomized controlled trials are currently pending. SCS is prone to placebo, lessebo and nocebo as well as blinding effects which may impact interpretation of outcomes, particularly when studies are underpowered.

CONCLUSION

Therapies such as SCS may build on current evidence and be shown to improve specific gait features in PD. Early negative trials should be interpreted with caution, as more evidence will be required to develop effective methodologies in order to drive clinical outcomes.

Trans-Spinal Direct Current Stimulation in Neurological Disorders: A systematic review

BACKGROUND AND PURPOSE

Trans-spinal direct current stimulation (tsDCS) is a noninvasive stimulation technique that applies direct current stimulation over spinal levels. However, the effectiveness and feasibility of this stimulation are still unclear. This systematic review summarizes the effectiveness of tsDCS in clinical and neurophysiological outcomes in neurological patients, as well as its feasibility and safety.

METHODS

The search was conducted using the following databases: PEDro, Scopus, Web of Science, CINAHL, SPORTDiscus, and PubMed. The inclusion criteria were: Participants : people with central nervous system diseases; Interventions : tsDCS alone or in combination with locomotion training; Comparators : sham tsDCS, transcranial direct current stimulation, or locomotion training; Outcomes : clinical and neurophysiological measures; and Studies : randomized clinical trials.

RESULTS

Eight studies with a total of 143 subjects were included. Anodal tsDCS led to a reduction in hypertonia, neuropathic pain intensity, and balance deficits in people with hereditary spastic paraplegia, multiple sclerosis, and primary orthostatic tremor, respectively. In contrast, cathodal tsDCS only had positive effects on balance and tremor in people with primary orthostatic tremor. No severe adverse effects were reported during and after anodal or cathodal tsDCS.

DISCUSSION AND CONCLUSIONS

Although certain studies have found an effect of anodal tsDCS on specific clinical outcomes in people with central nervous system diseases, its effectiveness cannot be established since these findings have not been replicated and the results were heterogeneous. This stimulation was feasible and safe to apply. Further studies are needed to replicate the obtained results of tsDCS when applied in populations with neurological diseases.

Novel approaches to motoneuron disease/ALS treatment using non-invasive brain and spinal stimulation: IFCN handbook chapter

Non-invasive brain stimulation techniques have been exploited in motor neuron disease (MND) with multifold objectives: to support the diagnosis, to get insights in the pathophysiology of these disorders and, more recently, to slow down disease progression. In this review, we consider how neuromodulation can now be employed to treat MND, with specific attention to amyotrophic lateral sclerosis (ALS), the most common form with upper motoneuron (UMN) involvement, taking into account electrophysiological abnormalities revealed by human and animal studies that can be targeted by neuromodulation techniques. This review article encompasses repetitive transcranial magnetic stimulation methods (including low-frequency, high-frequency, and pattern stimulation paradigms), transcranial direct current stimulation as well as experimental findings with the newer approach of trans-spinal direct current stimulation. We also survey and discuss the trials that have been performed, and future perspectives.

Hereditary spastic paraplegia: Novel insights into the pathogenesis and management

Hereditary spastic paraplegia is a genetically heterogeneous neurodegenerative disorder characterised primarily by muscle stiffness in the lower limbs. Neurodegenerative disorders are conditions that result from cellular and metabolic abnormalities, many of which have strong genetic ties. While ageing is a known contributor to these changes, certain neurodegenerative disorders can manifest early in life, progressively affecting a person's quality of life. Hereditary spastic paraplegia is one such condition that can appear in individuals of any age. In hereditary spastic paraplegia, a distinctive feature is the degeneration of long nerve fibres in the corticospinal tract of the lower limbs. This degeneration is linked to various cellular and metabolic processes, including mitochondrial dysfunction, remodelling of the endoplasmic reticulum membrane, autophagy, abnormal myelination processes and alterations in lipid metabolism. Additionally, hereditary spastic paraplegia affects processes like endosome membrane trafficking, oxidative stress and mitochondrial DNA polymorphisms. Disease-causing genetic loci and associated genes influence the progression and severity of hereditary spastic paraplegia, potentially affecting various cellular and metabolic functions. Although hereditary spastic paraplegia does not reduce a person's lifespan, it significantly impairs their quality of life as they age, particularly with more severe symptoms. Regrettably, there are currently no treatments available to halt or reverse the pathological progression of hereditary spastic paraplegia. This review aims to explore the metabolic mechanisms underlying the pathophysiology of hereditary spastic paraplegia, emphasising the interactions of various genes identified in recent network studies. By comprehending these associations, targeted molecular therapies that address these biochemical processes can be developed to enhance treatment strategies for hereditary spastic paraplegia and guide clinical practice effectively.

Effect of transcutaneous spinal direct current stimulation on spasticity in upper motor neuron conditions: a systematic review and meta-analysis

STUDY DESIGN

A systematic review and meta-analysis of clinical trials.

OBJECTIVES

To determine the effect of non-invasive transcutaneous spinal direct current stimulation (tsDCS) on spasticity, activity limitations and participation restrictions in various upper motor neuron diseases.

METHODS

Six databases including CINAHL plus, Cochrane CENTRAL, Embase, MEDLINE, SCOPUS and Web of Science were searched for the relevant records from January 2008 to December 2022. Two reviewers independently selected and extracted data on spasticity, activity limitations and participation restrictions. The risk of bias was evaluated using the PEDro scale while the GRADE approach established the certainty of the evidence.

RESULTS

Eleven studies were identified of which 5 (45.5%) were rated as having a low risk of bias and 8 (72.7%) were meta-analyzed. The meta-analyses did not show any significant differences between cathodal (SMD = -0.67, 95% CI = -1.50 to 0.15, P = 0.11, I2 = 75%, 6 RCTs) or anodal (SMD = 0.11, 95% CI = -0.43 to -0.64, p = 0.69, I2 = 0%, 2 RCTs) and sham tsDCS for spasticity. There was also no significant difference between active and sham tsDCS for activity limitations (SMD = -0.42, 95% CI = -0.04 to 0.21, p = 0.2, I2 = 0%, 2 RCTs) and participation restrictions (MD = -8.10, 95% CI = -18.02 to 1.82, p = 0.11, 1 RCT).

CONCLUSIONS

The meta-analysis of the available evidence provides an uncertain estimate of the effect of cathodal tsDCS on spasticity, activity limitation and participation restriction. It might be very helpful, or it may make no difference at all. However, considering the level of the evidence and the limitation in the quality of the majority of the included studies, further well-designed research may likely change the estimate of effect.

TRIAL REGISTRATION

PROSPERO CRD42021245601.

Gait analysis patterns and rehabilitative interventions to improve gait in persons with hereditary spastic paraplegia: a systematic review and meta-analysis

Background

Hereditary spastic paraplegias (HSPs) are a group of inheritance diseases resulting in gait abnormalities, which may be detected using instrumented gait analysis. The aim of this systematic review was 2-fold: to identify specific gait analysis patterns and interventions improving gait in HSP subjects.

Methods

A systematic review was conducted in PubMed, Cochrane Library, REHABDATA, and PEDro databases, in accordance with reporting guidelines of PRISMA statement and Cochrane's recommendation. The review protocol was recorded on the PROSPERO register. Patients with pure and complicated HSP of any age were included. All types of studies were included. Risk of bias, quality assessment, and meta-analysis were performed.

Results

Forty-two studies were included: 19 were related to gait analysis patterns, and 24 were intervention studies. The latter ones were limited to adults. HSP gait patterns were similar to cerebral palsy in younger subjects and stroke in adults. Knee hyperextension, reduced range of motion at knee, ankle, and hip, reduced foot lift, and increased rapid trunk and arm movements were reported. Botulinum injections reduced spasticity but uncovered weakness and improved gait velocity at follow-up. Weak evidence supported intrathecal baclofen, active intensive physical therapy (i.e., robot-assisted gait training, functional exercises, and hydrotherapy), and functional electrical stimulation. Some improvements but adverse events were reported after transcranial magnetic stimulation, transcutaneous spinal direct current stimulation, and spinal cord stimulation implant.

Conclusion

Knee hyperextension, non-sagittal pelvic movements, and reduced ROM at the knee, ankle, and hip represent the most peculiar patterns in HSP, compared to diplegic cerebral palsy and stroke. Botulinum improved comfortable gait velocity after 2 months. Nonetheless, interventions reducing spasticity might result in ineffective functional outcomes unveiling weakness. Intensive active physical therapy and FES might improve gait velocity in the very short term.

Outcome Measures and Biomarkers for Clinical Trials in Hereditary Spastic Paraplegia: A Scoping Review

Hereditary spastic paraplegia (HSP) is characterized by progressive lower limb spasticity. There is no disease-modifying treatment currently available. Therefore, standardized, validated outcome measures to facilitate clinical trials are urgently needed. We performed a scoping review of outcome measures and biomarkers for HSP to provide recommendations for future studies and identify areas for further research. We searched Embase, Medline, Scopus, Web of Science, and the Central Cochrane database. Seventy studies met the inclusion criteria, and eighty-three outcome measures were identified. The Spastic Paraplegia Rating Scale (SPRS) was the most widely used (27 studies), followed by the modified Ashworth Scale (18 studies) and magnetic resonance imaging (17 studies). Patient-reported outcome measures (PROMs) were infrequently used to assess treatment outcomes (28% of interventional studies). Diffusion tensor imaging, gait analysis and neurofilament light chain levels were the most promising biomarkers in terms of being able to differentiate patients from controls and correlate with clinical disease severity. Overall, we found variability and inconsistencies in use of outcome measures with a paucity of longitudinal data. We highlight the need for (1) a standardized set of core outcome measures, (2) validation of existing biomarkers, and (3) inclusion of PROMs in HSP clinical trials.

Case report: High-frequency repetitive transcranial magnetic stimulation for treatment of hereditary spastic paraplegia type 11

Hereditary spastic paraplegia (HSP) is a heterogeneous group of inherited neurodegenerative disorders that currently have no cure. HSP type 11 (SPG11-HSP) is a complex form carrying mutations in the SPG11 gene. Neuropathological studies demonstrate that motor deficits in these patients are mainly attributed to axonal degeneration of the corticospinal tract (CST). Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique that can induce central nervous system plasticity and promote neurological recovery by modulating the excitability of cortical neuronal cells. Although rTMS is expected to be a therapeutic tool for neurodegenerative diseases, no previous studies have applied rTMS to treat motor symptoms in SPG11-HSP. Here, we report a case of SPG11-HSP with lower extremity spasticity and gait instability, which were improved by applying high-frequency rTMS (HF-rTMS) at the primary motor cortex (M1). Clinical and physiological features were measured throughout the treatment, including the Modified Ashworth Scale (MAS), Berg Balance Scale (BBS), the timed up and go (TUG) test and the 10-meter walk test time (10 MWT). The structure and excitability of the CST were assessed by diffusion tensor imaging (DTI) and transcranial magnetic stimulation (TMS), respectively. After treatment, the patient gained 17 points of BBS, along with a gradual decrease in MAS scores of the bilateral lower extremity. In addition, the TUG test and 10 MWT improved to varying degrees. TMS assessment showed increased motor evoked potential (MEP) amplitude, decreased resting motor threshold (RMT), decreased central motor conduction time (CMCT), and decreased difference in the cortical silent period (CSP) between bilateral hemispheres. Using the DTI technique, we observed increased fractional anisotropy (FA) values and decreased mean diffusivity (MD) and radial diffusivity (RD) values in the CST. It suggests that applying HF-rTMS over the bilateral leg area of M1 (M1-LEG) is beneficial for SPG11-HSP. In this study, we demonstrate the potential of rTMS to promote neurological recovery from both functional and structural perspectives. It may provide a clinical rationale for using rTMS in the rehabilitation of HSP patients.

Modeling Electric Fields in Transcutaneous Spinal Direct Current Stimulation: A Clinical Perspective

Clinical findings suggest that transcutaneous spinal direct current stimulation (tsDCS) can modulate ascending sensitive, descending corticospinal, and segmental pathways in the spinal cord (SC). However, several aspects of the stimulation have not been completely understood, and realistic computational models based on MRI are the gold standard to predict the interaction between tsDCS-induced electric fields and anatomy. Here, we review the electric fields distribution in the SC during tsDCS as predicted by MRI-based realistic models, compare such knowledge with clinical findings, and define the role of computational knowledge in optimizing tsDCS protocols. tsDCS-induced electric fields are predicted to be safe and induce both transient and neuroplastic changes. This could support the possibility to explore new clinical applications, such as spinal cord injury. For the most applied protocol (2-3 mA for 20-30 min, active electrode over T10-T12 and the reference on the right shoulder), similar electric field intensities are generated in both ventral and dorsal horns of the SC at the same height. This was confirmed by human studies, in which both motor and sensitive effects were found. Lastly, electric fields are strongly dependent on anatomy and electrodes' placement. Regardless of the montage, inter-individual hotspots of higher values of electric fields were predicted, which could change when the subjects move from a position to another (e.g., from the supine to the lateral position). These characteristics underlines the need for individualized and patient-tailored MRI-based computational models to optimize the stimulation protocol. A detailed modeling approach of the electric field distribution might contribute to optimizing stimulation protocols, tailoring electrodes' configuration, intensities, and duration to the clinical outcome.

Spinal cord stimulation may improve gait and cognition in hereditary spastic paraplegia with mental retardation: a case report

BACKGROUND

Hereditary spastic paraplegia (HSP) include various sporadic and hereditary neurodegenerative disorders, characterized by progressive spasticity and weakness of lower limbs, possibly associated to additional features.

CASE PRESENTATION

We report a male HPS patient in his 40 s, showing mental retardation associated with language impairment, dysarthria, and increased urinary frequency. Three months after treatment with electric chronic high-frequency cervical spinal cord stimulation (HF-SCS), he showed an amelioration of motor symptoms (lower limbs spasticity and gait), dysarthria, cognitive functioning (language and constructive praxic abilities), and urinary symptoms (decreased urinary frequency). Single-photon emission computed tomography (SPECT) showed a postoperative increase of cerebral perfusion in right frontal cortex and temporal cortex bilaterally.

CONCLUSION

In our patient, HF-SCS might have induced an activation of ascending neural pathways, resulting in changes in activity in various cortical areas (including sensory-motor cortical areas), which may give rise to a modulation of activity in spared descending motor pathways and in neural networks involved in cognitive functions, including language. Although further studies in patients with HPS are needed to clarify whether HF-SCS can be a suitable treatment option in HSP, our observation suggests that HF-SCS, a minimally invasive neurosurgical procedure, might induce beneficial effects of on various symptoms of such orphan disease.

Non-Invasive Electrical Stimulation in Patients with Neurodegenerative Ataxia and Spasticity: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

BACKGROUND

There are limited treatment options for patients with neurodegenerative ataxia and spasticity. Non-invasive electrostimulation (NES) is receiving increasing interest because of its ease of implementation, cost-effectiveness, and safety. We conducted a meta-analysis to evaluate the efficacy of NES.

METHODS

We screened Medline and Embase for studies using NES in ataxias and spasticity. Key outcome measurements of effectiveness included changes in: (1) Modified Ashworth Scale (MAS) scores, (2) cerebellar brain inhibition (CBI), (3) 9-hole peg test (9HPT), (4) 8-meter walking time (8MWT), (5) International Cooperative Ataxia Rating Scale (ICARS) scores, (6) Scale for Assessment and Rating of Ataxia (SARA) scores.

RESULTS

Seven randomised controlled trials (RCTs) involving 203 patients were included. There were significant improvements in MAS (MD -0.42, 95% CI -0.76 to -0.08, P=0.015), CBI (MD -0.35%, 95% CI -0.42 to -0.28, P<0.001), 8MWT (MD -1.88 seconds, 95% CI -3.26 to -0.49, P=0.008), ICARS (MD -7.84, 95% CI -11.90 to -3.78, P<0.001), and SARA (MD -3.01, 95% CI -4.74 to -1.28, P<0.001). There was almost no heterogeneity across all outcomes except for CBI (I² =79%). No significant changes in 9HPT were observed when comparing NES to a sham procedure (MD -3.52 seconds, 95% CI -9.15 to 2.10, P=0.220). Most included studies were at low risk of bias, and no severe adverse effects were reported.

CONCLUSION

We demonstrated that NES is an effective treatment for improving coordination and balance, and increased exercise capacity in patients with ataxia and spasticity. There was also a significant modulation of CBI in ataxic patients.

Trans-Spinal Electrical Stimulation Therapy for Functional Rehabilitation after Spinal Cord Injury: Review

Spinal cord injury (SCI) is one of the most debilitating injuries in the world. Complications after SCI, such as respiratory issues, bowel/bladder incontinency, pressure ulcers, autonomic dysreflexia, spasticity, pain, etc., lead to immense suffering, a remarkable reduction in life expectancy, and even premature death. Traditional rehabilitations for people with SCI are often insignificant or ineffective due to the severity and complexity of the injury. However, the recent development of noninvasive electrical neuromodulation treatments to the spinal cord have shed a ray of hope for these individuals to regain some of their lost functions, a reduction in secondary complications, and an improvement in their life quality. For this review, 250 articles were screened and about 150 were included to summarize the two most promising noninvasive spinal cord electrical stimulation methods of SCI rehabilitation treatment, namely, trans-spinal direct current stimulation (tsDCS) and trans-spinal pulsed current stimulation (tsPCS). Both treatments have demonstrated good success in not only improving the sensorimotor function, but also autonomic functions. Due to the noninvasive nature and lower costs of these treatments, in the coming years, we expect these treatments to be integrated into regular rehabilitation therapies worldwide.

Recent advances in understanding hereditary spastic paraplegias and emerging therapies

Hereditary spastic paraplegias (HSPs) are a group of rare, inherited, neurological diseases characterized by broad clinical and genetic heterogeneity. Lower-limb spasticity with first motoneuron involvement is the core symptom of all HSPs. As spasticity is a syndrome and not a disease, it develops on top of other neurological signs (ataxia, dystonia, and parkinsonism). Indeed, the definition of genes responsible for HSPs goes beyond the 79 identified SPG genes. In order to avoid making a catalog of the different genes involved in HSP in any way, we have chosen to focus on the HSP with cerebellar ataxias since this is a frequent association described for several genes. This overlap leads to an intermediary group of spastic ataxias which is actively genetically and clinically studied. The most striking example is SPG7, which is responsible for HSP or cerebellar ataxia or both. There are no specific therapies against HSPs, and there is a dearth of randomized trials in patients with HSP, especially on spasticity when it likely results from other mechanisms. Thus far, no gene-specific therapy has been developed for HSP, but emerging therapies in animal models and neurons derived from induced pluripotent stem cells are potential treatments for patients.

Is there hope that transpinal direct current stimulation corrects motoneuron excitability and provides neuroprotection in amyotrophic lateral sclerosis?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of largely unknown pathophysiology, characterized by the progressive loss of motoneurons (MNs). We review data showing that in presymptomatic ALS mice, MNs display reduced intrinsic excitability and impaired level of excitatory inputs. The loss of repetitive firing specifically affects the large MNs innervating fast contracting muscle fibers, which are the most vulnerable MNs in ALS. Interventions that aimed at restoring either the intrinsic excitability or the synaptic excitation result in a decrease of disease markers in MNs and delayed neuromuscular junction denervation. We then focus on trans‐spinal direct current stimulation (tsDCS), a noninvasive tool, since it modulates the activity of spinal neurons and networks. Effects of tsDCS depend on the polarity of applied current. Recent work shows that anodal tsDCS induces long‐lasting enhancement of MN excitability and synaptic excitation of spinal MNs. Moreover, we show preliminary results indicating that anodal tsDCS enhances the excitatory synaptic inputs to MNs in ALS mice. In conclusion, we suggest that chronic application of anodal tsDCS might be useful as a complementary method in the management of ALS patients.

Transcutaneous spinal direct current stimulation shows no effect on paired stimulation suppression of the somatosensory cortex

Transcutaneous spinal direct current stimulation (tsDCS) is a safe and convenient method of neuromodulation. It has been proven to alter sensory processing at cervicomedullary level by amplitude changes of the P30 response of tibial nerve somatosensory evoked potentials (TN SEPs). With knowledge that tsDCS affects cortical circuits, we hypothesized that tsDCS may also affect intracortical excitability of the somatosensory cortex assessed by paired stimulation suppression (PSS). Fourteen healthy men were included in this prospective, single-blinded, placebo-controlled crossover study. Single (SS) and paired stimulation (PS) TN SEPs were recorded over the scalp before, immediately as well as 30 and 60 min after applying 15 min of tsDCS over the twelfth thoracic vertebra. Each volunteer underwent three independent and randomized sessions of either cathodal, anodal or sham stimulation. tsDCS showed no effect on peak-to-peak amplitudes or latencies of cortical P40-N50 response after SS. Furthermore, tsDCS failed to induce significant changes on amplitude ratios of PSS, thus showing no impact on intracortical excitability of the somatosensory cortex in healthy subjects. Further research is required to reveal the different mechanisms and to strengthen clinical use of this promising technique.

Polarity-dependent adaptations of motoneuron electrophysiological properties after 5-wk transcutaneous spinal direct current stimulation in rats

Transcutaneous spinal direct current stimulation applied systematically for 5 wk evoked polarity-dependent adaptations in the electrophysiological properties of rat spinal motoneurons. After anodal polarization sessions, motoneurons became more excitable and could evoke higher maximum discharge frequencies during repetitive firing than motoneurons in the sham polarization group. However, no significant adaptive changes of motoneuron properties were observed after repeated cathodal polarization in comparison with the sham control group.

Non-invasive treatment of patients with upper extremity spasticity following stroke using paired trans-spinal and peripheral direct current stimulation

Background

Muscle spasticity is a common impediment to motor recovery in patients with chronic stroke. Standard-of-care treatments such as botulinum toxin injections can temporarily relieve muscle stiffness and pain associated with spasticity, but often at the expense of increased muscle weakness. Recent preclinical investigations of a non-invasive treatment that pairs trans-spinal direct current stimulation and peripheral nerve direct current stimulation (tsDCS+pDCS) provided promising data for a novel approach based on bioelectronic medicine for the treatment of patients with post-stroke spasticity.

Methods

Twenty-six patients with upper limb hemiparesis and wrist spasticity at least 6 months after their initial stroke participated in this single-blind crossover design study to test whether tsDCS+pDCS reduces chronic upper-extremity spasticity. Subjects received five consecutive daily sessions (20 min of stimulation or sham) of anodal tsDCS+pDCS, separated by a one-week washout period. The sham condition always preceded the active condition. Clinical and objective measures of spasticity and motor function were collected before and after each condition, and for five weeks after the completion of the active intervention.

Results

Subjects treated with active tsDCS+pDCS demonstrated significant reductions in both Modified Tardieu Scale scores (summed across the upper limb, P < 0.05), and in objective torque measures (Nm) of the spastic catch response at the wrist flexor (P < 0.05), compared to the sham condition. Motor function also improved significantly (measured by the Fugl-Meyer and Wolf Motor Function Test; P < 0.05 for both tests) after active treatment.

Conclusions

tsDCS+pDCS intervention alone significantly reduced upper limb spasticity in participants with stroke. Decreased spasticity was persistent for five weeks after treatment, and was accompanied by improved motor function even though patients were unsupervised and there was no prescribed activity or training during that interval.

Trial registration

NCT03080454, March 15, 2017.

Beyond the target area: an integrative view of tDCS-induced motor cortex modulation in patients and athletes

Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique used to modulate neural tissue. Neuromodulation apparently improves cognitive functions in several neurologic diseases treatment and sports performance. In this study, we present a comprehensive, integrative review of tDCS for motor rehabilitation and motor learning in healthy individuals, athletes and multiple neurologic and neuropsychiatric conditions. We also report on neuromodulation mechanisms, main applications, current knowledge including areas such as language, embodied cognition, functional and social aspects, and future directions. We present the use and perspectives of new developments in tDCS technology, namely high-definition tDCS (HD-tDCS) which promises to overcome one of the main tDCS limitation (i.e., low focality) and its application for neurological disease, pain relief, and motor learning/rehabilitation. Finally, we provided information regarding the Transcutaneous Spinal Direct Current Stimulation (tsDCS) in clinical applications, Cerebellar tDCS (ctDCS) and its influence on motor learning, and TMS combined with electroencephalography (EEG) as a tool to evaluate tDCS effects on brain function.

Long-lasting modifications of motoneuron firing properties by trans-spinal direct current stimulation in rats

Trans-spinal direct current stimulation (tsDCS) is a novel neuromodulatory technique that has been used during neurological rehabilitation and sports to modulate muscle activation. However, the physiological mechanisms that underly the long-lasting functional effects of polarization are not yet fully understood, nor are their relationships with specific neuronal populations. The acute facilitatory and depressive effects of anodal and cathodal polarization on motoneurons have been recently demonstrated, and the aim of this study was to determine whether tsDCS-evoked modulations of motoneuron properties are able to persist over several hours. Intracellular recordings from multiple antidromically identified rat motoneurons were performed both before and after the application of tsDCS (0.1 mA for 15 min), at various time points up to 180 min after the offset of anodal or cathodal tsDCS. The examined effects of anodal polarization included decreased rheobase, voltage threshold, the minimum and maximum currents necessary for rhythmic firing, increased rhythmic firing frequencies and the slope of the f-I relationship. The majority of these facilitatory changes to threshold and firing properties were sustained for 30-60 min after polarization. In contrast, the significant effects of cathodal polarization were absent, except the short-lasting decreased ability for motoneurons to induce rhythmic activity. This study provides direct evidence that a single polarization session can alter the electrophysiological properties of motoneurons for at least one hour and provides a basis for the further use of tsDCS techniques under conditions where the sustained modification of motoneuron firing is desired.

Hereditary spastic paraplegia: from diagnosis to emerging therapeutic approaches

Hereditary spastic paraplegia (HSP) describes a heterogeneous group of genetic neurodegenerative diseases characterised by progressive spasticity of the lower limbs. The pathogenic mechanism, associated clinical features, and imaging abnormalities vary substantially according to the affected gene and differentiating HSP from other genetic diseases associated with spasticity can be challenging. Next generation sequencing-based gene panels are now widely available but have limitations and a molecular diagnosis is not made in most suspected cases. Symptomatic management continues to evolve but with a greater understanding of the pathophysiological basis of individual HSP subtypes there are emerging opportunities to provide targeted molecular therapies and personalised medicine.