Modulatory effect of continuous theta burst stimulation in patients with essential tremor

Pathophysiological Role of Primary Motor Cortex in Essential Tremor

BACKGROUND

Essential tremor (ET) is one of the most prevalent movement disorders. However, the complete understanding of ET pathophysiology remains elusive.

OBJECTIVE

To explore the pathophysiological role of primary motor cortex (M1) in ET, specifically exploring its neurophysiological changes and their correlation with voluntary motor abnormalities.

METHODS

We recruited 30 ET patients and 18 healthy controls (HC). Evaluations were conducted on patients using clinical scales. Transcranial magnetic stimulation (TMS) was used to assess M1 excitability, including motor thresholds and motor evoked potentials (MEPs) input/output curve, together with intracortical excitability measures. Long-term potentiation (LTP)-like plasticity of M1 was tested using intermittent theta-burst stimulation (iTBS). Objective assessments of tremor and voluntary movement execution during finger-tapping were conducted through kinematic analysis. Finally, we explored the potential relationship between TMS, clinical, and kinematic data.

RESULTS

Compared with HC, ET patients had lower excitability, intracortical inhibition, and lower LTP-like plasticity of M1. ET patients also exhibited slower finger-tapping performance compared with HC. Among ET patients, the degree of movement slowing during finger-tapping correlated with alterations in corticospinal excitability. Specifically, reduced M1 excitability was associated with lower finger-tapping velocity. No other correlations were found.

CONCLUSIONS

The study findings reveal neurophysiological alterations of M1 in ET and demonstrate correlations between excitability measures and voluntary motor performance. These results provide novel insight into the pathophysiology of ET, emphasizing the role of M1 changes in this condition. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Protocol for a Phase 2 randomized controlled patient-assessor blinded study: efficacy and safety of combined cortical and cerebellar dual-target transcranial magnetic stimulation for the treatment of essential tremor

Background

Essential tremor (ET) is the most common neurological movement disorder with few treatments and limited therapeutic efficacy, research into noninvasive and effective treatments is critical. Abnormal cerebello-thalamo-cortical (CTC) loop function are thought to be significant pathogenic causes of ET, with the cerebellum and cortex are common targets for ET treatment. In recent years, transcranial magnetic stimulation (TMS) has been recognized as a promising brain research technique owing to its noninvasive nature and safety. In this study, we will use left M1 cortex continuous theta-burst stimulation (cTBS) combined with right cerebellar hemisphere 1 Hz repetitive transcranial magnetic stimulation (rTMS) dual-target stimulation to explore the Safety, feasibility and efficiency of this dual-target stimulation mode, and the mechanism of its therapeutic effect.

Methods

Twenty-four patients with ET will be randomly assigned to three groups: dual-target stimulation, single-target stimulation, or sham stimulation. The single-target stimulation group will receive stimulation of the right cerebellar hemisphere for 10 days, whereas the dual-target stimulation group will be given stimulation of both the left M1 cortex and the right cerebellar hemisphere. The sham stimulation group will be given sham stimulation for 10 days. Tremor will be assessed using both the subjective The Essential Tremor Rating Assessment Scale (TETRAS) and objective accelerometer-based tremor analysis. at baseline (before stimulation), after the first, fifth, tenth days of treatment (D1, 5, 10), 24 h after 10 days of treatment (D10-24 h), and 1, 2, 3, and 4 weeks after stimulation (W1, 2, 3, 4).

Discussion

This is a Phase 2 randomized, controlled, patient-assessor blinded clinical trial. The goal of this study is to investigate the Safety, feasibility and efficiency of TMS for the treatment of ET.

Limited Potential of Repetitive Transcranial Magnetic Stimulation for Treatment of Essential Tremor: A Systematic Review

Essential tremor (ET) is a prevalent movement disorder characterized by action tremors, predominantly affecting the upper limbs. While various pharmacological and non-pharmacological interventions have shown efficacy in managing ET, the therapeutic role of repetitive transcranial magnetic stimulation (rTMS) remains uncertain. This systematic review synthesizes evidence from clinical trials investigating rTMS as a treatment for ET. Despite some open-label trials reporting reductions in tremor severity, double-blinded studies revealed no significant difference between active and sham rTMS, suggesting a strong placebo effect. The findings indicate that while rTMS can reduce tremor scores, its therapeutic efficacy in ET remains unproven. Future research should focus on improving sham designs and conducting larger, rigorously controlled trials to clarify rTMS's role in ET management. Current evidence supports considering alternative treatments, such as deep brain stimulation, over rTMS for ET.

Neuromodulation techniques - From non-invasive brain stimulation to deep brain stimulation

Over the past 30 years, the field of neuromodulation has witnessed remarkable advancements. These developments encompass a spectrum of techniques, both non-invasive and invasive, that possess the ability to both probe and influence the central nervous system. In many cases neuromodulation therapies have been adopted into standard care treatments. Transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and transcranial ultrasound stimulation (TUS) are the most common non-invasive methods in use today. Deep brain stimulation (DBS), spinal cord stimulation (SCS), and vagus nerve stimulation (VNS), are leading surgical methods for neuromodulation. Ongoing active clinical trials using are uncovering novel applications and paradigms for these interventions.

cTBS over primary motor cortex increased contralateral corticomuscular coupling and interhemispheric functional connection

Objective.Transcranial magnetic stimulation is a non-invasive brain stimulation technique that changes the activity of the cerebral cortex. Contralesional continuous theta burst stimulation (cTBS) has been proposed and verified beneficial to stroke motor recovery. However, the underlying mechanism is still unclear.Approach.20 healthy right-handed subjects were recruited in this study, receiving real-cTBS over their left primary motor cortex or sham-cTBS. We designed the finger tapping task (FTT) before and after stimulation and recorded the accuracy and reaction time (RT) of the task. The electroencephalogram and surface electromyogram signals were recorded during the left finger pinching task (FPT) before and after stimulation. We calculated cortico-muscular coherence (CMC) in the contralateral hemisphere and cortico-cortical coherence (CCC) in the bilateral hemisphere. The two-way repeated measures analysis of variance was used to analyze the effect of cTBS.Main results.In the FTT, there was a significant main effect of 'time' on RT (F(1, 38) = 24.739,p< 0.001). In the FPT, the results showed that there was a significant interaction effect on the CMC peak and area in the beta band (peak:F(1, 38) = 8.562,p= 0.006; area:F(1, 38) = 5.273,p= 0.027), on the CCC peak in the alpha band (F(1, 38) = 4.815,p= 0.034) and area in the beta band (F(1, 38) = 4.822,p= 0.034). The post hoc tests showed that the CMC peak (W= 20,p= 0.002), the CMC area (W= 13,p= 0.003) and the CCC peak (t= -2.696,p= 0.014) increased significantly after real-cTBS. However, there was no significant decrease or increase after sham-cTBS.Significance.Our study found that cTBS can improve CMC of contralateral hemisphere and CCC of bilateral hemisphere, indicating that cTBS can strengthen cortico-muscular and cortico-cortical coupling.

Evidence from Indian studies on safety and efficacy of therapeutic transcranial magnetic stimulation across neuropsychiatric disorders- A systematic review and meta-analysis

Repetitive transcranial magnetic stimulation (rTMS) is potentially effective as an augmentation strategy in the treatment of many neuropsychiatric conditions. Several Indian studies have been conducted in this regard. We aimed to quantitatively synthesize evidence from Indian studies assessing efficacy and safety of rTMS across broad range of neuropsychiatric conditions. Fifty two studies- both randomized controlled and non-controlled studies were included for a series of random-effects meta-analyses. Pre-post intervention effects of rTMS efficacy were estimated in "active only" rTMS treatment arms/groups and "active vs sham" (sham-controlled) studies using pooled Standardized Mean Differences (SMDs). The outcomes were 'any depression', depression in unipolar/bipolar depressive disorder, depression in obsessive compulsive disorder (OCD), depression in schizophrenia, schizophrenia symptoms (positive, negative, total psychopathology, auditory hallucinations and cognitive deficits), obsessive compulsive symptoms of OCD, mania, craving/compulsion in substance use disorders (SUDs) and migraine (headache severity and frequency). Frequencies and odds ratios (OR) for adverse events were calculated. Methodological quality of included studies, publication bias and sensitivity assessment for each meta-analyses was conducted. Meta-analyses of "active only" studies suggested a significant effect of rTMS for all outcomes, with moderate to large effect sizes, at both end of treatment as well as at follow-up. However, except for migraine (headache severity and frequency) with large effect sizes at end of treatment only and craving in alcohol dependence where moderate effect size at follow-up only, rTMS was not found to be effective for any outcome in the series of "active vs sham" meta-analyses. Significant heterogeneity was seen. Serious adverse events were rare. Publication bias was common and the sham controlled positive results lost significance in sensitivity analysis. We conclude that rTMS is safe and shows positive results in 'only active' treatment groups for all the studied neuropsychiatric conditions. However, the sham-controlled evidence for efficacy is negative from India.

Conclusion

rTMS is safe and shows positive results in "only active" treatment groups for all the studied neuropsychiatric conditions. However, the sham-controlled evidence for efficacy is negative from India.