Coherent Structural and Functional Network Changes after Thalamic Lesions in Essential Tremor

Efficacy and Safety of Magnetic Resonance-Guided Focused Ultrasound Thalamotomy in Essential Tremor: A Systematic Review and Metanalysis

BACKGROUND

Magnetic resonance-guided focused ultrasound (MRgFUS) is an established surgical treatment for essential tremor, providing tremor relief without the need for an incision or general anesthesia. Meta-analyses have been limited in their exploration of the durability of the treatment effect.

OBJECTIVES

The study aimed to assess the treatment effect and safety of this procedure over time. Different to other meta-analyses, this study assessed the durability of efficacy over time from 1 month to 5 years follow-up. Investigating the recurrence of tremor was an important target of this work.

METHODS

A systematic search of the literature utilizing set search criteria was conducted with the PubMed, Scopus, Web of Science, and Cochrane library databases, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Data analysis was conducted in R, utilizing a random-effects model for meta-analysis and a mixed-effects model for meta-regression.

RESULTS

Forty-five studies met the inclusion criteria, of which 42 were included in the analyses. Significant changes in hand tremor, total tremor, disability scores, and quality of life scores were demonstrated across the time points investigated, the pooled standardized mean differences being -2.36 (P < 0.0001), -2.08 (P < 0.0001), -2.85 (P < 0.0001), and -1.41 (P < 0.0001) 1 year post-operation. Sensory symptoms and unsteadiness adverse events were frequently observed, with pooled proportions of 22% (95% CI 15%; 31%) and 23% (95% CI 16%; 31%) 1 month post-MRgFUS.

CONCLUSION

Although the procedure demonstrated efficacy and safety across the studies evaluated, meta-regression analysis suggests a decrease in treatment effect over time that requires further investigation. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Beyond the cerebello-thalamo-cortical tract: Remote structural changes after VIM-MRgFUS in essential tremor

INTRODUCTION

Essential tremor (ET) is a progressive disorder characterized by altered network connectivity between the cerebellum, thalamus, and cortical regions. Magnetic Resonance-guided Focused Ultrasound (MRgFUS) of the ventral intermediate nucleus (VIM) is an effective, minimally invasive treatment for ET. The impact of MRgFUS interventions on regional Gray Matter Volume (GMV) are as yet not well understood.

METHODS

Forty-six patients with medication-resistant ET underwent unilateral VIM-MRgFUS. Voxel-based morphometry was applied to investigate GMV changes over a time span of 6 months in the whole brain and the thalamus in particular to investigate local and distant effects.

RESULTS

Clinically, contralateral tremor significantly decreased by 68 % at 6 months following MRgFUS. In addition to local GMV decreases in thalamic nuclei (VIM, ventral lateral posterior, centromedian thalamus and pulvinar), VBM revealed remote GMV decreases in the ipsilesional insula and the anterior cingulate cortex as well as the contralesional middle occipital gyrus. Increased GMV was found in the right superior and middle temporal gyrus, as well as in the left inferior temporal gyrus. There was no significant correlation between regional GMV declines and tremor improvement. However, temporal volume increases were associated with improved motor-related functional abilities and quality of life outcomes.

CONCLUSION

Our findings implicate distributed structural changes following unilateral VIM-MRgFUS. Structural losses could reflect Wallerian degeneration of VIM output neurons or plasticity due to decreased sensory input following tremor improvement.

Intraprocedural Three-Dimensional Imaging Registration Optimizes Magnetic Resonance Imaging-Guided Focused Ultrasound and Facilitates Novel Applications

BACKGROUND AND OBJECTIVE

Transcranial magnetic resonance-guided focused ultrasound (MRgFUS) has revolutionized ablative treatment of essential tremor in recent years. However, limitations in precision targeting may account for suboptimal efficacy and significant side effects. We describe a simple intraprocedural three-dimensional image-guided lesion shaping technique that can improve overall outcomes of MRgFUS for essential tremor and facilitate expansion to novel indications.

METHODS

A retrospective review of 84 consecutive MRgFUS procedures performed at Pennsylvania Hospital was performed. Comparison of patient demographics, treatment parameters, and clinical outcomes before and after implementation of this protocol was conducted. Further application of this technique in pallidotomy treatments and ablative disconnection of hypothalamic hamartoma are described.

RESULTS

After implementation, the median of total number of sonications (7 vs 9, P = .001), number of therapeutic sonications (3 vs 4, P < .0001), and interval time between the first and last sonication (46:10 vs 68:53 minutes, P = .0004) were significantly reduced. Patients expressed greater satisfaction of treatment (94.1% vs 82.4%, P = .018), greater global impression of change (CGI) (7 vs 6, P = .033), and reduced median number of side effects at 6 months (0 vs 1, P = .026). We also successfully implemented this protocol for novel indications.

CONCLUSION

Intraprocedural lesion shaping for MRgFUS is a simple and versatile imaging protocol augmentation that improves ablation precision and can improve treatment efficacy and broader neurological application.

MRgFUS of the nucleus ventralis intermedius in essential tremor modulates functional connectivity within the classical tremor network and beyond

BACKGROUND

Magnetic resonance-guided focused ultrasound (MRgFUS) of the thalamic ventral intermediate nucleus is an incisionless lesional treatment for essential tremor.

OBJECTIVE

To examine relationships between tremor severity and functional connectivity in patients with essential tremor and to assess long-term changes in the tremor network after sonication of the ventral intermediate nucleus.

METHODS

Twenty-one patients with essential tremor (70.33 ± 11.32 years) were included in the final analysis and underwent resting state functional magnetic resonance imaging at 3 T before and 6 months after treatment. Tremor severity (Fahn-Tolosa-Marin Clinical Rating Scale) was evaluated and functional connectivity was investigated using independent component analysis.

RESULTS

MRgFUS of the thalamic ventral intermediate nucleus reduced contralateral tremor effectively. Multiple regression analysis revealed exclusively negative correlations between FC and tremor severity, notably in the right cerebellar lobe VI and the left cerebellar lobe VIIIa (cerebellar network), in the left occipital fusiform gyrus (lateral visual network), the anterior division of the left superior temporal gyrus (fronto-parieto-temporal network), and in the posterior division of the left parahippocampal gyrus and the bilateral lingual gyri (default mode network). Six months after treatment, increased functional connectivity was observed in almost all tremor-associated clusters, except the cluster localized in the left cerebellum.

CONCLUSIONS

Our findings suggest that tremor-related activity in essential tremor extends beyond the classical cerebellar network, additionally involving areas related to visual processing. Functional restoration of network activity after sonication of the ventral intermediate nucleus is observed within the classical tremor network (cerebellum) and notably also in visual processing areas.

Whole-brain network transitions within the framework of ignition and transfer entropy following VIM-MRgFUS in essential tremor patients

Magnetic resonance-guided focused ultrasound (MRgFUS) lesioning of the ventralis intermedius nucleus (VIM) has shown promise in treating drug-refractory essential tremor (ET). It remains unknown whether focal VIM lesions by MRgFUS have broader restorative effects on information flow within the whole-brain network of ET patients. We applied an information-theoretical approach based on intrinsic ignition and the concept of transfer entropy (TE) to assess the spatiotemporal dynamics after VIM-MRgFUS. Eighteen ET patients (mean age 71.44 years) underwent repeated 3T resting-state functional magnetic resonance imaging combined with Clinical Rating Scale for Tremor (CRST) assessments one day before (T0) and one month (T1) and six months (T2) post-MRgFUS, respectively. We observed increased whole brain ignition-driven mean integration (IDMI) at T1 (p < 0.05), along with trend increases at T2. Further, constraining to motor network nodes, we identified significant increases in information-broadcasting (bilateral supplementary motor area (SMA) and left cerebellar lobule III) and information-receiving (right precentral gyrus) at T1. Remarkably, increased information-broadcasting in bilateral SMA was correlated with relative improvement of the CRST in the treated hand. In addition, causal TE-based effective connectivity (EC) at T1 showed an increase from right SMA to left cerebellar lobule crus II and from left cerebellar lobule III to right thalamus. In conclusion, results suggest a change in information transmission capacity in ET after MRgFUS and a shift towards a more integrated functional state with increased levels of global and directional information flow.

Limb Preference Changes after Focused-Ultrasound Thalamotomy for Tremor

BACKGROUND

Magnetic resonance-guided focused-ultrasound (MRgFUS) thalamotomy is an effective treatment for essential and other tremors. It targets the ventrointermedius (Vim) nucleus, which is the thalamic relay in a proprioceptive pathway, and contains kinesthetic cells. Although MRgFUS thalamotomy reduces some risks associated with more invasive surgeries, it still has side effects, such as balance and gait disturbances; these may be caused by the lesion impacting proprioception.

OBJECTIVES

Our aim was to quantitatively measure the effects of MRgFUS on proprioception and limb use in essential tremor patients. We hypothesized that this thalamotomy alters proprioception, because the sensorimotor Vim thalamus is lesioned.

METHODS

Proprioception was measured using the Kinarm exoskeleton robot in 18 patients. Data were collected pre-operatively, and then 1 day, 3 months, and 1 year after surgery. Patients completed four tasks, assessing motor coordination and postural control, goal-directed movement and bimanual planning, position sense, and kinesthesia.

RESULTS

Immediately after surgery there were changes in posture speed (indicating tremor improvement), and in bimanual hand use, with the untreated limb being preferred. However, these measures returned to pre-operative baseline over time. There were no changes in parameters related to proprioception. None of these measures correlated with lesion size or lesion-overlap with the dentato-rubro-thalamic tract.

CONCLUSIONS

This is the first quantitative assessment of proprioception and limb preference following MRgFUS thalamotomy. Our results suggest that focused-ultrasound lesioning of the Vim thalamus does not degrade proprioception but alters limb preference. This change may indicate a required "relearning" in the treated limb, because the effect is transient. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

MRI-guided focused-ultrasound thalamotomy in essential tremor: Immediate and delayed changes in cortico-muscular coherence and cortico-cortical out-strength

OBJECTIVE

Drug-resistant essential tremor (ET) can be treated by Magnetic-Resonance-guided Focused-Ultrasound (MRgFUS) targeted to thalamic ventralis-intermediate nucleus (ViM). We are presenting the results obtained in ET patients by evaluating the cortico-muscular coherence (CMC) and the out-strength among cortical areas.

METHODS

We recorded MEG-EMG signals in 16 patients with predominant tremor on the right upper limb. The examination was performed the day before MRgFUS (T0) treatment, 24 hours (T1), and 3-months (T2) after lesioning the left ViM. Normalized CMC (nCMC) and cortico-cortical out-strength among cortical areas were assessed during isometric extension of the right hand.

RESULTS

According to the Essential Tremor Rating Assessment Scale, 13 of 16 patients were considered responders. At T1, in the beta-band, nCMC increased in the left hemisphere, namely in the areas directly involved in motor functions. At T2, the nCMC in non-motor areas decreased and the out-strength from other examined cortical areas toward the left motor-area decreased.

CONCLUSIONS

In patients positively responding to MRgFUS, the CMC increased in the motor-area of the treated hemisphere immediately after the treatment, while the reorganization of CMC and cortico-cortical out-strength toward the cortical motor area occurred with a delay.

SIGNIFICANCE

The effective treatment with MRgFUS corresponds with a readjustment of the CMC and of the communication between cortical areas.

Advancing brain network models to reconcile functional neuroimaging and clinical research

Functional magnetic resonance imaging (fMRI) captures information on brain function beyond the anatomical alterations that are traditionally visually examined by neuroradiologists. However, the fMRI signals are complex in addition to being noisy, so fMRI still faces limitations for clinical applications. Here we review methods that have been proposed as potential solutions so far, namely statistical, biophysical and decoding models, with their strengths and weaknesses. We especially evaluate the ability of these models to directly predict clinical variables from their parameters (predictability) and to extract clinically relevant information regarding biological mechanisms and relevant features for classification and prediction (interpretability). We then provide guidelines for useful applications and pitfalls of such fMRI-based models in a clinical research context, looking beyond the current state of the art. In particular, we argue that the clinical relevance of fMRI calls for a new generation of models for fMRI data, which combine the strengths of both biophysical and decoding models. This leads to reliable and biologically meaningful model parameters, which thus fulfills the need for simultaneous interpretability and predictability. In our view, this synergy is fundamental for the discovery of new pharmacological and interventional targets, as well as the use of models as biomarkers in neurology and psychiatry.