Magnetic resonance imaging-guided focused ultrasound thalamotomy for essential tremor: 5-year follow-up results

Initial outcomes and safety of MR guided focused ultrasound (MRgFUS) thalamotomy for essential tremor of the first FUS Medical Unit in Portugal

BACKGROUND

 The magnetic resonance imaging-guided focused ultrasound (MRgFUS) has emerged as an innovative treatment for patients with medically refractory essential tremor (ET).

OBJECTIVE

 This retrospective observational study aims to present the results of the first five patients with medically refractory ET who underwent MRgFUS treatment at this pioneering medical unit in Portugal.

METHODS

 We conducted a retrospective chart review for the first five patients who underwent unilateral MRgFUS thalamotomy of the ventral intermediate (Vim) nucleus to treat medically refractory ET at our medical unit.

RESULTS

 The mean patient age was 65.4 (26-84) years, and 60% were male. All patients had a family history of ET. The mean duration of disease was 17.4 years (range 10-24 years), and their dominant hand was the right. According to personal preference, the thalamotomy was performed on the left side in four patients, and on the right side in one. The MRgFUS thalamotomy led to significant improvements in both the clinical rating scale for tremor (CRST) score, by 62%, and the CRST composite score for the treated hand, by 73%. All patients experienced improvements in functionality and quality of life, by 52%. No severe adverse events were observed, and those that did occur during and following the procedure were mild and transient.

CONCLUSION

 The initial results from Portugal's first MRgFUS medical unit indicate promising outcomes, with improvement in quality of life, as well as mild and temporary adverse events These findings contribute to the growing body of literature supporting the efficacy and safety of MRgFUS as a viable treatment option for patients with medication-resistant ET.

Magnetic Resonance-Guided Focused Ultrasound (MRgFUS)-Thalamotomy for Essential Tremor: Lesion Location and Clinical Outcomes

BACKGROUND

Factors predicting clinical outcomes after MR-guided focused ultrasound (MRgFUS)-thalamotomy in patients with essential tremor (ET) are not well known.

OBJECTIVE

To examine the clinical outcomes and their relationship with patients' baseline demographic and clinical features and lesion characteristics at 6-month follow-up in ET patients.

METHODS

A total of 127 patients were prospectively evaluated at 1 (n = 122), 3 (n = 102), and 6 months (n = 78) after MRgFUS-thalamotomy. Magnetic resonance imaging (MRI) was obtained at 6 months (n = 60). Primary outcomes included: (1) change in the Clinical Rating Scale of Tremor (CRST)-A+B score in the treated hand and (2) frequency and severity of adverse events (AEs) at 6 months. Secondary outcomes included changes in all subitems of the CRST scale in the treated hand, CRST-C, axial tremor (face, head, voice, tongue), AEs, and correlation of primary outcomes at 6 months with lesion characteristics. Statistical analysis included linear mixed, standard, and logistic regression models.

RESULTS

Scores for CRST-A+B, CRST-A, CRST-B in the treated hand, CRST-C, and axial tremor were improved at each evaluation (P < 0.001). Five patients had severe AEs at 1 month that became mild throughout the follow-up. Mild AEs occurred in 71%, 45%, and 34% of patients at 1, 3, and 6 months, respectively. Lesion volume was associated with the reduction in the CRST-A (P = 0.003) and its overlapping with the ventralis intermedius nucleus (Vim) nucleus with the reduction in CRST-A+B (P = 0.02) and CRST-B (P = 0.008) at 6 months.

CONCLUSIONS

MRgFUS-thalamotomy improves hand and axial tremor in ET patients. Transient and mild AEs are frequent. Lesion volume and location are associated with tremor reduction. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

MR-guided focused ultrasound in movement disorders and beyond: Lessons learned and new frontiers

The development of MR-guided focused ultrasound (MRgFUS) has provided a new therapeutic tool for neuropsychiatric disorders. In contrast to previously available neurosurgical techniques, MRgFUS allows precise impact on deep brain structures without the need for incision and yields an immediate effect. In its high-intensity modality (MRgHIFU), it produces accurate therapeutic thermoablation in previously selected brain targets. Importantly, the production of the lesion is progressive and highly controlled in real-time by both neuroimaging and clinical means. MRgHIFU ablation is already an accepted and widely used treatment for medically-refractory Parkinson's disease and essential tremor. Notably, other neurological disorders and diverse brain targets, including bilateral treatments, are currently under examination. Conversely, the low-intensity modality (MRgLIFU) shows promising prospects in neuromodulation and transient blood-brain barrier opening (BBBO). In the former circumstance, MRgLIFU could serve as a powerful clinical and research tool for non-invasively modulating brain activity and function. BBBO, on the other hand, emerges as a potentially impactful method to influence disease pathogenesis and progression by increasing brain target engagement of putative therapeutic agents. While promising, these applications remain experimental. As a recently developed technology, MRgFUS is not without challenges and questions to be addressed. Further developments and broader experience are necessary to enhance MRgFUS capabilities in both research and clinical practice, as well as to define device constraints. This clinical mini-review aims to provide an overview of the main evidence of MRgFUS application and to highlight unmet needs and future potentialities of the technique.

Magnetic resonance-guided focused ultrasound unilateral thalamotomy for medically refractory essential tremor: 3-year follow-up data

Introduction

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy of the ventralis intermediate (Vim) nucleus is an "incisionless" treatment for medically refractory essential tremor (ET). We present data on 49 consecutive cases of MRgFUS Vim thalamotomy followed-up for 3 years and review the literature on studies with longer follow-up data.

Methods

A retrospective chart review of patients who underwent MRgFUS thalamotomy (January 2018-December 2020) at our institution was performed. Clinical Rating Scale for Tremor (CRST) and Quality of Life in Essential Tremor (QUEST) scores were obtained pre-operatively and at each follow-up with an assessment of side effects. Patients had post-operative magnetic resonance imaging within 24 h and at 1 month to figure out lesion location, size, and extent. The results of studies with follow-up ≥3 years were summarized through a literature review.

Results

The CRST total (baseline: 58.6 ± 17.1, 3-year: 40.8 ± 18.0) and subscale scores (A + B, baseline: 23.5 ± 6.3, 3-year: 12.8 ± 7.9; C, baseline: 12.7 ± 4.3, 3-year: 5.8 ± 3.9) and the QUEST score (baseline: 38.0 ± 14.8, 3-year: 18.7 ± 13.3) showed significant improvement that was stable during the 3-year follow-up. Three patients reported tremor recurrence and two were satisfactorily retreated. Side effects were reported by 44% of patients (severe: 4%, mild and transient: 40%). The improvement in tremor and quality of life in our cohort was consistent with the literature.

Conclusion

We confirmed the effectiveness and safety of MRgFUS Vim thalamotomy in medically refractory ET up to 3 years.

Magnetic Resonance-Guided Focused Ultrasound without Anesthesiologist Support

INTRODUCTION

Magnetic resonance-guided focused ultrasound (MRgFUS) is an effective treatment option for essential tremor (ET) and tremor dominant Parkinson's disease (TDPD), which is often performed with sedation or in the presence of an anesthesiologist in an effort to minimize adverse events and maximize patient comfort. This study explores the safety, feasibility, and tolerability of performing MRgFUS without an anesthesiologist.

METHODS

This is a single academic center, retrospective review of 180 ET and TDPD patients who underwent MRgFUS treatment without anesthesiologist support. Patient demographics, intra-procedural treatment parameters, peri-procedural adverse events, and 3-month Clinical Rating Scale for Tremor Part B (CRST-B) scores were compared to MRgFUS studies that utilized varying degrees of anesthesia.

RESULTS

There were no anesthesia related adverse events or unsuccessful treatments. There were no early treatment terminations due to patient discomfort, regardless of skull density ratio. 94.6% of patients would repeat the procedure again. The most common side effects during treatment were facial/tongue paresthesia (26.3%), followed by nausea (22.3%), dysarthria (8.6%), and scalp pain (8.0%). No anxiolytic, pain, or antihypertensive medications were administered. The most common early adverse event after MRgFUS procedure was gait imbalance (58.3%). There was a significant reduction of 83.1% (83.4% ET and 80.5% TDPD) of the mean CRST-B scores of the treated hand when comparing 3-month and baseline scores (1.8 vs. 10.9, n = 109, p < 0.0001).

CONCLUSION

MRgFUS without intra-procedural anesthesiologist support is a safe, feasible, and well-tolerated option, without an increase in peri-procedural adverse events.

Magnetic resonance-guided focused ultrasound thalamotomy for essential tremor patients with low skull density ratio: a case-matched analysis

Introduction

Skull density ratio (SDR) is the ratio between the mean Hounsfield units of marrow and cortical bone, impacting energy transmission through the skull. Low SDR has been used as an exclusion criterion in major trials of magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy for medication-refractory essential tremor (ET). However, some studies have suggested that patients with low SDR can safely undergo MRgFUS with favorable outcomes. In this case-matched study, we aim to compare the characteristics, sonication parameters, lesion sizes, and clinical outcomes of patients with low SDR vs. patients with high SDR who underwent unilateral MRgFUS thalamotomy for medication-refractory ET.

Methods

Between March 2016 and April 2023, all patients (n = 270) who underwent unilateral MRgFUS thalamotomy for medication-refractory ET at a single institution were classified as low SDR (<0.40) and high SDR (≥0.40). All clinical and radiological data was prospectively collected and retrospectively analyzed using non-case-matched and 1:1 case-matched methodology.

Results

Thirty-one patients had low SDR, and 239 patients had high SDR. Fifty-six patients (28 in each cohort) were included in 1:1 case-matched analysis. There were no significant differences in baseline characteristics between the two groups in both non-case-matched and 1:1 case-matched analyses. In both analyses, compared to patients with high SDR, patients with low SDR required a significantly higher maximum sonication power, energy, and duration, and reached a lower maximum temperature with smaller lesion volumes. In the non-case-matched and case-matched analyses, low SDR patients did not have significantly less tremor control at any postoperative timepoints. However, there was a higher chance of procedure failure in the low SDR group with three patients not obtaining an appropriately sized lesion. In both analyses, imbalance was observed more often in high SDR patients on postoperative day 1 and month 3.

Discussion

ET patients with SDR <0.40 can be safely and effectively treated with MRgFUS, though there may be higher rates of treatment failure and intraoperative discomfort.

Outcomes and Prognostic Factors of Magnetic Resonance-guided Focused Ultrasound Thalamotomy for Essential Tremor at 2-year Follow-up

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an effective treatment for essential tremor (ET). However, its long-term outcomes and prognostic factors remain unclear. This study aimed to retrospectively investigate 38 patients with ET who underwent MRgFUS thalamotomy and were followed up for >2 years. The improvement in tremor was evaluated using the Clinical Rating Scale for Tremor (CRST). Adverse events were documented, and correlations with factors, such as skull density ratio (SDR), maximum mean temperature (T-max), and lesion size, were examined. Furthermore, the outcomes were compared between two groups, one that met the cutoff values, which was previously reported (preoperative CRST-B ≤ 25, T-max ≥ 52.5°C, anterior-posterior size of lesion ≥ 3.9 mm, superior-inferior [SI] size of lesion > 5.5 mm), and the other that did not. The improvement rate was 59.4% on average at the 2-year follow-up. Adverse events, such as numbness (15.8%), dysarthria (10.5%), and lower extremity weakness (2.6%), were observed even after 2 years, although these were mild. The factors correlated with tremor improvement were the T-max and SI size of the lesion (p < 0.05), whereas the SDR showed no significance. Patients who met the aforementioned cutoff values demonstrated a 69.8% improvement at the 2-year follow-up, whereas others showed a 43.6% improvement (p < 0.05). In conclusion, MRgFUS is effective even after 2 years. The higher the T-max and the larger the lesion size, the better the tremor control. Previously reported cutoff values clearly predict the 2-year prognosis, indicating the usefulness of MRgFUS.

The evolution of ventral intermediate nucleus targeting in MRI-guided focused ultrasound thalamotomy for essential tremor: an international multi-center evaluation

Background

The ventral intermediate nucleus (VIM) is the premiere target in magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy for tremor; however, there is no consensus on the optimal coordinates for ablation. This study aims to ascertain the various international VIM targeting approaches (VIM-TA) and any evolution in practice.

Methods

International MRgFUS centers were invited to share VIM-TAs in 2019 and 2021. Analyses of any modification in practice and of anatomical markers and/or tractography in use were carried out. Each VIM-TA was mapped in relation to the mid-commissural point onto a 3D thalamic nucleus model created from the Schaltenbrand-Wahren atlas.

Results

Of the 39 centers invited, 30 participated across the study period, providing VIM-TAs from 26 centers in 2019 and 23 in 2021. The results are reported as percentages of the number of participating centers in that year. In 2019 and 2021, respectively, 96.2% (n = 25) and 95.7% (n = 22) of centers based their targeting on anatomical landmarks rather than tractography. Increased adoption of tractography in clinical practice and/or for research was noted, changing from 34.6% to 78.3%. There was a statistically significant change in VIM-TAs in the superior-inferior plane across the study period; the percentage of VIM-TAs positioned 2 mm above the intercommissural line (ICL) increased from 16.0% in 2019 to 40.9% in 2021 (WRST, p < 0.05). This position is mapped at the center of VIM on the 3D thalamic model created based on the Schaltenbrand-Wahren atlas. In contrast, the VIM-TA medial-lateral and anterior-posterior positions remained stable. In 2022, 63.3% of participating centers provided the rationale for their VIM-TAs and key demographics. The centers were more likely to target 2 mm above the ICL if they had increased experience (more than 100 treatments) and/or if they were North American.

Conclusion

Across the study period, FUS centers have evolved their VIM targeting superiorly to target the center of the VIM (2 mm above the ICL) and increased the adoption of tractography to aid VIM localization. This phenomenon is observed across autonomous international centers, suggesting that it is a more optimal site for FUS thalamotomy in tremors.

The Optimal Targeting for Focused Ultrasound Thalamotomy Differs between Dystonic and Essential Tremor: A 12-Month Prospective Pilot Study

BACKGROUND

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is increasingly used to treat drug-resistant essential tremor (ET). Data on MRgFUS thalamotomy in dystonic tremor (DT) are anecdotal.

OBJECTIVES

To investigate efficacy, safety, and differences in target coordinates of MRgFUS thalamotomy in DT versus ET.

METHODS

Ten patients with DT and 35 with ET who consecutively underwent MRgFUS thalamotomy were followed for 12 months. Although in both groups the initial surgical planning coordinates corresponded to the ventralis intermediate (Vim), the final target could be modified intraoperatively based on clinical response.

RESULTS

Tremor significantly improved in both groups. The thalamic lesion was significantly more anterior in DT than ET. Considering both ET and DT groups, the more anterior the lesion, the lower the odds ratio for adverse events.

CONCLUSIONS

MRgFUS thalamotomy is safe and effective in DT and ET. Compared to classical Vim coordinates used for ET, more anterior targeting should be considered for DT.

Longitudinal MR imaging after unilateral MR-guided focused ultrasound thalamotomy: clinical and radiological correlation

Introduction

Magnetic-resonance-guided focused ultrasound (MRgFUS) thalamotomy uses multiple converging high-energy ultrasonic beams to produce thermal lesions in the thalamus. Early postoperative MR imaging demonstrates the location and extent of the lesion, but there is no consensus on the utility or frequency of postoperative imaging. We aimed to evaluate the evolution of MRgFUS lesions and describe the incidence, predictors, and clinical effects of lesion persistence in a large patient cohort.

Methods

A total of 215 unilateral MRgFUS thalamotomy procedures for essential tremor (ET) by a single surgeon were retrospectively analyzed. All patients had MR imaging 1 day postoperatively; 106 had imaging at 3 months and 32 had imaging at 1 year. Thin cut (2 mm) axial and coronal T2-weighted MRIs at these timepoints were analyzed visually on a binary scale for lesion presence and when visible, lesion volumes were measured. SWI and DWI sequences were also analyzed when available. Clinical outcomes including tremor scores and side effects were recorded at these same time points. We analyzed if patient characteristics (age, skull density ratio), preoperative tremor score, and sonication parameters influenced lesion evolution and if imaging characteristics correlated with clinical outcomes.

Results

Visible lesions were present in all patients 1 day post- MRgFUS and measured 307.4 ± 128.7 mm3. At 3 months, residual lesions (excluding patients where lesions were not visible) were 83.6% smaller and detectable in only 54.7% of patients (n = 58). At 1 year, residual lesions were detected in 50.0% of patients (n = 16) and were 90.7% smaller than 24 h and 46.5% smaller than 3 months. Lesions were more frequently visible on SWI (100%, n = 17), DWI (n = 38, 97.4%) and ADC (n = 36, 92.3%). At 3 months, fewer treatment sonications, higher maximum power, and greater distance between individual sonications led to larger lesion volumes. Volume at 24 h did not predict if a lesion was visible later. Lesion visibility at 3 months predicted sensory side effects but was not correlated with tremor outcomes.

Discussion

Overall, lesions are visible on T2-weighted MRI in about half of patients at both 3 months and 1 year post-MRgFUS thalamotomy. Certain sonication parameters significantly predicted persistent volume, but residual lesions did not correlate with tremor outcomes.

Treating the Brain With Focused Ultrasound

Focused ultrasound is an early stage, noninvasive therapy with the potential to treat a range of medical conditions. Like diagnostic ultrasound, it uses sound waves above the range of human hearing. But its purpose is to interact with tissues in the body, rather than just produce images of them. In focused ultrasound, multiple, intersecting beams of high frequency sound are aimed to converge on specific targets deep within the body. There, the ultrasound energy can act in multiple ways to either modify or destroy tissue.

MRgFUS thalamotomy for the treatment of tremor: evaluation of learning curve and operator's experience impact on the procedural and clinical outcome

BACKGROUND

MRgFUS Vim ablation is increasingly used for the treatment of tremor in ET e PD patients but there is little published research on the importance of operator experience in this procedure. This study aims to evaluate the learning curve and the influence of the operator experience on the procedural and clinical outcomes.

METHODS

We retrospectively evaluated 90 patients (38 ET, 52 PD) submitted to MRgFUS unilateral thalamotomy in the period between February 2018 and July 2020. Clinical endpoints, procedural times, and technical parameters were recorded in all procedures. Based on the time of treatment, patients were divided into three groups of 30 units each, comparing all variables between each time period group.

RESULTS

In Group A, the average patient preparation time was 120.6 min, the treatment time was 105.2 min, the number of was sonications 14.1, and the mean target shifts 3.1. In Group B, the mean preparation time was 105.5 min, the treatment time was 89.5 min, the number of sonications was 13.2, and the target shifts 3.0. Group C showed inferior values of preparation time (101.9 min), treatment time (71.7 min), numbers of sonications (10.6), and shifts (1.7). Thalamotomy-related complications occurred in 9 patients of Group A, 2 of Group B, and 5 of Group C. Tremor relapse occurred in 7 patients of Group A, 3 of Group B, and 2 of Group C. The days of hospitalization were comparable in the three groups.

CONCLUSIONS

The operators experience is associated with the improvement of clinical and procedural outcome in MRgFUS thalatomy for the treatment of ET and PD tremor.