Magnetic resonance-guided focused ultrasound for Parkinson's disease since ExAblate, 2016-2019: a systematic review

Clinical neurophysiology in the treatment of movement disorders: IFCN handbook chapter

In this review, different aspects of the use of clinical neurophysiology techniques for the treatment of movement disorders are addressed. First of all, these techniques can be used to guide neuromodulation techniques or to perform therapeutic neuromodulation as such. Neuromodulation includes invasive techniques based on the surgical implantation of electrodes and a pulse generator, such as deep brain stimulation (DBS) or spinal cord stimulation (SCS) on the one hand, and non-invasive techniques aimed at modulating or even lesioning neural structures by transcranial application. Movement disorders are one of the main areas of indication for the various neuromodulation techniques. This review focuses on the following techniques: DBS, repetitive transcranial magnetic stimulation (rTMS), low-intensity transcranial electrical stimulation, including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), and focused ultrasound (FUS), including high-intensity magnetic resonance-guided FUS (MRgFUS), and pulsed mode low-intensity transcranial FUS stimulation (TUS). The main clinical conditions in which neuromodulation has proven its efficacy are Parkinson's disease, dystonia, and essential tremor, mainly using DBS or MRgFUS. There is also some evidence for Tourette syndrome (DBS), Huntington's disease (DBS), cerebellar ataxia (tDCS), and axial signs (SCS) and depression (rTMS) in PD. The development of non-invasive transcranial neuromodulation techniques is limited by the short-term clinical impact of these techniques, especially rTMS, in the context of very chronic diseases. However, at-home use (tDCS) or current advances in the design of closed-loop stimulation (tACS) may open new perspectives for the application of these techniques in patients, favored by their easier use and lower rate of adverse effects compared to invasive or lesioning methods. Finally, this review summarizes the evidence for keeping the use of electromyography to optimize the identification of muscles to be treated with botulinum toxin injection, which is indicated and widely performed for the treatment of various movement disorders.

Focused Ultrasound for Treatment of Movement Disorders: A Review of Non-Food and Drug Administration Approved Indications

INTRODUCTION

MRI-guided focused ultrasound (FUS) is an incisionless thermo-ablative procedure that may be used to treat medication-refractory movement disorders, with a growing number of potential anatomic targets and clinical applications. As of this article's publication, the only US Food and Drug Administration (FDA)-approved uses of FUS for movement disorders are thalamotomy for essential tremor (ET) and tremor-dominant Parkinson's Disease (PD), and pallidotomy for other cardinal symptoms of PD. We present a state-of-the-art review on all non-FDA approved indications of FUS for movement disorders, beyond the most well-described indications of ET and PD. Our objective was to summarize the safety and efficacy of FUS in this setting and provide a roadmap for future directions of FUS for movement disorders.

METHODS

A state-of-the-art review was conducted on use of FUS for non-FDA approved movement disorders. All movement disorders excluding FDA-approved uses for ET and PD were included.

RESULTS

A total of 25 studies on 172 patients were included. In patients with tremor plus dystonia syndromes (n = 6), ventralis intermediate nucleus of the thalamus (VIM)-FUS gave >50% tremor reduction, with no improvement in dystonia and worsened dystonia in 2/6 patients. Ventral-oralis complex (VO)-FUS gave >50% improvement for focal hand dystonia (n = 6) and 100% return to musical performance in musician's dystonia (n = 6). In patients with multiple sclerosis (MS) and tremor (n = 3), improvement in tremor was seen in 2 patients with a favorable skull density ratio; no MS disease change was noted after VIM-FUS. In patients with tremor and comorbid ataxia syndromes (n = 3), none were found to have worsened ataxia after VIM-FUS; all had clinically significant tremor improvement. Subthalamic nucleus (STN)-FUS for PD (n = 49) gave approximately 50% improvement in PD motor symptoms, with dystonia and mild dyskinesias as possible adverse effects. Cerebellothalamic tract (CTT-FUS) for ET (n = 42) gave 55-90% tremor improvement, with gait dysfunction as a rare persistent adverse effect. Pallidothalamic tract (PTT-FUS) for PD (n = 50) gave approximately 50% improvement in motor symptoms, with mild speech dysfunction as a possible adverse effect.

CONCLUSION

VIM-FUS appeared safe and effective for heterogenous tremor etiologies, and VO-FUS appeared most effective for isolated segmental dystonia. STN-FUS was effective for PD symptom reduction; postoperative dystonia and mild on-medication dyskinesias required medical management. Tractography-based targeting with CTT-FUS for ET and PTT-FUS for PD demonstrated promising early results. Larger prospective trials with long-term follow-up are needed to the evaluate the safety and efficacy non-FDA approved indications for FUS.

Efficacy and safety of magnetic resonance-guided focused ultrasound for Parkinson's disease: a systematic review and meta-analysis

Objective

Magnetic resonance imaging-guided focused ultrasound (MRgFUS) is a novel noninvasive treatment for drug-resistant Parkinson's disease (PD) related tremor. This study aims to evaluate MRgFUS's efficacy and safety in PD through a systematic review and meta-analysis, examining pre-and post-treatment MDS-UPDRSIII and/or CRST scores and associated adverse events.

Materials and methods

We conducted an extensive literature search across PubMed, Embase, Web of Science, and Cochrane Library databases, screening studies based on set criteria and analyzing MDS-UPDRSIII, CRST, and adverse events pre- and post-MRgFUS treatment.

Results

Out of 468 retrieved articles, 20 studies involving 258 patients, spanning 2014-2023, were included.17 studies indicated significant MDS-UPDRSIII score reductions post-MRgFUS treatment, while 3 showed significant CRST score declines. In the "on" medication state, pooled MDS-UPDRSIII scores at 1, 3, 6, and 12 months were 12.18 (95% CI: 5.83-18.52), 12.10 (95% CI: 8.22-15.97), 14.85 (95% CI: 9.28-20.41), and 20.65 (95% CI: 12.15-29.14) respectively. In the "off" state, scores were 11.45 (95% CI: -3.50-26.40), 14.71 (95% CI: 4.95-24.46), 21.52 (95% CI: 19.28-23.75), and 22.28 (95% CI: 15.26-29.30). Adverse events were typically mild and transient, with speech disturbances, ataxia, and sensory abnormalities being common post-operative neurological complications.

Conclusion

MRgFUS offers an effective and relatively safe treatment option for patients with drug-resistant PD-related tremor.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, No. CRD42023428332.

A rapid element pressure field simulation method for transcranial phase correction in focused ultrasound therapy

Transcranial focused ultrasound ablation has emerged as a promising technique for treating neurological disorders. The clinical system exclusively employed the ray tracing method to compute phase aberrations induced by the human skull, taking into account computational time constraints. However, this method compromises slightly on accuracy compared to simulation-based methods. This study evaluates a fast simulation method that simulates the time-harmonic pressure field within the region of interest for effective phase correction. Experimental validation was carried out using a 512-element, 670 kHz hemispherical transducer for fourex vivoskulls. The ray tracing method achieved a restoration ratio of 64.81% ± 4.33% of acoustic intensity normalized to hydrophone measurements. In comparison, the rapid simulation method demonstrated improved results with a restoration ratio of 73.10% ± 7.46%, albeit slightly lower than the full-wave simulation which achieved a restoration ratio of 75.87% ± 5.40%. The rapid simulation methods exhibited computational times that were less than five minutes for parallel computation with 8 threads. The incident angle was calculated, and a maximum difference of 6.8 degrees was found when the fixed position of the skull was changed. Meanwhile, the restoration ratio of acoustic intensity was validated to be above 70% for different target positions away from the geometrical focus of the transducer. The favorable balance between time consumption and correction accuracy makes this method valuable for clinical treatment applications.

Tremor in Parkinson's Disease: From Pathophysiology to Advanced Therapies

Background

Tremor is one of the most prevalent symptoms in Parkinson's Disease (PD). The progression and management of tremor in PD can be challenging, as response to dopaminergic agents might be relatively poor, particularly in patients with tremor-dominant PD compared to the akinetic/rigid subtype. In this review, we aim to highlight recent advances in the underlying pathogenesis and treatment modalities for tremor in PD.

Methods

A structured literature search through Embase was conducted using the terms "Parkinson's Disease" AND "tremor" OR "etiology" OR "management" OR "drug resistance" OR "therapy" OR "rehabilitation" OR "surgery." After initial screening, eligible articles were selected with a focus on published literature in the last 10 years.

Discussion

The underlying pathophysiology of tremor in PD remains complex and incompletely understood. Neurodegeneration of dopaminergic neurons in the retrorubral area, in addition to high-power neural oscillations in the cerebello-thalamo-cortical circuit and the basal ganglia, play a major role. Levodopa is the first-line therapeutic option for all motor symptoms, including tremor. The addition of dopamine agonists or anticholinergics can lead to further tremor reduction. Botulinum toxin injection is an effective alternative for patients with pharmacological-resistant tremor who are not seeking advanced therapies. Deep brain stimulation is the most well-established advanced therapy owing to its long-term efficacy, reversibility, and effectiveness in other motor symptoms and fluctuations. Magnetic resonance-guided focused ultrasound is a promising modality, which has the advantage of being incisionless. Cortical and peripheral electrical stimulation are non-invasive innovatory techniques that have demonstrated good efficacy in suppressing intractable tremor.

Neuromodulation of cognition in Parkinson's disease

Neuromodulation is a widely used treatment for motor symptoms of Parkinson's disease (PD). It can be a highly effective treatment as a result of knowledge of circuit dysfunction associated with motor symptoms in PD. However, the mechanisms underlying cognitive symptoms of PD are less well-known, and the effects of neuromodulation on these symptoms are less consistent. Nonetheless, neuromodulation provides a unique opportunity to modulate motor and cognitive circuits while minimizing off-target side effects. We review the modalities of neuromodulation used in PD and the potential implications for cognitive symptoms. There have been some encouraging findings with both invasive and noninvasive modalities of neuromodulation, and there are promising advances being made in the field of therapeutic neuromodulation. Substantial work is needed to determine which modulation targets are most effective for the different types of cognitive deficits of PD.

Lafora disease: Current biology and therapeutic approaches

The ubiquitin system impacts most cellular processes and is altered in numerous neurodegenerative diseases. However, little is known about its role in neurodegenerative diseases due to disturbances of glycogen metabolism such as Lafora disease (LD). In LD, insufficiently branched and long-chained glycogen forms and precipitates into insoluble polyglucosan bodies (Lafora bodies), which drive neuroinflammation, neurodegeneration and epilepsy. LD is caused by mutations in the gene encoding the glycogen phosphatase laforin or the gene coding for the laforin interacting partner ubiquitin E3 ligase malin. The role of the malin-laforin complex in regulating glycogen structure remains with full of gaps. In this review we bring together the disparate body of data on these two proteins and propose a mechanistic hypothesis of the disease in which malin-laforin's role to monitor and prevent over-elongation of glycogen branch chains, which drive glycogen molecules to precipitate and accumulate into Lafora bodies. We also review proposed connections between Lafora bodies and the ensuing neuroinflammation, neurodegeneration and intractable epilepsy. Finally, we review the exciting activities in developing therapies for Lafora disease based on replacing the missing genes, slowing the enzyme - glycogen synthase - that over-elongates glycogen branches, and introducing enzymes that can digest Lafora bodies. Much more work is needed to fill the gaps in glycogen metabolism in which laforin and malin operate. However, knowledge appears already adequate to advance disease course altering therapies for this catastrophic fatal disease.