Focused ultrasound and other lesioning in the treatment of tremor

The role of interleukin (IL)-2 cytokine family in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder, which primarily impacts the nervous system, marked by its immune and inflammatory characteristics. The interleukin-2 (IL-2) cytokine family has a crucial role in regulating both neuroinflammation and immune activity, positioning it as one of the critical immune pathways in PD. Balancing pro-inflammatory and anti-inflammatory signals in PD heavily depends on the IL-2 cytokine family, that includes IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21. This balance is vital for neuron survival and resistance to degeneration. Disruptions in IL-2 signaling can upset the equilibrium among regulatory T cells (Tregs) and pro-inflammatory T cells, such as Th1 and Th17, further aggravating the chronic neuroinflammation typical of PD. In PD, a decline in IL-2 or receptor dysfunction can hinder Treg activity, leading to increased inflammation and neurodegeneration. Similarly, IL-15 and IL-21 supports cytotoxic immune cell function, including natural killer (NK) cells and CD8+ T cells, which may exacerbate neuronal damage by sustaining pro-inflammatory processes. Moreover, IL-4 and IL-7 have anti-inflammatory roles in maintaining T cell homeostasis, and their dysregulation can contribute to interruption of the blood-brain barrier and increased infiltration of immune cells into the central nervous system. Targeting the IL-2 cytokine family in Parkinson's disease has shown therapeutic potential by expanding Tregs, which reduce neuroinflammation and promote dopaminergic neuron survival. Recombinant IL-2 and IL-2/anti-IL-2 complexes have demonstrated efficacy in animal models, enhancing Treg function and leading to improved neuroprotection. Additionally, IL-4-based therapies have been explored for their ability to shift microglia toward a neuroprotective phenotype, further enhancing neuronal survival by modulating inflammatory responses and cellular metabolism. Current research is exploring how to optimize cytokine delivery while minimizing immune side effects, with the goal of developing more targeted therapies for PD.

AI-Driven Advances in Parkinson's Disease Neurosurgery: Enhancing Patient Selection, Trial Efficiency, and Therapeutic Outcomes

Parkinson's disease (PD) is a progressive neurodegenerative disorder marked by motor and non-motor dysfunctions that severely compromise patients' quality of life. While pharmacological treatments provide symptomatic relief in the early stages, advanced PD often requires neurosurgical interventions, such as deep brain stimulation (DBS) and focused ultrasound (FUS), for effective symptom management. A significant challenge in optimizing these therapeutic strategies is the early identification and recruitment of suitable candidates for clinical trials. This review explores the role of artificial intelligence (AI) in advancing neurosurgical and neuroscience interventions for PD, highlighting the ways in which AI-driven platforms are transforming clinical trial design and patient selection. Machine learning (ML) algorithms and big data analytics enable precise patient stratification, risk assessment, and outcome prediction, accelerating the development of novel therapeutic approaches. These innovations improve trial efficiency, broaden treatment options, and enhance patient outcomes. However, integrating AI into clinical trial frameworks presents challenges such as data standardization, regulatory hurdles, and the need for extensive validation. Addressing these obstacles will require collaboration among neurosurgeons, neuroscientists, AI specialists, and regulatory bodies to establish ethical and effective guidelines for AI-driven technologies in PD neurosurgical research. This paper emphasizes the transformative potential of AI and technological innovation in shaping the future of PD neurosurgery, ultimately enhancing therapeutic efficacy and patient care.

Thalamic Deep Brain Stimulation Versus Magnetic Resonance-Guided Focused Ultrasound in Tremor Patients: A Retrospective Single-Surgeon Comparison

BACKGROUND

Bilateral deep brain stimulation (DBS) and unilateral magnetic resonance-guided focused ultrasound (MRgFUS), with potential future second-side treatment targeting the thalamic ventral intermediate nucleus (VIM), are currently the two best-established interventions for pharmaco-resistant tremors, but treatment selection is hampered by the lack of comparative evidence.

OBJECTIVE

To provide the first direct within-center and within-surgeon comparison between bilateral VIM-DBS and unilateral VIM-MRgFUS, applying consistently timed and elaborated efficacy and safety assessements.

METHODS

In this retrospective study, we included patients having received bilateral VIM-DBS (n = 30) or unilateral VIM-MRgFUS (n = 52) performed by one single neurosurgeon between 2014 and 2022. Efficacy was primarily measured by the improvement of the Washington Heights-Inwood Genetic Study of Essential Tremor scale in the more affected hand at 6 months. Regarding safety, we compared treatment-, procedure-, and hardware-related adverse events (AEs), graded by impact on activities of daily living (ADLs), and serious AEs (SAEs), retrospectively defined based on prolonged/repeated hospitalizations or persistent symptoms affecting ADLs.

RESULTS

We found equivalent tremor reduction in the more affected hand (DBS: 62.4% [41.3-87.9] vs. MRgFUS: 69.4% [42.4-77.7]; P = 0.958), but contralateral and axial tremors improved only with bilateral DBS. DBS was associated with a higher rate of procedure- and hardware-related AEs (17% vs. 2%; P = 0.023) but a nonsignificantly lower rate of persistent treatment-related AEs affecting ADLs at 6 months (7% vs. 13%; P = 0.343). Overall, the rates of SAEs (23.3% vs. 19.2%; P = 0.779) and persistent deficits affecting ADLs at 6 months (10% vs. 13%; P = 0.82) were similar.

CONCLUSIONS

Despite distinct safety profiles, both interventions produced a similar burden of AEs. Tremor control was equivalent on the more affected side, whereas contralateral and axial tremors improved only after bilateral DBS. © 2025 International Parkinson and Movement Disorder Society.

Intestinal dysbiosis leads to the reduction in neurochemical production in Parkinson's disease (PD)

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms, with emerging research suggesting a critical link between intestinal dysbiosis and PD progression. This review explores the pathophysiological mechanisms underlying PD, such as alpha-synuclein aggregation, mitochondrial dysfunction, neuroinflammation, and oxidative stress, while focusing on the impact of gut dysbiosis on intestinal barrier function and its role in reduced neurochemical production. The clinical features of PD, including dopamine, serotonin, and GABA deficiencies, are examined, with a focus on how dysbiosis contributes to neurotransmitter depletion. Current treatments of PD, such as levodopa and dopamine agonists, are discussed alongside gut health therapies such as probiotics, prebiotics, and Fecal Microbiota Transplantation (FMT). Future therapeutic directions, including synbiotics, engineered microbes, phage therapy, and the integration of machine learning (ML) and artificial intelligence (AI), are explored. The chapter also considers preventive strategies, such as lifestyle adjustments and early gut health monitoring using modern diagnostic tools and biosensors. Furthermore, a strong need for continued research into the gut-brain axis (GBA) to develop more effective, gut-targeted therapies for managing PD is discussed.

Magnetic resonance-guided focused ultrasound in dystonia: a scoping review

BACKGROUND

Magnetic resonance guided focused ultrasound (MRgFUS) is a non-invasive therapeutic technique that utilizes focused ultrasound waves to generate heat at specific tissue targets within the brain. This emerging technology holds promise for its precision and potential benefits in comparison to traditional surgical interventions. This investigation involves a scoping review, summarizing insights from various studies that explore the advantages, limitations, and outcomes associated with MRgFUS in the treatment of dystonia.

METHODS

This scoping review was conducted using the Preferred Reporting Items for Systematic reviews and Meta-analysis Extension for Scoping Reviews (PRISMA-ScR) guidelines. Data available on MRgFUS use in the management of different types of dystonia were extracted.

RESULTS

There is limited data available (n = 11). In the surveyed literature, MRgFUS has consistently shown clinical benefit in patients with dystonia. It is an emerging avenue of treatment and has its challenges.

CONCLUSION

This scoping review highlighted the early but encouraging applications of MRgFUS in dystonia management. While data was limited, existing studies consistently demonstrated positive clinical outcomes. The non-invasive and precise nature of MRgFUS positions it as a promising avenue for further research, despite the challenges associated with its emergent status. This review sets the stage for future inquiries, emphasizing its potential as a valuable tool in dystonia treatment.

Illusions of Self-Motion during Magnetic Resonance-Guided Focused Ultrasound Thalamotomy for Tremor

OBJECTIVE

Brain networks mediating vestibular perception of self-motion overlap with those mediating balance. A systematic mapping of vestibular perceptual pathways in the thalamus may reveal new brain modulation targets for improving balance in neurological conditions.

METHODS

Here, we systematically report how magnetic resonance-guided focused ultrasound surgery of the nucleus ventralis intermedius of the thalamus commonly evokes transient patient-reported illusions of self-motion. In 46 consecutive patients, we linked the descriptions of self-motion to sonication power and 3-dimensional (3D) coordinates of sonication targets. Target coordinates were normalized using a standard atlas, and a 3D model of the nucleus ventralis intermedius and adjacent structures was created to link sonication target to the illusion.

RESULTS

A total of 63% of patients reported illusions of self-motion, which were more likely with increased sonication power and with targets located more inferiorly along the rostrocaudal axis. Higher power and more inferiorly targeted sonications increased the likelihood of experiencing illusions of self-motion by 4 and 2 times, respectively (odds ratios = 4.03 for power, 2.098 for location).

INTERPRETATION

The phenomenon of magnetic vestibular stimulation is the most plausible explanation for these illusions of self-motion. Temporary unilateral modulation of vestibular pathways (via magnetic resonance-guided focused ultrasound) unveils the central adaptation to the magnetic field-induced peripheral vestibular bias, leading to an explicable illusion of motion. Consequently, systematic mapping of vestibular perceptual pathways via magnetic resonance-guided focused ultrasound may reveal new intracerebral targets for improving balance in neurological conditions. ANN NEUROL 2024;96:121-132.

Neuronal population activity in the olivocerebellum encodes the frequency of essential tremor in mice and patients

Essential tremor (ET) is the most prevalent movement disorder, characterized primarily by action tremor, an involuntary rhythmic movement with a specific frequency. However, the neuronal mechanism underlying the coding of tremor frequency remains unexplored. Here, we used in vivo electrophysiology, optogenetics, and simultaneous motion tracking in the Grid2dupE3 mouse model to investigate whether and how neuronal activity in the olivocerebellum determines the frequency of essential tremor. We report that tremor frequency was encoded by the temporal coherence of population neuronal firing within the olivocerebellums of these mice, leading to frequency-dependent cerebellar oscillations and tremors. This mechanism was precise and generalizable, enabling us to use optogenetic stimulation of the deep cerebellar nuclei to induce frequency-specific tremors in wild-type mice or alter tremor frequencies in tremor mice. In patients with ET, we showed that deep brain stimulation of the thalamus suppressed tremor symptoms but did not eliminate cerebellar oscillations measured by electroencephalgraphy, indicating that tremor-related oscillations in the cerebellum do not require the reciprocal interactions with the thalamus. Frequency-disrupting transcranial alternating current stimulation of the cerebellum could suppress tremor amplitudes, confirming the frequency modulatory role of the cerebellum in patients with ET. These findings offer a neurodynamic basis for the frequency-dependent stimulation of the cerebellum to treat essential tremor.

Magnetic resonance imaging of radiofrequency thalamotomy for tremor: what is it about?

This scientific commentary refers to 'Radiofrequency thalamotomy for tremor produces focused and predictable lesions shown on magnetic resonance images', by Ishihara et al. (https://doi.org/10.1093/braincomms/fcad329).

Shedding light on ultrasound in action: Optical and optoacoustic monitoring of ultrasound brain interventions

Monitoring brain responses to ultrasonic interventions is becoming an important pillar of a growing number of applications employing acoustic waves to actuate and cure the brain. Optical interrogation of living tissues provides a unique means for retrieving functional and molecular information related to brain activity and disease-specific biomarkers. The hybrid optoacoustic imaging methods have further enabled deep-tissue imaging with optical contrast at high spatial and temporal resolution. The marriage between light and sound thus brings together the highly complementary advantages of both modalities toward high precision interrogation, stimulation, and therapy of the brain with strong impact in the fields of ultrasound neuromodulation, gene and drug delivery, or noninvasive treatments of neurological and neurodegenerative disorders. In this review, we elaborate on current advances in optical and optoacoustic monitoring of ultrasound interventions. We describe the main principles and mechanisms underlying each method before diving into the corresponding biomedical applications. We identify areas of improvement as well as promising approaches with clinical translation potential.

Improving Sonication Efficiency in Transcranial MR-Guided Focused Ultrasound Treatment: A Patient-Data Simulation Study

The potential improvement in sonication efficiency achieved by tilting the focused ultrasound (FUS) transducer of the transcranial MR-guided FUS system is presented. A total of 56 cases of patient treatment data were used. The relative position of the clinical FUS transducer to the patient's head was reconstructed, and region-specific skull density and porosity were calculated based on the patient's CT volume image. The total transmission coefficient of acoustic waves emitted from each channel was calculated. Then, the total energy penetrating the human skull-which represents the sonication efficiency-was estimated. As a result, improved sonication efficiency was by titling the FUS transducer to a more appropriate angle achieved in all 56 treatment cases. This simulation result suggests the potential improvement in transcranial-focused ultrasound treatment by simply adjusting the transducer angle.

Usefulness of thalamic beta activity for closed-loop therapy in essential tremor

A partial loss of effectiveness of deep brain stimulation of the ventral intermediate nucleus of the thalamus (VIM) has been reported in some patients with essential tremor (ET), possibly due to habituation to permanent stimulation. This study focused on the evolution of VIM local-field potentials (LFPs) data over time to assess the long-term feasibility of closed-loop therapy based on thalamic activity. We performed recordings of thalamic LFPs in 10 patients with severe ET using the ACTIVA™ PC + S (Medtronic plc.) allowing both recordings and stimulation in the same region. Particular attention was paid to describing the evolution of LFPs over time from 3 to 24 months after surgery when the stimulation was Off. We demonstrated a significant decrease in high-beta LFPs amplitude during movements inducing tremor in comparison to the rest condition 3 months after surgery (1.91 ± 0.89 at rest vs. 1.27 ± 1.37 µV2/Hz during posture/action for N = 8/10 patients; p = 0.010), 12 months after surgery (2.92 ± 1.75 at rest vs. 2.12 ± 1.78 µV2/Hz during posture/action for N = 7/10 patients; p = 0.014) and 24 months after surgery (2.32 ± 0.35 at rest vs 0.75 ± 0.78 µV2/Hz during posture/action for 4/6 patients; p = 0.017). Among the patients who exhibited a significant decrease of high-beta LFP amplitude when stimulation was Off, this phenomenon was observed at least twice during the follow-up. Although the extent of this decrease in high-beta LFPs amplitude during movements inducing tremor may vary over time, this thalamic biomarker of movement could potentially be usable for closed-loop therapy in the long term.

Radiofrequency thalamotomy for tremor produces focused and predictable lesions shown on magnetic resonance images

Radiofrequency thalamotomy is a neurosurgical management option for medically-refractory tremor. In this observational study, we evaluate the MRI features of the resultant lesion, their temporal dynamics, and how they vary depending on surgical factors. We report on lesion characteristics including size and location, as well as how these vary over time and across different MRI sequences. Data from 12 patients (2 essential tremor, 10 Parkinson's disease) who underwent unilateral radiofrequency thalamotomy for tremor were analysed. Lesion characteristics were compared across five structural sequences. Volumetric analysis of lesion features was performed at early (<5 weeks) and late (>5 months) timepoints by manual segmentation. Lesion location was determined after registration of lesions to standard space. All patients showed tremor improvement (clinical global impressions scale) postoperatively. Chronic side-effects included balance disturbances (n = 4) and worsening mobility due to parkinsonism progression (n = 1). Early lesion features including a necrotic core, cytotoxic oedema and perilesional oedema were best demarcated on T2-weighted sequences. Multiple lesions were associated with greater cytotoxic oedema compared with single lesions (T2-weighted mean volume: 537 ± 112 mm³ versus 302 ± 146 mm³, P = 0.028). Total lesion volume reduced on average by 90% between the early and late scans (T2-weighted mean volume: 918 ± 517 versus 75 ± 50 mm³, t = 3.592, P = 0.023, n = 5), with comparable volumes demonstrated at ∼6 months after surgery. Lesion volumes on susceptibility-weighted images were larger than those of T2-weighted images at later timepoints. Radiofrequency thalamotomy produces focused and predictable lesion imaging characteristics over time. T2-weighted scans distinguish between the early lesion core and oedema characteristics, while lesions may remain more visible on susceptibility-weighted images in the months following surgery. Scanning patients in the immediate postoperative period and then at 6 months is clinically meaningful for understanding the anatomical basis of the transient and permanent effects of thalamotomy.

Translational strategies and systems biology insights for blood-brain barrier opening and delivery in brain tumors and Alzheimer's disease

The blood-brain barrier (BBB) plays a critical role in determining the effectiveness of systemic treatments for brain diseases. Over the years, several innovative approaches in BBB opening and drug delivery have been developed and progressed into clinical testing phases, including focused ultrasound (FUS) with circulating microbubbles, mannitol-facilitated delivery of anti-neoplastic drugs, receptor-mediated transcytosis (RMT) by antibody-drug conjugates (ADCs), and viral vectors for gene therapy. We provided a comprehensive review of the most recent clinical applications of these approaches in managing brain tumors and Alzheimer's disease (AD), two major devastating brain diseases. Moreover, the spatial-temporal molecular heterogeneity of the BBB under disease states emphasized the importance of utilizing emerging spatial systems biology approaches to unravel novel targets for intervention within BBB and tailor strategies for enhancing drug delivery to the brain. SEARCH STRATEGY AND SELECTION CRITERIA: Data for this Review were identified by searches of clinicaltrials.gov, MEDLINE, Current Contents, PubMed, and references from relevant articles using the search terms "blood-brain barrier", "CNS drug delivery", "BBB modulation", "clinical trials", "systems biology", "primary or metastatic brain tumors", "Alzheimer's disease". Abstracts and reports from meetings were included only when they related directly to previously published work. Only articles published in English between 1980 and 2023 were included.

Deep brain stimulation, lesioning, focused ultrasound: update on utility

Procedures for neurological disorders such as Parkinsons Disease (PD), Essential Tremor (ET), Obsessive Compulsive Disorder (OCD), Tourette's Syndrome (TS), and Major Depressive Disorder (MDD) tend to overlap. Common therapeutic procedures include deep brain stimulation (DBS), lesioning, and focused ultrasound (FUS). There has been significant change and innovation regarding targeting mechanisms and new advancements in this field allowing for better clinical outcomes in patients with severe cases of these conditions. In this review, we discuss advancements and recent discoveries regarding these three procedures and how they have led to changes in utilization in certain conditions. We further discuss the advantages and drawbacks of these treatments in certain conditions and the emerging advancements in brain-computer interface (BCI) and its utility as a therapeutic for neurological disorders.

Pharmacological Treatment of Tremor in Parkinson's Disease Revisited

The pathophysiology of Parkinson's disease (PD) tremor remains incompletely understood and there is a lack of clinical trials specifically addressing its pharmacological treatment. Levodopa is the most efficacious drug for most patients and should be used as primary approach to control troublesome tremor. While the efficacy of oral dopamine agonists on PD tremor has been demonstrated in controlled trials, there is no evidence of greater antitremor efficacy compared to levodopa. The magnitude of the antitremor effect of anticholinergics is generally lower than that of levodopa. Due to their adverse effects, anticholinergics have a limited role in selected young and cognitively intact patients. Propranolol may improve resting and action tremor and may be considered as an adjunct in patients with insufficient tremor response to levodopa and this also applies to clozapine, despite its unfavorable adverse effect profile. Treating motor fluctuations with MAO-B and COMT inhibitors, dopamine agonists, amantadine, or on-demand treatments such as subcutaneous or sublingual apomorphine and inhaled levodopa as well as with continuous infusions of levodopa or apomorphine will improve off period tremor episodes. For patients with drug-refractory PD tremor despite levodopa optimization deep brain stimulation and focused ultrasound are first-line considerations. Surgery can also be highly effective for the treatment medication-refractory tremor in selected patients without motor fluctuations. The present review highlights the clinical essentials of parkinsonian tremor, critically examines available trial data on the effects of medication and surgical approaches and provides guidance for the choice of treatments to control PD tremor in clinical practice.