Objective: To evaluate the efficacy and safety of staged bilateral magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy in patients with medication-refractory bilateral essential tremor (ET). Herein, safety results are reported.

Background: Patients who are bilaterally affected by ET should be offered bilateral tremor control. However, bilateral procedures (i.e. lesioning and stimulation) have historically been associated with a higher incidence of adverse events (AEs) than unilateral procedures [1]. MRgFUS provides advantages, such as sub-millimeter targeting precision, real-time monitoring, and ability to evaluate clinical benefit and side effects before definitive treatment. Procedures are incisionless with no brain-implanted hardware, reducing the risk of infection, intracranial hemorrhages, seizures, or skin erosion. Small studies have shown that bilateral MRgFUS thalamotomy is effective and has a safety profile similar to unilateral thalamotomy when treatment is sufficiently staged [2-4].

Method: Prospective, open label, single-arm, multicenter study. Patients underwent bilateral MRgFUS thalamotomy at least nine months after a unilateral procedure. The main safety endpoint was the incidence of device- or treatment-related AEs through 6 months post-treatment.

Results: Fifty-one patients (44 male) across 7 centers in the US were enrolled. Mean age was 73 years. There were no deaths, device-related severe or life-threatening events, or unexpected AEs. Of 188 reported events, 184 (97.9%) were mild (84.6%) or moderate (13.3%). Four severe events (2.1%) were unrelated to the device. Thirty events (16%) were transient (resolved within 72 hours). Of six procedure-related events (3.2%) that lasted more than 3 days, all resolved within 30 days. Ninety events (47.9%) were thalamotomy related, mainly numbness/tingling, dysarthria and ataxia; about half (43 of 90) resolved by Month 6. Ongoing events are being followed. Most (45 of 47) are mild and none have worsened. No severe balance or sensory deficits were reported throughout the 6 months.

Conclusion: Safety data reported herein reinforce evidence to date indicating a favorable risk/benefit profile for staged bilateral MRgFUS thalamotomy in ET. Most AEs were mild, and about half were transient, resolving within 6 months. The type and severity of AEs were consistent with those reported in unilateral MRgFUS thalamotomy.

References: 1. Alomar S et al. Speech and language adverse effects after thalamotomy and deep brain stimulation in patients with movement disorders: A meta-analysis. Mov Disord 2017;32(1):53-63.
2. Martínez-Fernández R et al. Bilateral staged magnetic resonance-guided focused ultrasound thalamotomy for the treatment of essential tremor: a case series study. J Neurol Neurosurg Psychiatry 2021;92(9):927-931.
3. Iorio-Morin C et al. Focused ultrasound thalamotomy for essential tremor (BEST-FUS phase 2 trial). Mov Disord 202;36(11):2653-2662.
4. Fukutome K et al. Bilateral magnetic resonance imaging-guided focused ultrasound thalamotomy for essential tremor. Stereotact Funct Neurosurg 2022;100(1):44-52.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/safety-of-staged-bilateral-mr-guided-focused-ultrasound-thalamotomy-for-essential-tremor/