Objective: This open label clinical trial evaluates the symptomatic motor improvement induced by Low Intensity Focused Ultrasound on essential tremor through clinical performance assessment in three patients.

Background: Essential tremor (ET) is a prevalent neurological disorder characterized by action tremor, primarily on upper limbs. A dysfunction of the dentato-rubro-thalamic-cortical tract appears to be involved. Its diagnosis is based on the clinical criteria of the MDS Task Force for Tremor. The main pillar of treatment is medication, such as propranolol and primidone. Even so, around 50% of patients remain symptomatic. Some refractory cases may benefit from bilateral deep brain stimulation in the thalamus or unilateral thalamotomy, using guided high-frequency ultrasound. Non-invasive neuromodulation has been studied as a complementary therapy to clinical treatment, such as Transcranial Magnetic Stimulation (TMS) and Direct Transcranial Current Stimulation (DTCS). Recently, the use of Low Intensity Focused Ultrasound (LIFU) has been studied as a neuromodulatory tool in tremor, capable of inducing reversible physiological effects in the nervous system, ranging from increased excitability to suppression in regions of interest.

Method: This case series reports outcomes from 3 patients undergoing LIFU for treatment of ET. The left ventral intermediate nucleus of the thalamus (VIM) was the chosen target, using MRI neuroimaging. Patients underwent two ten-minute sessions of LIFU with a 20 minutes break between. Evaluation through The Essential Tremor Rating Assessment Scale (TETRAS) performance subscale were applied immediately before, and immediately after the stimulation protocol.

Results: Three patients diagnosed with ET undergoing optimized drug treatment without complete symptoms control, due to severity of tremors or intolerance to side effects of drugs. They were submitted to LIFU and clinically assessed through TETRAS performance subscale immediately before and after stimulation. Results demonstrated a reduction on scale score of  at least 2 points, mainly on the upper limbs tremor assessment.

Conclusion: The evidences observed in the case series support LIFU’s potential as a practical and effective treatment aiming to reduce the severity of tremors and improve the quality of life. Findings serve as a starting point for further clinical trials.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/low-intensity-focused-pulsed-ultrasound-as-a-treatment-of-essential-tremor-a-case-series/