For patients with essential tremor (ET) who do not get acceptable relief from medications, deep brain stimulation (DBS) has been the gold standard of FDA-approved treatment since the late 1990s. Studies demonstrate that tremor reduction after unilateral DBS of the Vim thalamus ranges from 53% to 62% at 12 months postoperatively, with action tremor reduced up to 79%.
Yet not all ET patients are suitable candidates for this treatment, and the treatment landscape is shifting with the emergence of a newer, less invasive technology: MRI-guided focused ultrasound (MRgFUS).
Cedars-Sinai is one of only approximately 50 hospitals nationwide positioned to leverage MRgFUS technology with the Exablate Neuro device, manufactured by Insightec. The device was approved by the FDA for unilateral treatment of medication-refractory ET in 2016 and for treating a patient’s second side in 2022. The technology was also approved for tremor-predominant Parkinson’s disease. Additionally, it was approved for Parkinson’s with a target of the globus pallidus internus in 2022 (but is not yet covered by Medicare for this indication).
Using an acoustic lens to focus ultrasound waves, MRgFUS enables neurosurgeons to heat and ablate specific points in the brain with accuracy to less than a millimeter. Progressive sonication allows for heating at a low temperature to get a subtle effect, controlling a patient’s tremor without destroying critical tissue.
“In the case of older procedures, modulating impact was difficult. It was really one shot—we would insert a device and burn,” said Adam Mamelak, MD, director of the Functional Neurosurgery Program and professor of Neurosurgery at Cedars-Sinai. “Focused ultrasound changes the game by giving us the capacity to increase heat gradually, effectively putting a safety measure in place and minimizing the risk of the procedure.”
Enhanced safety is just one of the factors that make MRgFUS a compelling option for Vim thalamotomy. “DBS requires implanting electrodes via invasive surgery, whereas with ultrasound, we can ablate noninvasively and know exactly what we’re doing in real time,” said Chirag Patil, MD, associate professor of Neurosurgery.
“For older patients, or for those unable to stop taking blood thinners, surgery may not be possible. With focused ultrasound, there’s no blood work or anesthesia and little risk of infection. After a one-time treatment, patients go home the same day with their tremor better controlled. It’s pretty remarkable,” said Patil.
A recent article in the Journal of Neurosurgery confirms the benefits of MRgFUS, showing sustained and significant tremor improvement after five years. In the study, CRST scores for postural tremor for the treated hand were boosted by more than 73% from baseline at both 48 and 60 months post-treatment.
Mamelak notes that a key to successful treatment with MRgFUS is appropriate patient selection. “The two main criteria for eligibility are tremor being the patient’s overwhelming, dominant symptom and one side being worse than the other,” he said.
“Focused ultrasound can be used to treat both sides, but rapid bilateral lesioning can result in cognitive issues, so patients must wait a minimum of nine months between ablations. For those patients, DBS may be preferred,” explained Mamelak.
In late spring 2023, Mamelak and Patil, who have been specially trained on the Exablate Neuro device, will be performing the first MRgFUS procedures at Cedars-Sinai. The availability of the technology at Cedars-Sinai further enhances the medical center’s reputation for excellence in treating movement disorders.
"We have a very comprehensive program here, with the capacity to take care of a patient’s full range of needs,” Mamelak said. “One of our key points of distinction for any patient having focused ultrasound is that they will be screened by both the neurosurgeon performing the procedure and by a neurologist to ensure they are being treated appropriately and effectively.”
Indications for use
Candidates for MRgFUS must be at least 22 years old, have a confirmed diagnosis of ET or tremor-dominant Parkinson’s, and be unresponsive to or ineligible for at least two standard-of-care medications. During the procedure, patients remain awake to evaluate treatment response, including tremor improvement and potential adverse effects.
Those effects are likely to be short-term. “Many people do experience a transient sense of gait instability following treatment that can last up to three months,” Patil said. “But it almost always improves, and by one year out, balance typically returns to normal.”
On the horizon
Though MRgFUS is currently limited to treating ET and tremor-dominant Parkinson’s, its potential future applications are wide-ranging.
“The technology is imminently expandable to other things, and indications will undoubtedly continue to broaden over time,” Mamelak said. “One example is obsessive-compulsive disorder, which we have treated in the past with lesioning methods; focused ultrasound is already being tested for use in this arena.”
Other early-phase studies are looking at ways to leverage MRgFUS to deliver targeted chemotherapies for brain tumors.
“Twenty years ago, we would have thought this technology was something out of a science fiction novel,” Patil said. “Today, it’s changing the face of neurosurgical medicine.”
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Focused ultrasound is an incisionless, outpatient procedure that provides immediate and durable reduction in tremor with significant improvement in quality of life, as seen by the patient testing before and immediately after having the treatment for essential tremor.