Updated Report on Side Effects of Focused Ultrasound for ET

For people with essential tremor (ET) or their loved ones, I’m happy to tell you about a research report that came out toward the end of 2018. The article by Mohammed, et al.i presented statistics on the side effects of Focused Ultrasound (FUS) as a treatment to control ET. It incorporated data from nine previously published studies, for a total of 160 patients.

Tremor control through neurosurgery

Essential tremor is a movement disorder that most commonly affects the hands, head and voice. Since our hands are involved in practically every personal, professional and recreational task, “the shakes” create disabilities that range from annoying or frustrating to severely impairing. While medication is the first line of treatment, it is ineffective for about 50% of people; among those who find it effective, a large number have to increase doses over time until eventually medication no longer works. When tremors resist drug treatment, it is called refractory ET.

Those who develop refractory ET are usually encouraged to consider a neurosurgery to control tremors. Such procedures intervene in the brain’s thalamus, a center that “forwards” abnormal tremor signals out to the body. There are two types of procedures:

  1. Deep brain stimulation (DBS) uses implanted electrodes to stimulate the thalamus. They are connected by wires in the neck to a battery pack surgically placed in the chest.
  2. Thalamotomy ablates (destroys) the part of the thalamus that forwards signals to the hands. It used to be done by inserting image-guided probes into the brain, but now FUS is quickly replacing physical probe insertion with precise, noninvasive image-guided sonic energy to accomplish the destruction. In most cases, only the dominant hand is treated since destroying both sides at once increases the chance of side effects.

Side effects of neurosurgery

Any treatment that intervenes in the brain always has some risk of side effects, so doctors and patients are interested in treatments that have a good success record with the least risks. Both DBS and surgical insertion of thalamotomy probes are effective in controlling tremors but both require drilling a hole in the skull. This “exposes patients to the risk of intracranial [inside the skull] complications, such as bleeding and infection.”ii While DBS can be modulated to adjust to tremor severity, there are additional considerations such as possible electrode migration, surgery to replace batteries, and a very small risk of stroke or bleeding in the brain. Patients also report side effects such as tingling in the face or slurred speech, which are usually temporary but may linger for months.

Since FUS is “beamed” through the skull, no skin incision or hole drilled in the skull is necessary. This means is virtually no risk of infection or probes/wires creating a bleeding risk. The success rate of FUS in controlling tremors at 12 months is equal to that of DBS. So, what are the side effects?

Side effect report

That is the question that Mohammed’s team wanted to address. The found that the most commonly reported side effects at three months after treatment were dizziness and some loss of movement control in the legs or other body parts, but by 12 months after treatment these tended to go away on their own. At the same time, they experienced significant improvement in their quality of life thanks to regaining the normal use of their dominant hand.

No long-term results yet

DBS has been around for over two decades, while FUS was FDA-approved in 2016 to control ET. In a 2-year follow up studyiii of 67 patients who had FUS, only a few reported lingering movement problems at one year. However, “At two-year follow up, the patients’ degree of tremor improvement was sustained, and they did not develop new adverse effects that had not already emerged immediately after the procedure.”iv The fact that no more side effects developed, while success continued at the 2-year mark, is great news for those with refractory ET who want their tremors gone but are fearful of an invasive neurosurgical procedure. Despite the lack of long-term follow up, over a thousand people with ET have now been treated worldwide, and interest in FUS to control tremors continues to snowball.

Sperling Neurosurgery Associates is proud to be a leading U.S. center in offering MRI-guided FUS. This outpatient procedure provides tremor control of the dominant hand, and the results are immediate. Please visit our patient testimonials page to explore the patient experience, or contact us for a consultation.

iMohammed N, Patra D, Nanda A. A meta-analysis of outcomes and complications of magnetic resonance-guided focused ultrasound in the treatment of essential tremor. Neurosurg Focus. 2018;44:E4.
iiMoawad, Heidi. “Ultrasound Ablation in the Treatment of Essential Tremor.” Neurology Times, Jan. 16, 2019. http://www.neurologytimes.com/parkinson-disease/ultrasound-ablation-treatment-essential-tremor
iiiChang JW, Park CK, Lipsman N. A prospective trial of magnetic resonance-guided focused ultrasound thalamotomy for essential tremor: Results at the 2-year follow-up. Ann Neurol. 2018;83:107-114.
ivMoawad, Ibid.

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