September 23, 2016
BY FRAN KRITZ
As many as 10 million people have essential tremor, a neurologic condition that causes involuntary and rhythmic shaking, mostly in the hands, but shaking can also occur in the head, arms, voice, and torso, according to the International Essential Tremor Foundation. The condition is sometimes mistaken for Parkinson's disease because tremor is a symptom of Parkinson's. But unlike with essential tremor, tremor in Parkinson's disease is one of many symptoms including a shuffling gait and movement difficulties, says Todd Herrington, MD, PhD, a neurologist at Harvard Medical School and Massachusetts General Hospital.
Essential tremor is incurable but it can be treated with beta blockers and anticonvulsant medication as well as deep brain stimulation (DBS), which involves a neurostimulator, a battery-operated medical device similar to a pacemaker that is surgically implanted into the chest. The neurotransmitter delivers electrical stimulation to targeted areas of the brain that control movement, blocking the abnormal nerve signals that cause tremor. Studies show that it improves arm tremor by 50 to 90 percent, says Dr. Herrington.
Ultrasound Burns Brain Cells
Now, a new treatment has been approved by the US Food and Drug Administration (FDA) that might help patients who haven't responded to other therapies. Called focused ultrasound thalamotomy, the device directs intersecting and concentrated beams of ultrasound energy that heat then burn away a portion of the thalamus, a part of the brain thought to generate some involuntary movement. During the procedure, the patient wears a helmet-like device and lies in a magnetic resonance imaging (MRI) machine. Images on a monitor help surgeons guide the ultrasound beams, and the amount of energy is increased incrementally until surgeons see a lessening of the tremor. No anesthesia or incision is required.
"Individual ultrasound beams pass through the scalp, skull, and brain tissue. Once at the target, the multiple beams converge to a precise focal point. This is a permanent treatment in which some brain cells causing the tremor are burned away," explains Vibhor Krishna, MD, a neurosurgeon at Ohio State Wexner Medical Center, one of six medical centers in the US that performed clinical trials on the procedure. "We hope to increase the effectiveness of this treatment by improving visualization of the brain region involved through advanced neuroimaging," adds Dr. Krishna.
FDA Approval Based on Small Clinical Trial
The double-blind, placebo-controlled trial, which was published in the New England Journal of Medicinein August, involved 76 patients with essential tremor who had previously not responded to medication. Fifty-six patients were randomly selected for focused ultrasound and 20 for a fake treatment but those patients were able to switch to the actual treatment three months later.
Patients treated with ultrasound showed nearly a 50 percent improvement in their tremors and motor function three months after treatment compared to their baseline score, while patients in the control group had no improvement. Some even experienced a slight worsening before they switched to the treatment group. A year after the procedure, improvement had dropped to 40 percent. Researchers and clinicians are following up with patients to see if the decrease stabilizes or if it's an indication that improvement wanes over time, says Dr. Krishna.
Procedure Has Side Effects
Patients in the clinical trials reported numbness or tingling in the fingers, headache, imbalance and unsteadiness, loss of control of body movements, and gait problems. The energy beams can cause tissue damage beyond the treatment site, as well as hemorrhaging, skin burns, and blood clots.
Not everyone is a candidate for the procedure, according to the FDA, including anyone who has an implantable medical device such as a pacemaker, people who are allergic to contrast dyes used for MRIs, pregnant women, and people with unstable blood pressure.
Pros and Cons
"We don't yet know how long the effects will last," says Dr. Herrington, who was not involved in the clinical trials. The procedure is also irreversible and even though it's termed noninvasive, that's not entirely accurate, he says. "Surgeons create a permanent hole in the brain." Advantages include no risk of infection at the incision site and no need to replace a neurostimulator battery periodically as is the case with DBS. And in rare cases, says Dr. Herrington, the neurotransmitter used for DBS can fail, and another surgery is needed to remove it.
Approval Limitations
Focused ultrasound thalamotomy for essential tremor is approved for use on one side of the brain only and surgeons are most likely to choose the side that is causing tremor in the dominant hand, says Dr. Herrington. "As the device has wider use, we'll have a chance to see how long the effects last and whether we can push it to treat symptoms on both sides," says Dr. Herrington. "I think it's an exciting tool but will take more time to understand how exactly it fits." Dr. Herrington says another upside is that the location where the energy is directed is similar to targets used for DBS so surgeons are already familiar with the anatomy involved.
Covering the Cost
Insightec, an Israeli company that manufactures ExAblate Neuro, the focused ultrasound device, is in talks with Medicare and private insurers about coverage and expects to have answers by next year, says Rick Schallhorn, vice president of neurosurgery at Insightec.
Meanwhile, the medical centers that conducted the clinical trials have the device so patients should discuss the option with their physician. The procedure, which is not yet covered by Medicare or insurance, currently costs more than $30,000, which includes the device and the surgery.
For more information about focused ultrasound thalamotomy for essential tremor, visit the FDA at bit.ly/FDA-Tremor or Insightec, the company that created the device, at bit.ly/ExAblateNeuro. Also, talk to your doctor to see if the procedure is something for you to consider. For more about essential tremor, visit our archives at bit.ly/NN-Ess
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