Published October 25, 2026 at 10:00 AM CDT

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Up to 10 million adults in the United States experience a movement disorder called essential tremor, which causes rhythmic shaking in their hands and sometimes their head and voice. UT Health San Antonio’s Dr. Alexander Papanastassiou says that in some of these patients, symptoms can be disabling. He is the director of Stereotactic, Functional and Epilepsy Neurosurgery at UT Health San Antonio and a professor of neurosurgery at UT San Antonio.

“Things that can be real problems are eating, drinking, and hygiene, like brushing hair and teeth or getting dressed,” Papanastassiou says. “It also typically affects writing.”

There are medications to treat essential tremor, but they don’t control symptoms in about half the people who use them, Papanastassiou says. For these patients, UT Health San Antonio offers MRI-guided focused ultrasound.

David Constante

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UT Health San Antonio

Alexander Papanastassiou, MD
Professor, Department of Neurosurgery
Long School of Medicine at UT San Antonio
Neurosurgeon and Director of Stereotactic, Functional and Epilepsy Neurosurgery at UT Health San Antonio

“A person goes into the MRI scanner, and there’s a special helmet with over 1,000 ultrasound transducers,” Papanastassiou explains. “And each one emits ultrasound waves. Where those waves meet, they create heat.”

That heat targets the tiny area of the brain that causes the tremor. The neurosurgeon uses the heat to create a small lesion that disrupts the abnormal electrical activity that is causing the tremor. Papanastassiou says this typically reduces it by 80%.

“That type of tremor relief is usually good enough that it will get people back to things that they were having trouble with, like eating, drinking, often writing,” Papanastassiou says, and some can get back to doing things they love but that tremors made impossible. “It may have been years since they gave up fishing or since they gave up crochet — things they forgot they’d given up because of the tremor.”

However, there is a balance to be struck between treatment effects and side effects, Papanastassiou says. If a neurosurgeon heats too large an area, the procedure can cause clumsiness or difficulty walking. If the target area is too small, the improvement in the tremor may not be as good as it could be.

“One of the ways that we avoid side effects is by making the lesion the Goldilocks ‘just right’ size,” Papanastassiou says. “Just big enough that it controls 80% of symptoms, on average, but not so big that it extends into neighboring areas that we want to avoid.”

Although the procedure is non-surgical, patients must have their hair clipped close to the scalp. The treatment is delivered with a specialized cap through which cold water is circulated. Hair can trap tiny air bubbles that block the ultrasound waves. Once a patient’s hair is cut, sound waves can more easily travel through the water around the head, then through the skin, bone, and brain to the target area.

For many essential tremor patients, this is all worth it for the improved outcomes, which — in 80% of patients — last for at least five years, according to Papanastassiou. “Because certainly we want the basics in life like eating, drinking, getting dressed and writing," Papanastassiou says, "but we also want the things that make life pleasurable and make us happy to be alive.”

Science & Medicine is a collaboration between TPR and The University of Texas Health Science Center at San Antonio that explores how scientific discovery in San Antonio advances the way medicine is practiced everywhere.