New Ultrasound Treatment for Parkinson’s Disease

Focused ultrasound, guided in real time by MRI, can now destroy tiny, precisely chosen targets deep in the brain without a single incision, and it is reshaping how doctors treat Parkinson’s disease. The technology, known as MR-guided focused ultrasound (MRgFUS), concentrates hundreds of ultrasound beams through the intact skull so they converge on a point roughly the size of a grain of rice, heating that spot enough to create a permanent lesion. Several brain targets have been tested, each addressing a different cluster of Parkinson’s symptoms, and the clinical results over the past decade have been striking enough to earn regulatory approvals and spark a wave of new trials.

How the Procedure Works

A patient lies inside an MRI scanner wearing a helmet-like transducer array fitted over the shaved head. The helmet contains over a thousand individual ultrasound elements, each firing at a slightly different angle so that their energy converges on one focal point inside the brain. Because the skull distorts and absorbs ultrasound unevenly, the system uses CT and MRI data to calculate how to adjust each beam’s timing and power so they arrive at the target in phase. The MRI does double duty: it shows the anatomy the surgeon is aiming at, and it continuously measures the temperature at and around the focal point in real time.¹ The physician starts with low-energy test shots, watches the thermal map to confirm the beam is landing exactly where intended, and asks the patient to perform hand tasks or answer questions to check for side effects before gradually increasing the power to ablative temperatures. The whole session takes a few hours, and the patient is awake and talking throughout.

Targeting the Thalamus for Tremor

The first and most established application is thalamotomy, a lesion in the ventral intermediate nucleus (Vim) of the thalamus, a relay station in the brain’s tremor circuit. This target has been used by neurosurgeons for decades with conventional surgery, but focused ultrasound lets them make the lesion without opening the skull. In a study of 26 patients with tremor-dominant Parkinson’s disease, treatment immediately eliminated or nearly eliminated hand tremor on the treated side in all patients. About a fifth still had some finger tingling a year later, and a small percentage had lasting unsteadiness, but most side effects resolved within months.²

Longer follow-up data confirm that the benefit holds. A cohort tracked for up to five years showed that tremor scores on the treated side remained significantly improved compared with baseline, though some tremor crept back in a minority of patients: two out of the group saw complete return, and eight had partial recurrence.³ A separate study using brain imaging before and after thalamotomy showed that tremor relief correlated with measurable changes in the neural circuit connecting the cerebellum to the thalamus and motor cortex, essentially confirming that the lesion was disrupting the loop that drives the tremor.⁴

Subthalamic Nucleus for Broader Motor Symptoms

Tremor is only one piece of Parkinson’s disease. Stiffness, slowness of movement, and difficulty initiating actions can be equally disabling. The subthalamic nucleus (STN) has long been the preferred target for deep brain stimulation because lesioning or stimulating it can improve the full range of motor symptoms, and focused ultrasound is now being used to create a small lesion there too.

A randomized, sham-controlled trial published in the New England Journal of Medicine compared focused ultrasound subthalamotomy with a fake procedure. Motor scores on the treated side dropped by roughly half in the active group, while the sham group barely changed. The difference was large and statistically clear.⁵ A pilot study had earlier shown a roughly 53% improvement in treated-side motor scores at six months when patients were off medication, establishing proof of concept.⁶

A prospective study looking at the individual motor features found that at six months, rigidity improved by about 84%, tremor by about 92%, and slowness of movement by about 69% on the treated side.⁷ A head-to-head comparison of thalamotomy and subthalamotomy for medication-resistant tremor suggested that the subthalamic target may produce a stronger and more lasting effect on tremor specifically, though both targets delivered significant relief.⁸

Pallidotomy for Dyskinesia and Motor Fluctuations

Many people with Parkinson’s who have been on levodopa for years develop involuntary, often writhing movements called dyskinesia, or unpredictable swings between “on” periods (when medication works) and “off” periods (when it wears off). A different target, the globus pallidus internus (GPi), has historically been the go-to for these problems. Focused ultrasound pallidotomy is now being tested here as well.

A systematic review of the available studies found that dyskinesia scores improved by roughly 43 to 59% at three to twelve months after pallidotomy, with the benefit sustained over a year.⁹ The profile differs meaningfully from subthalamotomy: pallidotomy primarily reduces dyskinesia and smooths out motor fluctuations, while subthalamotomy has its biggest impact on the cardinal motor symptoms themselves. In practice, the choice of target depends on which symptoms are most disabling for a given patient.

How It Compares to Deep Brain Stimulation

Deep brain stimulation (DBS) has been the gold standard surgical treatment for Parkinson’s for more than two decades. It involves implanting thin electrodes into the brain connected to a battery-powered pulse generator under the skin of the chest. Focused ultrasound and DBS are fundamentally different tools aimed at some of the same problems, so patients and clinicians naturally want to know how they stack up.

A network meta-analysis comparing the two approaches for Parkinson’s tremor found no significant difference in tremor suppression between focused ultrasound thalamotomy and the various DBS targets.¹⁰ A broader comparison that also looked at overall motor performance and quality of life found that focused ultrasound subthalamotomy actually ranked first for on-medication motor improvement, ahead of STN-DBS and GPi-DBS.¹¹

The practical trade-offs matter as much as efficacy numbers. DBS is adjustable after implantation: if symptoms change or side effects emerge, the stimulation settings can be reprogrammed. It is also potentially reversible if the electrodes are removed. Focused ultrasound, by contrast, creates a permanent lesion, so if the lesion lands slightly off target or the patient develops unwanted effects, there is no “undo” button. On the other hand, focused ultrasound requires no implanted hardware, no general anesthesia, no surgical wound in the scalp, and no ongoing device maintenance like battery replacements.¹² For older patients, people who are poor candidates for surgery under general anesthesia, or those who simply do not want implanted hardware, focused ultrasound fills a gap that DBS cannot.

Side Effects and What to Watch For

Because the ultrasound beams pass through brain tissue on their way to the target, structures near the focal point can be affected. The most common side effects after thalamotomy are tingling or numbness in the fingers or face, and gait unsteadiness. In a study of 103 thalamotomy patients, about one in six developed sensory side effects lasting beyond three months, and these followed predictable anatomical patterns depending on exactly where the lesion sat relative to the sensory relay in the thalamus.¹³ In the randomized thalamotomy trial, finger tingling occurred in about 39% of treated patients, unsteadiness in about 35%, and facial tingling in about 27%. Most of these faded, but tingling persisted at one year in roughly a fifth of patients.²

Subthalamotomy has its own profile. The randomized trial found that the procedure could cause involuntary movements (dyskinesia) on the opposite side of the body, which makes sense because the subthalamic nucleus normally exerts a braking effect on movement and destroying it can temporarily release that brake. These events were generally manageable by reducing levodopa doses. Speech and swallowing difficulties have also been reported, particularly when both sides of the brain are treated.

The Challenge of Treating Both Sides

Parkinson’s disease almost always affects both sides of the body, but focused ultrasound has largely been applied to one side at a time. The reason is historical caution: bilateral ablative brain procedures carry a known risk of compounding side effects, especially in speech, swallowing, and balance, because both hemispheres share control of these functions.

Recent trials have cautiously tested staged bilateral procedures, treating the worse side first and then coming back months later for the other side. A staged bilateral subthalamotomy study found that four of the treated patients developed involuntary movements after the second procedure, though these resolved within three months in all cases. Speech disturbances occurred in four patients and gradually improved, with only mild residual effects remaining at six months. No cognitive or behavioral problems were detected.¹⁴

A separate multicenter trial of staged bilateral pallidothalamic tractotomy, which targets a fiber tract rather than a nucleus, reported that the unilateral procedure was both safe and effective. However, adding the second side provided only a small additional motor benefit while increasing the rate of persistent moderate or severe side effects, particularly in speech, gait, and balance.¹⁵ The takeaway from these early bilateral results is that it can be done, but patient selection and counseling about the added risks need to be rigorous. For many patients, unilateral treatment of the worse side combined with continued medication for the other side may remain the safer path.

How Long the Benefits Last

A permanent brain lesion does not change over time the way a stimulation setting can drift, so the key question is whether Parkinson’s disease progression eventually overwhelms the benefit. The longest published follow-up data for subthalamotomy now extends to five years. In 32 patients who completed that follow-up, treated-side motor scores were still about 54% better than before the procedure, a level of improvement essentially unchanged from what was measured at three years.¹⁶ Total motor scores across both sides of the body showed a 27% improvement, which makes sense: the untreated side continued to be affected by disease progression while the treated side held steady. Three-year data from the same cohort had shown a 52% improvement on the treated side, confirming the stability of the benefit.¹⁷

These durability numbers are encouraging, but they come with an important caveat. Parkinson’s disease is progressive. The lesion addresses motor circuitry dysfunction, not the underlying loss of dopamine-producing neurons. Over enough years, disease progression on the untreated side and in non-motor domains will advance regardless. Focused ultrasound is not slowing disease progression; it is providing sustained symptomatic relief in the circuitry it disrupts.

Who Qualifies and Who Doesn’t

Not everyone with Parkinson’s disease is a candidate. The skull itself is the biggest physical barrier. Ultrasound passes more efficiently through denser, more uniform bone, and the ratio of cortical bone density to overall skull density, called the skull density ratio (SDR), is used as a screening parameter.¹⁸ Patients with a lower SDR require more energy to reach ablative temperatures, and clinical trials have historically used SDR thresholds (often 0.40 or 0.45) to screen candidates.

However, the picture is more nuanced than a simple cutoff suggests. A study of 189 essential tremor patients found no statistically significant difference in clinical outcomes between those above and below an SDR of 0.45, or even below 0.40, though the procedure was more efficient at higher ratios because target temperatures were reached more easily.¹⁹ Another study confirmed that patients with SDRs below 0.40 could still achieve successful thalamotomy lesions, though they needed more sonication energy to get there.²⁰ So a low SDR does not automatically disqualify someone, but it does make the procedure harder and may mean longer treatment times or, in some cases, an inability to reach the needed temperature.

Beyond skull characteristics, good candidates generally have medication-refractory symptoms, meaning their tremor or other motor problems persist despite optimized drug therapy. People with cognitive impairment, significant psychiatric conditions, or certain brain abnormalities on MRI are typically excluded. The patient also needs to be able to lie still in an MRI scanner for several hours while awake.

Beyond Ablation: Opening the Blood-Brain Barrier

The most futuristic application of focused ultrasound in Parkinson’s disease is not about destroying tissue at all. At much lower intensities, focused ultrasound combined with injected microbubbles can temporarily and reversibly open the blood-brain barrier, the tightly sealed lining of blood vessels in the brain that normally blocks most drugs from entering brain tissue.²¹ This opens the door to delivering therapies that currently cannot reach the brain.

In animal models of Parkinson’s disease, researchers have used this technique to deliver gene therapy vectors carrying instructions for producing a growth factor called GDNF, which supports the survival and function of dopamine neurons. The approach achieved widespread expression of the therapeutic gene throughout the targeted brain region after a single intravenous injection.²² In nonhuman primates, focused ultrasound successfully opened the blood-brain barrier in brain regions involved in Parkinson’s and delivered viral vectors carrying therapeutic genes to those areas.²³

There is also early interest in whether blood-brain barrier opening might help clear alpha-synuclein, the misfolded protein that clumps inside neurons and drives Parkinson’s disease progression. The relationship between neuroinflammation, blood-brain barrier function, and alpha-synuclein accumulation is an active area of investigation, though whether focused ultrasound-mediated barrier opening actually accelerates clearance of these toxic aggregates has not been established in humans.²⁴ Separately, low-intensity focused ultrasound without microbubbles is being studied for its potential to modulate brain activity and influence inflammatory and neurotrophic signaling pathways relevant to Parkinson’s.²⁵ These non-ablative approaches are still largely preclinical, but they represent a fundamentally different ambition: not just treating symptoms, but potentially slowing the disease itself.

Quality of Life Beyond Motor Scores

Clinical trials naturally focus on motor scores because they are measurable and standardized, but what patients care about is whether they can button a shirt, hold a coffee cup, or write their name. Studies that have tracked quality-of-life measures after focused ultrasound thalamotomy found improvements in both daily activities and overall well-being after the procedure.²⁶ These gains matter because Parkinson’s tremor often causes social embarrassment and withdrawal in addition to functional disability. People stop eating in public, avoid handshakes, and give up hobbies that require fine motor control. Eliminating or substantially reducing tremor on even one side can meaningfully change daily experience in ways that a motor score alone does not capture.

Nonmotor symptoms like sleep disturbance, anxiety, and depression are also common in Parkinson’s disease, and whether focused ultrasound has any indirect benefit on these through improved motor function and reduced disability is still being explored. The available evidence suggests the treatment does not worsen cognition or mood, which is itself a meaningful finding given that some surgical interventions carry neuropsychiatric risks. For patients weighing their options, the conversation is shifting from “should I have surgery?” to “which procedure fits my symptom profile, my anatomy, and my priorities?” Focused ultrasound has earned a legitimate place in that conversation.