Brain Surgery with Sound Waves Proves Safer Than Expected

A new study of patients who underwent focused ultrasound brain surgery on both sides of their brain shows surprisingly minimal cognitive effects, challenging long-held fears about bilateral brain procedures.

The research, involving 21 patients with severe essential tremor, found that 95% of cognitive test scores remained stable after the second-sided procedure, with only 2% showing decline. This represents the largest and most comprehensive cognitive assessment of bilateral focused ultrasound thalamotomy to date, offering new hope for patients whose tremors haven’t responded to medication.

The findings address a critical concern that has limited treatment options for essential tremor patients, who often face a difficult choice between living with debilitating symptoms and risking potential cognitive consequences from bilateral brain interventions.

When Medications Fail

Essential tremor affects roughly 1% of the global population, making it one of the most common movement disorders. While the condition primarily causes action tremor in the arms and hands, severe cases can devastate daily activities like eating, drinking, and writing, leading to social isolation and reduced quality of life.

Traditional treatment begins with medications like beta-blockers and anti-seizure drugs. However, a substantial proportion of patients either don’t achieve adequate tremor control or experience intolerable side effects, leaving them with few options beyond neurosurgical intervention.

Focused ultrasound thalamotomy has emerged as a precise, minimally invasive alternative to traditional brain surgery. The technique uses concentrated sound waves to create small, controlled lesions in the ventral intermediate nucleus of the thalamus—a brain region that regulates movement when overactive in essential tremor patients.

The Bilateral Challenge

While the FDA approved unilateral focused ultrasound for essential tremor in 2016, bilateral treatment remained more controversial. Historical experience with traditional bilateral thalamotomy procedures showed increased risks of speech and cognitive problems, making doctors cautious about treating both sides of the brain.

The FDA’s December 2022 approval of staged bilateral focused ultrasound rekindled interest in treating both brain hemispheres, but evidence regarding cognitive safety remained limited. Previous studies suffered from small sample sizes—often fewer than 12 participants—or relied on brief cognitive screening tests that might miss subtle but important changes.

How do you balance the potential benefits of improved tremor control against unknown cognitive risks? This question has left many patients and doctors in difficult positions, particularly when tremor affects both hands severely.

Comprehensive Cognitive Testing

The Toronto-based research team conducted the most thorough cognitive evaluation to date, testing 21 patients before and approximately four months after their second-sided procedure. All participants had previously undergone successful unilateral treatment at least one year earlier.

The neuropsychological battery was specifically designed to minimize motor demands while evaluating multiple cognitive domains:

• Global cognition and attention – including focused attention and working memory tasks
• Processing speed – how quickly patients could complete mental tasks
• Executive function – planning, inhibition, and mental flexibility
• Memory – both immediate and delayed recall abilities
• Language skills – word fluency and naming abilities
• Visuospatial processing – spatial reasoning and visual perception

Importantly, the researchers analyzed results both at the group level and individually, allowing them to detect changes in specific patients that might be masked by overall averages—a crucial methodological advancement that provided much more detailed insights into cognitive safety.

Remarkable Stability

The results proved reassuring across multiple measures. At the group level, no cognitive test showed statistically significant decline after accounting for multiple comparisons. Even a test that initially appeared to show decline—the color naming task—involved only a median increase of one second in completion time, with no individual patients showing reliable decline on this measure.

The individual-level analysis revealed even more compelling evidence of cognitive safety. Among 371 individual test scores analyzed across all patients, 94.6% remained stable, 3.5% improved, and only 1.9% declined. No patient declined on more than two cognitive tests, and no single test showed decline in more than two patients.

Perhaps most importantly, the three patients who entered the study with mild cognitive impairment showed similar patterns of stability, with 94.4% of their test scores remaining unchanged and only one score declining across all three patients combined.

The Reliable Change Innovation

The study’s sophisticated statistical approach represents a major advancement in assessing cognitive outcomes. Rather than relying solely on group averages, the researchers calculated Reliable Change Indices for each patient—a method that distinguishes true cognitive change from normal measurement variability or practice effects.

This individual-level analysis proved crucial because it revealed that apparent stability at the group level wasn’t masking widespread individual declines. If the procedure caused true cognitive problems, the researchers would have expected to see systematic declines across many patients—a pattern that simply didn’t emerge.

The medication analysis provided additional reassurance. Most patients either remained off tremor medications or maintained stable doses throughout the study period, and those whose medications were reduced showed no consistent pattern of cognitive change, suggesting that the cognitive stability wasn’t simply due to medication effects.

Clinical Impact and Limitations

As expected, patients showed significant tremor improvement in their treated hand, with Clinical Rating Scale for Tremor scores dropping from 18.2 at baseline to 8.9 at follow-up. This tremor reduction, combined with the cognitive safety findings, suggests that bilateral focused ultrasound can provide meaningful benefit without the cognitive costs historically associated with bilateral brain interventions.

However, the researchers acknowledge important limitations. The study likely represents optimal outcomes since only patients without significant problems from their first procedure received second-sided treatment. The sample was also predominantly white and well-educated, potentially limiting generalizability to more diverse populations.

The relatively small number of patients with mild cognitive impairment means more research is needed to understand safety in this vulnerable population. Additionally, the four-month follow-up period, while standard for this type of research, doesn’t capture potential longer-term cognitive changes.

Changing the Treatment Landscape

These findings could fundamentally alter treatment discussions for essential tremor patients. The historical fear of bilateral brain procedures has left many patients with limited options when unilateral treatment provides insufficient benefit. The demonstration that cognitive decline is neither consistent nor widespread following bilateral focused ultrasound opens new possibilities for more complete tremor control.

The research also validates the precision advantage of focused ultrasound over traditional surgical approaches. The ability to create precisely targeted lesions while minimizing damage to surrounding brain tissue appears to translate into meaningful clinical benefits in terms of cognitive preservation.

For the estimated millions of people worldwide living with medication-refractory essential tremor, these results offer hope that effective treatment doesn’t require choosing between tremor control and cognitive function—a false choice that has limited treatment options for far too long.