HONOLULU — New imaging data may explain how transcutaneous afferent patterned stimulation (TAPS), a noninvasive, wearable therapy, works in patients with essential tremor (ET).

In a small study that showed a decrease in tremor symptoms in patients with ET after 90 days of use with a TAPS device (Cala kIQ system), PET imaging also showed that TAPS was associated with significant changes in metabolic activity in key areas of the brain’s tremor circuitry.

Specifically, increased activity was observed in the ipsilateral (the side of the stimulation) areas of the cerebellum and diencephalon.

“I think the most exciting thing was the strength of the correlation between the clinical outcomes that we saw and the brain modulatory effects,” study co-author Alex Kent, PhD, vice president of research at Cala Health, San Mateo, California, told Medscape Medical News.

“This gives physicians an understanding of how the therapy is functioning, and it gives some real data from which to talk with a patient — to show how it changes the dynamics of the brain areas involved in essential tremor,” he said.

The findings were presented on October 6 in a poster session at the International Congress of Parkinson’s Disease and Movement Disorders (MDS) 2025.

Exploring ‘Downstream’ Effects

Treatments for ET commonly include medication and surgical treatment, such as deep brain stimulation. However, these therapies can carry substantial adverse events.

Noninvasive TAPS therapy provides “alternating electrical pulses to the median and radial nerves, calibrated to each patient’s tremor frequency,” the investigators noted. 

The FDA cleared TAPS in 2018 for the treatment of hand tremor symptoms in ET, and the Cala kIQ system was launched in 2023 for tremor relief. It is a device that is worn on one hand, sort of like a wristwatch or Fitbit.

According to guidance from the International Essential Tremor Foundation, TAPS (and/or other noninvasive devices) is recommended as an optional add-on to first-line pharmacologic treatments, or prior to or in combination with second- and third-line treatments.

While several previously published studies have shown effectiveness for Cala TAPS therapy, a small pilot study has also suggested that cerebellar metabolism might be altered after 90 days of TAPS use. In the current study, the researchers sought to use PET imaging to better assess changes in brain metabolism. 

The study was created “to really understand what the downstream effects were of peripheral nerve stimulation,” Kent said.

Eleven patients 21 years or older were enrolled, with nine patients completing the full study protocol. 

The Essential Tremor Rating Assessment Scale (TETRAS) tests were administered pre- and post-stimulation. PET scans were done at baseline and at day 90 visits. During that period, patients wore the device and self-administered TAPS twice a day in their own homes. 

Acute, Sustained Response

Results showed significantly increased activity in both the ipsilateral cerebellum and the ipsilateral diencephalon (P < .01 for both) at day 90.

Increased fluorodeoxyglucose (FDG) uptake was observed in the cerebellum, which was more prominent in the ipsilateral side. FDG uptake in the ipsilateral diencephalon also showed a modest increase, “which reflects activation of thalamic and subthalamic nuclei, areas important in ET relay circuitry,” the researchers wrote. 

The stimulated hand showed a decrease in total TETRAS score from 5.9 ± 1.9 at day 1 before receiving stimulation to 3.9 ± 1.6 at treatment day 90 pre-stimulation (P = .04) and to 3.7 ± 1.3 at day 90 post-stimulation (P = .02), “showing a 34% improvement,” Kent said.

Additionally, there was a significant change on day 1 between pre-stimulation and post-stimulation (P = .04). 

“So we’re seeing an acute response within a day,” as well as a sustained effect, Kent noted. 

Finally, there was a correlation between clinical improvement and cerebellar activity.

Change in standardized uptake value ratio, which reflects FDG uptake, was significantly negatively correlated with change in TETRAS scores from day 1 to day 90 in the ipsilateral cerebellum (r = -0.71; P = .03) and the ipsilateral diencephalon (r = -0.69; P = .04).

“The degree of improvement in tremor symptoms with TAPS directly corresponds to the amount of metabolic change in the ipsilateral cerebellum, confirming prior findings, and in the diencephalon,” the investigators wrote.

Kent said the takeaway message from this study and other recent research is that “with a noninvasive device, we are able to modulate the same brain areas that are otherwise needing to be targeted with more invasive procedures,” including deep brain stimulation. 

‘A Good Start’

Commenting for Medscape Medical News, Jamie Adams, MD, chief of the Movement Disorders Division and associate director of the Center for Health + Technology at the University of Rochester, Rochester, New York, noted that although it was “intriguing” to see metabolic changes in the brain based on a wrist-worn device, the study was quite small. 

“I think it’s a good start, but certainly a longer, larger study is needed,” said Adams, who was not involved with the research.

She noted that a longer-duration study could possibly show whether the benefit lasts over time.

“That’s a concern for some of these stimulation devices — that the benefit does not sustain for long periods. There’s initially some benefit that may not last,” Adams said.

“But I think the changes in brain activity were certainly interesting and perhaps support that there would be some longitudinal change. I would love to see [more] of that data,” she added.

The study was funded by Cala Health. Kent reported being an employee of Cala Health. Adams reported having no relevant financial relationships.