New research suggests that noninvasive peripheral nerve stimulation relieves symptoms in patients with essential tremor (ET).
Stimulation delivered with a wrist-worn device was better than a sham intervention at calming tremors and had a favorable side effect profile, a new study shows.
“The device did provide some dramatic relief” and some activities of daily living were improved, author Rajesh Pahwa, MD, Laverne & Joyce Rider Professor, chief, Parkinson & Movement Disorders Division, Department of Neurology, University of Kansas Medical Center, and director, Parkinson Foundation Center of Excellence, Kansas City, told Medscape Medical News.
However, said Pahwa, it’s an early study and the still-investigational device is not yet “ready for prime time.”
The research will be presented April 25 at the upcoming American Academy of Neurology (AAN) 2018 Annual Meeting in Los Angeles, California.
ET is the most common movement disorder, affecting an estimated 10 million Americans, the researchers note, and that number is expected to grow as the population ages.
The condition is characterized by involuntary oscillatory movements, typically between 4 and 12Hz. It can produce oscillations in the voice and unwanted movements of the head and limbs.
Tremor in the hands and forearm is particularly problematic because it makes it difficult to carry out daily activities, such as writing, typing, eating, and drinking.
Although the precise mechanisms of ET are uncertain, it’s thought that tremulous activity originates within a central tremor network.
Experts believe there’s a need for an alternative to current treatment approaches for ET. The main drug choices — the β-blocker propranolol and the anticonvulsant primidone — are not effective for all patients, and many patients can’t tolerate them, as is the case with other medications, including benzodiazepines.
“So our options are very limited at this stage as far as medical treatment is concerned,” said Pahwa.
Deep-brain stimulation that involves implantation of a stimulator within the brain can be very effective in reducing tremors in patients with ET. However, this involves a highly invasive surgical procedure that carries significant risks.
Wrist Band
The new device resembles a slightly larger version of an Apple watch. On the inside of the wrist band are electrodes that stimulate the median and radial nerves.
“The current is usually not at a level that makes patients uncomfortable,” said Pahwa. Some may report they feel it a little while others may not, he said.
The front of the band has an “on” and “off” switch.
The thought is that stimulation with this new device sends signals along the sensory nerves to the central nervous system, which affects the circuitry in the brain and improves tremors, said Pahwa.
He and his colleagues carried out two studies of the device, an acute study and an at-home chronic study.
In the acute study, researchers randomly assigned 77 patients to receive peripheral nerve treatment or sham stimulation of the tremor dominant hand. The sham stimulation was very mild; Pahwa described it as “substimulation.”
Investigators evaluated tremor before and after a single stimulation session. They used the patient-rated Bain & Findley activities of daily living scale and the physician-rated Tremor Research Group Essential Tremor Rating Assessment Scale (TETRAS) dominant upper limb scale.
The Bain & Findley scores significantly improved with the treatment compared with the sham (P = .001).
“If you look overall, there was about a 20% difference compared with sham,” said Pahwa.
“If you go to specific tasks, unlocking a door with a key, picking up change, holding a cup, and dialing a phone were all significantly improved,” while other tasks improved but not significantly.
As for TETRAS, which assessed tasks such as holding the arm straight out in front of the body, the study showed the therapy produced significant improvements compared with sham (P = .017).
Here, too, the improvement in scores for the active stimulation compared with sham was about 20%.
“There was definitely a group of patients who had dramatic improvements,” commented Pahwa.
He pointed out that these are patients in whom medicines are not providing adequate control but whose tremors are not severe enough to be considered for invasive surgery.
However, he cautioned that this is preliminary research and that a larger study is needed.
“We have to look at it more closely and see if there are certain people who respond and certain people who don’t respond.”
The study also found that the therapy was safe. Patients did not report any significant adverse events. About 3% of patients experienced mild effects, such as skin redness and irritation, but these spontaneously resolved without intervention.
Chronic Study
For the chronic study, researchers randomly assigned 61 patients to treatment, sham, or standard of care.
The at-home sham group did not receive stimulation but only wore the device. Standard of care was whatever therapy patients were already receiving, whether medications for tremor or nothing at all. These patients didn’t wear the device so no recordings were available.
Patients in the treatment group were asked to turn on the device while performing certain tasks a minimum of two sessions each day for 4 weeks.
One of the aims of this study was to determine whether the device is useful and safe in the home environment over a period of time, said Pahwa. “We wanted to know if patients would use it at home. Is it something they could use if they were, say, eating or using a computer?”
Although the researchers didn’t formally measure patient satisfaction, many patients reported that it did made a difference to their daily activities.
In this study, researchers collected baseline tremor characteristics, including tremor frequency, as well as tremor characteristics and response over the course of the study.
This information, said the authors in their abstract, may provide “key insights” into evaluating and treating tremor.
Pahwa foresees a day when technology is advanced to the point where the stimulation will turn on only when certain tasks are performed.
“For example, if you’re writing, it will start stimulating and if you’re just sitting it will not.”
He believes that the device could help reduce symptoms in other movement disorders, including Parkinson’s disease.
“Intriguing” Results
Commenting on the study for Medscape Medical News, movement disorders specialist Anna Hohler, MD, associate professor of neurology, Boston University School of Medicine, Massachusetts, and a fellow of the American Academy of Neurology, said it was small but “intriguing.”
The results are not that surprising because peripheral nerve stimulation has been an area of interest for patients with tremor but are “very welcome,” said Hohler.
“This novel approach could open up a new window of opportunity for treatment of this very common and often disabling movement disorder.”
This new nerve stimulation approach is needed, and further research should support this line of research for treatment, added Hohler.
The study was supported by Cala Health Inc. Pahwa and Hohler have disclosed no relevant financial relationships.
American Academy of Neurology (AAN) 2018 Annual Meeting. Abstract P4.474. To be presented April 25, 2018.
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