Essential tremor is the world鈥檚 most common movement disorder, affecting an estimated 7 million people in the U.S. alone. The hallmark of this disease is an involuntary, rhythmic shaking during intentional movement, complicating everyday tasks like writing, eating and drinking. When resting or sleeping, however, most patients have few or no symptoms.
The disease can be treated with a surgical procedure called , or DBS, where a neurosurgeon implants an electrode deep in the brain; this wire is then tunneled under the skin to a battery in the chest, which provides electrical stimulation that quiets the symptoms. In current use, however, these implanted devices are constantly 鈥渙n鈥� 鈥� delivering stimulation even when a patient doesn鈥檛 need it 鈥� which wastes valuable battery life.
For the first time, 天美影视传媒 researchers have combined electrodes on top of the brain to sense movement in the parts of the body that experience essential tremor, along with a deep brain electrode, to deliver stimulation only when it鈥檚 needed. The approach, developed by electrical engineers, UW Medicine researchers and ethicists at the at UW, is described in a to be published in a forthcoming issue of .
It鈥檚 an important step toward developing fully-implanted, closed-loop deep brain stimulators to treat disorders like essential tremor and Parkinson鈥檚 disease 鈥� devices that one day might be controlled by the patient鈥檚 own thoughts or movements.
鈥淲e鈥檇 ultimately like to give individuals that ability and choice,鈥� said co-author , a UW electrical engineering doctoral candidate and member of the CSNE team. 鈥淥ne side effect of deep brain stimulation can be difficulty speaking, for instance. So if you鈥檙e about to drink a glass of water, you might want to turn up the stimulation so your hand doesn鈥檛 shake. If you鈥檙e answering the phone, perhaps you鈥檇 want to turn it down so your speech isn鈥檛 affected.鈥�
Delivering deep brain stimulation also can extend the battery life of these implanted devices, which currently last only three to five years.聽 Lengthening battery life is important because replacing the battery requires surgery, which carries risks to the patient such as infection.
鈥淲e鈥檙e saving about half of the battery power, based on our subjects so far, which was one of our main motivations,鈥� said senior author and UW electrical engineering professor . 鈥淏ut even more interesting are some early indications that suggest our closed-loop system results in better patient performance, with less tremor, better control of their hands and fewer side effects.鈥�
In the video above, essential tremor patients drew spirals under three conditions 鈥� with their deep brain stimulator turned off (left), with the device constantly on (middle) and with the UW CSNE system that delivers stimulation as needed (right). In the latter two conditions, patients experienced significant and comparable relief from tremor symptoms that cause their hands to shake.
The project originated in a partnership between the CSNE and medical device manufacturer Medtronic to test new ways of with essential tremor patients. This system not only delivers electrical stimulation like traditional DBS systems, but also has the capability to sense and respond to electrical signals generated by the brain itself. The UW team received an investigational device exemption from the U.S. Food and Drug Administration for these tests.
To treat essential tremor, a surgeon typically implants an electrode in the thalamus of a patient鈥檚 brain. It鈥檚 wired down the neck to another implanted device housed under the clavicle that contains a battery and the electronics that drive the system. This 鈥渙pen-loop鈥� system, in clinical use today, delivers constant deep brain stimulation at levels set by a doctor.
In three patients who received the Medtronic Activa PC+S Deep Brain Stimulation system, UW Medicine surgeons also implanted a small strip of electrodes on top of the brain鈥檚 motor cortex, the part of the brain that controls movement. The electrode strip can be used to sense when a hand or other extremity affected by essential tremor is moving. In a key innovation, the team developed machine learning algorithms to 鈥渄ecode鈥� neural signals coming from the brain and correlate them with essential tremor symptoms that warrant treatment by stimulation.
The neural biomarkers and algorithms used to 鈥渄ecode鈥� them differ by disease. While a similar treatment approach has been documented for Parkinson鈥檚 disease, this is the first time neural signals have been used to selectively treat essential tremor.
鈥淭his is exciting both for treating those patients with essential tremor, but also for future uses,鈥� says , a CSNE team leader and neurosurgeon with the UW Medicine Neurosciences Institute.聽 鈥淭his represents the first time a person can control their implanted device through the voluntary use of brain signals. We now can see a direct path to all sorts of uses in stroke, paralysis or other neurologic conditions that may be treated in the future using this general approach.鈥�
Most essential tremor patients have symptoms only during intentional movement 鈥� when they move their arm to eat, drink or write, for instance. The UW CSNE closed-loop system detects that movement and only delivers stimulation to quiet the tremor symptoms when needed.
鈥淒BS results in some of my most grateful patients,鈥� said team member and co-author , a neurosurgeon at the UW Medicine Neurosciences Institute who implanted the devices. 鈥淭hey used to call this disease 鈥榖enign essential tremor,鈥� but it isn鈥檛 that benign. Patients don鈥檛 go out to eat because they spill food and drink. They stop having friends over because they can鈥檛 pour a cup of coffee. They can鈥檛 sign checks. They need help getting dressed. Regular DBS works really well to give people their lives back. What we are working on is taking a really good treatment and making it even better.鈥�
To test how well the systems worked, the research team asked the patients to perform simple motor tasks 鈥� such as drawing a spiral shape with a pen, writing sentences or trying to hold their hands steady 鈥� under three conditions: With their Medtronic implanted deep brain stimulator turned off, with the system that delivered constant stimulation and with the new system that only delivered stimulation as needed.
With no stimulation, the patients experienced tremor throughout the tasks. The effectiveness of the CSNE team鈥檚 new system in quieting the tremor symptoms was comparable to the open-loop system 鈥� but with greater energy savings.
In the experiments described in the paper, the computational tasks were performed on an external laptop next to the patient. Next steps include transferring that computational power to the device implanted in the patient鈥檚 chest wall 鈥� thus creating a fully-implanted, closed-loop deep brain stimulator. The team has received FDA approval to move onto the next step in real-world testing, which is sending patients home with their stimulators in closed-loop mode.
The research was funded by Medtronic, the National Science Foundation and the U.S. Department of Defense.
Co-authors include , a Medtronic biomedical engineer who joined the company after performing the research as a UW doctoral student and CSNE team member, and philosophy doctoral student , who at the CSNE in the .
For more information, contact Chizeck at chizeck@uw.edu. To reach UW Medicine co-authors, contact Susan Gregg at 206-616-6730 or sghanson@uw.edu
Grant numbers: NSF: EEC-1028725