A Keck Medicine of USC neurologist discusses adaptive DBS, the next generation of deep brain stimulation.
For all the strides deep brain stimulation (DBS) has made in treating movement disorder symptoms, perhaps the greatest advancement has been in mastering when and how best to incorporate this life-changing tool in a patient’s treatment plan.
Xenos Mason, MD, a neurologist and movement disorder specialist with Keck Medicine of USC and the USC Deep Brain Stimulation Center, explains how his team’s extensive experience with DBS has optimized patient treatment.
In addition, he discusses how the USC Deep Brain Stimulation Center is using its foundational expertise to deliver the next generation of DBS: adaptive DBS.
Leaders in DBS and asleep DBS
The USC Deep Brain Stimulation Center has long stood at the forefront of DBS to treat patients with movement disorders such as Parkinson’s disease, dystonia and essential tremor. Often, these are patients for whom medication alone has not been sufficiently effective. DBS can help them manage their symptoms, regain their independence and improve their quality of life.
By implanting electrodes into the brain and connecting these to a pacemaker-like device in the chest, DBS delivers targeted electrical stimulation to modulate the neural circuits in the brain that cause uncontrolled movements and reduce mobility.
As pioneers in DBS, the physicians of the USC Deep Brain Stimulation Center specialize in the most advanced DBS methods. The center is, for instance, the only one in Southern California that provides the option of implanting DBS electrodes in the brain while a patient is asleep. Asleep DBS implantation is performed entirely within an MRI scanner while the patient remains asleep, an option that some feel more comfortable with versus undergoing surgery that requires a period of awake physical examination.
The next frontier: Adaptive DBS
The USC Deep Brain Stimulation Center is now offering adaptive DBS, the latest advancement in DBS. Unlike conventional DBS, wherein electrodes are set to deliver constant electrical stimulation to the brain, adaptive DBS tracks a patient’s brain activity in real time and uses this information to adjust when and how much electrical stimulation to deliver.
“With conventional DBS, the same electrical stimulation is applied throughout the day, and it doesn’t change in response to any information that’s given to the system,” Mason explains. Adaptive DBS, however, senses the activity of the brain cells surrounding the implanted electrodes and measures the frequency at which the local brain networks are oscillating.
In patients with movement disorders, physicians pay special attention to one particular frequency: the beta frequency range (frequency within the 10-20 Hz range), which is usually increased at rest and decreased during movement. In patients with Parkinson’s disease, beta frequencies are too high, making it more difficult for them to move.
Adaptive DBS tailors the strength of electrical stimulation based on a patient’s beta band oscillations. “With adaptive DBS, we can decrease the strength of these beta oscillations by increasing electrical stimulation to the area,” Mason says. “By doing that, we make it easier for the patient to move.”
As a patient’s beta band frequencies rise and fall, adaptive DBS likewise adapts, automatically increasing or decreasing the strength of electrical stimulation as needed. “It’s a beautiful, closed loop,” Mason says. “Once the stimulation causes the beta frequencies to go down, the system can adapt again. This is the first time that closed loop has really been enabled for deep brain stimulation.”
Since FDA approved the first adaptive DBS system this February, the USC Deep Brain Stimulation Center is one of the few centers to offer adaptive DBS. Mason says his team thinks ongoing research will show that adaptive DBS can help reduce the amount of “off time” during which patients struggle with stiffness, slowness or tremor, and subsequently increase their “on time.”
“From what we have been shown in conferences, it seems like with adaptive stimulation, people can have about an hour or an hour-and-a-half more time during the day when their movements are more fluid, more relaxed and easier for them,” he says. “To put it simply, people can gain more time during the day when they’re able to function and do the things they enjoy: play with their kids, cook, dress, etc.”
As adaptive DBS evolves, so will its applications for different types of movement disorders. There are certain subtypes or symptoms of Parkinson’s disease that may end up responding better to adaptive DBS, Mason says. In addition, he points out, “right now, we don’t have the correct input signal to use for essential tremor, but I think we’re going to get there in the next few years. When we do, essential tremor might be very amenable to adaptive DBS because when the strength or amplitude of the tremor increases, the amplitude of the stimulation can be increased. When the tremor subsides, as it naturally does, we can decrease the amount of stimulation.”
Adaptive DBS may also provide opportunities to reduce some of the side effects of stimulation. As Mason explains, “When we increase the amplitude of electrical stimulation to completely suppress someone’s tremor, we might run into side effects like slurring of speech or changes in balance or vision. There are sometimes trade-offs with the amount of tremor control we can achieve. But because adaptive DBS lets us dynamically adjust the strength of stimulation according to the strength of the tremor, by decreasing the strength of electrical stimulation when warranted we can at times eliminate or reduce the strength of side effects substantially.”
Mason and his colleagues foresee the day when sensors grow more sophisticated — for instance, implanted so that they can track a patient’s level of wakefulness or measure their emotional drive to accomplish a task. Innovation will also expand tracking tools, such as a wristwatch that can sense the level of tremors occurring, or a wrist sensor or ankle sensor that measures the level of a person’s activity.
“As we advance in the next five or 10 years, especially with artificial intelligence and machine learning, we’re going to be able to integrate more signals into these closed-loop systems in order to respond more comprehensively,” Mason says. “Right now, this is just the first step.”
Optimizing DBS treatment
Mason emphasizes that it’s critical for physicians to know how to integrate DBS in a patient’s treatment, especially as newer technologies come to market.
“People tend to focus most on the technology itself; however, the hardest part is actually understanding how you should integrate DBS into a functional practice that prioritizes a patient’s wellness and their holistic clinical treatment,” Mason says. In other words, many physicians can learn to “press buttons,” but “the hard part is knowing when DBS should be deployed in the right ways for the right people.”
In some cases, overexcitement and overfocus on the technology can lead physicians and patients to want to use DBS in situations that aren’t ideal.
“You need to understand where DBS fits into the experience of a person’s day,” Mason says. “What can it actually do? What is the proper role of this therapy in improving people’s lives? And when should a patient be focusing on other parts of multidisciplinary care to improve their function, like physical therapy, psychotherapy and socializing with friends and family — all factors that play an important role in good function and symptom control throughout the day.”
At the USC Deep Brain Stimulation Center, DBS is just a part of comprehensive treatment. The center’s multidisciplinary team includes neurologists, neurosurgeons, psychiatrists, nurse practitioners, clinical psychologists, neuropsychologists and social workers who collaboratively tackle a patient’s condition from all angles for best results.
Physicians must also understand the limitations of DBS treatment and set patient expectations accordingly. As Mason says, “You need to understand what the system can and cannot do and when you’ve reached the end of your capabilities as a technical proceduralist — when you need to extend and venture into the humanistic parts of your care.”
He adds: “The hardest moments I have is talking to patients about symptoms that DBS was never designed to treat — or when DBS did treat their symptoms for a period of time but then, expectedly, the symptoms overcame the capacities of this technology.”
The limitations of DBS can be difficult for patients to accept “because DBS can give patients a perceived degree of control over the course of their disease,” he says. The reality is, however, that for “relentlessly progressive” diseases like Parkinson’s disease, a cure doesn’t yet exist, and therapy does reach its limits.
When it does, he says, physicians have an important role to play in helping patients reorient their focus on other parts of life they can control, such as the amount of exercise they get, or the amount of time they spend with friends and family. “The conversation with the patient at that point revolves around how we need to reorient the patient’s care and priorities away from DBS and towards a more holistic model of how to improve their function,” he says.
“Those conversations, I’ve realized over the years, are as important as the DBS itself,” Mason says.
The future of DBS is bright
As DBS continues to evolve, it will take experts long experienced in DBS treatment to hone its role in patient care. Mason and his team outline some of the most exciting advancements to come in DBS and treating movement disorders overall.
The first is stem cell therapy for treating Parkinson’s disease, an area of active research at the USC Deep Brain Stimulation Center. Another is leveraging artificial intelligence and smart monitors to expand the number and variety of input signals for DBS.
Finally, more progress will be made in advancing the use of individualized neuroimaging to guide DBS treatment. “Right now, we’re using 3D modeling of a patient’s neuroanatomy based on an MRI scan to create a map of where to place electrodes. In the future, that map is going to become more detailed, and it’s going to integrate more advanced pieces of information, such as information about the connections between different regions of the brain,” Mason says. “We’re going to start looking at functional networks — not just the structure of the brain but what areas of the brain fire together and tend to be more functionally connected. What networks are we actually stimulating with DBS?”
“We’re going to use that information much more comprehensively,” he predicts.
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