This Epilepsy Explained focuses on Responsive Neurostimulation, or RNS. Dr. Mark Richardson, Director of Functional Neurosurgery at Massachusetts General Hospital and Professor of Neurosurgery at Harvard Medical School, provides an overview of RNS, explaining what it is, who should consider getting one, how it differs from other neuromodulation devices, and what patients can expect from RNS. In “RNS Explained”, Dr. Richardson answers the following questions.
Video Transcript
What is RNS and how does it differ from VNS and DBS?
So RNS therapy stands for responsive neurostimulation, and this is a really unique therapy in that it’s the first and still only bidirectional brain computer interface that’s been approved in medicine. Although most people with epilepsy still probably haven’t heard about it. And we have a problem in epilepsy surgery in general where only about 1% of patients who have benefit from epilepsy surgery actually get it.
We have a real hope though that this personalized medicine approach, which is really one of the best examples across medicine that we have for personalizing therapy with the device, will really change how people think about epilepsy surgery. And the reason is this device is implanted in the brain with two very thin leads. These are thin wires that can be customized to the part of the epilepsy network where seizures are occurring and the device is on all the time recording brain data. And when it senses a seizure, it stimulates. And over time, this has the potential to stop seizures individually, but also to suppress the seizure network, so that people get the benefits of seizure reduction without having to have a traditional open surgery.
And this differs from VNS, which is vagal nerve simulation, where we implant an electrode on the vagal nerve and we have a generic indirect effect on brain activity. And it differs from DBS where also thin wires are placed in the brain, but the sensing ability of that device is minimal and it cannot respond in real time to therapy. So I would call these approaches non-personalized. And RNS is really novel cutting-edge therapy in medicine that has real potential to improve quality of life in people with epilepsy.
Who should consider getting an RNS device and when should it be considered?
People with epilepsy who should consider getting an RNS device are those who should consider epilepsy surgery in general. And these are people who are having seizures despite having tried just two appropriate medications. So you don’t need to cycle through every one. And people with epilepsy should not think about surgery as a last resort because it’s typically much safer than people understand.
The traditional way we think about epilepsy surgery is we want to find one spot in the brain that we could potentially remove with a traditional surgery and cure the person. However, there are many people with epilepsy who don’t respond well enough to medication because of side effects or number of seizures or severity who are not going to have one place that we can find to take out and cure the epilepsy. And those people in particular are well suited for the RNS system that can be customized to affecting a broad network, including people with generalized epilepsies for which we’re finding this works very well. So the answer to the question of when this should be considered is when you have tried two medications and you’re still having seizures.
What are the risks of having an RNS device implanted?
The risk of having an RNS device implanted are typically much lower than people would think. And here I think it’s important to talk about the risk of epilepsy surgery in general. So even our traditional surgeries that people think of as high risk or a last resort such as temporal lobectomy or removing part of the frontal lobe are very safe, especially when you compare those risks to the risk of ongoing uncontrolled seizures, and take into account the risk for sudden unexplained death and epilepsy or SUDEP. So people with epilepsy whose seizures are not controlled by medication have about 90 times greater risk of dying from SUDEP than those who have seizures controlled with medication.
Then if we look at RNS surgery and the risk associated with that, they’re even lower than the risk of resection surgery. And what we’re talking about there is about a 1% chance of having bleeding in the brain or on the brain that would result in a permanent neurologic deficit, like a problem with movement or with speech. So that is a real risk and it’s a risk that’s taken upfront. But compared to someone’s lifetime, especially in kids who also have the risk of uncontrolled epilepsy affecting their development, the risk of RNS surgery is much lower than the risk associated with ongoing uncontrolled seizures.
And I think that’s a really important message, and that people think about surgery as something that’s scary and that’s a last resort. But the reality is if you have seizures that aren’t controlled by medication, you’re in between a rock and a hard place. And the risk associated with surgery at that point are actually quite low, especially compared to the quality of life gain that people are expected to get with this therapy.
Are there any potential side effects that may be experienced with an RNS device?
There are potential side effects from RNS therapy, but these are minimal to none. The side effect that we see sometimes especially in patients with generalized epilepsy where we’re using this device a lot more and implanting a brain region called the thalamus or other patients where we might use the thalamus as part of the RNS therapy is something called a paresthesia. So that’s a tingling. It’s a sensory side effect, and the person who’s doing the programming can just change the settings in a way that minimizes or reduces that side effect to zero.
The type of side effect that people often worry about, I think, is the brain stimulation going to change their mind? Is it going to change their thinking or cognition? And the answer there is no. In fact, we would expect in many cases for cognition to improve. And there’s data from the RNS clinical trial that supports this idea that if we can reduce the seizure burden significantly, then the rest of the brain can function more effectively and things like mood and cognition can improve.
And I think one thing that’s important to note in relation to DBS, where the therapy is on all the time, including at night, with RNS therapy that’s just customized to responding to the epileptic activity in the brain, the rest of the time the brain is allowed to function without being perturbed by the electrical stimulation. There may be some benefits in terms of sleep and memory to having this type of responsive neurostimulation that’s not on all the time. So the long and short of that is the side effects are very, very minimal and a lot of benefits with this therapy.
What kind of maintenance is required with an RNS device?
The main type of maintenance that’s required with RNS therapy is for the patient or the patient’s parent or caregiver to download the data from the device. And the way this is done is currently by holding a wand over the portion of the skull where the pulse generator, which is the small computer that does all the work is implanted, that is implanted in a tray that sits in the skull. That idea might sound weird or scary to people, but it’s a really straightforward surgery to put that in. And you cannot tell that someone has one of these devices. Everything, of course, is under the skin.
So ideally that data would be downloaded to the laptop that comes with the surgery every day. But it’s not the end of the world if you miss some days or you miss a week when you’re on vacation. That data automatically gets uploaded to the cloud where it’s available for the clinical team.
And this is, even though it is maintenance, you can also think of it in a way that the patient actually is able to exercise some participation, some control over the treatment of their disease. They’re actively acquiring data that’s going to help their epilepsy doctor to optimize the therapy for them. And for parents of kids with epilepsy, this is not maintenance. They really can finally do something to help. And the device, of course, is monitoring the child all the time, and they’re facilitating the upload of the data, which of course is helping the clinical team.
The more traditional type of maintenance that you might think of is battery life and how often you have to replace the device. That currently is about once every 10 years, but eventually this device is going to be rechargeable, and it’ll also have wireless transmission capabilities so that one doesn’t have to physically hold the telemetry wand to the head. That’ll connect through a wireless system to a hub that will upload the data.
When and how will I know if the RNS device is making a difference in my seizures?
The way a patient will know about the difference the therapy is making is in some ways similar to traditional surgery, and in some ways it’s different. So the way it’s similar is that only over time do we know if a certain surgical therapy is going to work just like medication. So we do an intervention and we wait and see what the patient reports is happening. And so over time, the expectation is that, and this would take months, sometimes it can take a year or longer to get an optimum effect, the patient’s going to notice their thinking is better, seizure frequency is less. They feel better in the morning if they’re having seizures at night. If they’re able to reduce medication, then they may also feel better.
And this brings us to a second point, which is the use of the data. So being able to evaluate the daily brain recordings might allow the clinical team to determine that the seizure frequency looks like it’s declining before the patient is even reporting this.
In addition, the expectation is that the clinical team will use the brain recordings to be aggressive about reducing medication. So the idea is to use that objective data in order to determine if it’s safe to taper medication. If a new medication is needed, the team can look and see how did that affect the brain recordings? Does it look like seizure activity is dropping? Is it staying the same? Medication is not doing anything?
So this is one of the real advantages of the system is that the data can be used, the subjective data can be used, and we’re not completely dependent on the subjective reporting of the patient. Sometimes the patients don’t know when they’re having seizures. They don’t have someone watching them all the time, but the device is on and watching you.
