The Responsive Neurostimulation (RNS) System for Epilepsy

What to expect from this brain implant that controls seizures

The responsive neurostimulation (RNS) system is a type of interventional treatment for epilepsy that is based on delivering therapeutic electrical stimulation to the brain in response to a seizure. It is an implantable device, which was approved in 2013 by the United States Food and Drug Administration (FDA) for the treatment of epilepsy for adults aged 18 or older. 

The system is composed of a small implantable computer that is placed within the skull and attached to one or two electrical wires, each with an electrode that is placed in or on the brain. A company called NeuroPace currently produces the RNS system.

Indications for the RNS

The RNS system is one of the interventional treatment options for people with refractory and focal epilepsy.

Refractory Epilepsy 

If you continue to experience seizures despite trying multiple anti-seizure medication regimens, or if you can’t tolerate the side effects of your anti-seizure medications, your epilepsy may be considered refractory. Epilepsy surgery or device implants are often considered for treatment of refractory epilepsy.

Focal Epilepsy 

Focal epilepsy is a type of epilepsy characterized by symptoms such as repetitive mouth or eye movements, arm-jerking, or leg-shaking. Focal epilepsy may involve both sides of the body and may produce impairment of consciousness.

These types of seizures are called focal seizures or partial seizures because they involve one area of the brain, unlike generalized seizures, which involve the whole brain and cause shaking and jerking of the whole body, usually with accompanying loss of consciousness and confusion afterward. 

Focal seizures begin in a specific area of the brain, and may spread to involve a widespread area of the brain within milliseconds. The area of the brain where a focal seizure begins is technically referred to as a seizure focus. If you have focal epilepsy, you may have one seizure focus or several seizure foci, and your doctors can usually consistently define them on your electroencephalogram (EEG). The RNS system can be positioned to specifically target one or two seizure foci, which is why it is indicated for focal epilepsy.

What to Expect If You Have Focal Seizures

Epilepsy Surgery

There are different kinds of epilepsy surgery, and several types of devices are used for the treatment of refractory epilepsy. If your seizures don’t improve with medication, and if epilepsy surgery is being considered as an option for you, your doctors will consider and discuss the different types of epilepsy procedures with you.

The best treatment plan for you is based largely on your seizure type. There are also other important considerations, such as whether you are healthy enough to undergo epilepsy surgery and whether you can manage the maintenance and care of an anti-seizure device.

How the RNS System Works

The system is called responsive neurostimulation because it sends electrical neurostimulation to stop a seizure in response to the seizure activity in the brain. 

If you have this procedure, a computer with a battery will be implanted inside your skull and one or two electrodes, each with four contacts, will be placed in or on your brain in the areas where your seizures begin, which are your seizure foci. Once it is implanted, the device doesn’t work right away. It has to be programmed after it collects and records your brainwave activity for a few weeks.

Once the device is placed, the contacts detect electrical activity in the brain. This information is recorded on the computer that is in your skull. Every day, you need to use a magnetic wand to download the data from the computer onto a laptop or desktop computer.

Every few days, you need to share the data with a patient account that will be set up for you. Your doctor can collect this data and view the pattern of your brain activity, noting the brainwave patterns that tend to occur immediately before or right at the start of your seizures.

Then, your doctor will program the device so that it can recognize the characteristics of your seizure activity and quickly respond by sending electrical stimulation to your brain to stop the seizure within milliseconds. The system decreases seizures by sending an electrical impulse to your seizure foci via the electrodes. It is not completely clear why it decreases seizures, but there are several possible mechanisms that may explain how it works.

Mechanisms

It has been suggested that the electrical stimulation delivered by the RNS device may interrupt the altered electrical activity that is produced by an impending seizure. This interruption of abnormal brain activity may then allow your normal brain function to resume.

It has also been suggested that the stimulation provided by the RNS device may trigger the release of inhibitory neurotransmitters, which are chemicals that are naturally produced by the brain. The RNS-stimulated release of these neurotransmitters can stop the erratic nerve activity of the seizure before it spreads in the brain.

Pre-Surgical Testing

Before you have an RNS system implanted, you need to have pre-surgical testing with an EEG, which can identify and locate your seizure focus. If you have a consistent seizure focus or two consistent foci, you may be a candidate for RNS therapy. If you have generalized seizures or more than two seizure foci, then you would not be a candidate for the RNS system.

You will also need a brain-imaging test, such as a brain MRI, so that your doctors can be sure that there are no lesions in your brain, such as tumors or infections that would need to be treated.

Surgical Implantation

You will have your procedure in the operating room or in a procedural suite under sterile conditions. You will need to have general anesthesia for your procedure, so you need to abstain from eating or drinking from the night prior to your surgery. Your surgery is expected to last between two to four hours. 

The device is placed using a stereotactic neurosurgical procedure. This means that your doctors will use imaging guidance to direct the wire or wires and their attached electrode contacts to their target location, near your seizure foci. 

You will most likely spend the night in the hospital, and you will need to be examined after your procedure to make sure that everything went as planned before you can go home.

Post-Operative Plan

Your device will not be activated to send electrical stimulation right away, but it will be ready to record your brain activity either immediately or shortly after it is placed. After several weeks, your doctor will program your device, and you will be asked to keep a record of your seizures to assess for improvement. If your seizures do not improve, your device may need to be reprogrammed.

Recovery and Risks

After the procedure, your wound in your scalp will need to heal, which can take a few days. There is a small risk of infection or bleeding in the days after surgery. There is also a slight risk that the device could become dislodged at any point, particularly if you experience head trauma.

There is a chance that the device may not reduce your seizures, even after several adjustments. If this is the case, it may need to be completely removed.

Long-term outcomes of the RNS system are not known because the system has only been available for a few years.

Seizure Outcomes

The device has been studied in hundreds of patients, and the effects and side effects have been carefully followed.

RNS Pros

  • Reduces seizure frequency

  • Reduces rate of sudden unexpected death in epilepsy (SUDEP)

  • Reduces required dose of anti-seizure medication

RNS Cons

  • Requires surgery for implantation

  • Long-term outcomes are not known

  • The device may not help at all for some individuals

It has been shown to reduce the rate of sudden unexpected death in epilepsy (SUDEP). People who have had the RNS system also experience a reduction in seizure frequency and severity. This decline in seizure frequency and severity improves over time after placement of the device.

The system has been tested against controls, meaning that study participants with epilepsy had the device implanted, but didn’t have the electrical stimulation programmed. The studies were also carried out as double-blind studies, so the patients and their doctors did not know which group had the device programmed to respond to seizures and which did not.

A relatively large research study, including over 100 people who had the RNS device implanted for seizure treatment, showed a 44 percent reduction of seizure frequency one year after the device was implanted, and a 53 percent reduction in seizure frequency two years after the device was implanted. The same study reported a reduction in seizure frequency ranging between 70 and 77 percent six years after the device was placed.

If you use the RNS system, you may still need to take anti-seizure medication. Most of the time, the RNS system has been shown to reduce the required dose of anti-seizure medication. 

The United States Food and Drug Administration (FDA) studied the results of the RNS system prior to its approval. Now that the system is being used more extensively, outcomes and side effects are still being closely followed.

Quality of Life

People who have the RNS system implanted for control of epilepsy generally report that they are more alert throughout the day. Studies show that people who use the system may also experience improvements in cognition and mood, and these outcomes are likely to continue to be studied over the coming years.

A Word From Verywell 

If you have refractory epilepsy, you may be a candidate for epilepsy surgery or for placement of an epilepsy device. The process of pre-surgical testing may take some time, as placement of electrodes has to be done with precision. While the RNS system would require some participation on your part, you may find it helpful for controlling your seizures.

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Article Sources
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  •  Devinsky O, Friedman D, Duckrow RB, et al. Sudden unexpected death in epilepsy in patients treated with brain-responsive neurostimulation. Epilepsia. 2018 Mar;59(3):555-561. DOI: 10.1111/epi.13998.

  • Sisterson ND, Richardson RM. Long-Term Results of Responsive Neurostimulation in Different Seizure Onset Locations. Neurosurgery. 2018 Jan 1;82(1):N3-N4. DOI: 10.1093/neuros/nyx543.