The Responsive Neurostimulation (RNS) System for Epilepsy

The responsive neurostimulation system (RNS) is an interventional treatment for epilepsy that's based on delivering therapeutic electrical stimulation to the brain in response to a seizure. The system is composed of a small, implantable computer that's placed in the skull and attached to one or two electrical wires, each with an electrode that is placed in or on the brain.

NeuroPace currently produces the RNS system, which was approved by the U.S. Food and Drug Administration (FDA) in 2013 for treating epilepsy in adults. 

Indications

The RNS system is one of the interventional treatment options for people with the following types of epilepsy, which involve only one area of the brain:

• Refractory epilepsy: If you continue to experience seizures despite trying multiple anti-seizure medications, or if you can’t tolerate the side effects of them, your epilepsy may be considered refractory. Epilepsy surgery or device implants such as RNS are often considered for treating refractory epilepsy.
• Focal epilepsy: Focal epilepsy is characterized by symptoms such as repetitive mouth or eye movements, arm jerking, or leg shaking. These seizures may involve both sides of the body and can impair consciousness.

While focal seizures begin in a specific area of the brain (known as the seizure focus), they may become widespread within milliseconds. With this type of epilepsy, you may have one seizure focus or several seizure foci, and your healthcare providers can usually identify 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 the RNS System Does

The system gets its name because it responds to seizure activity in the brain, sending electrical neurostimulation to your seizure foci to stop the event. The device is implanted in your skull, spends time recording brain activity, and is then programmed by your healthcare provider so that the treatment is most effective.

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's seizure foci.

The contacts detect electrical activity in the brain, and this information is recorded on the implanted computer. Every day, you need to use a magnetic wand to download the data from the computer onto a laptop or desktop computer. Data should be shared via a patient account that is set up for you every few days.

Your healthcare provider can then 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. Based on this, she 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.

Why It Works

It is not completely clear why this decreases seizures, but there are several possibilities:

• 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.
• 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 through your brain.

Pre-Surgical Testing

Before you have an RNS system implanted, you need to have pre-surgical testing with an EEG to identify and locate your seizure focus/foci. 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're not a candidate for RNS.

You will also need a brain-imaging test, such as magnetic resonance imaging (MRI), so your healthcare providers can see whether there are lesions in your brain, such as tumors or infections, that need to be treated.

Surgical Implantation

You'll have your RNS implanted in an operating room or a sterile procedural suite. You'll need to have general anesthesia, so you can't eat or drink anything starting the night before your surgery. The procedure itself is expected to take between two and four hours.

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

You'll most likely spend the night in the hospital, and you'll 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 healthcare provider 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, the incision in your scalp will need to heal, which can take a few days. There's a small risk of infection or bleeding in the days after surgery, and a slight risk that the device could become dislodged at any point, particularly if you experience head trauma.

It's also possible that the device may not reduce your seizures, even after several adjustments. If this is the case, it may need to be removed.

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

Outcomes

The device has been studied in hundreds of patients, and the effects and side effects have been carefully followed. That gives you and your healthcare provider several pros and cons to weigh when considering this treatment.

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 healthcare providers 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 seizure frequency was reduced by:

• 44 percent one year after implantation
• 53 percent two years after implantation
• 70 percent to 77 percent six years after implantation

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

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 they may also experience improvements in cognition and mood, and these outcomes are likely to continue to be studied over the coming years.

Summary

If you have refractory epilepsy, you may be a candidate for epilepsy surgery or for placement of an epilepsy device like RNS. The process of pre-surgical testing may take some time, as electrode placement has to be done with precision. While the RNS system requires some participation on your part, you may find it helpful for controlling your seizures. And because it'll probably mean you can take a lower dose of medication, it could lead to fewer side effects as well.