The Importance of Pre-Surgical Evaluation for Epilepsy

You might think epilepsy is rare, but the reality is that 1 in 26 people will develop the neurological condition during their lifetime, according to the Epilepsy Foundation. In fact, anyone, at any age, can develop the seizure disorder.

The good news: Up to 70% of people living with epilepsy can be seizure-free through antiseizure medications, according to the World Health Organization.

But what about people with drug-resistant or uncontrolled seizures, meaning they continue to experience seizures despite trying two or more medications? They may be candidates for presurgical evaluation, which can help them understand why they continue to have seizures and what their treatment team can do to help them potentially become seizure-free.

We spoke with Dr. Rohit Kuruvilla, a neurologist and epileptologist with Houston Methodist, about presurgical evaluation for epilepsy and what people can expect from the experience.

Who needs a presurgical evaluation for epilepsy?

Dr. Kuruvilla says that the seizures of about two-thirds of people with epilepsy will be well-controlled through medication — 40% will become seizure-free with the first medication they try, another 20%-25% will get seizures under control after trying a second medication.

Patients usually start an epilepsy medication at a low dose and increase it until they find the level that controls their seizures, called an adequate dose. But Dr. Kuruvilla notes that for some patients, what's a sufficient dose for most patients isn't enough to control their seizures.

"There's a diminishing return with each new medication, so if the seizures continue despite trying adequate doses of two different medications, that's when we say we really need to do an epilepsy presurgical evaluation," Dr. Kuruvilla says. "Basically, after that point is when we say, 'OK, we're not sure if the seizures are going to be controlled by medication.'"

What is a presurgical evaluation for epilepsy?

For most patients, the first phase involves tests designed to help their treatment team pinpoint the origin of the seizures in the brain.

"The first step is capturing seizures while patients are on EEGs (electroencephalograms), recording their seizure and seeing the electrical activity associated with that," Dr. Kuruvilla says. "We bring patients into the epilepsy monitoring unit (EMU), usually for a couple of days to a week, and we decrease their medications and try to bring on seizures. Seeing what happens when they have a seizure and the associated electrical activity can potentially show us that all of their seizures are consistently coming from one spot in their brain."

Other tests during this phase can include magnetic resonance imaging (MRI), positron emission tomography (PET scan) and neuropsychology testing. Each test can give the treatment team critical insights about potential causes of the seizures as well as how they may impact someone's daily life.

"An MRI can help us see if there's some structural cause of their seizures, such as a lesion, tumor, abnormal blood vessels," Dr. Kuruvilla says. "A PET scan will basically look at the glucose metabolism or glucose uptake of different parts of the brain. That's helpful in conjunction with the MRI to say, 'OK, maybe we don't see a structural cause of the seizures, but this part of the brain is definitely hyperactive.'"

Dr. Kuruvilla says that patients will also undergo neuropsychology testing. These tests will assess everything from a person's memory, cognition, language skills and any potential mood changes.

"With neuropsychology testing, what we're testing is various functions of the brain, sort of like standardized testing, to see if there's one specific part that patients have difficulty with," Dr. Kuruvilla says. "So, if we're saying, 'OK, we think the MRI shows there's a lesion here, the EEG shows that the seizures are coming from that same area. Do they already have some cognitive deficits because of these seizures or because of the lesion?'"

Dr. Kuruvilla says neuropsychology tests help the treatment team make a risk-benefit analysis in deciding whether or not a patient should undergo surgery.

"We want to know if it's OK to take out that lesion or tissue without causing any damage," he says. "We want to make sure that we're not causing more harm than good with a removal of that area."

Dr. Kuruvilla says that for some individuals, the information gathered from phase one testing fits perfectly, and the epileptologists, neurosurgeons, radiologists and neuropsychologists all agree on the cause of the seizures and that a surgery would be a low-risk option. Those patients could move on to have a procedure if they would like to. For others, more testing may be required.

"For some individuals, not everything matches up. The EEG shows the seizures come from one section of the brain, but the MRI doesn't show a lesion, the PET scan doesn't show a lesion," Dr. Kuruvilla says. "That's when we have to proceed to what we call phase two evaluation, doing similar EEG studies through a surgery where we place electrodes inside of the brain."

These intracranial depth electrodes, Stereo-EEG or SEEG, are small, flexible electrodes attached to wires that are placed deep in the brain to locate the precise area of seizure activity. SEEG can also be used to stimulate different areas to aid in mapping motor and language functioning.

"Prior to a SEEG, all the epileptologists, neurosurgeons, radiologists and the neuropsychologist help determine what areas that we should be looking into as potential sources for seizure," Dr. Kuruvilla says. "And during the procedure, we would mark off any areas that, if we were to take out that part of the brain, it wouldn't affect anything. So it helps us not only determine where the seizures are coming from but also trying to exclude any tissue that is actively involved in any everyday tasks."

Generally, individuals may stay a little longer in the EMU for phase two testing, Dr. Kuruvilla notes. It's a similar concept to phase one, where the individual is admitted to the EMU, and their medications are lowered or stopped to elicit seizures.

"Usually, a patient undergoing phase two would be with us for a week or so, maybe a week and a half," Dr. Kuruvilla says. "They would then have those electrodes removed, and then we would re-discuss as a team. If then we say, 'Oh, all of the EEG information during phase two evaluation points to one area,' then we can proceed to offer a surgical option. But this is a step-by-step discussion with the treatment team and the patient."

Does surgical evaluation always lead to epilepsy surgery?

For some people with epilepsy, evaluation will not lead to surgery.

"Generally, I would say that occurs more often in people who have a normal MRI or the MRI doesn't necessarily fit what's being seen with other tests," Dr Kuruvilla says. "Sometimes we find that people are having seizures from multiple different locations, so there's not one trouble spot that we can remove."

There are options for those individuals, Dr. Kuruvilla says. For some patients, neuromodulation devices can be an alternative to help manage their seizures. These devices include vagal nerve stimulation, responsive neurostimulation and deep brain stimulation.

In a vagal nerve stimulation procedure, a device is inserted that sends regular pulses of electricity to the vagal nerve, helping to control seizure activity in the brain. The responsive neurostimulation device is placed or inserted in or around the affected area of the brain. The device delivers personalized treatment to respond to a person's unique electrical brain activity.

For those unable to have laser ablation or resection surgery on the affected area of the brain, these devices can help reduce the number of seizures someone experiences. The device chosen will be based on an individual's unique profile.

"Responsive neurostimulation requires that you have two places where the seizures are coming from, and those places were confirmed on stereo EEG, for example," Dr. Kuruvilla says. "So you have more options after the stereo EEG, even if it's determined that someone may not be a surgical candidate, or we couldn't find exactly where the seizures are coming from. There's still some progress in terms of management."

Vagal nerve stimulators and deep brain stimulators are used more often to treat people with generalized epilepsy. The whole brain is involved with generalized epilepsy, where it is wired in a way that makes the person more susceptible to seizures.

Surgical evaluation can offer insights for those with epilepsy

Dr. Kuruvilla says that surgical evaluation for epilepsy can offer a lot of information about a person's seizures, including potential causes. He also acknowledges that the concept of testing that may lead to brain surgery can be intimidating. And while someone may not be ready for epilepsy surgery now, their feelings may change down the road should their seizures continue.

"We don't want patients to say, 'Oh, if I do this, I'm committing, and I have to have brain surgery.' It's all about providing information in order for patients to make that decision for themselves," says Dr. Kuruvilla.

"Sometimes patients will say, 'I'm fine with holding off on epilepsy surgery,' and then two to three years down the line, it's still a problem that hasn't resolved. They've tried different medications, and they will then say, 'OK, my risk tolerance has changed. I just can't deal with this anymore.' Evaluation is information gathering to meet people where they're at."