Cortical Stimulation Accurately Guides Epilepsy Surgery

June 17, 2019

Using cortical stimulation to induce seizures in epileptic patients requiring surgery appears to give accurate information on the location and extent of the epileptogenic zone and is associated with a high level of good surgical outcomes, a new study shows.

Senior author Birgit Frauscher, MD, Montreal Neurological Institute and Hospital, McGill University, Montréal, Quebec, Canada, explained to Medscape Medical News that for patients with drug-resistant epilepsy, surgery is a possible treatment option, with resection of a small part of the brain where the seizures are believed to originate.

While the area needed to be resected can often be identified by scalp EEG and other noninvasive tests, more information is needed in a minority of patients. This can be obtained by stereoelectroencephalography (SEEG) in which electrodes are inserted into the brain in an attempt to localize the origin of the seizures.

"This is a well-established practice," Frauscher noted. "Patients are taken off any antiseizure medication and monitored for a few weeks in-hospital waiting for spontaneous seizures to occur, which may be detected and recorded by the electrodes. In some cases, stimulation is applied through the electrodes in an attempt to generate seizures."

For many years the researchers have been using cortical stimulation at the Montreal Neurological Institute and Hospital to help identify the source of the seizures, but it wasn't clear whether it was accurately determining the source of spontaneous seizures and what cortical stimulation was contributing regarding surgical outcomes, Frauscher said. To date, no study has systematically addressed whether relying on induced seizures to plan the surgery is as effective as relying on spontaneous seizures.

"Our data from this study show that if seizures were induced with cortical stimulation then there was a high likelihood of the patient being seizure-free after surgery," she said. "This suggests that the stimulation procedure is accurately identifying the origin of the seizures, which can then be resected."

If a seizure is induced by stimulation of an electrode, it seems the hot spot may be more reliably established, the study found. Spontaneous seizures, on the other hand, "can happen anywhere — we may pick it up on an electrode but it is not necessarily in the hot spot," Frauscher said.

"I'm very excited about these results," Frauscher added. "This study shows we can be sure that we've found the hot spot that needs to be resected by using the stimulation and we can get much quicker results than waiting for spontaneous seizures, which can take weeks. The use of cortical stimulation will allow a much shorter work-up period, with patients being in hospital for just a few days rather than 2 to 3 weeks."

The study was published online in JAMA Neurology on June 10.

Seizure-Onset Zone

The primary aim of this study was to investigate whether the removal of the cortical stimulation-informed, seizure-onset zone (a marker for the epileptogenic zone) is associated with good surgical outcome, defined as Engel class I–seizure free.

To do this, the researchers analyzed data from 103 consecutive patients with focal drug-resistant epilepsy who underwent SEEG between 2007 and 2017 in two tertiary epilepsy centers: Montreal Neurological Institute in Canada and Grenoble-Alpes University Hospital in France. All patients underwent cortical stimulation and subsequent surgical resection of the presumed epileptogenic zone.

Results showed that 59 patients (57.3%) had seizures induced by the cortical stimulation. Patients with cortical stimulation–induced typical electroclinical seizures had a higher likelihood of a good surgical outcome compared with patients without such induced seizures.

The percentage of patients with cortical stimulation-induced seizures was higher in the good surgical outcome group (70.5%) than in the poor outcome group (47.5%; P = .02).

In addition, the percentage of the resected contacts encompassing the stimulation-informed, seizure-onset zone correlated with surgical outcome (median 63% in the good outcome group vs 33% in the poor outcome group).

"Now we know that stimulation-induced seizures are very similar to spontaneous seizures, we can reduce hospital time. Instead of being in hospital for 2 weeks, patients can maybe be there for 48 or 72 hours and we only need to record maybe one additional spontaneous seizure and not several, and that is a huge difference," Frauscher said.

The study was supported by Canadian Institutes of Health Research, the Savoy Epilepsy Foundation, and Fonds de la recherche en santé du Québec.

JAMA Neurol. Published online June 10, 2019. Abstract

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