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Placement of the electrodes for stereotactic electroencephalography. Photograph by Brennan Wesley.
Placement of the electrodes for stereotactic electroencephalography. Photograph by Brennan Wesley.

Retuning the Brain

Minimally invasive therapies provide good seizure control for patients with medication-refractory focal epilepsy

By Kimberly McGhee
lPhotography by Brennan Wesley

Epilepsy affects an estimated 3.4 million Americans, whose quality of life and sense of independence can be decreased and chances of self-injury increased by seizures. “When you have a seizure, the electrical activity of the brain, which is usually in harmony, becomes out of tune,” explained William A. Vandergrift, M.D., a neurosurgeon at the MUSC Health Comprehensive Epilepsy Center, the only level 4 epilepsy center in South Carolina.

Although most patients achieve good seizure control with pharmacological therapy, one in three does not. Surgery to remove tissue from the epileptogenic zone — the area from which the seizure originates — has been shown to provide good seizure control in 75 percent of patients with medication-refractory focal epilepsy. However, some patients are reluctant to undergo open brain surgery.

Fortunately, a growing number of minimally invasive therapies designed to “retune” the brain’s electrical field are available for these patients at the MUSC Health Comprehensive Epilepsy Center. A team of epilepsy specialists, including neurosurgeons, neurologists, physician assistants, nurse practitioners, dietitians and speech pathologists, guide patients to the therapy that is best for them.

Identifying the epileptogenic zone

Surgery and the less invasive laser ablation, which uses heat to destroy seizure-generating brain tissues, can only be performed in patients with a clearly identified epileptogenic zone, the removal or ablation of which would not compromise memory, language or other critical neurological functions. Clues about the origin of the seizure are provided by the symptoms associated with its onset and by brain imaging such as MRI, PET scans and/or SPECT scans.

In addition to these traditional tools, MUSC Health also uses high-definition scalp electroencephalography (EEG) as well as surgically placed intracranial stereotactic EEG (SEEG) to precisely locate the origin of the seizure. In high-definition EEG, a cap with as many as 256 electrodes is placed on the scalp to provide detailed information about potential trouble spots. This information is then used to define the targets for SEEG, the definitive method for localizing the epileptogenic zone, which involves placement of deep electrodes in the areas of the brain thought to be generating seizures. “It is not possible to have intracranial SEEG covering the entire brain,” said Leonardo Bonilha, M.D., Ph.D., an epilepsy neurologist at MUSC Health who chairs the working group on high-definition EEG for the American Clinical Neurophysiology Society. “We use high-definition EEG to localize where SEEG goes. High-definition EEG can enable people to get SEEG and sometimes get surgery or ablation that otherwise could not.”

Laser ablation

Laser ablation offers a minimally invasive treatment option for patients who refuse or are not candidates for surgery. A thin fiberoptic wire sheathed in a protective catheter is inserted through a very small burr hole in the patient’s skull and directed to the mesial structures of the temporal lobe. A laser is used to heat and destroy the targeted tissue in the epileptogenic zone; carbon dioxide in the catheter cools the wire to ensure that heat is administered only to the targeted region. Magnetic resonance thermography, which provides a real-time heat map of the brain, enables the surgeon to very precisely ablate the appropriate tissue. For a few patients, in which the source of the seizure extends beyond the hippocampus and amygdala to the surrounding temporal tissue that is not ablated or removed, laser ablation may not achieve adequate seizure control. These patients are still eligible to undergo open surgery if laser ablation does not lead to a cure.

Electrical stimulation

Responsive neurostimulation (RNS) and vagus nerve stimulation (VNS) both involve implantation of a device that delivers electric stimulation to prevent the onset or spread of a seizure. For RNS, the neurostimulator is placed in the patient’s skull and is attached to electrodes in up to two suspected epileptogenic regions of the brain. For VNS, a stimulator is implanted in the chest and is attached to leads that are wrapped around the vagus nerve in the neck, a nerve known to be important for autonomic function. Responsive neurostimulation is a closed loop system — after a training period, the device can monitor for changes that indicate the onset of a seizure and deliver an electrical charge to disrupt it. In contrast, VNS delivers electrical stimulation at regular intervals, whether or not a seizure is imminent. If the patient implanted with a VNS system or a family member senses the approach of a seizure, he or she can wave a special magnet over the stimulator to generate an additional pulse in the hopes of preventing it. An investigational closed-loop VNS system that delivers electrical stimulation in response to increases in heart rate, which often occur before and during seizure, is in development.

What it means for patients

“Having SEEG and laser ablation and these new vagus nerve stimulators and responsive neurostimulators help us help patients without subjecting them to antiquated epilepsy surgery,” said Vandergrift. “The exciting thing is that we can take someone who is debilitated by seizures and put them through a minimally invasive process and return them back to a full life.”