by Lily Wong, MD
The goal of using medications for epilepsy is to eliminate seizures without significant side effects. When more than two antiepileptic medications have failed to control seizures, the chance of obtaining seizure control by adding or substituting other medications is low. Among newly diagnosed adult patients with epilepsy, about 50% become seizure-free with their first antiepileptic medication, while an additional 11% of patient on the second medication. Children may have a slightly higher response rate to medications than adults. However, after two to three drugs have failed to control seizures, less than 5-10% of children will achieve seizure freedom with further medication. Patients whose seizures do not respond to more than two appropriate seizure medications, at therapeutic doses, have “medically refractory epilepsy.” Surgery for epilepsy may be an option for some children and adult patients when medications do not control seizure and referral to an epilepsy surgery center for further evaluations should be considered. In children, early referral for epilepsy surgery may optimize development, which may be affected by frequent seizures.
What is “brain surgery” for epilepsy?
There are several types of operations which can be done for epilepsy. Resective surgery, involves removing abnormal brain tissue that is generating the seizures. Resective surgery can be an option if there is a single seizure focus identified that is not involved in important day-to-day functions such as strength for movements, language, memory, or vision. In other surgeries, the goal is to disrupt the connections involved in the spread of seizure activity; however no brain tissue is removed. Surgeries in this category include multiple subpial transection, functional hemispherectomy, and corpus callosotomy. Finally, there are stimulator devices where electrical pulses are transmitted by wires inserted into the brain, such as deep brain stimulation, and they should also be considered brain surgery for epilepsy.
It is important to understand that brain surgery for epilepsy is not an alternative to taking anti-seizure medications. Surgery is a potential option for those that do not have a complete response to medications. The goal of most surgeries is to allow patients to become seizure-free while continuing to take medications. However, medications can often be reduced in patients who respond to surgery.
What tests are needed to see if brain surgery is a good option?
An evaluation at an epilepsy surgery center is necessary to find out if a patient is a candidate for any type of brain surgery (stimulator, brain resection, or disconnection surgeries). The goal of the evaluation is to find out if there is a single area of the brain where the seizure starts. The best outcomes among the different types of brain surgeries are in those patients who have a single area of seizure activity where resective brain surgery can be performed. Evaluations for brain surgery for epilepsy should happen at an epilepsy center where there is a team of health care providers who will review information about your seizure history.
The initial visit may include reviewing information about seizure history and response to antiepileptic medications. Blood tests are done to look at the level of antiepileptic drug in the blood. In children, blood tests are sometimes done to see if there are genetic reasons for epilepsy. Magnetic resonance imaging (MRI) of the brain is important to see if there are any abnormalities or scar tissue that could cause seizures. A baseline electroencephalogram (EEG) records information about the electrical activity of the brain, which is helpful to determine where seizures might come from. The baseline EEG typically does not capture the patient’s typical seizures because of the short duration, and seizure monitoring with continuous EEG and video recording for several days is necessary.
To confirm the region of the brain responsible for seizures, patients are admitted into Epilepsy Monitoring Unit and several seizures are typically recorded. To record seizures, your usual antiepileptic medications may be decreased or stopped during the monitoring by your neurologist. You should never stop your seizure medication before admission to the monitoring unit, unless directed to do so by your neurologist.
In more complicated epilepsy cases, other tests are also done. During the continuous video EEG monitoring, a radioactive dye can be injected during a typical seizure and again after a period of no seizure. Single photon emission computed tomography (SPECT), which is type of scan that looks at blood flow in the brain, is done soon after each of these two injections. The two SPECT scans, with and without seizure, are compared to each other and to the patient’s MRI brain to analyze where the seizure originated (subtraction ictal SPECT co-registered to MRI, or SISCOM). Positive emission tomography (PET) is another type of scan which looks at metabolic activity in the brain, by using radioactive glucose (sugar) or other molecules, injected in between seizures.
Who is a candidate for resective brain surgery?
In selected children and adults who have seizures recorded on continuous video EEG and MRI abnormality restricted to the temporal lobe, no additional tests are done to locate where seizure activities are coming from. Baseline psychometric tests to evaluate memory, learning, ability, and language and visual field test to look at the peripheral side vision are done as baseline prior to surgery. Sodium Amytal test (Wada test) locates whether the speech and memory centers are in the right or left side of the brain, but this may be difficult to do in children.
For patients in whom the area of brain that is causing the seizures is more difficult to localize, all evaluations are typically presented to a group of health care providers, including adult and/or pediatric epileptologists (neurologists who specialize in epilepsy), neurosurgeons, neuroradiologist, and psychologists at an epilepsy surgery conference. A group consensus is made to determine whether the patient is a surgical candidate. More direct and invasive monitoring of seizure activity may be necessary to pin-point the brain areas involved in seizures. This requires brain surgery where small electrodes, “depth or subdural electrodes”, are placed on the surface of the brain. Similar to the video EEG monitoring on the scalp, several seizures are recorded. Antiepileptic medications may be decreased or stopped during the monitoring by the neurologist. Before proceeding to surgery to remove part of the brain, the electrodes used to record seizures can be also used to stimulate the brain so that the epileptologist can determine where certain vital brain functions are located. This cortical stimulation mapping may be important for the epileptologist and neurosurgeon to customize surgery and minimize risks of resective brain surgery.
What are the results of resective brain surgery for epilepsy?
All patients continue on the antiepileptic medication after surgery. Although some may ultimately be able to wean off medicine after several months, others will need to continue medication long-term. The result of resective brain surgery depends on the region of the brain causing seizures. The best results are in those patients who have seizures from the temporal lobe, particularly in patients who have an MRI brain abnormality only in the temporal lobe. After resective brain surgery for epilepsy, up to 60 to 80 percent of patients with temporal lobe epilepsy may be seizure free. About 25 to 50 percent of people who have frontal lobe epilepsy may be without seizures. About a third of patients overall may have reduced number of seizures and about 10 to 20 percent may have no change in their seizure pattern.
What are the risks of brain surgery?
All surgical procedures carry risks of anesthesia, bleeding, and infection. For resective brain surgery, there are additional risks depending on the area of the brain being treated. This may include difficulties with memory, learning, language, muscle weakness or coordination, and vision. These potential problems should be considered with risks of seizures and side effects of antiepileptic drugs, which may not give additional seizure control.
What if resective brain surgery is not an option?
There are also surgeries to implant stimulator devices. Stimulators are battery-powered devices which send programmed pulses of electricity. There are two general types of devices available: one that targets a nerve in your neck region (vagus nerve stimulator) and others which target the brain (deep brain stimulator, response neurostimulator, and cortical stimulator). Vagus nerve stimulators are silver-dollar sized battery devices typically implanted under the skin of the left chest. Wires are threaded underneath the skin along the left side of the neck to the vagus nerve. Pulses of electricity from the battery stimulator are delivered every few minutes. Patients with vagus nerve stimulator may use a magnet to give additional electric pulses to stop a generalized convulsive seizure during their typical warning. Vagus nerve stimulator can be implanted in children and adults.
There are also brain surgeries with stimulators in which wires are guided to deep brain regions (deep brain stimulator) to prevent spread of seizures. Stimulator wires can also be guided directly to brain areas affected by seizure activities (cortical stimulator, response neurostimulator). All stimulator devices for which wires are guided into the brain are currently under investigation for FDA approval. Many patients benefit from reduced number of seizures with stimulator devices, but most patients do not become seizure-free. Stimulator settings can be adjusted at the neurologist’s office to optimize seizure control without additional surgeries. If these treatments are not an option, your doctor my recommend the ketogenic diet, modified Atkins diet, or further medication trials.
Mayo Clinic, Rochester
Last Reviewed: 7/15/11
Article from the June 2011 Epilepsy.com Spotlight Newsletter. Other articles in this issue inclue:
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