Overview
Over the last decade, multiple surgical options have become available for patients with epilepsy that does not respond to medication. Neurostimulation devices may be used to alter abnormal brain activity. These devices may be used for different types of epilepsy when patients have tried and failed two or more anti-epileptic drugs (AEDs). Which device is best for the patient is decided by the treating neurologist. The patient is likely to continue on AEDs even after the device is implanted, but the goal is to reduce the number of and the severity of seizures.
What it is
Neuromodulation for epilepsy is a new approach that can be an alternative to traditional epilepsy surgical approaches or work in synergy with them. There are three types of neuromodulation currently approved for epilepsy:
- Deep Brain Stimulation (DBS)
- Responsive Neurostimulation (RNS)
- Vagal Nerve Stimulation (VNS).
They each work by stimulating seizure-causing brain circuits to prevent or abort seizures.
RNS involves placing two electrodes on the surface of the brain or into the brain, in or around the area which is most likely the onset region for the seizure. The device records brain waves (EEG). EEGs that show seizure onset are recognized and then an impulse is delivered to stop a seizure. The patient can upload the data collected by the neurostimulator to a secure web-based application so the neurologist can access it. In DBS, electrodes are placed in the brain, but instead of being placed in an area with seizure, they are placed in an area that serves as a relay station for brain signals.
Determining a Course of Treatment
RNS is used as a treatment for adults with partial-onset seizures with one or two seizure onset zones and whose seizures have not been controlled with two or more antiepileptic drugs. DBS is used as a treatment for adults with focal seizures who have not been responsive to two or more antiepileptic drugs and could not be treated with other types of epilepsy surgery.
RNS and DBS are used when a patient’s epilepsy does not respond to anti-seizure medications and they are not suitable candidates for other epilepsy surgeries.
How it works
VNS requires an electrode to be implanted along a nerve in a neck with a battery below the skin in the chest. By stimulating this nerve, signals are sent to the brain which alter seizure-causing brain circuits to reduce seizures in a non-specific way.
DBS uses electrodes implanted directly into the seizure-causing circuits of the brain, and also has a battery below the skin in the chest wall. DBS and VNS both stimulate according to a constant schedule, and can be triggered to provide extra stimulation, if a patient feels a seizure coming.
RNS is a new modality for the treatment of epilepsy which records neural activity and directly stimulates brain networks causing seizures only when an oncoming seizure is detected. The RNS battery is implanted within the skull, so no wires run down along the neck (beneath the skin) as would be required for VNS or DBS. This approach has the significant advantage that neural recordings of seizures can be saved and uploaded to track seizure frequency as related to changes in device programming or medications.
Who can benefit?
Neuromodulation for epilepsy is typically used for patients with medication-refractory epilepsy who have seizures that begin in a focal manner (that is, they start in one or a very few parts of the brain), and for whom resecting that focus (through traditional neurosurgery) or ablating it (using a minimally-invasive laser) is not a good option. In some cases, patients who have had resections or ablations with less than the full desired benefit can have neuromodulation as a synergistic therapy.
Individuals with any of the following criteria may be unsuitable candidates for neuromodulation:
- Symptoms are not substantially reducing a patient’s quality of life
- Symptoms can be controlled with medications with minimal side effects
- Diagnosis other than focal epilepsy
- Suitable candidate for resective or other epilepsy surgeries
How can you determine what’s best for you?
Patients who are still having seizures, despite adequate trials of two or three medications, are generally designated “refractory” and may be considered eligible for surgery, if it is suspected that the seizures are beginning in a focal manner. For some of these patients, scalp electroencephalography (EEG) and brain imaging may provide enough evidence to identify the seizure focus. However, others may require implantation of electrodes into or over the brain to map out the origin and spread of seizures. Once a seizure focus is identified with sufficient certainty, the gold standard remains resection or ablation of that focus, if possible, as a means to achieve a cure. For some patients, these more standard approaches may not be feasible or sufficiently likely to produce a cure, so neuromodulation may be considered a good option to alleviate, or in some cases, cure seizures.
Patients who are interested are evaluated by a comprehensive epilepsy team that includes highly-specialized and experienced neurologists, neuropsychiatrists and neurosurgeons. Patients collaborate with this team to express their desires, expectations and preferences so that the best, customized approach is designed to achieve their goals.
Symptoms
Patients with epilepsy commonly experience the following symptoms:
- Temporary confusion
- A staring spell
- Loss of consciousness
- Uncontrollable jerking movements of arms or legs
- Emotional responses such as fear, anxiety or déjà vu
Testing & Diagnosis
Before surgery, the patient is evaluated by a neurologist to determine if the type of epilepsy is best treated by neuromodulation. The implanting neurosurgeon will take a full history and physical examination to ensure that the patient is a good surgical candidate.
Surgery
This procedure, performed by a neurosurgeon, usually takes about two to three hours. The patient usually stays overnight. There is a small risk of infection. Other surgical risks include inflammation or pain at the incision site. The device may malfunction, similar to any other electrical device.
The procedure may be done at one or two settings. During the first phase of the surgery, electrodes are inserted through a hole in the skull and placed inside the brain at the appropriate spot using pre-operative information. The battery may be placed at the same time in the skull for RNS or in the chest for DBS. Often the DBS surgery battery placement is performed at a second stage.
The battery looks like a heart pacemaker. Newer devices may be smaller. Some batteries must be charged daily while others do not require charging. All batteries need to be replaced at some point with a less invasive procedure that requires only opening the incision, but no additional work in the brain.
Follow-up
The stimulator is most commonly activated two to four weeks after implantation. The treating neurologist programs the stimulator in his or her office with a small hand-held computer. The amount of stimulation varies by case, but is usually initiated at a low level and slowly increased to a suitable level for the individual.
Possible Side Effects
It may take several months before patients notice improvement in seizures. Side effects are most commonly related to stimulation and usually improve over time.
- Feelings of muscle tightness
- Changes in voice/speech
- Loss of balance
- Impaired vision
- Numbness or tingling sensations
- Lightheadedness
- Unwanted mood changes
These symptoms are only temporary while patients adjust to their new devices. Altering the stimulation may relieve symptoms. Patients should let the doctor know if these symptoms occur. In addition, patients should call their physician before undergoing any medical tests that might affect, or be affected by, neuromodulation or before you have any other surgery.