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Vagus nerve stimulator as a treatment for intractable epilepsy.

Abstract: Vagus nerve stimulation was recently approved for control of medically intractable seizures. This therapy provides some relief of seizures for selective patients, however seizure freedom using this device is uncommon. Vagus nerve stimulation appears to work by calming "hyperexcited" nerve cells and reverting brain activity to its" normal patterns. Many people do have significant relief in the intensity and duration of their seizures and report improved quality of life using this device.

Introduction

The Epilepsy Foundation of America estimates about 2.5 million Americans have epilepsy. Of the nearly 150,000 people who develop the disorder each year, at least 10-20% suffer from uncontrolled seizures. (3) Worldwide, epilepsy affects an estimated 50 million people. Multiple seizures can have a significant impact on a person's quality of life. The ability to secure a job or participate in social activities may be affected. Typically, most seizures are adequately controlled with medication. A new medication or a change in the current medication may be all that is required to control seizures. If the patient does not respond to medications, the remaining therapy options include polytherapy (combination of two or more antiepileptic drags (AEDs), less effective second line drugs), or epilepsy surgery. (5) The number of patients who are not responsive to medication or candidates for surgery is relatively small. However their lives are significantly affected. The purpose of this manuscript is to introduce the vagus nerve stimulator as a new option for patients with uncontrolled seizures thus enhancing their quality of life.

Vagus nerve stimulation was recently approved for control of medically intractable seizures. The vagus nerve stimulator is a treatment option in patients for whom other less invasive treatments have failed. This device is used in patients who are experiencing medically intractable simple or complex partial seizures with or without secondary generalization. To be defined as having medically intractable epilepsy, a patient has tried at least three of the major AEDs, without success. The stimulator is also offered to patients in whom seizure surgery is not an option. (6) The stimulator interrupts epileptic seizures by sending an electrical stimulus to the brain and is used to treat patients who are refractory to antiepileptic medications. Both the effectiveness and safety of the device have been tracked since 1989. In many patients, the number of seizures has decreased with stimulation. Other patients may have significant reductions in intensity and duration of seizures. The advent of this procedure has offered a new option for the patient with uncontrolled seizures thus enhancing their quality of life.

Vagus Nerve Stimulation

The vagus nerve, cranial nerve number X, innervates the pharynx and soft palate, blood vessels, heart, lungs and the gastrointestinal tract. Most of the individual nerve fibers within the vagus nerve are afferent, transmitting information to the brain. Within the brain, these afferent tracts extend to areas of the brain, including those known to be involved with epilepsy, namely, the hippocampus and cortex.

Vagus nerve stimulation as a treatment for intractable seizures has been investigated since the 1930s. More recent studies have addressed this treatment modality to control epileptic seizures. The mechanisms by which the nerve stimulator controls, seizures is not fully understood. Vagus nerve stimulation appears to work by calming "hyperexcited" nerve cells and reverting brain activity to its normal patterns. It may also enhance the release of chemical building blocks that bolster cellular membranes in the central nervous system, adding stability to neurons and making them less excitable.

The vagus nerve stimulator is composed of an implantable pulse generator and two electrode wires. The generator weighs approximately two ounces and is the size and shape of a cardiac pacemaker. It contains a battery and computer chips which are covered by a titanium case. The generator is surgically implanted into the left upper chest beneath the skin. The electrode wires, which are attached to the generator, are tunneled under the skin and attached to the left vagus nerve in the neck. The left vagus nerve is selected due to the lower percentage of cardiac efferent fibers to the atrioventricular node as compared to the right. (4) An incision is required at the neck and left upper chest. The operative procedure takes approximately two hours and is performed under general anesthesia. The patient may go home the same day, or may be kept overnight for observation.

The patient is given a two week recovery period, to allow for healing before the stimulator is activated. The activation procedure is performed in the physician's office using a laptop computer and a wand designed for this purpose. The generator is programmed to deliver intermittent stimulation to the vagus nerve. A specialized program allows the clinician to determine the strength of the stimulation needed, the duration of the stimulation phase and the non-stimulation interval. Frequency of stimulation can be adjusted by reprogramming the device to either enhance seizure control or minimize undesired effects.

Another feature of the vagus nerve stimulator is the ability to activate the device when the patient experiences an aura. This activation can be performed by the patient or caregiver. The patient is supplied with a hand held magnet which when placed over the stimulator, can generate an additional pulse. The magnet must be held in place for approximately two seconds. The additional pulse does not interfere with the programmed settings. The stimulator can also be deactivated in case of emergency or malfunction, by taping the hand-held magnet directly over the device.

Because the vagus nerve innervates the pharynx, heart, lungs, bronchi and the gastrointestinal tract, vagus nerve stimulation can cause adverse side effects such as hoarseness, coughing, tingling, shortness of breath, nausea and dysphagia. In addition, there may be a tingling sensation in the neck, and a brief cough when the signal intensity is increased. Hoarseness is due to the stimulation of the left vocal cord via the left laryngeal nerve branch of the vagus nerve. The hoarseness diminishes over time and eventually the patient may become unaware of this change in voice quality.

Magnetic resonance imaging (MRI) of the body is contraindicated for patients who have a vagus nerve stimulator, however cranial MRI can safely be performed using a head coil. Using a body coil may produce heating of the stimulator and electrode wire. Battery life of the device is 3-5 years. A surgical procedure, under local anesthesia, is required to replace the battery.

Patient Education

Preoperatively, patients should be instructed on common side effects reported for the Vagus Nerve Stimulator. These include a tingling sensation in the neck and mild hoarseness in the voice, both of which occur only during stimulation. Surgery typically takes 1-2 hours and may require an overnight hospitalization. Some centers are performing this procedure on an outpatient basis. Patient should be told that if they have a small frame, or are very thin, the device will be visible as a small bulge below the left collar bone.

Postoperatively, they will need to report the clinicians office for device programming at the two week interval and then monthly as needed to assure correct program settings. If patients experience an aura before their seizures, they should be instructed on using the magnet to provide an extra stimulation. The magnet should be used as soon as an aura is noticed. The magnet will override the normal stimulation program. Once the magnet activated stimulation ends, the system will return to the program set by the clinician. The magnet can be used as often as needed. However, if the patient finds that they are using the magnet more frequently, they should notify the clinician who may be able to further adjust their device settings.

Patients should be taught to disable their VNS system, in the event they notice an unusual or painful stimulation. They are to hold the magnet over the device and tape it to the chest wall and contact the clinician immediately. The magnet should be stored away from credit cards, computer disks and other items affected by strong magnetic fields. It is recommended that the magnet be kept at least ten inches away from these items if possible.

Case Studies

Outcomes from vagus nerve stimulation vary, therefore two distinct case studies are presented.

The road to independence has been a long one for this woman in her mid forties. She is able to drive a car now, but for 20 years she relied on others to transport her around town, because the complex partial seizures that wracked her body daily prevented her from driving herself. Her life changed because she had to be dependent on people. In 1990, she received the vagus nerve stimulator. After implantation, the patient described her seizures as not as severe and shorter duration; she felt better afterward. During the first several years after she received the implant, physicians adjusted frequency of stimulation and adjusted her medication. She has now been seizure-free for more than two years which has significantly enhanced her quality of life.

DH is a 34 year-old man who had his first seizure at the age of 22 years. His first seizure episode consisted of status epilepticus. Although he had a one year seizure-free interval after the initiation of seizure medication, he then had a recurrence of seizures which became intractable to the use of phenytoin (Dilantin), phenobarbital, carbamazepine (Tegretol), valproic acid (Depakote), felbamate (Felbatol), lamotrigine (Lamictal) and gabapentin (Neurontin). He was having approximately 25 complex partial seizures (CPS) per month.

He was evaluated for resective seizure surgery in 1995. Because his seizure data revealed bitemporal seizure onset, he would need further evaluation with depth electrodes and subtemporal strips to localize his seizure focus. He decided to participate in a drug study instead of undergoing invasive monitoring.

Initially he was placed in a drug study with vigabatrin (Sabril). After approximately six months he had no significant reduction in seizures. He then decided to participate in the vagus nerve stimulator study. His stimulator was implanted on November 6, 1996. He remained on his maintenance seizure medications which were phenytoin 600 mg daily, and gabapentin 1200 mg in the morning and afternoon, and 1600 mg at bedtime. The VNS was activated on November 28, 1996.

The following month he experienced 11 CPS and an eight day seizure free interval. This was approximately a 50% reduction in seizure frequency. He was experiencing intermittent hoarseness which began when the VNS was activated and occurred when the stimulator fired. Otherwise, his neurological examination was unchanged from his baseline which was normal. Medications were continued at maintenance doses. He had nine CPS in January, ten CPS in February, and 13 CPS in March. In February his phenytoin dose was decreased to 500 mg daily because of balance problems and an inability to perform tandem gait. Two weeks later, his phenytoin level was 32 mcg/mL; however, his symptoms had resolved. In March, his seizures became more intense and he began having fails with approximately 50% of his events. Lamotrigine was then added to his phenytoin and gabapentin therapy with the plan to eventually taper the phenytoin. In April, phenytoin was tapered over a 20 day interval. Lamotrigine dose was now at 200 mg in the morning and 300 mg in the evening. During April and May he averaged 16 seizures a month, but no falls. For the next five months he averaged eight seizures a month. He was maintained on lamotrigine and gabapentin.

DH continued to complain of intermittent voice change throughout this interval, although he did not consider it to be a serious side effect. He also began to experience paresthesias of the left neck which he described as a tingling sensation. This would occur during certain position changes, when the VNS would fire.

In February of 1997, DH decided that although he had had some decrease in seizure frequency, he wanted to strive for complete seizure freedom. He wished to resume the resective seizure surgery evaluation. He was experiencing an average of seven seizures a month.

On May 22, 1997, the VNS was turned off to evaluate if there was any significant change is seizure frequency using this device. No significant difference was noted and the device was surgically removed in July. DH underwent a Wada test, and subsequently had further evaluation with invasive electrodes. This evaluation served to localize his seizure focus to the right anterior temporal lobe. He underwent a right anterior temporal lobectomy on October 16, 1997. DH has now been seizure free since resective surgery. He remains on antiepileptic medications and has returned to work.

Summary

Use of the vagus nerve stimulator is limited to those who have epilepsy which has been refractory to other treatment modalities. It is adjunctive treatment and is used in conjunction with with antiepileptic medications. This therapy provides some relief of seizures for some patients, however seizure freedom using this device is rare. Many people do have significant relief in the intensity and duration of their seizures and report improved quality of life using this device. Resective surgery in persons with partial seizures remains the most successful treatment option for the elimination of seizures. However, for persons who have multiple seizure foci or who are not good resective surgery candidates for other reasons, the vagus nerve stimulator provides another option for treatment which may provide some relief of seizures and therefore improvement in quality of life. As seizures are brought under control, patients may be able to resume driving according to individual state regulations. This may certainly increase their degree of independence and general feeling of satisfaction with life. With increased mobility, socialization and possibly employment opportunities will improve. Even without the ability to drive, the relief of not being afraid of having a seizure in public may greatly increase socialization. As the stimulator decreases seizures, the reliance on multiple medications may decrease as well. With fewer medications, the risks of cognitive and other side effects is reduced. Financially, there should be fewer visits to physician's offices, emergency departments and to the local laboratory for drug levels. A general improvement in all dimensions of quality of life can be expected as seizures are brought under control using the vagus nerve stimulator.

References

(1.) Arbour R: Controlling seizures with a vagal nerve stimulator. Nursing 1997; 27(6):32cc1-2,34cc4.

(2.) Devinski O: Quality of life with epilepsy. Page 1145 in: The Treatment of Epilepsy: Principles and Practice. Wyllie E. (editor) Williams & Williams, 1997.

(3.) Guin P, Ringdahl D, Lilly D et al: Seizure Disorders. Shands Hospital, 1996.

(4.) Rutecki P: Anatomical, physiological, and theoretical basis for the antiepileptic effect of vagus nerve stimulation. Epilepsia 1990; 31 (supp 2):S1-S6.

(5.) Swoboda KJ, Drislane FW: Seizure disorders: Syndromes, diagnosis, and management. Comprehensive Therapy 1994; 20(2):67-73.

(6.) Salinsky MC, Uthman BM, Ristanovic RK et al: Vagus Nerve Stimulation Study Group: Vagus nerve stimulation for the treatment of medically intractable seizures. Arch Neurol 1996; 53:1176-1180.

Questions or comments about this article may be directed to: Coleen Counsell, RN, MSN, Nurse Manager, Shands Hospital at the University of Florida, Box 100335, Gainesvile, Florida 32610.

Christie Snively, MSN, ARNP works with the Seizure Surgery Program at Shands Hospital at the University of Florida. Donna Lilly, MSN, ARNP works with the Seizure Surgery Program at Shands Hospital at the University of Florida.
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Author:Snively, Christie; Counsell, Colleen; Lilly, Donna
Publication:Journal of Neuroscience Nursing
Geographic Code:1USA
Date:Oct 1, 1998
Words:2538
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