Treatment-resistant epilepsy and depression are two debilitating conditions that severely impact the overall quality of life of patients and their caretakers.
Fortunately, new treatment options have emerged for patients with epilepsy while neuromodulation may also offer hope for those suffering from depression. In particular, vagal (or vagus) nerve stimulation (VNS) has been shown to offer benefits in both conditions.
VNS refers to the application of a small electrical current to the vagus nerve in the neck. This large nerve originates from the brainstem and travels through the neck area to terminate in several organs including the heart, the lungs and the gastrointestinal system. It participates in several critical functions including heart rate control, peristalsis and the size of airway openings.
VNS is currently approved in the United States for the treatment of intractable epilepsy and depression.
Patients suffering from epilepsy can be considered for VNS if they have failed a sufficient treatment trial of at least two (2) anti-epileptic medications. VNS does not replace medications and the therapy is added on to the regimen that works the best for the patient. Although not curative, VNS can improve seizure control in patients and the therapeutic effect tends to increase over time. On average, patients experience approximately a 25% reduction in seizure frequency after three months of therapy, with the benefits increasing over time. Approximately 50%-60% of patients will experience a 50% reduction in seizure frequency after two years of therapy. This improvement in efficacy over time is likely the result of progressive device programming and broad neuromodulatory changes in the body’s epilepsy cascade.
Despite being used in the clinical setting for several years, the mechanism of action of VNS is not fully understood. It is thought that the stimulation leads to modulation in the local brainstem circuitry; in turn, these local circuits engage more widespread pathways leading to desynchronization in the epileptogenic zones.
The broad effects of VNS make this therapy beneficial for patients with multifocal or generalized epilepsy where a specific seizure focus cannot be identified and treated surgically. VNS does not require the identification of a focus and thus can still reduce seizure frequency in those cases.
Initial clinical experience with VNS suggested that it may improve depression. Epilepsy patients treated with VNS reported enhanced mood, even in cases where the seizure frequency was not reduced. Subsequent dedicated clinical trials demonstrated that VNS can reduce the severity of major depression by about 30%. Patients with depression of moderate severity and who have experienced some improvement with medication are more likely to benefit from the therapy.
VNS is not curative for depression but it can add another dimension to the overall treatment plan. Patients who undergo this therapy should continue to closely follow the recommendations of their mental health providers. In particular, patients should continue to take their medications and attend their therapy sessions.
VNS surgery involves the insertion of two main components: the lead (wire) and the generator. The lead is inserted through a small incision in the anterior mid-neck area. Through this incision, the vagus nerve is identified and isolated and the dedicated lead is gently secured to it. The preferred method is to implant the device on the left side of the body.
The generator is inserted in the upper chest area. Through technological advancements, the size of the pulse generator has reduced over time. Therefore, the insertion requires only a small incision typically located about 1 inch under the clavicle. It is secured in place to the subcutaneous tissue. Finally, the lead is tunneled under the skin from the neck to the chest; all of the components are discreetly implanted under the skin. Specific implanted generator options can be discussed with your neurosurgeon.
After surgery, patients generally remain in the hospital for one day. We recommend keeping the wounds dry for a few days and to avoid scratching the surgical sites to help prevent infection.
The patient should plan to meet with their neurologist, in the case of epilepsy, or their psychiatrist, in the case of depression within a month of the surgery.
The electrical impulse produced by the device is adjusted by the physician’s programmer. The programmer communicates non-invasively with the implanted device. Typically, the generator is adjusted gradually over time to make sure that the stimulation is well-tolerated. Possible side-effects include hoarseness of the voice and shortness of breath.
VNS is administered in cycles with the pulse being sent for a few seconds every few minutes. Providers can adjust the intensity and the frequency of the pulse as well as the duration of the on/off cycles. The patient may elect to administer additional impulses using a magnet provided with the device. This feature is especially useful in patients who can feel an aura or sensation before a seizure.
For more information about Vagal Nerve Stimulation, please contact the office of our restorative neurosurgery specialist, Dr. Jean-Philippe Langevin at 310-582-7433.