Vagal Nerve Stimulation (epilepsy)

Aside from brain operations the only other current non-experimental surgery to help manage uncontrolled seizures is vagus nerve stimulation (also known as VNS).

This surgery does not involve the brain directly, but instead the brain is effected by stimulating the vagus nerve in the neck, which transfers this stimulation to the brain. By stimulating the vagus nerve in the neck, the signal is transferred to the brain and causes the brain to less likely manifest seizures.

There are 12 pairs of nerves that originate directly from the brain; all the other nerves of the body originate from the spinal cord. Animal studies have shown that stimulating the vagus nerve desynchronizes the brain's cortical EEG (electrical rhythms). Since a seizure is hyper-synchrony of brain processes, and VNS influences brain processes to be more de-synchronized, there can be a substantial decrease in the probability of seizure occurrence. By promoting a more de-synchronized state VNS achieves better seizure control than what medications alone can achieve in people with uncontrolled epilepsy.

Unfortunately, VNS can only rarely completely control seizures, though in many patients VNS dramatically improves their epilepsy. Generally, in about 35% to 45% of people implanted with VNS achieve a 50% or greater reduction in their seizure frequency (that is the number of seizures over a given time period). And, in some patients drug doses can be reduced with effective VNS treatment. VNS is meant to be adjunctive therapy, which means that it is used in combination with medications to improve the seizure control over what medications can achieve alone.

The three most common reasons VNS is used to manage refractory epilepsy is when cranial surgery can not be performed since the patient is not a candidate for this, when cranial surgery has not completely controlled the seizures and additional control is still needed, and when patients who might be cranial surgery candidates do not wish to undergo cranial surgery. Click here to learn more.

Surgery for VNS is much simpler than cranial surgery. Patients undergoing VNS do not stay in the hospital overnight (it is someday surgery). The procedure takes only 1 hour and 15 minutes to perform, and the possible complications are infrequent and not nearly as severe as the complications associated with brain surgery. Infection and injury to the vagus nerve, both occurring in about 1% of the procedures performed, are the most important risks. The associated risks of VNS are much less severe than the risks associated with cranial surgery.

VNS, like chronic medication treatment, also has associated side effects. Common side effects of VNS are hoarseness of voice when the device is stimulating, which is usually once for 20 to 30 seconds every 5 minutes, tingling in the throat, shortness of breath with exertion, cough, and occasionally GI complaints.

By changing the parameters of stimulation most of the adverse side effects can be eliminated. This is done with telemetry (radio signals) to communicate with the system that is implanted totally under the skin. Another important attribute of VNS therapy is that it is reversible, since if it is not effective it can be removed leaving no permanent effects.

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