Epilepsy

 

An epileptic seizure is an abnormal electrical discharge in the brain, typically associated with involuntary movements, loss of consciousness or convulsions. The symptoms of a seizure are related to the functions of the brain areas where the abnormal nervous activity takes place. Epilepsy is a chronic neurological disorder with recurrent epileptic seizures.

Epilepsy occurs in ~0.6 % of the Dutch population. Despite elaborate knowledge about the cause of epilepsy, good results with epilepsy surgery and a number of effective anti-epileptic drugs, almost 30.000 people (approx. 30 %) continue to have seizures. Part of this population can benefit from the vagus nerve stimulation (VNS). 

Vagus Nerve Stimulation (VNS)

The vagus nerve is a nerve which comes from the brain and projects to organs in the thorax and stomach. Humans have a left and a right vagus nerve, both of which are mainly transmitting information from the body towards the brain. With VNS, an electrode is placed around the left vagus nerve, which is connected to a pulse generator. At this moment Cyberonics is the only company that can and may provide the VNS system. The pulse generator - with a thickness of 7 mm, a volume of 8 cc and a weight of 16 gr - consists of a battery, an antenna and a microprocesser for the control of the applied electrical pulses. When the vagus nerve is stimulated artificially, signals travel through this nerve towards the brain. These signals can thus suppress the epileptic seizures in the brain.

The working mechanism of VNS

The exact mechanism through which VNS suppresses the epileptic attacks is still unknown. However, much is known already about the processes involved. Signals evoked by VNS enter the brain in different areas. The effects VNS has on some of these areas may explain the mechanism of VNS on epileptic seizures.

  • Increased synaptic activity in the thalamus and its projections to the cortex bilaterally, leading to an increased alertness and possibly  decreased synchronicity between and within cortical areas.
  • Increased synaptic activity in the insula, hypothalamus and other components of the central autonomous system.
  • Decreasing synaptic activity in the amygdala, hippocampus and other parts of the limbic system.
  • Increased release of norepinephrine (or noradrenaline), and possibly also serotonin in large parts of the brain.

Who is VNS for?

VNS has been shown to be suitable for epilepsy patients of all ages. However, patients do have to meet certain requirements.

  • Anti-epileptic drugs do not or not sufficiently reduce seizures.
  • Patient is not suitable for or does not want epilepsy surgery (surgical isolation or removal of epileptic focus).
  • Patient did not benefit from epilepsy surgery.

Procedure

For VNS treatment the patient will have to go through three phases.

For the intake phase the possible VNS candidate is invited for a consultation with the neurologist. During this consult, the doctor will look at the history of the epilepsy and will explain about the procedure, possible side effects and the risks. If the patient has been found suitable for VNS, he or she will be referred to the neurosurgeon, who will look at possible contra indications and will perform the actual implantation.    

In the implantation phase the electrode will be placed around the vagus nerve under general anesthesia and connected to the pulse generator subcutaneously. This pulse generator is implanted under the collar bone or at the arm pit. Therefore, two 5 cm incisions are required. The incisions are made in the direction of skin folds. As a consequence these incisions are hardly visible after recovery. The complete operation takes 1 to 1.5 hours. In most cases, the patient can go home the next day. In the two weeks following the implantation procedure, the pulse generator is turned off in order to allow the wound to heal.

After 10 to 14 days the pulse generator will be turned on by the neurologist for the first time and the control phase starts. Starting at the lowest current amplitudes, the VNS system is set to the optimal parameters over a course of several months in small steps. Hereafter, a check-up visit will take place twice a year. The standard settings are for 30 seconds current pulses are generated at 30 Hz, followed by a 5 minute period during which no current is delivered to the vagus nerve. This cycle is repeated 24 hours a day. In addition, the patient has the possibility to induce an extra stimulation of the VNS system using a magnet. This can be useful if the patient feels a seizure coming up. The extra stimulation can prevent or diminish the severity of the seizure. With the same magnet it is possible for the patient, if he/she wishes, to stop stimulation completely for a certain time

The results of VNS

The therapeutic effect of VNS increases over time. The average seizure reduction is more than 30% and after 1 year approx. 40% of the VNS users has a reduction in seizures of more than 50%. In children 60% of the VNS users have a seizure reduction of more than 50%. In addition to an effect on seizure frequency, VNS also has a positive effect on seizure intensity and on the recovery following an attack. Threequarters of the VNS users reduce the number or the dosage of there anti-epileptic drugs. Besides the effects on epileptic attacks, VNS users report an improved mood, better memory and enhanced alertness. VNS has a high user satisfaction and leads in most cases to a better quality of life.

Side effects

VNS has relatively small adverse events. The most important side effects involve the vocal cords. This concerns hoarseness, coughing and shortness of breath. These effects get weaker over time and after three years only a small minority continues to have these complaints.  

Also see:

opent in een nieuw venster Epilepsie Vereniging Nederland (EVN)

opent in een nieuw venster Vns Therapy (Cyberonics company)