Depression
Depression is a common disorder. Ten to twenty percent of the population will suffer from one at some point in their lifes. In most cases, a depression can be treated adequately with medication and/or psychotherapy. In approximately 30% of the patients these treatments do not or not suffictiently have the desired effect. These patients mey be suitable for electroconvulsion therapy (ECT). With ECT a controlled epileptic insult is evoked under general anesthesia. Recently, vagus nerve stimulation has been recognized as a therapy for treatment-resistant depression. This therapy has been developed for the treatment of epilepsy, but has been shown to have an antidepressant effect.
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.
The working mechanism of VNS in depression
The exact mechanism of the antidepressant effect of VNS is unknown. However, much is known already about the processes involved.
Stimulation of the left vagus nerve has a clear effect on both sides of the brain. De neuronal activity in brain areas involved in mood regulation, change under influence of VNS. Among others, this concerns the amygdala, the thalamus and the prefrontal cortex. In addition, VNS affects the levels of serotonin and noradrenalin. These neurotransmitters play an important role in mood regulation.
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 psychiatrist. During this consult, the doctor will look at the history of the current depressive episode 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 psychiatrist 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, check-up visits will take place at least twice a year. The standard settings are for 30 seconds current pulses are generated at 20 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. The patient is provided with a magnet, which makes it possible for the patient to stop stimulation completely for a certain time.
The battery life duration is dependent on use, but on average 5 to 6 years. The battery can be replaced with a small surgical procedure.
The results of VNS
From studies it is known that 30 to 60% of the patients has improved considerably after a year of VNS. Some of these patients are completely free of depressive symptoms. It is not possible to predict which patients will benefit from the treatment.
The effects of VNS are not instantaneous and on average depressive symptoms continue to decrease 6 to 12 months after therapy onset. There is a strong variation between patients, of which some improve strongly after several weeks already.
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.
VNS therapy for depression is currently not covered by health insurance in the Netherlands.
Also see:
VNS therapy