Deep brain stimulation (DBS) in the treatment of dystonia

What does the treatment involve?

The treatment consists of placing electrodes in the globus pallidus nuclei of the brain, which will perform a pacemaker function to modulate the abnormal 'beat' of the neurones. The goal of this neurosurgery is to reduce undesirable muscle spasms (forms of dystonia, myoclonic movements, tremors) and improve voluntary motor activity during manipulation, walking, and coordination of movements in general, so that the patient's quality of life improves.

The system is implanted under the skin and is not visible to others. The only visible scar is on the skin of the abdomen, where the battery is implanted.

The team that performs this intervention at Vall d'Hebron Hospital is made up of experts in paediatrics and neurofunctional surgery in our centre and the Germans Trias i Pujol Hospital.

What are the components that make up a stimulation apparatus?

The device is made up of three components:

• Electrodes: These are very thin wires placed in the globus pallidus nuclei of both cerebral hemispheres, the right and the left. Each electrode is divided into different contacts with a millimetric separation between them.
• Extension: This is a cable that is placed under the skin and connects the electrodes to the neurostimulator.
• Neurostimulator: This is a battery placed under the abdominal or thoracic skin that generates the electrical impulses necessary for the treatment of the disease. In children, the battery is always rechargeable.

It is important to use the device well and to charge the battery periodically. Otherwise, if the stimulator were left without power, the system would shut off and the symptoms that had improved with electrical stimulation would reappear.

When is a patient a candidate for treatment?

At Vall d'Hebron University Hospital, deep brain stimulation (DBS) is performed in infants and adolescents when medication has not yielded good results, and once the professionals decide that the risk-benefit relationship is favourable for the specific patient, individually.

The intervention is carried out in children over 6 years of age who suffer from moderate or severe intensity movement disorders with a negative impact on quality of life, and who do not present other associated severe neurological problems.

What happens during the surgery?

In order to carry out the intervention, before the surgery a magnetic resonance scan of the patient is taken. Then, on the day of surgical intervention, the neurosurgery team plans the coordinates for the electrodes in the brain nucleus that is intended to be stimulated, using the patient's brain MRI images and neuro-navigation software. At the same time, with the patient anaesthetised in the operating theatre, a stereotaxic frame is placed on the head.

A computed tomography (CT) scan is then performed on the patient and the images of the MRI and CT are merged to obtain the coordinates to place the electrodes.

Through two frontal incisions, the electrodes are placed in the brain nucleus to be stimulated, and the extension connecting the electrodes to the neurostimulator (battery) are placed under the skin behind the ear to the abdomen.

Once the system is implanted, a new CT is performed to check electrode localization and rule out complications.

What risks does brain stimulation neurosurgery have?

The intervention is carried out by a team of professionals led by a neurosurgeon specializing in stereotaxic surgery. It is considered a 'minimally invasive' operation with very low risks. The possible difficulties are as follows:

During the operation:

• Bleeding: extremely rare in children. In most cases this is minor and asymptomatic
• Suboptimal placement of electrodes.

After the intervention:

• Worsening of movement disorders: Stimulation can temporarily worsen movement disorders; this is a reversible situation that is resolved by reprogramming stimulation parameters.
• Surgical wound infections: They are very rare, may require antibiotic treatment in some cases, and in others the removal of the prosthesis.
• Fractures of the electrodes or extensions due to direct blows to the implanted system: a new surgical intervention will be required to change the extension or electrode.

How does the patient's life change after neurostimulation?

On the third day after surgery, the neurostimulator is activated and stimulation parameters programmed. The beneficial effects of electrical stimulation take weeks to appear. Normally the full benefits are obtained around 12 months after the intervention.

When neurostimulation is effective, infants regain mobility, improve manipulation and autonomy in their day-to-day life, can write and paint, eat independently, walk, and run again. Usually, it is possible to reduce or withdraw the medication that the patient took to control the undesirable movements before the intervention. However, cerebral neurostimulation is compatible with other medical treatments.

It is important to understand that this therapy improves symptoms, but does not cure the disease that produces them. It also does not improve the mental health problems that the patient may have, although when stimulation is very effective and improves motor symptoms and pain, it can produce very positive changes in the quality of life of the patient.

What is the patient’s day-to-day life like?

In their day-to-day existence, once stimulation is adjusted, the patient has a normal life. They can participate in sports activities and have a great deal of autonomy. Of course, this treatment does require medical monitoring, and the patient must come in for a check-up at least once a year.

The patient will have no strange feelings caused by stimulation, but when changes are made during medical visits they may experience a mild and transient sensation of tingling or muscle tension.

Is it an effective long-term treatment?

This is an effective treatment for years, although some parameters may need to be adjusted if the disease worsens.

In cases where no improvement occurs, it is possible to turn off the neurostimulator without any further surgery. Neurostimulation is a reversible procedure, and once stimulation is turned off, the patient returns to their pre-intervention medical condition.

How long will the device battery last?

Children and adolescents carry a rechargeable neurostimulation system. Patients need to charge the battery once a week, for about 1 or 2 hours. It is a very simple system that children can do without the need for help. The system is charged by telemetry, by direct contact with the region of the abdomen where the battery is implanted, without plugging any power cables in.

The device has a half-life of approximately 20 years. After that, it would be necessary to change the implanted battery via local surgery.

What precautions should the patient take?

To facilitate communication with other people regarding the precautions that must be followed, the patient is given a card explaining about the stimulation device implanted, where surgery was performed and who the reference doctors are.

During their day to day existence patients must take care to avoid exposing the system to electromagnetic fields that may interfere with the stimulation apparatus.

• Metal detectors in airports, courthouses, etc. must be avoided. Using the information card, patients should report that they have an implanted pacemaker system.
• Patients should be careful not to strike the extensions and the stimulator, as they can be broken. We recommend avoiding contact sports such as martial arts.

In hospitals:

• Scheduled magnetic resonance scans: The patient must tell the stimulation team neurologists because, despite being compatible, guidelines and a protocol must be followed.
• Dental surgery and procedures (dentist): Bipolar electric scalpels may be used when the apparatus is active. The family must carry the remote in order to deactivate the system during surgery if necessary.
• Tests such as electrocardiogram or encephalogram: In order to be able to perform these it is necessary to turn off the stimulation for the duration of the test, otherwise, stimulation could cause interference.