Deep brain stimulation (DBS) in adults is a one- or two-stage procedure under both local and general anesthesia. Deep brain stimulation in children is usually performed under general anesthesia. In adults, the first stage begins with application of a stereotactic frame using sedation and local anesthesia. A stereotactic MRI scan is then performed to identify the deep brain target (this takes about 30 minutes). Coordinates are determined for the electrode and a safe trajectory down to the target is identified. The patient is taken back to the operating room and placed comfortably on the operating room table. The patient is monitored by the anesthesia service. After the hair and stereotactic frame are prepared, a small scalp shave is performed. The skin is numbed with local anesthetic and a small incision is made. A 14mm hole is made in the skull bone. The dura (covering of the brain) is opened and a tiny area of the brain is exposed. The probe is then passed down toward the deep brain structures.
In thalamic deep brain stimulation, the DBS electrode is placed down into the thalamus and testing is begun. Electrical impulses are sent from the tip of the electrode into the thalamus. One hopes to identify a brain location where the tremor can be stopped effectively. At the same time, the surgical team monitors for any side effects of stimulation (persistent numbness of the face, mouth, hand or leg, heaviness or weakness of the limb, change in speech). If good results are obtained, the electrode is left in place and anchored to a plastic clip that has been attached to the skull opening. The wound is then closed.
In stage two of the operation, the patient is given a general anesthetic and put to sleep. The side of the head, neck and upper chest is prepared and draped. A small incision is made below the collarbone to allow creation of a small pouch underneath the skin that will hold the stimulator pulse generator (battery). A small incision is made behind the ear and a cable passed from the chest incision up to the head (all under the skin). This cable is then attached to the electrode coming out of the brain using a small plastic cover. The entire system remains underneath the skin. Generally, the chest incision is closed with an invisible stitch that does not need to be removed. The scalp stitches (in the front and behind the ear) are closed with nylon.
In subthalamic deep brain stimulation, the procedure is similar. However, once the skull opening has been created safely, a microelectrode (very small metal wire) is inserted into the brain toward the thalamus and subthalamic region. A neurophysiologist participates in the identification of specific brain cells in these regions. The purpose is to map out the area optimize placement of the electrode. Often the room will be dark during this time period. The patient will be kept comfortable during this time as the brain is evaluated. The time for microelectrode recording can take several hours. Once the appropriate area is identified, test stimulation is performed in order to check that the electrode is in a safe location that will not disturb brain function. When the safe area is identified, the electrode will be left in place and clipped to the skull bone-fastening device. If both sides of the brain are to be operated on at the same setting, a second incision will be made on the other side and the procedure repeated. This will again take several hours.
Subthalamic deep brain stimulation is a longer operation. For most patients, the first stage of the operation (placing electrodes into the brain) will all be performed in one day. The patient will be observed overnight in the hospital. The scalp incisions will be closed and the patient will return to the hospital 3-7 days later for the second stage of the procedure. At the second stage, performed under a general anesthetic, the cables and batteries will inserted into the neck and chest area. Once the device is inserted, the patient will return to the neurology clinic. The stimulators will be turned on by the neurologist and his team several weeks later.
For globus pallidus deep brain stimulation, the procedure is similar to that described above with several exceptions. In dystonia patients, the electrodes are placed into the brain using MRI stereotactic guidance, and then checked using stimulation. For most patients, both electrode insertion (under local anesthesia) and cable and pulse generator placement (under general anesthesia) is performed on the same day.
Potential complications in deep brain stimulation
We are only beginning to understand the brain and its functions and pathways. At the same time, our understanding of the causes of complex Parkinson’s disease, tremor and dystonia is somewhat simplistic. It is not surprising therefore that despite many good outcomes that can be achieved with deep brain stimulation surgery, there are side effects that can be identified. Some of these side effects are related to placement of the electrode into the brain, some are side effects related to the hardware and it’s components, and some are due to stimulation of the brain.
•Side effects related to placement of the device. These include complications from local or general anesthesia, application of the stereotactic frame (scalp infection), exposure of the skull and brain surface (bleeding of the scalp or bleeding on the surface of the brain), and stroke (bleeding within the brain itself, 1% risk of significant bleeding within the deep brain from placing the electrode. This can cause stroke or death. If life threatening, the patient would need urgent brain surgery to stop the bleeding and save the patient’s life. This is often the most serious complication of open brain surgery.
•Wound Infection. This can occur from cutting the skin and exposing the brain or other tissues. The risk of infection is 3-5%. Patients are placed on antibiotics at the time of surgery to try to minimize this. If an infection occurs, part or all of the system will have to be removed and then replaced several months later. The patient will remain on a standard course of antibiotics until the infection is completely treated.
•Complications from hardware and its components. Hardward-related problems can also occur. These include fracture or breakage of the deep brain stimulation wire or cable and need for subsequent replacement.
•Battery failure. On average the batteries last 3-5 years, but will require replacement over time. Some patients will turn off their system at night in order to extend the life of the battery. This depends on the problem being treated.
•Erosion of the plastic cable or device through the skin. If the patient is quite thin and the amount of soft tissue under the skin is limited, the system could exert pressure on the skin and erode through. If this is the case, the skin would have to be revised and the system removed.
•Migration of the wire. The plastic cap that anchors the deep brain stimulation wire to the skull can break. This could lead to movement of the wire either deeper into the brain or further out of the brain. We use what we believe is the best anchoring device available for our patients. This complication is very uncommon.
Complications related to deep brain stimulation
Deep brain stimulation can cause both positive and negative effects to the brain. This is due to the fact that many critical brain functions are located within a very small distance of each other. In some patients stimulation could improve walking, but cause side effects related to arm or leg function. Some side effects could include numbness of the face, arm hand or leg, stiffness or weakness of the limb, double vision, closure of the eyelids, change in mood, thinking problems, facial weakness, dizziness, lightheadedness, or imbalance. The stimulator can usually be adjusted to treat these effects. In some patients, stimulation benefits occur together with some side effects.
In patients who undergo surgery on both sides of the brain at the same operation, surgeons have noted that some may develop confusion. In such patients, this confused state has lasted anywhere from a few days to several weeks. It is usually temporary.
If you have deep brain stimulation surgery performed, you have to inform your dentist or surgeon when you need dental work or surgery. You must also inform any physician who may want to order an MRI scan on your brain or body.
Benefits of deep brain stimulation
It is hoped that deep brain stimulation will lead to significant benefit of your movement disorder. This could include reduction of tremor to allow you or your family member to use their hand or leg efficiently, or reduction in head tremor.
For patients that undergo subthalamic deep brain stimulation, it is important to know that the goal of the procedure is to improve the condition in the "off" medication state. Many patients with Parkinson’s disease have both "on" and "off" medication states. The "on" state is when the medications appear to be working and when the patient is more loose and nimble. The "off" state is when the patient is slower and stiffer. Deep brain stimulation does not usually improve the "on" state (the patients best condition), but hopes to improve the patient when they are in their worst state. It also hopes to improve dyskinetic movement abnormalities.
It is important to know that it may take many hours of physician or physician extender programming to optimize the stimulation parameters. Every patient is different. The neurology team will work with you to tune the stimulator to the parameters that may give you the most benefit. At the same time they may adjust your medication. The stimulators can be programmed in many different ways (the voltage, the frequency with which the stimulus is delivered to the brain, the length of each stimulus, and the shape of the stimulus and region that it influences the brain cells) and each patient may be different.
