Deep Brain Stimulation
DBS surgery involves placing fine electrodes within the brain, usually on both sides. There are several sites for stimulation that can be effective in the treatment of PD. The most common site for stimulation is the subthalamic nucleus (STN). This is a small area towards the bottom of the brain. It is one structure that makes up the basal ganglia. The basal ganglia are collection of nerve cells that assist in the control of movement and are where the symptoms of PD are generated. The other targets for treating PD are the globus pallidus (GPi) and thalamus, which are also part of the basal ganglia networks.
DBS surgery involves placing the electrodes in a very small region within the brain without ever actually seeing the target. To place the electrodes in the correct site, several complex surgical and neurophysiological techniques are used during the surgery.
DBS surgery is therefore unique in that it is one of the few operations performed with the patient awake. This is daunting for the patient, but most patients tolerate the procedure very well.
Related condition to DBS
Before DBS Surgery
People with PD who are poorly controlled with medication are usually referred to a Movement Disorders Neurologist trained in DBS, such as the DBS Clinic at Westmead Hospital. The patient is assessed for whether DBS surgery will help their symptoms, as well as ensuring that there are no medical conditions that would increase the risks of surgery. The first consideration is whether adjustments to the medical management such as changing medication may help. Treatment options are discussed in relation to the individual, including the possible benefits and risk, including DBS and other advanced treatments for PD. Those patients who wish to consider DBS surgery will then be enrolled in a protocol for assessing whether they are good candidates for surgery.
The routine assessment protocol includes:
On the day before surgery
Most patients are admitted to hospital on the day before surgery. This allows the medication to be managed and the patient’s condition to be more closely monitored. It also allows for some routine investigations like blood tests, ECG and chest x-rays to be performed, and review by the anaesthetist if required. In some instances, these will be performed prior to admission at the preadmission clinic.
In most cases a significant area of the scalp will be shaved for the surgery. We advise that patients should shave their hair prior to admission to hospital.
On the day of the surgery
DBS surgery is a complex process. Several steps are involved:
- The patient will need to fast for the procedure just like for any other operation where an anaesthetic is involved.
- The patient is first taken from the ward to the radiology department for the first step of the procedure: attaching the stereotactic frame to the patient’s head. The frame is attached to the skull with four pins so that it cannot move during the operation. This, of course, is scary for most patients, however, the use of local anaesthetic and a very small amount of intravenous sedative makes this part of the procedure run smoothly. it usually takes only a few minutes.
- The next step is to have a high-resolution CT brain scan. The patient is then transferred to the operating room.
The surgery itself consists of two main sections – inserting the electrodes into the brain (done while the patient is awake) and inserting the ‘pacemaker’ (done with the patient under general anaesthesia).
Inserting the electrodes into the brain
Step 1 – The operating theatre
- Once in theatre, the next step is to make the patient comfortable while they are lying on the operating table. The table is padded, and the head of the bed is gently elevated. A pillow is often placed under the knees. The frame, which holds the patient’s head, is attached to the table. The scalp is scrubbed to clean it, and some more local anaesthetic is injected.
Step 2 – Scans
- During this period the neurologist and neurosurgeon will discuss the scans and finalise the targets on the computer. The DBS target cannot be seen on the CT scan, so we use a computer to carefully align the CT scan with the prior MRI scan. The target can be seen on the MRI, and its location on the CT, so its 3D coordinates in reference to the stereotactic frame can then be calculated. The path that the electrode is to take through the brain will be determined.
Step 3 – Connecting the Stereotactic Frame
- Once that process is completed, the main part of the stereotactic frame is set to the desired co-ordinates and connected to the frame that is already attached to the patient. The head is again cleaned with antiseptic solution and drapes are placed around the site for the scalp incision. These are positioned so that the patient can see the other staff in the room and easily communicate with them. Throughout the procedure the anaesthetist will monitor the patient’s condition. The scalp is incised after injecting more local anaesthetic. This is painless although the patient will feel some pushing sensations.
Step 4 – Electrode Insertion
- To pass the electrode into the brain a hole, (termed a burr hole), must be placed in the skull on each side. These are normally drilled at this point in the procedure. Again, this part of the procedure is anxiety provoking to most patients. The drill is designed so that it stops as soon as it reached the inside of the skull. Its shape means that it cannot go too far. It is noisy because the sound is transmitted by the skull to the ears. Each hole however takes less than a minute to drill. The anaesthetist often administers some sedation so that the process is tolerated well.
Step 5 – Nerve Cell Activity
- The side of the brain opposite to the side of the body that is most severely affected is operated on first. After drilling the burr hole, the covering of the brain is opened, and a tiny incision is made in the surface of the brain. A cannula, attached to a device called a micro-drive, is carefully introduced into the brain. Through the cannula a very thin electrode is placed into the brain. The micro-drive sits on the stereotactic frame and allows a microelectrode to be advanced through the brain by very small distances at a time. This microelectrode is used to record nerve cell activity, as is travels through an area of the brain. The pattern of nerve cell activity is very helpful to confirm that the electrode is in the correct location. The neurologist may ask you to perform several tasks, such as reaching out, to look for changes in nerve cell activity.
Step 6 – Stimulation Test
- Stimulation, just like the long-term DBS, is then tested using the same microelectrode. This is another tool to ensure that the electrode is well positioned. It is done at several points along the path of the microelectrode. At each point, the stimulation is gradually increased to determine the voltage needed to gain good effects and increased further to find the voltage that causes side effects. We are looking for the site that gives the best effects at low voltage and only causes side effects at high voltages. The neurologist will ask you to perform several tasks to assess the amount of benefit. You will be asked to say when you experience side effects, such as tingling in part of the body, contraction (pulling) of muscles of the face or hand, or double vision. It is important that the stimulation is increased until side effects occur – this is helpful to predict the long-term effects of DBS at that site and to confirm the electrode is well positioned. Some patients find this part of the procedure tiring.
Step 7 – Responses
- In some cases, the nerve cell recordings do not clearly identify the target or the responses to test stimulation do not show good effects. The microelectrode is then withdrawn and re-inserted in a slightly different location (around 2mm to one side), where it is predicted that better effects can be achieved. This does not involve drilling another burr hole. The nerve cell activity and test stimulation are repeated. In most cases, however excellent results are obtained at the first position.
Step 8 – DBS Electrode Insertion
- Once the optimal position has been identified, the microelectrode is removed, and the DBS electrode is inserted at the same location. This is done while using a mobile x-ray machine. It is just one more way to ensure that the electrode is in the correct position within the brain. Once the final position is achieved the electrode is ‘locked’ to the skull using a small plastic cap that sits in the burr hole.
Step 9 – Adjustments
- At that point the co-ordinates of the frame are adjusted, and a microelectrode is placed on the other side. Again, the electrical impulses from the neurons are recorded and the results of test stimulation are determined. When the neurologist and neurosurgeon are satisfied with the position, the other DBS electrode is positioned and ‘locked’ onto the skull.
Step 10 – Finalisation
- Once both electrodes are in position the wound is closed with some sutures. The frame can then be removed which involves undoing the skull pins. This takes only a few seconds and is painless.
Inserting the pacemaker
The anaesthetist then puts the patient to sleep under general anaesthesia for the second part of the procedure. Most of the time, this is done immediately after the electrode insertion, but can be done later.
- Extension leads are connected to the brain electrodes, and these are tunnelled under the skin to where the IPG (implanted pulse generator, often called ‘pacemaker’) will be placed.
- The stimulator is placed under the skin through an incision just below the right collar bone (clavicle).
- The extension leads are then connected to the IPG. Then the wound is closed, and dressings are applied.
- The patient is then woken from the anaesthetic and taken to the recovery room where they are monitored after the anaesthetic.
The time taken to perform the procedure varies from patient to patient but on average would take around 4 – 5 hours’ total.
Afterwards the patient is taken to the intensive care or high dependency unit where they can be monitored by doctors and nurses overnight. The patient is usually talking and interacting with staff and one or two close relatives.
The day after surgery a routine CT scan is obtained. A further scan is performed a few days later so that exact position of the electrodes can be checked against the pre-operative MRI scan.
Risks of the Surgery
There are significant risks associated with DBS surgery. Prior to surgery patients should consider these risks and their potential consequences before consenting to the procedure. There are risks in relation to the surgery itself, as well as long term adverse effects.
The following is a list of the main issues related to DBS surgery:
Issues related to the long-term effects of stimulation include:
Expectations of the Surgery
It is essential that all patients who consent to DBS surgery have reasonable expectations of the surgery. The following points are emphasised
DBS is not a cure for PD. PD is a progressive condition and DBS surgery does not halt or reverse this progression. Therefore, patients may experience a decrease in the benefit of DBS surgery over a long period.
The overall success rate of surgery depends on the reasons for having the surgery. The average improvement in activities of daily living is 50% while the average improvement in movement scores according to the UPDRS is 52%.
The two most important indications for surgery are dyskinesias and motor fluctuations. In a review of outcomes from the literature, the average reduction in dyskinesias is approximately 70% with a similar reduction in ‘off’ times.
Medication for PD is almost always still required after surgery. The reduction in levodopa equivalent medication after surgery is approximately 55%. In many cases the dose will be able to be reduced. However, the aim of the surgery is to make the medication more effective by reducing motor fluctuations and dyskinesias. In general, nothing is gained by stopping PD medications, and complete withdrawal of medications is not a goal for surgery. In fact, many patients are worse off if medications are reduced too much.
The hospital stay is quite variable and depends on the patients’ overall condition prior to surgery and whether the stimulator is programmed while in hospital or afterwards. If the programming occurs after hospital, then patients normally stay around 5 days. During the hospital stay the patient receives daily physiotherapy. Patients will receive prophylactic subcutaneous heparin injections and are required to wear stockings to prevent DVTs. After surgery, there is normally some discomfort around the wound and analgesia is provided. However, the amount of analgesia is required is usually small. Constipation is a common complaint after surgery and is usually due to analgesics. Patients should inform staff if this becomes an issue.
The wound is normally cleaned, and the dressing changed each day. After discharge no dressing is required. You may shower and pat the wound dry with a clean towel afterwards. While the wound may get wet, do not soak it in the bath or in a pool for at least 2 weeks after the surgery. Do not rub the wound. If there are any concerns such as excessive redness, pain or ooze then you should attend your general practitioner as the first step.
Medication adjustment and DBS programming are required frequently in the post-operative period. This begins immediately after surgery. Frequent assessment by the neurologist is required, becoming less frequent as things stabilise after the first few weeks.
For STN DBS, the PD medications are generally reduced to half the usual dosage and adjusted according to the response after that. The dosage is not reduced when the target is the GPi.
The DBS system is checked soon after surgery. It is not turned on until the patient has recovered from the surgery and the “microlesion effect” begins to subside. Most patients have the DBS turned on, and several adjustments made prior to leaving hospital. Ongoing changes are made according to the response. The location of the electrodes on post-operative CT scan helps to choose the best contact for stimulation.
Around 1-2 months after surgery, patients are asked to attend the DBS clinic for a detailed assessment of the effects of DBS. This is generally done after overnight withdrawal of medications. Each of DBS contacts (four on each side, so eight in total) are tested for benefit and side effects. The contact that gives the best effects and fewest side effects is chosen for long-term DBS.
Patients will be given an Access DBS control device, which allows them to turn the DBS system on or off, and to adjust the amount of DBS within pre-specified limits. Your neurologist will show you how to use the Access controller.
An appointment is usually made for the patient to be reviewed by their neurosurgeon around 6 weeks after the surgery.
The stimulator is dependent on a battery. The battery will of course run down over time. The time taken for the battery to run down varies depending on the programming used for stimulation. In most cases the battery will need to be replaced in 3-5 years. Battery replacement is normally straightforward and is performed under general anaesthesia. The old incision on the chest is re-opened, the old stimulator disconnected and removed, the new stimulator is connected and inserted, and the wound closed. The new stimulator is programmed and turned on. The procedure usually takes around 30 minutes.
This information was provided to assist you. While it has been prepared to provide accurate information the practice and techniques of surgery will differ between surgeons. Likewise, the information is a generalisation in relation to the surgery and will vary between patients depending on the individual and their pathology. This information cannot cover all aspects of the surgery especially in relation to surgical risks and should not be considered an exhaustive explanation.
PD is a complex condition which affects every patient differently. This information is for general advice and cannot account for the needs of every individual. Please inform your doctors of any specific issues or concerns. Please discuss what you hope to gain from DBS surgery – your specific goals.
For further information relating to this technology, please click here for the Medtronic website.