DBS Surgery for Parkinson's Disease
The core features of Parkinson’s Disease (PD), namely slowness, stiffness and shakiness, typically respond well to medication. However, PD progresses with time and the response to medications often becomes complicated by motor fluctuations (where the benefit of each dose of medication lasts only for as little as an hour) and dyskinesias (excessive involuntary movements). Patients fluctuate between OFF (medications not working, very stiff and immobile) and DYSKINESIAS (excessive involuntary movements) and very little quality ON time (medications working, mobile). Careful adjustments of medications can sometime help, but may not fix the problem, and the motor fluctuations and dyskinesias continue to reduce quality of life.
The most common reason to have DBS is to control motor fluctuations and dyskinesias. Other reasons include tremor that is resistant to medication, and inability to tolerate medications due to other side effects (e.g. severe L-DOPA induced sleepiness). Other options for treating motor fluctuations and dyskinesias include daytime infusion of apomorphine using a programmable pump connected to a needle that is inserted each day.
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. These include:
- Stereotaxy: Stereotaxy is a method that enables a probe or electrode to be placed within the brain without seeing it. By using a stereotactic frame (CRW frame) combined with a preoperative CT and MRI scan, the electrode can be directed towards the target very accurately
- Microelectrode recording: Different neurons within the brain have different patterns of electrical activity. These tiny electrical currents can be recorded. By listening to the different sounds obtained by recording from these neurons, the neurologist and neurosurgeon can be confident of where the electrode is within the brain
- Testing: The main reason for the patient to remain awake during the initial part of the procedure is to enable the neurologist to test the patient’s response to stimulation. By confirming that tremor and rigidity improve with stimulation, as well as determining that there are no unwanted effects of stimulation, one can be confident that there will be long term improvement when the electrode is positioned at that site
- Intra-operative x-ray: Finally, when placing the electrode into its final position, an x-ray is performed to again confirm its correct placement
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.
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:
- L-DOPA challenge –where the response to L-DOPA is recorded on video and measured using clinical rating scales. Usually, patients should have an improvement of >30% following an adequate dose of medication
- Neuropsychological assessment – detailed testing of thinking and memory is required to minimise the risks of surgery
- Psychiatric assessment – seeing a psychiatrist with experience in PD and DBS is important. Undergoing DBS surgery is a very stressful process, and unrecognised or untreated psychiatric symptoms can worsen with surgery
- Hi-resolution MRI scan – to identify the target structure (typically STN) and to ensure that there are no brain changes that increase the risks of surgery
- Neurosurgical consultation – it is important to meet the neurosurgeon, to discuss the procedure in detail, to discuss the potential benefits and risks, and have any questions answered
- It is important to meet with the DBS neurologist several times prior to surgery. This ensures that there is a detailed understanding of how PD affects the individual, to discuss treatment options, to discuss DBS-related issues, and to build a therapeutic alliance
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).
- Once in the operating 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
- During this period the neurologist and neurosurgeon will discuss the scans and finalised 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
- 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
- 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
- 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
- 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 of 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
- 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
- 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
- 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
- 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
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:
Stroke / Intracerebral haemorrhage / Death: The concern of most patients and their doctors is the risk of bleeding within the brain. This is called intracerebral bleeding. In some cases, it can be minor and have no serious effects but in other cases it might cause paralysis of one side of the body, inability to speak, unconsciousness and even death. The risk of serious neurological deficit such as paralysis or death is approximately 2% with an overall risk of some bleeding of approximately 4%.
Infection: There is a risk of infection will all operations but those that involve prolonged procedures or implantation of a foreign material such as an electrode or stimulator have a higher rate of infection. While most superficial wound infections can be treated by antibiotics, infections involving the electrodes or stimulator may necessitate removal of these components to allow the infection to clear. Therefore, the procedure may need to be repeated. Steps are taken to reduce the chance of infection including the use of antibiotics during and after the surgery.
Lack of benefit from DBS: Unfortunately, DBS may not achieve the desired or expected benefit. This is very uncommon, but can occur.
Electrode migration: Despite excellent recordings and responses to test stimulation, it is possible that the final DBS electrode migrates, and the benefit of stimulation can diminish over time. This may require another DBS surgery to re-position the electrode to a better location.
Post-operative confusion, agitation or hallucinations: This can be a problem for some patients, and may require the temporary use of extra medications. It usually settles within a few days.
Post-operative dyskinesias: The process of DBS surgery causes a “microlesion effect”. There is mild swelling where the electrodes have been, which subsides typically over a few days. The result of this swelling may include involuntary movements (dyskinesias) similar to an excessive dose of PD medication. Although potentially disconcerting, post-operative dyskinesias are not a bad sign.
Issues related to the long-term effects of stimulation include:
Unwanted effects of stimulation:In some cases, unwanted effects of the stimulation, or poor therapeutic results of stimulation, may reflect incorrect positioning of the electrodes. This may occur even despite all the precautions described earlier in this document. Careful re-programming of the stimulation parameters can generally mean that good benefit is obtained without significant adverse effects.
Mood disturbance and suicide: There is a risk of depression with DBS surgery but this risk is low. Those with depression prior to surgery may also have an increased risk of depression after surgery. The risk of significant mood disturbance may be about 0.5-2%. Suicide is rare, but the risks increases before as well as after DBS surgery. The reason for this is not clear – it can occur even after excellent improvement with DBS.
Cognition:Some patients may experience problems with speech and verbal fluency. However, most patients have no alteration of cognition after surgery.
Hardware / device failure: The stimulator is a complex medical device. There is a potential for the device to malfunction. This is very rare but can occur, which results in a sudden worsening of PD symptoms, the same as if the DBS is turned off. In addition, it is possible for the extension leads to fracture. This can occur from repetitive neck movements and may necessitate their replacement. DBS failure can be serious, and you should seek immediate advice from your DBS team if there is a sudden worsening of PD symptoms on one or both sides of the body.
Wound infection, erosion of the skin overlying the DBS hardware: Can occur in the longer term. Treatment may require long term intravenous antibiotics, revision surgery or even removal of the affected hardware.
Worsening of speech or balance: In some cases, up to 10-20% of people suffer a worsening of speech or balance following DBS. Speech problems are more likely to occur if the speech is already soft and hard to understand even when medications are working well. Similarly, balance problems are more prone to become worse if there are balance problems or falls, even when the medications are working well. Adjustment of DBS parameters and medications can sometimes be helpful, but speech and balance problems can sometimes remain significant. However, the benefit of DBS on the other aspects of PD means that patients do not ask for the DBS to be turned off because of problems with speech or balance.
PD progression:It is important to remember that PD is a progressive condition, and the symptoms will worsen slowly with time. DBS does not halt this process, but can relieve some of the symptoms. In general, the symptoms that improve with medications also improve with DBS. Over the years, symptoms may occur that do not respond to medications or DBS. This is not because the treatment no longer works, but is because the PD has continued to progress. There is no indication that DBS stops working, and there are patients who continue to benefit from DBS more than 10 years later.
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 patient 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.
Please contact Prof Owler’s or Dr Mahant’s office if there are any further concerns or questions.