What Is Deep Brain Stimulation?
Deep brain stimulation (DBS) has evolved as an important and established treatment for movement disorders. While DBS is not a cure for movement disorders, it can successfully treat symptoms by disrupting the abnormal patterns of brain activity that become prominent in these diseases. Using a fully implantable neurostimulation system, DBS provides a targeted, adjustable, non-destructive, and reversible means of modulating the pathological of brain circuits. Patients with Parkinson’s disease, essential tremor, dystonia, and other movement disorders such as Tourette syndrome, who do not obtain a satisfactory response from optimal medical therapy, may be considered candidates for surgical intervention.
In the past, the neurosurgical treatments consisted chiefly of procedures that produced lesions to selected areas of the brain in order to control the movement disorder ("ablative surgery"). These procedures involved making an incision in the scalp, drilling a hole through the skull, and then advancing a "probe" (electrode) into the portion of the brain that was thought to be functioning abnormally. Heating the tip of the electrode then resulted in lesioning the target brain area to produce a reduction of the abnormal or involuntary movement on the opposite side of the body. Although effective in most cases, risks included weakness on the opposite side of the body, numbness, poor coordination, speech disturbance and other complications. These potential risks are compounded when the procedure is performed bilaterally (on both sides).
DBS has replaced the traditional ablative procedures, as the surgical treatment of choice for a variety of movement disorders such as Parkinson's disease, tremors, dystonia and tics. As a result of improved understanding of the anatomy and function of the basal ganglia, (the part of the brain involved in Parkinson's disease and other movement disorders), coupled with refinements in imaging and surgical techniques, DBS is gaining wide acceptance as a chronic treatment of not only tremor, but also other symptoms of Parkinson's disease, complications related to levodopa therapy, such as motor fluctuations and dyskinesias, and other movement disorders such as dystonia. The major advantage of DBS over the traditional ablative procedures is that the stimulating electrodes and parameters (frequency of stimulation, pulse width, and amplitude) can be adjusted and "customized" to the needs of the individual patients.
Since the early 1990s, clinicians from around the world, including those at Baylor College of Medicine, began to explore different brain targets to control the various movement disorders. The current data, based on the extensive experience at Baylor and abroad, provide compelling evidence that chronic, high-frequency stimulation of the ventral intermediate (VIM) nucleus of the thalamus, the subthalamic nucleus (STN) and the globus pallidus (GPi) improves essential tremor and tremor in Parkinson's disease. The STN and GPi control not only tremor, but also motor slowness, rigidity, gait, and, most importantly, levodopa-related motor fluctuations and dyskinesias in patients with moderately advanced Parkinson's disease.
DBS is currently being used in selected centers around the world, including Baylor College of Medicine, to treat a variety of movement disorders. In collaboration with Dr. Viswanathan, from the Department of Neurosurgery, we have implanted over 500 DBS devices. Patients interested in being evaluated to determine whether they are candidates for DBS should contact the Parkinson's Disease Center and Movement Disorders Clinic, Baylor College of Medicine, Department of Neurology (713) 798-2273.
Benefits and Limitations of Surgery
In patients with Parkinson's disease (PD), surgery is generally recommended at a time when medications cannot adequately control symptoms. Patients are most often referred for deep brain stimulation (DBS) surgery when they have experienced problems with dyskinesias (excessive involuntary movements that occur as a consequence of PD medications) and fluctuations (the beneficial effects of medications do not last long enough between doses). When there are no further adjustments that can be made with medications because of these problems, surgery may be a way to limit complications from medications and to improve motor function. It is important to note that surgery will NOT work any better than medications ever did. The major benefits of DBS surgery in this case are to decrease "off" time and to reduce or eliminate dyskinesias. Additionally, many patients report that their quality of life improves substantially after DBS. Medications can be gradually reduced after DBS, but this is not always the case and may depend on many factors.
In PD, motor symptoms (tremor, rigidity, slowness/incoordination, walking/balance problems) that do not get better with medications will generally not get better following DBS surgery. The only exception is when the surgery is being primarily done to control tremor that has failed to improve with medications. Additionally, DBS is NOT a cure for PD, and it probably does not slow or stop the underlying progression of the disease. Some symptoms such as balance difficulties, speech problems, swallowing difficulties, and cognitive decline develop or worsen as PD progresses, and cannot be addressed with DBS adjustment. Finally, the non-motor complications of PD, such as depression, problems with thinking or memory, constipation, urinary changes, or pain, are also not likely to be markedly improved by DBS. It is absolutely imperative that patients have realistic expectations and a clear understanding about the anticipated outcomes and potential risks before consenting to the procedure.
Essential Tremor and Dystonia
Patients with essential tremor (ET) or dystonia (including cervical dystonia or torticollis) can reasonably expect that their tremors or involuntary muscle contractions or postures can be better controlled with DBS than with medications alone. However, there may be several factors that influence how well this can be done, including individual patient characteristics, duration of disease, and distribution of symptoms. DBS surgery will not help with balance problems or other associated features such as neuropathy or hearing loss. Tremors of the head or trunk are more difficult to treat but can improve.
Patients undergoing treatment for Tourette syndrome (TS) should be aware that DBS in this condition is still under investigation and there are no guarantees about the outcome. In our experience to date, tics can substantially improve, but they do not go away completely. There may also be some improvements in co-morbidities such as obsessive-compulsive disorder and attention deficit disorder. Surgery is generally reserved for severe cases in which all medical and psychological therapies have been exhausted and unsuccessful.
Risks Associated with DBS Surgery
There are potential risks associated with any brain surgery, including infection, intracerebral bleeding, leaks of the fluid surrounding the brain (cerebrospinal fluid), strokes, headaches seizures, weakness, sensory changes, technical problems, wound healing problems, disfiguring scars, prolonged hospitalization, and need for additional surgery. Additionally, there may be potential risks associated with receiving anesthesia. The percentage of patients who report or experience these complications is low, but may be different according to the surgeon that is performing the procedure. It is a good idea for patients to discuss individual complications rates with their neurosurgeon.
Additionally, there may be potential risks related to the programming of the DBS device, which begins a few weeks after the surgical process is complete. When making adjustments to the DBS, there may be immediate short-lived side effects such as tingling, tightening sensations, visual changes, or speech problems. Much of the time, these may be eliminated by further DBS adjustment. However, certain effects may not become apparent until hours or days after the adjustment. These may include any of the above symptoms, but also mood or behavior changes, involuntary movements, worsening of the underlying symptoms, or walking and balance problems, including falls. Patients undergoing DBS for ET, especially if the procedure is done on both sides of the brain, are particularly prone to developing problems with speech or gait/balance changes. It is important that these problems are communicated to the neurologist if they occur so that they can be rectified as soon as possible. There may be several ways that these problems can be addressed, but it is possible that the changes required to minimize such side effects will lead to less symptom control.
Less commonly, and in the long term, there may be device complications that include loss of effect, unexpected side effects, fracture or breakage of the wiring, change of position of the electrode within the brain, or infection. Some of these problems, if they develop, may require removal of the device or portions of the device.
Patient Selection for DBS Surgery
There is a preoperative process that all patients being considered for surgery will undergo, but this differs according to the condition being treated.
The patient and his/her neurologist will decide together when it is time to consider DBS. All patients will undergo an "on/off" evaluation in which their PD symptoms are assessed under conditions of no medication ("off"), and again with the full/maximal effect of medications ("on"). This is done by asking the patient to come in for evaluation first thing in the morning without having taken any PD medications. The neurologist will make an assessment of symptoms and document a physical exam on video. The patient will then take his/her usual first dose of medications. Once this dose has "kicked in" another assessment of symptoms will occur with another video documentation. This is done in order to gain a better understanding of which motor symptoms improve with medications which helps guide patient expectations of outcomes after DBS, and to ensure that DBS really does have some benefit to offer an individual.
Patients are also required to undergo a neuropsychological assessment to gain a better understanding of their baseline thinking skills and psychological state. Symptoms of depression or anxiety should be appropriately addressed prior to undergoing brain surgery. The presence of cognitive problems, such as dementia, may indicate a patient who is at risk of further cognitive decline after DBS, leading to more disability. Furthermore, the presence of dementia produces practical obstacles to achieving optimal outcomes. Patients with dementia may have difficulty accurately observing and articulating their symptoms, making adjustment of DBS parameters more difficult. Neuropsychological evaluation before surgery also provides an important baseline assessment; in cases where cognitive or emotional problems occur after surgery, the testing can be repeated and compared to preoperative scores to help determine the cause of the problems.
Preoperative assessment of tremor severity by formal scales is usually done so that the neurologist has a baseline against which to measure the response to DBS. ET patients are also asked to undergo preoperative neuropsychological assessments for the same reasons as outlined above.
Preoperative assessments of dystonia symptoms are done for reasons similar to those in ET patients. Neuropsychological assessments may also be considered.
Preoperative video evaluation, tic rating scales, and neuropsychological assessments are obtained before surgery. In some cases, a psychiatric evaluation is required. These and other factors related to a patient's social or psychological state and support network are considered together in determining if DBS is appropriate.
All cases are reviewed at a consensus conference attended by the treating neurologist, neuropsychologist and neurosurgeon, at which time recommendations are made for or against surgery, and regarding which brain location should be stimulated. All patients will receive a follow-up call from their neurologist explaining whether surgery was recommended or not, and which location of stimulation was thought to be most beneficial. Patients will have an opportunity to ask further questions at this point before proceeding with actual surgical appointments.
DBS Surgical Procedure
DBS electrode placement is typically done in the awake patent using a stereotactic frame. In this procedure, a rigid frame, or halo, is attached to the patient’s head just before surgery after the skin on the scalp is anesthetized with a local anesthetic. A brain imaging study is obtained with this frame in place and the images are used to calculate the position of the desired brain target and to help guide instruments to that target with minimal brain trauma. The stereotactic frame is then fixed to the operating table, a patch of hair is shaved and the scalp is washed. After making the scalp completely numb, an incision is made and a small opening in the skull is created.
The DBS lead (a thin wire), which contains four electrodes, is then surgically inserted into the desired target and tested to verify optimal placement. The lead is ultimately connected to an extension wire that passes from the scalp area under the skin to the chest. Here it is connected to an implantable pulse generator (IPG), a pacemaker-like device, which can deliver pulses with a variety of parameters, modes, and polarities to the target brain area. The IPG is surgically implanted under the skin in the upper chest area near the collar-bone or under the skin in the lower abdomen, much like a pacemaker. The IPG delivers continuous electrical pulses through the electrodes to produce the desired effects of DBS stimulation.
The patient can activate or deactivate the DBS system by placing a magnet over the chest area that contains the IPG. The IPG is a metal "box" about two inches in diameter and about one-half inch thick, similar to a cardiac pacemaker. It contains a small battery and produces the electrical pulses needed for stimulation. The typical battery life is expected to be approximately five years, but this may vary depending on the individual settings and hours of use per day. The battery cannot be replaced without replacing the entire IPG. Replacing the IPG involves minor surgery. This needs to be done every three to four years. The Activa® RC Neurostimulator (Medtronic) is available and is the first rechargeable DBS neurostimulator. It has an expected battery life of four to nine years, and patients can choose daily or weekly battery recharge options.
DBS Programming After Surgery
A few weeks after surgery, the movement disorders specialist will use a hand-held programmer to test different electrodes and determine the settings that provide the most benefit with the least side effects. This initial programming session after DBS surgery can last around one hour. This guides future programming sessions, which are usually performed every three to four weeks for at least two to three more visits to determine the optimal settings for stimulation.
Patients should be aware that DBS is not a cure for Parkinson's disease and the IPG settings need to be adjusted in subsequent programming sessions. During the follow-up DBS visits, there will be a fee for the adjustment and reprogramming of pulse generator (CPT code 95971, 95974, 95975) for stimulator adjustment and for a routine follow-up visit. It is our policy that we require payment at the time of service (except for Medicare patients). We do, however, provide assistance in filing for Medicare/Third Party Payer reimbursement.
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©2018 Joseph Jankovic, M.D.