Deep Brain Stimulation: A New Option for Tourette Syndrome
Deep Brain Stimulation (DBS) has emerged as a potential option for select Tourette syndrome (TS) patients whose motor and/or vocal tics significantly impact the quality of life despite maximal use of other treatment options. The media buzz surrounding DBS for TS has been exciting; however, it has created many questions for patients and their families to consider. In this update we aim to address the most commonly asked questions and also we aim to update the current state of DBS for TS.
What is Deep Brain Stimulation (DBS)?
DBS is a relatively new procedure that utilizes an implantable electrode to alter the activity of brain circuitry.
The procedure is FDA approved for Parkinson’s disease, essential tremor, dystonia and OCD, and currently utilized for patients who have not responded to standard medical or behavioral therapy, and who have no cognitive difficulties or “minimal” cognitive (thinking issues) dysfunction may be appropriate candidates.
There are two essential components to the hardware involved in DBS, the implantable electrodes and the programmable pulse generator. The DBS electrode is implanted into a specific target within the brain and the pulse generator, or neurostimulator, is implanted under the skin just below the collar bone (or in the abdomen for women); an extension cable passes under the skin and connects the electrode to the neurostimulator. The DBS electrode has four contact points, the sites through which electricity is delivered. Active contacts can be selected by computer and multiple settings can be adjusted for individual patient needs. The settings can be adjusted for different pulse widths (how long each pulse of stimulation lasts), frequencies (how many pulses are delivered each second), and amplitudes of stimulation (how much voltage is delivered).
How would DBS help someone with Tourette Syndrome?
DBS has the potential to “neuromodulate” abnormal communication that occur deep within the brains of people with TS. So far researchers have probed into several areas in the brain of people with TS (the centromedian thalamus, the internal globus pallidus, the external globus pallidus, and the anterior limb of the internal capsule) and they have had mixed success. The best target for “neuromodulation” has yet to be determined, however it does appear that DBS has positive results in some patients.
What does it mean to have a multidisciplinary/interdisciplinary screening prior to DBS and why is it important?
An important concept to understand when evaluating any potential DBS candidate is that successful surgery usually requires a multi/interdisciplinary approach. For TS a neurologist, psychiatrist or general practitioner can serve an important role in identifying and in triaging potential DBS candidates. However, prior to surgery, potential candidates should be comprehensively evaluated by an experienced team. The goal of the evaluation is to make sure that the candidate is optimally suited for DBS and can fully participate in the various operative and post-operative procedures. These teams should optimally include a psychiatrist experienced in TS, a neurologist experienced in TS, a neurosurgeon experience in DBS, and a neuropsychologist. In some cases social work, physical, occupational and speech therapy may be useful. Additionally, adequate imaging must be performed (usually a MRI and/or CT), and the results of each part of the screening should be discussed in a DBS team meeting/board. The results of this team meeting should be shared with the patient and the family to be sure expectations may be reasonably addressed by the overall decision on the recommended approach to therapy.
Who is a good candidate for DBS?
Probably the most crucial step for successful DBS is careful patient selection. Careful consideration of patient characteristics will directly impact outcome. Despite the widespread use of DBS, there are no standardized criteria for selection of candidates. The TSA has recently published recommendations for DBS surgery in the journal Movement Disorders. Below are some general considerations for patients and families.
- The diagnosis of Tourette Syndrome must be made by an expert psychiatrist and/or neurologist.
- The Yale Global Tic Severity Scale should be performed and must reveal incapacitation with severe distress, self-injurious behavior, and/or quality of life disruption. OCD, Depression, and ADHD are not exclusionary provided tics are the major difficulty requiring surgical intervention.
- Must be over 25 by FDA guidelines and TSA guidelines and many studies may exclude Tourette patients younger than this age. There may be exceptional cases where younger patients are acceptable candidates for DBS surgery.
- The patient’s TS symptoms must have failed to response to conventional therapy for tics. To meet these criteria, subjects must have been treated by a psychiatrist or neurologist experienced in Tourette Syndrome (usually treated with at least three different pharmacological classes: an alpha-adrenergic agonist, dopamine antagonists (typical and atypical), and a benzodiazepine).
- Patients must have received stable and optimized treatment of comorbid or other medical, neurological, and psychiatric disorders for the previous 6 months.
- If the patient has a tic that is focal or addressable by botulinum toxin treatment this should be considered.
- If present, psychiatric disorders such as anxiety, depression, or bipolar disorder must be treated and stable.
- Patients must be screened for dementia or cognitive dysfunction that will place the patient at risk for worsening cognition (thinking), and/or may impact the ability to cooperate with tasks involved in the study.
- Patients should have been evaluated for the suitability, and implementation, if suitable, of behavioral interventions to reduce tic severity.
If I sign up for DBS, is a commitment required?
DBS requires a significant time commitment, and patients and families must be motivated to undergo not only the procedure but also the challenges associated with the pre-operative workup and the significant follow-up after the procedure. The family must be willing to return for multiple evaluations and they must realize that the average patient may be programmed 4-8 times in the first six months following surgery. Most experienced centers have begun to shy away from performing DBS in patients unless there is a spouse or a committed caregiver (especially a caregiver that can provide travel). Many patients and families are under the erroneous impression that DBS therapy is a “light switch,” and once they are turned on the journey comes to an abrupt and miraculous end. The truth is, that following activation of the device there are still many battles to be endured with both DBS programming (there are thousands of potential settings), and medication changes. Patients and families must be willing to agree to multiple programming and to medication adjustments. Patients can ultimately become DBS failures simply from a lack of commitment to the process.
What have been the results of DBS to date?
The largest open label (non randomized control study) study of Tourette Syndrome DBS utilized a single brain target and was published in a recent issue of the Journal of Neurology, Neurosurgery and Psychiatry. Although three targets have been tested in small series for Tourette Syndrome, the authors of the largest work focused on a part of the brain called the centromedian-parafascicular complex of the thalamus (CM). Other parts of the brain including the internal globus pallidus (GPI), external globus pallidus (GPE), and the anterior limb of the internal capsule (ALIC) have also emerged as potentially effective areas for amelioration of medication refractory tic, however they have been less studied. The authors reported DBS significantly decreased motor tics, in 18 patients, but the therapy was less effective for phonic tics. The therapy was commented to not be as “promising” as the authors had hoped in addressing behavioral manifestations of Tourette Syndrome, despite improvements on the social scale of the Yale Global Tic Rating Instrument. Many groups are experimenting with differing targets and approaches to Tourette Syndrome DBS and to date there is no consensus except that motor tic responds better than behavioral manifestations of the syndrome.
What are the complications of DBS?
DBS has short and long term “potential” complications. The DBS device is a “foreign body” in the brain and under the skin so infection is a primary worry, and can occur in 5% or more of implanted patients. One of the biggest worries is that the during placement of the DBS electrodes there will be bleeding or alternatively a stroke that may lead to weakness, numbness, changes in vision, and/or changes in speech. The DBS device can fracture/break, migrate out of position, or malfunction requiring an another surgical procedure to replace or reposition the electrode. DBS frequently affects speech, and particularly verbal fluency (getting words out of the mouth). There can be worsening of cognition or mood, and in rare cases associated suicidal thoughts (another reason why patients must be carefully screened and followed).
The largest risk of a DBS procedure is failure to achieve the patient’s pre-operative expectations, and this is why it is absolutely critical that both patients and physicians have focused pre-operative discussions.
What is the future of DBS for Tourette Syndrome and where are the research studies being conducted?
What is needed for DBS to move forward as a viable therapy for severe TS are carefully controlled studies. These studies should be undertaken by experienced multidisciplinary teams, and should be guided by experts in performing clinical trials. Evaluations should be performed by blinded raters. Despite the positive results of this and other studies, we must learn the lessons which have resulted in DBS failures in other disorders, and make serious early attempts to avoid them in TS. Currently we are aware of two centers that have received FDA investigational device exemptions to perform Tourette DBS studies in the United States (Case Western, Cleveland OH, and University of Florida, Gainesville); U of F also has with a NIH-funded study of DBS). There may be other centers with FDA and/or institutional review board clearance to perform DBS, and as we become aware of these centers we will post them to the website
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