Deep Brain Stimulation (DBS) for Dystonia

Deep brain stimulation (DBS) is a neurosurgical procedure that has been used to treat many movement disorders, including dystonia. Dystonia is a neurological disorder characterized by involuntary muscle contractions resulting in repetitive movements, abnormal postures, or both. Surgery would be considered after the effectiveness of medications and other rehabilitation interventions diminish. DBS has been developed, and its effectiveness established, as a treatment for dystonia, and is approved, using a "humanitarian device exemption," from the Food and Drug Administration (FDA) for specific forms of dystonia. Deep brain stimulation first received FDA approval for the treatment of tremors in Parkinson's disease in 1997, and 2002, extended to address the advanced movement disorders of Parkinson's disease.

Explanation of How Deep Brain Stimulation is Used for Dystonia

Deep brain stimulation involves surgically implanting a device that emits electrical signals to specific brain areas regulating movement. For dystonia, that area is usually the globus pallidus internus (GPi). The GPi is a deep part of the basal ganglia, a group of nuclei important for regulating motor function. Deep brain stimulation is delivered by controlled electrical current to help normalize abnormal brain activity and reduce involuntary muscle contractions inherent in dystonia.

The DBS system has three components:

• Leads (Electrodes): These are multiple very thin insulated wires that are implanted directly into the GPi. An imaging technique such as an MRI or CT scan will be used to assist in the placement of the leads in the appropriate targets.
• Implantable Pulse Generator (IPG): A battery-operated device implanted under the skin, usually in the chest region. The IPG produces the electrical impulses sent through the leads to the brain.
• Extension: The extension is a wire that connects the IPG to the electrodes, and is tunneled under the skin for connection to the electrodes from the chest to the head. 

The electrical stimulation is able to modify the generalized pallidum, modifying neural activity, which in turn helps alleviate the abnormal signals that lead to dystonia. While deep brain stimulation does not cure or slow the progression of dystonia, it can result in a significant reduction in symptoms. Even with progression of the disease, DBS provides consistent symptom relief, providing nearly identical levels of percent improvement.

Types of Dystonia: 

Based on the type of dystonia, there are various levels of effectiveness observed out of deep brain stimulation:

• 1. Primary/Hereditary Dystonia: Such as torticollis, also known as cervical dystonia, and DYT1 dystonia, or dystonia musculorum deformans, are primariliy genetic; and respond well to DBS. Patients will most likely find these forms of dystonia do resolve with significant relief of dystonia symptoms, often stated as experiencing a good percentage of improvement from studies at anywhere from 80-99%. 
• 2. Tardive Dyskinesia: Because this movement disorder may result from prolonged exposure to a medication, drugs, or act deceptively as normal movement, there are random abnormal movements of the face, mouth, and eyes. DBS can help with reducing these sympathetic abnormal movements at the level of 80% in these patients quite often. 
• 3. Secondary Dystonia (Dystonia associated with Cerebral Palsy): Secondary dystonias may be defined as abnormal movement as a result of a brain injury of some neurological disorder, such as cerebral palsy. Upon treating children with cerebral palsy and resultant secondary dystonia with DBS, we often observe less substantial but still limited response of any improvement ranging from 10-20% of treatment. Though with clinical experience and more study, we continue to explore this hypothesis regarding the most beneficial treatment using the device for secondary dystonia. 

Assessment of DBS surgery candidates

The choice to pursue DBS surgery is an important one that needs careful assessment. The following group of patients are generally the most favorable candidates for DBS:

• Patients with Genetic Dystonia: Patients with hereditary dystonias such as DYT1 will benefit tremendously from DBs surgery if it is done early enough. Early treatment can stop permanent skeletal deformities that occur from having to endure protracted abnormal contractions of the muscle (especially for children), and surgery should be performed before these deformities become permanent.
• Adults with Cervical Dystonia (Torticollis): Patients who do not respond to medicines if medicine, botulinum toxin, and/or do not tolerate medicines may wish to consider DBS surgery. Surgery would especially be helpful for patients with pain or severely unusual head and neck movement who are suffering through a significant amount of disruption from their daily life.
• Patients with Tardive Dyskinesia: DBS surgery can be an alternative therapy when medicines are not an effective therapy or do not control their symptoms well. DBS can reduce a variety to almost no movements and improve quality of life for patients. 

Patients Who May Not Be Candidates for DBS Surgery

Not every dystonia patient will be an appropriate individual for DBS surgery. There are various settings or reasons that may not render the procedure ideal: 

• Poor Health: Patients that are too ill to receive surgery, possibly with some severe heart or lung issue, may not be a suitable candidate for this intervention.
• Secondary Dystonia due to Cerebral Palsy: Dystonia specifically from a cerebral palsy, given typically little improvement with standard dystonia therapy, may not justify surgery related complications and risks. Each of these patients must be evaluated on a case by case basis.
• Dependent on Cardiac Devices: Any potential consideration regarding cardiac pacemakers or defibrillators must be evaluated carefully. Generally, it is safe to implant DBS generators greater than 8 inches apart from cardiac devices. However, whether a cardiac device would be affected may impact whether to perform DBS. If the cardiac device is necessary for survival, then DBS is not advised.
• Requires Regular MRI for Scans: Both the DBS systems and the scans themselves can be dangerous and effectively damage to brain tissue when combined, and because one needs a regularly recurring MRI, the patient may need to reconsider DBS; with that considered, a regular head MRI may be done, but not recommended, patients will require the indicative head scan under specialty head MRI caps.
• Taking Anticoagulant Medications: For patients on blood thinners or medications such a Coumadin or Aggrenox, increased risk related to surgery may require consideration by the healthcare provider. Each time a patient may need to discontinue them, needs to be evaluated. 

Timing Challenges of DBS Surgery

The timing of DBS surgery is important to maximize the benefits of surgery:

• Genetic Dystonia: Early intervention is important to limit long-term bone deformity, notably for children. Surgery should be considered once the movement disorder leads to a significantly poor quality of life.
• Adult-Onset Dystonia: The patient should consider surgery when symptoms are no longer possible to control with medications or other interventions such as botulinum toxin injections.
• Tardive Dyskinesia: Surgery might become warranted once patients fail to respond to standard medical therapies.

Expected Outcomes and Benefits of DBS for Dystonia

DBS can provide important improvement in excess movements and posture, and the time from initiation of DBS to maximum benefit can vary from a few days to a few months. Unlike most movement disorders, dystonia symptoms may take somewhat longer to respond to DBS. Improvement can range from 3 months to 12 months.

• Genetic Dystonia: Several studies have shown an improvement of 80-99%. DBS is an effective device for these patients. A major outcome is reducing muscle contractions, however improved activity is a hallmark of this group.
• Cervical Dystonia (Torticollis): Patients will frequently report 40-60% improvement. Pain relief; improvement of the neck turning (torsional distribution) is common, however improvements in either domain can be variable. Patients may respond to treatment for one (e.g. pain) but not the other (e.g. tension distribution).
• Tardive Dyskinesia: Almost all patients report a marked improvement in excess movements; around 80% will experience a positive benefit. 
• Secondary Dystonia (e.g., Cerebral Palsy): The response is generally modest, with improvements ranging from 10-20%. These outcomes suggest that while DBS may offer some benefits, it is not a universal solution for all forms of dystonia.

Possible Dangers and Consequences of DBS Operation

As with every surgical operation, there are risks associated with DBS usage. Being aware of these risks can help patients make an informed decision. 

• Intracranial Hemorrhage: The risk of bleeding in the brain ranges between 1% - 3%, which could lead to devastating problems like speech loss, paralysis, coma, or even death.
• Infection: Approximately 5% of patients will develop an infection in the surgical area, and more than likely the DBS system will need to be extracted.
• Device-Related Issues: Occasionally DBS will produce little to no benefit for safety reasons. Generally, this is due to suboptimal hits or leads being positioned. If this occurs the patient may require a revision surgery to reposition the electrodes. 
• Anesthesia risks: Anesthesia risks are varied depending on the patient's overall health and medical history; they can involve reactions to the anesthesia or complications involving the surgical procedure. 
• Hardware Failure: There are rare complications of device malfunction, lead erosion, battery failure, etc. When this occurs surgical intervention may be necessary to repair or replace the component. 

Pre-Operative Assessment for DBS

Before undergoing the surgery procedures, patients typically go through a pre-operative evaluation for possible DBS surgery. This evaluation process typically involves: 

​​Initial consultation. The patient should call the DBS team and request a pre-assessment, during which they will receive educational materials regarding the procedure itself, best outcomes, and ramifications involved. 

Review of medical history. Clinical notes will be requested from the patient's neurologist and primary care doctor for assessment of general medical history as it relates to the history of dystonia.

Neurological Assessment: Obviously, if the patient has not been evaluated previously, the next step is to get a consult with a neurologist with specialty training in movement disorders. The evaluation initially will confirm the patient's diagnosis and determine whether or not a DBS has potential benefit.

Imaging. MRI or CT scans will be conducted to map the target area of the brain before the DBS electrodes are placed. This provides for accurate placement of the electrodes in the brain. 

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After DBS surgery, patients require a recovery interval to recuperate from the surgical procedure. Changes in the settings of DBS are usually done over several weeks to maximize symptom control and device benefit. Follow-up visits from the DBS team are crucial to monitor and adjust settings, battery life checking as well as address any issues or side effects. Resumen La estimulacin cerebral profunda ha emergido como una terapia prometedora para ayudar a controlar las formas de distona ms refractarias, logrando mejoras importantes en la sintomatologa y calidad de vida asociada. DBS is not a cure, but it can be particularly effective when symptoms are no longer well controlled by medications or other treatments. With the correct choice of suitable patients and intervention time, DBS is able to provide long-term advantages for those experiencing this most pernicious neurological disorder. Ongoing research into DBS technology and techniques has the potential to improve both efficacy and safety, raising hopes for a growing number of dystonia patients in years ahead.