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Deep Brain Stimulation for Dystonia: What You Need to Know

Article for Spasmodic Torticollis Magazine & Website

 

DEEP BRAIN STIMULATION FOR DYSTONIA: WHAT YOU NEED TO KNOW

William J. Marks, Jr., M.D.

Associate Professor of Neurology
Medical Director, Center for the Surgical Treatment of Movement Disorders
University of California, San Francisco

Director, Center for Parkinson’s Disease & Movement Disorders
San Francisco Veterans Affairs Medical Center

 

Introduction

Deep brain stimulation uses an implanted medical device to deliver precisely targeted electrical stimulation to the brain to treat the symptoms of movement disorders.  The treatment, also known as DBS or by the brand name of Activa Therapy (Medtronic Neurological), is approved by the Food and Drug Administration in the United States to reduce the symptoms of tremor disorders and Parkinson’s disease.  Deep brain stimulation is available under a more limited approval, called a humanitarian device exemption (HDE), to treat certain forms of dystonia.  There is considerable experience with the use of DBS to treat tremor and Parkinson’s disease—with more than 30,000 patients treated worldwide.  Significantly less experience exists, however, in using DBS to treat various forms of dystonia, including cervical dystonia (spasmodic torticollis), although this is an evolving area about which knowledge is rapidly accumulating.  About 500 patients with dystonia throughout the world have received DBS thus far.  The goal of this article is to review what DBS is, what results might be expected, and when it might be reasonable for an individual to consider DBS for the treatment of cervical dystonia.

 

DBS: The Device and The Surgery

Deep brain stimulation uses a device with three implantable components: brain leads, neurostimulators, and extension wires (see figure).  The DBS leads, containing an array of four electrodes on each tip, are implanted into the deep brain targets, usually for dystonia in an area of the brain called the globus pallidus internus (GPi), during a neurosurgical procedure.  The neurostimulators (also called implantable pulse generators and sometimes called the “pacemakers”) are implanted under the collarbone, though they can be located elsewhere.  Extension wires, tunneled under the skin, connect the brain leads to the neurostimulators.  All of the device components are fully implanted under the skin; there are no external wires.

The specific techniques used for DBS surgery vary somewhat between the centers that offer this therapy, but procedures are generally similar.  The first part of the surgery, during which the brain leads are implanted, is performed using an external reference system attached to the patient’s head.  This often consists of a rigid metal frame (called a stereotactic head frame) mounted to the skull on the day of surgery but sometimes consists of small markers temporarily embedded into the surface of the skull and an apparatus attached at the site of entry into the skull (called a frameless system).  A brain scan (MRI and/or CT scan) is performed prior to or on the day of surgery.  This scan, in conjunction with the coordinates on the frame or frameless system, allows the surgeon to locate the areas into which the DBS leads will be inserted.  This part of the surgery is often performed with the patient receiving light sedation and local numbing medicine at the area of the incisions, although the procedure can be performed under general anesthesia with the patient fully asleep in situations where dystonic postures are extreme or in young children.  After a strip of hair just behind the frontal hairline is shaved, one or two incisions are made in the scalp.  Next, small holes, each about the diameter of a quarter, are drilled to allow the surgeon access to the brain.  Equipment is mounted on the frame or frameless system that allows the surgical team to insert instruments into the brain in a precisely controlled manner.  At this point, sedation is turned off and the patient is awake while recordings of brain activity are made using very fine electrodes (called microelectrodes).  This mapping of brain activity allows the surgical team to identify very precisely the part of the brain controlling movement.  This part of the procedure is usually done with the patient awake, since the patient may be asked to move an arm or leg to activate these brain areas and later asked about side effects during test stimulation.  Once the ideal site is identified, the actual DBS lead is inserted into this spot.  The same mapping procedure is then performed on the opposite side of the brain, with insertion of a DBS lead on that side.  Once the leads are in place, they are connected to a temporary external stimulator, and with the patient awake on the operating room table, stimulation is turned on.  The intensity of stimulation is gradually increased, and patients are examined and asked to report any side effects they may perceive, such as tightness of the face, arm, or leg; change in speech; visual changes; or other symptoms.  During this testing, levels of stimulation that exceed those needed to treat the patient’s symptoms are tested in order to determine the level at which side effects occur.  Thus, the goal is to deliberately produce mild and temporary side effects to ensure the DBS lead is in the proper position.  It is important for patients to realize that these side effects will go away when the stimulation is turned down and that most patients do not observe any improvement in their dystonia symptoms during this testing in the operating room.

Once testing is completed, the neurostimulators and extensions may be placed (typically with the patient asleep under general anesthesia) right away, or the patient may come back to the hospital a few days or weeks later for this stage of the operation.  Most patients remain in the hospital for 1-2 days following their brain surgery.  For those patients who receive the neurostimulator implant at a later time, this is usually done on an outpatient basis.  Healing usually takes a few weeks, during which time patients may experience some headache and soreness at the site of the incisions and where the extension wires have been tunneled.

 

Days to weeks after device implantation, stimulation is activated.  Using the DBS programmer, the clinician can non-invasively select which electrodes on the DBS lead to use to deliver stimulation, as well as the stimulation settings themselves (including amplitude, pulse width, and frequency of stimulation).  Usually the one or two electrodes within, or closest to, the motor controlling region of each GPi are activated.  Typical stimulation parameters include amplitude of 2.0-4.0 Volts, pulse width of 90-450 microseconds, and frequency of 135-185 Hertz (stimulations per second).  Beneficial effects commonly take weeks or even months to become evident.

Following activation of stimulation, some patients may experience a transient worsening in dystonic spasm that necessitates a reduction in stimulation intensity.  As acclimatization to stimulation occurs, stimulation parameters can then gradually be increased.  The time course for response varies among patients; some exhibit rapid improvement in dystonic signs, but in most patients there is a lag of days, weeks, or even months after initiation of stimulation until improvement is seen, with full benefits sometimes taking many months to be seen.  It is not currently understood exactly how DBS can help the symptoms of dystonia.  It is known that in dystonia the function of motor controlling circuits in the brain, including the globus pallidus, is disturbed.  The electrical stimulation provided by DBS may block the abnormal brain activity that is taking place or may somehow override the abnormal activity and allow motor controlling circuits to function in a more normal manner.

Modern surgical techniques used in DBS surgery have become very sophisticated, and DBS surgery is safe—although not risk free.  It is important that individuals potentially interested in DBS talk with their DBS team about the complications seen at their center and the rates at which they have occurred.  An uncommon but serious complication of the surgery itself is bleeding in the brain, which occurs in about 1-2% of surgeries.  If this occurs, it almost always does so at the time of the surgery, although rarely bleeding in the brain can occur within days after the procedure.  If bleeding in the brain occurs, no symptoms may be produced and the bleeding may only be discovered on a brain scan obtained after the surgery.  The bleeding can, however, produce significant and permanent stroke-like symptoms, such as weakness, problems speaking, or difficulty thinking.  Another complication of surgery is infection, occurring in about 3-4% of patients.  When infection occurs, it tends to occur weeks to months following the surgery, requires treatment with intravenous antibiotics, and often necessitates removal of one or more of the DBS device components.  Following successful treatment of the infection, repeat surgery can usually take place to implant new device components.  Another complication of DBS surgery is suboptimal positioning of the DBS lead.  Despite the meticulous imaging and mapping techniques used for the surgery, the DBS lead may end up several millimeters away from the desired location, preventing the patient from achieving adequate benefit.  A suboptimally located DBS lead is readily identifiable on a post-operative brain scan, which shows the exact location of each brain lead.  In such a situation, insertion of a new DBS lead into a more desirable location is usually required. 
Besides complications from the surgery, the brain stimulation itself may produce side effects.  These can usually be reduced or eliminated by adjustment of the stimulation settings and electrode selections.

 

Results & Expected Outcomes of DBS for Cervical Dystonia

Deep brain stimulation has only recently been used to treat dystonia, and thus efficacy and outcome data are relatively limited and continue to evolve.  The majority of patients worldwide have been treated with DBS directed at the globus pallidus internus, though other brain targets (thalamus and subthalamic nucleus) have been used.

Patients with primary generalized dystonia, in which dystonia is not caused by brain injury and affects the whole body, seem to experience the most predictable and dramatic benefit from DBS.  Outcomes in primary generalized dystonia treated with DBS have been documented more than in any other form of dystonia to date.  Accumulating evidence supports the efficacy of globus pallidus deep brain stimulation for cervical dystonia in some patients.  Most reports thus far consist of individual case reports or series with small numbers of patients, although larger and multi-center studies are underway.  The vast majority of patients have been treated with bilateral stimulation (stimulation on both sides of their brain).  Average improvement in the standardized clinical rating scale used to assess cervical dystonia (the Toronto Western Spasmodic Torticollis Rating Scale, or TWSTRS) ranges from a 48-76% reduction in the overall severity of symptoms.  Average improvements in disability and pain scores range from 60-75% and 38-100%, respectively.  Despite these favorable overall improvements, some individual patients fail to experience any meaningful benefit.  Some patients with modest improvement in the extent of neck pulling nevertheless report significant improvement in the pain associated with their cervical dystonia.
 

When to Consider DBS for Cervical Dystonia

Initial treatment of cervical dystonia is always with medication.  Commonly used oral medications include anticholinergic medications, baclofen, benzodiazepines, and dopaminergic drugs.  For cervical dystonia, local treatment with botulinum toxin (type A or B) can be highly effective.  These treatments do have limitations in some patients.  Oral drugs are often only modestly effective in suppressing dystonic symptoms, and the side effects of these medications commonly impose a dose ceiling for their tolerable use.  Treatment with botulinum toxin injections may provide a robust effect initially, but this may wane over time, and some patients never achieve an adequate level of symptom control with this strategy.  For patients with dystonia in whom symptoms are inadequately controlled with oral medications and optimized botulinum toxin injections, the use of deep brain stimulation may provide improved symptom control and enhanced functional capacity.

People with cervical dystonia may wish to consider DBS if
Their dystonic symptoms (pulling and pain) are sufficiently troublesome to interfere with daily functioning
They have tried appropriate oral medications and botulinum toxin administered in an appropriate manner without adequate relief of symptoms
They are free from serious health problems that would make the surgery too risky
They understand and are willing to accept the potential risks of surgery, including potentially serious and permanent complications
They are willing to cooperate with awake brain surgery
They are willing to return for repeated adjustments of the DBS system
They have realistic expectations about the outcome from DBS, understanding that they may experience minimal or no benefit from DBS
They understand that benefit may take time (months to many months) to occur
They understand issues related to their device, including the need to take certain precautions, the possibility of device breakage or malfunction, and the need to have their neurostimulator replaced (a brief outpatient procedure not involving brain surgery) when the battery nears the end of service (typically after 1-3 years)

 

Conclusions & Suggested Resources

For some patients with cervical dystonia experiencing disabling symptoms despite treatment with oral medications and botulinum toxin injections, deep brain stimulation is a treatment alternative that may provide significant improvement in symptoms.  Although DBS does not cure dystonia, for many patients DBS can suppress symptoms to allow a higher level of function and less discomfort.  Though not risk-free, DBS surgery is relatively safe, and the ability to adjust the stimulation settings can allow clinicians to maximize symptom control and minimize side effects.  Centers specializing in DBS for tremor disorders and Parkinson’s disease may or may not have significant experience in using DBS to treat dystonia, and individuals contemplating DBS should discuss with their prospective DBS team their experience, complication rates, and outcomes in using DBS to treat dystonia.

Additional information concerning DBS for the treatment of dystonia can be found at the Medtronic website  www.newhopefordystonia.com.