Deep Brain Stimulation for Dystonia
Deep Brain Stimulation for Dystonia
Erwin B. Montgomery Jr. MD
Dr. Sigmund Rosen Scholar in Neurology
Professor of Neurology
University of Alabama at Birmingham
September 21, 2011
Deep Brain Stimulation (DBS) is a remarkable therapy for dystonia, succeeding when all manner of medications and botulinum toxin injections have failed. To be sure, intra-muscular injections of botulinum toxin are the preferred treatment for focal dystonia, such as cervical dystonia. But when these injections fail or the number and distributions of involved muscles is too great, DBS is a good option. While most patients do not get sufficient benefit from medications, it is important to exhaust the medication options because the small but significant surgical risks.
DBS consists of implanting electrodes into certain targets in the brain. The usual target is a part of the brain called the globus pallidus interna. The electrodes are placed through a small opening in the skull about the diameter of a quarter. The other end of the electrode exits the skull and travels beneath the skin to an extension wire placed under the skin just behind the ear. This extension wire tunnels under the skin to an implanted pulse generator (IPG) under the skin over the chest. The IPG is much like a heart pacemaker. The IPG can be programmed to change the electrical stimulation of the brain. The IPG is mostly battery that will run out in four to five years depending on how much electrical energy is required for stimulation. For patients whose battery runs out quicker a rechargeable battery is available. Unfortunately, the rechargeable IPG is very expensive and most insurers and hospitals are reluctant to cover the additional cost, even if it may save repeated surgeries to replace non-rechargeable IPGs.
Getting the electrodes into exactly the right location is critically important. There are two general ways this is done and relate to whether or not microelectrode recordings of neuronal activities are used to locate the best target – Neurons communicated with pulses of electricity that can be recorded with the microelectrodes. By listening to the communications between neurons the neurophysiologist can determine where the electrode actually is and if not in the proper location, in which direction to move to find the best location. The use of microelectrode recordings does require experts but there are relatively few experts available. Also, the use of microelectrodes does add time and slight risk to the surgery. As a result some surgeons do not use the experts or the microelectrode recording and depend only on the MRI scans. In the opinion of this author, the use of MRI scans alone is not sufficient and there is considerable risk of not getting the electrodes in the right location. The consequence might be that the patient does not benefit and a second operation may be necessary to reposition the electrodes into the proper location. Again, in the opinion of this author, the additional time, expense, and slight risk is well worth it because microelectrode recordings give great assurance that the DBS electrodes will be in the optimal location. It is important for the patient, family and/or caregiver to discuss with the potential neurosurgeon whether or not he or she uses microelectrode recordings.
Because the DBS electrodes are placed through a small opening in the skull, the surgeon never actually sees the target. However, the surgeon knows roughly where the target is based on internal landmarks in the brain. These landmarks are the Anterior Commissure (AC) and the Posterior Commissure (PC). The surgeon must align these landmarks inside the brain with landmarks outside the head that the surgeon can see. This is done by placing a frame around the head and then the patient has an MRI scan with the frame in place. The MRI scan shows both the landmarks outside the head and the landmarks inside the brain. Now first the microelectrode and then the DBS electrode can be aligned with the landmarks outside the head such that the electrodes will reach the proper target relative to the landmarks in the brain.
The use of microelectrode recordings for refinement of the target location generally has to be done with the patient awake. During the recordings the patient is asked to make certain movements while neuronal activities are being recorded and analyzed. In addition, test electrical stimulation through the microelectrode is done and the patient asked to report any sensations. Interestingly, the brain does not feel pain. The scalp and covering of the skull is pain sensitive but these areas are anesthetized just as in a dentist’s office. Under certain circumstances the surgery with the microelectrode recordings can be done with the patient under a special anesthesia.
Most centers perform the surgeries in two stages. The first stage is to implant the DBS electrodes as described above. The second surgery is very brief and can be done with the patient asleep. This surgery is to tunnel the extension wire and to connect and place the IPG. Typically, the DBS system is turned on about one to two weeks later.
DBS programming can be complicated and therefore, it is critically important that the proper arrangements for post-operative DBS programming are in place before the DBS surgery. Unfortunately, there are no formal educational certifications for healthcare professionals in DBS programming so it is important for the patient, family member and/or caregivers to enquire as to the potential programmer’s experience.
Programming the DBS system is particularly complicated in dystonia. Even though most patients get a 70 to 80% improvement, it often takes months for the improvement to occur. This means that the patient, family member, and/or caregiver and the DBS programmer must be patient.
As can be appreciated from the above, DBS is complicated and requires a team with diverse skills. First, the movement disorders neurologist must determine whether or not the patient is a candidate for DBS. Second, the surgeon must perform the surgery in cooperation with the intra-operative neurophysiologist (preferably also a movement disorders neurologist) who does the microelectrode recordings, and the healthcare professional, such as a nurse practitioner or physician assistant, who performs the DBS programming under the supervision of the movement disorders neurologist. Successful DBS depends on the skills of the team and the skills depend to a large degree on the experience of the team. As with any skill, maintenance of those skills requires continued practice. This author finds it difficult to believe that any surgeon and team that perform less than 12 DBS surgeries per year can maintain optimal skills. Thus, it is very important for the patient, family member, and/or caregiver to enquire as to the surgeon’s and team’s ongoing experience in DBS surgery.
In deciding whether or not to have DBS, the patient, family member and/or caregiver need to decide whether a 70 – 80% improvement is worth taking a 3 -4% chance of a complication such as loss of strength, speech or changes in thinking and personality. The two main sources of risk are bleeding or stroke in the brain because the electrodes injure a blood vessel. Bleeding bad enough to cause a complication occurs in 1 – 2% (or 1 to 2 times out of 100) of patients. The second major concern is the risk of infection. About 1 – 2% patients will have an infection where the DBS electrode enters the skull. This poses a significant risk and often the DBS system has to be removed in order to allow the infection to be eradicated. Death can occur but this is extremely rare.
Who should consider DBS? Anyone whose quality of life is limited by their dystonia should consult a movement disorders neurologist expert in DBS. This does not mean that the patient automatically should have DBS. Often, the movement disorders neurologist is able to suggest alternative medications or different approaches to botulinum toxin injections. Most movement disorders neurologists would much rather see patients even if they don’t need DBS than to miss a patient who needs it but does not see the neurologist.
The criteria used by movement disorders/DBS neurologist are: 1) the patient has true dystonia; 2) they have exhausted all reasonable attempts at intra-muscular injections of botulinum by neurologists expert in botulinum toxin injections; 3) they have exhausted all reasonable attempts at medications; 4) their cognitive abilities such as memory and thinking are relatively intact; 4) their general health is good such that there are not added risks to surgery; and 5) the patient has ready access to experts in post-operative DBS programming.
The patient should have true dystonia. Dystonia causes abnormal postures in the affected body parts such as the head and neck or arm. Postures can be caused by musculoskeletal abnormalities such as severe arthritis, and these are not likely to be improved with DBS. Postures can be caused by sustained neuronal driving of the muscles. Many different neurons can drive muscles to produce abnormal postures indistinguishable from dystonia. To the best of our knowledge, only abnormal activity from the part of the brain called the basal ganglia is treatable by DBS, at least currently. Sometimes, patients may have dystonia as well as musculoskeletal abnormalities and the movement disorders neurologists must take some measures to determine which is the main problem.
Patients must either have a type of dystonia for which intra-muscular injections of botulinum toxin are either impractical or have proven to be ineffective. Effective use of intra-muscular botulinum toxin is a skill and like every skill depends on training and experience. Consequently, before recommending DBS, the movement disorders/DBS neurologist needs to assure everyone that the patient has had an adequate trial of intra-muscular injections of botulinum toxin in the hands of an expert.
Patients must exhaust all reasonable attempts at medication therapies. The difficulty is deciding what reasonable attempts are. For example, a medication may have a very low probability of helping and often may not be tried. However, no one wants to have a patient go to DBS surgery, experience some complication, and then recriminate themselves because that medicine was not tried before surgery. Medications that should be considered include: 1) anti-cholinergic such as trihexyphenidyl or benztropine; 2) carbidopa/levodopa; 3) dopamine antagonists, such as haloperidol; 4) dopamine depleting agents, such as tetrabenezine; and 5) baclofen. Also, it is important to know not only whether these medications were tried but also the maximum dose tried, to assure an adequate trial, and any side effects experienced.
DBS itself rarely causes problems with thinking or memory and if it does, worst case scenario, the DBS is turned off. The larger concern is injury to the brain while en route to the target. Typically, the DBS trajectory goes through the frontal lobes. Inadvertent injury to the frontal lobes, particularly if it occurs on both sides of the brain, can cause significant thinking and personality problems. It is possible and perhaps probable, that patients already experiencing difficulties with thinking, memory or personality may be at greater risk for worsening of these problems. That is not to say that patients with these problems should not have DBS surgery but rather, they need to carefully consider the increased risks and potential benefits.
DBS is very effective and reasonably safe. As in any medical decision, it is a balance between the risks and potential benefits. Everyone weighs the risks and potential benefits differently. It is not the prerogative of the physician to make that decision for the patient, family members and/or caregivers. Unfortunately, some physicians make recommendations on their assessment of the risks and benefits but how can they do that when they don’t even know what the patient is suffering. Rather, the responsibility of the physician is to educate the patient, family member, and/or caregiver and allow them to make an informed decision. One of the most frequent complaints from patients, family members and caregivers is “why did we wait so long”.
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