Deep Brain Stimulation for Cervical Dystonia (Spasmodic Torticollis)
Erwin B. Montgomery Jr., MD
Department of Neurology
National Primate Research Center
University of Wisconsin-Madison
December 15, 2004
Deep brain stimulation (DBS) recently has been approved by the Federal Food and Drug Administration (FDA) on the basis of a Humanitarian Device Exemption. This means that although DBS for cervical dystonia has not undergone the same rigorous clinical testing as DBS for Parkinson's disease, there is considerable evidence for safety and effectiveness of DBS for cervical dystonia. Reviewing many of the reports in the medical journals, 29 patients were described as having DBS and all 29 were reported to have significant improvement. This is welcome news for the many patients who do not get adequate relief from medications or botulinum toxin injections.
There are risks to DBS surgery; approximately 2% or 2 patients out of 100 will have a serious and/or permanent complication such as paralysis, loss of speech, changes in thinking memory or mood. Most often this is due to bleeding inside the brain or a stroke because the electrodes injure blood vessels. Although it would be exceptionally rare, there is the very slight chance of death. However, when patients are considering DBS not only do they have to weigh the risks of doing the surgery but they also have to weigh the risks of not doing the surgery. For many patients, not doing the surgery means continued suffering and disability from the cervical dystonia.
How is DBS surgery done? DBS requires the permanent implantation of electrodes deep in the brain. The most common target is the globus pallidus. This structure is approximately 4 to 5 inches deep in the brain and is approximately the size of a peach pit. The electrode is placed through a hole made in the skull about the size of a quarter. The surgeon never actually sees the target. However the surgeon knows that the approximate location of the globus pallidus relative to certain landmarks in the brain that the surgeon can see on CT or MRI scans. For example, the location of the GPi target is estimated to be 2-3 mm to the front, 20 mm to the side, and 5 mm below a midpoint in the brain that can be seen on the CT or MRI scan.
The surgeon needs to create landmarks outside of the brain that will line up with the landmarks inside the brain seen on CT or MRI scans. Most surgeons temporarily attach a metal frame to the outside of the head. The patient undergoes CT and/or MRI scans with the metal frame in place. The metal frame and the internal landmarks in the brain show up on the CT and MRI scans. The surgeon then lines up marks on the external frame that align with internal landmarks. Then the surgeon lines up the electrodes on the external metal frame which will point exactly at the target inside the brain.
While this method of aligning the external and internal landmarks is highly accurate, it is not accurate enough. That is why all experts offering this surgery use an additional method to find the exact target. This method requires recording the electrical activity generated by individual neurons. In the brain, neurons communicate or speak to each other with tiny sparks of electricity. Physicians first use temporary electrodes, called microelectrodes, with microscopic tips to record the electrical conversations of individual nerve cells. The tip of the electrode is about the size of three red blood cells placed side-by-side. When the right conversation is heard, the physician then knows where to place the permanent DBS electrode. In order to get the neurons talking about the right things, the physician in the operating room has to activate the neurons. This is done by moving or asking patients to move their arms, legs or hands.
The microelectrode recording of individual neurons is critical to the success of DBS surgery. While the FDA approved the implantation of DBS electrodes, the FDA does not rule on or supervise how the electrodes are implanted. Unfortunately, there are some surgeons who do not use microelectrode recordings and it is the opinion of most experts that their patients are less likely to get the maximum benefit with the minimum risk of complications. Consequently, it is up to the patient to be sure that wherever they have surgery, it is done by surgeons who employ microelectrode recordings.
The physician in the operating room also checks to see if stimulation through the electrode is going to help the patient or at the least, not cause any side effects. This means that the patient has to be awake in order to tell the physician what he or she is experiencing with the stimulation. Once the proper target is found, the permanent DBS electrode is put in place. The hole is filed by a plastic cap, the loose ends of the DBS lead tucked under the scalp and the incision is sown closed.
One might think that it would be very painful to be awake and have electrodes placed in the brain. It is a remarkable fact that the brain itself does not feel pain. What can cause pain are the skin and the covering of the bone of the skull. The surgeon injects anesthetics into the scalp much like a dentist does when working on a tooth. Just as during the dental procedure, the patient feels pushing and pressure but not sharp pain, the same is true for DBS surgery.
The usual course of events is as follows. The patient is admitted to the hospital early in the morning. The surgeon places the external metal frame onto the head. The frame is held in place by four sharp pins that pierce the skin and hold onto the bone of the skull. First, local anesthetic is injected into the scalp where the pins are to be placed. Once the metal frame is in place the patient undergoes a CT scan and MRI scan and then is taken to the operating room. There the patient lies on a table and the metal frame rigidly attached to the table so that the head will not move.
Next, the scalp on the top of the head is anesthetized. Then an incision approximately 3 inches long is made on each side of the top of the head. The incision is opened to expose the skull. Two small holes, one on each side, are drilled. Then the temporary microelectrodes are mounted onto the frame and the microelectrodes advanced into the brain. The electrical activity of neurons are recorded and tested as described above as the microelectrode is advanced. Often it takes multiple microelectrode passes in order to determine the exact location for the best placement of the permanent DBS electrode.
Once the best location is determined by the microelectrode recordings, the temporary microelectrodes are removed and the permanent DBS electrode is placed into the brain. The permanent DBS electrode is then connected to an external version of the impulse generator (pacemaker-like device) that will later be placed under the skin over the chest. The permanent DBS electrode undergoes test stimulation to be sure that the patient will tolerate stimulation later. If the patient tolerates the test stimulation, the permanent DBS lead is locked into position. The loose end is placed under the scalp, the incision is closed and the patient is moved from the operating room to his or her hospital room. This surgery may require 6 to 8 hours on average. Patients typically are discharged 2 to 3 days later.
Usually, one to two weeks later, the patient returns to the hospital for placement of the internal impulse generators (stimulators). This is done with the patient asleep under general anesthesia. The loose ends of the permanent DBS electrodes are freed and attached to extension wires. These wires are tunneled under the skin down the side of the head behind the ear, then down the side of the neck, to the chest where it is connected to the impulse generator. The impulse generator is then placed under the skin over the chest. The entire system is placed under the skin. This part of the procedure usually lasts an hour. The patient is awakened and usually spends the night in the hospital and then is discharged the next morning.
About one month after the first surgery when the permanent DBS electrodes have been implanted, the patient is seen in the outpatient clinic for the impulse generators to be turned on and the initial programming of the stimulators is done. Adjusting the stimulators for patients with dystonia is complicated. Unlike the symptom of tremor in patients with Parkinson's disease which reduces immediately when the proper stimulation settings are programmed, the dystonia may take weeks to months in order to respond. Patients should not be disappointed if they are not immediately better. Often it may take 6 or more months to achieve the best response.
Who should have DBS? There are a number of requirements. First, the cervical dystonia should be disabling, either physically or socially, such that the patient is willing to accept a 2 out 100 chance of a serious and/or permanent complication. How bad that is depends on the patient and no two patients judge their disability the same. Unfortunately, some physicians essentially make the decision for the patient by either not offering DBS or discouraging the patient based on the physician's conclusion that the symptoms are insufficient to warrant surgery. But how can any physician fully appreciate the degree of psychological, emotional, sociological and physical toll that is so idiosyncratic to each patient? Further, the ideal of patient autonomy would suggest that it is the patient's (or his or her representative's) prerogative to make the decision and the role of the physician is as an educator.
Given the small but definite risk of serious and/or permanent complications, the patient should first exhaust all reasonable alternatives such as medication and botulinum toxin injections. Medication alternatives include anticholinergics such as trihexyphenydyl (Artane). However, most adults are unable to tolerate the high doses required. If the most disabling symptoms are limited to a relatively small number of muscles, intra-muscular injections of botulinum toxin can be helpful. Oral baclofen may be helpful but excessive sedation is a considerable problem. There are rare cases of dystonia that respond dramatically to levodopa.
Patients who fail botulinum toxin injections would be good candidates for DBS. But first, it must be determined whether the failure was because of the botulinum toxin and not because of the failure of the physician to use the botulinum toxin effectively. Botulinum toxin injections can fail for a number of reasons such as not injecting the proper targets. Sometimes it is necessary to use the electrical activity generated by the affected muscle to find exactly the right target. Using the electrical activity of the abnormal muscles like radar to zero in on the target uses a method called electromyography (EMG). As in any skill, experience and practice are key and physicians may vary. One physician can be successful whereas another may not. Patients may develop neutralizing or blocking antibodies to the specific types of botulinum toxin. Sometimes substituting other types of botulinum toxin can be helpful. A neurologist with considerable experience should make the decision that a patient is refractory to botulinum toxin treatment.
Another alternative is partial and selective cutting of nerve fibers that go to the abnormally active muscle causing the cervical dystonia. Key is the careful selection and cutting of only those branches of the nerves that are going to the muscles contributing to the dystonia. While there are no risks of bleeding inside the head as in DBS and the risks of infection are considerably less, selective denervation still has considerable risks causing excessive weakness that may be irreversible. In addition, dystonia is a dynamic process with the patterns of muscle involvement changing over time. As the disease progresses muscles other than those initially denervated by become active in the dystonia. This could require repeated surgery with markedly increased risks for irreversible weakness. Unfortunately, there are no randomized or controlled studies directly comparing selective denervation to DBS.
Summary. DBS is safe and effective for the treatment of cervical dystonia. It is considered standard care and should be covered by any insurer. Most patients with cervical dystonia will never need DBS. Botulinum toxin injections remain the treatment of first choice for most patients. But for those patients who are not candidates for or fail botulinum toxin injections or medications, DBS can be a good alternative to continued pain and disability.
Director, Movement Disorders Program
Professor, Department of Neurology
Affiliate Scientist, National Primate Research Center
University of Wisconsin-Madison
I have been involved in providing Deep Brain Stimulation (DBS) since 1997 when I was asked to start the program at the Cleveland Clinic Foundation. In August 2003, I joined Dr. P. Charles Garell, Department of Neurosurgery, at the University of Wisconsin to offer DBS. I have been involved in over 200 DBS surgeries and have trained neurologists and neurosurgeons in conducting DBS surgeries. At least 8 cases were dystonia. I do research on how DBS works.
The Movement Disorders Program was created to provide specialized state-of-the-art care for patients with Movement Disorders such as dystonia. The program is staffed by neurologists, neurosurgeons, nurse practitioners and nurses. The program offers a full range of treatments for dystonia including medications, botulinum toxin injections and DBS. Information about the Movement Disorders program can be obtained by writing or calling the:
Movement Disorders Clinic
University of Wisconsin Hospital and Clinics 2B/2
600 Highland Ave.
Madison WI 53792-2425
Telephone (608) 262-0550
Fax (608) 265-1753
