Deep Brain Stimulation in Cervical Dystonia
Serena W. Hung, M.D.,
Medical College of Wisconsin, Milwaukee, Wisconsin.
Dystonia is a syndrome of sustained muscle contractions that produce twisting and repetitive movements and abnormal postures. Dystonia can involve any part of the body, and dystonia involving the neck is called cervical dystonia (also known as spasmodic torticollis). Before the advent of botulinum toxin, medications used in the condition include anticholinergic agents (e.g. trihexiphenidyl, benztropine), dopamine blockers (e.g. tetrabenazine), muscle relaxants (e.g. baclofen) and the effect has not been consistent. At times, it is rather disappointing. Botulinum toxin made a significant impact on the treatment of focal dystonia. By weakening the muscles that are contracting involuntarily, patients may regain normal posture and experience reduction in the pain associated with the condition. However, especially with the early formulation of botulinum toxin, development of antibodies would render the treatment ineffective. Some patients never got satisfactory control of their cervical dystonia despite escalating doses. In the past, various surgical procedures were performed for cervical dystonia, including peripheral denervation such as posterior ramisectomy, anterior cervical rhizotomy and microvascular decompression of the spinal accessory nerve. Lesioning (i.e. making a hole) in different parts of the basal ganglia have been attempted as early as the 1950s. In the mid 1990s, patients with generalized dystonia started undergoing deep brain stimulation (DBS) of the globus pallidus internus (GPi) with varying results. A few years later, reports of patients with cervical dystonia undergoing DBS started surfacing in the medical literature. Reports in the literature usually contain few patients, ranging from 1 to 10. The follow up duration also varies a great deal (between three weeks to two and a half years). Overall, deep brain stimulation seems to be an effective treatment for cervical dystonia. In Bittar et al that was published in 2005, 6 patients with cervical dystonia who underwent deep brain stimulation were followed between 24 to 48 months. Using one of the standard rating scales to evaluate the severity of cervical dystonia, Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS), the severity score improved by 58%, disability score improved by 62% and pain score improved by 58%. Another group from Canada reported similar results (Hung, et al 2006) in 10 patients followed for average of 2.5 years but the longest follow up was over 5 years – TWSTRS severity score improved by 54.8%, disability score improved by 59.1% and pain score 50.4%.
What are the selection criteria for DBS for cervical dystonia? What steps are taken to help with patient selection?
There are no established guidelines for patient selection for the procedure. Current practice for patient selection for this treatment would include failure to achieve adequate benefit from botulinum toxin, whether it is due to the ineffectiveness of the treatment, the unbearable side effects such as weakness of the neck with high doses or the development of antibodies to botulinum toxin which renders the medication ineffective. The patient’s amount of disability is taken into consideration since DBS carries a not insignificant amount of risk. If the patient is not significantly impaired by the cervical dystonia, then it may be too risky to undergo such a treatment. Patients have to be in general good health to undergo the surgery. Some patients will have to be cleared by their medical doctors to ensure that their heart, lungs and other body systems are healthy enough for the surgery. They will also undergo cognitive testing and MRI’s to evaluate for the appropriateness of surgery. If the patient has existing dementia or memory problems, the surgery may worsen the cognitive problems. If there is significant abnormality on MRI, the risk involved with surgery may be higher than usual, and in some cases, higher than acceptable.
Is DBS for cervical dystonia a safe procedure?
Since there are risks involved with any surgery, these risks need to be clearly explained to the patients and their caregivers so that they can make an informed decision. The most concerning risk involved in deep brain stimulation for any reason would be bleeding inside the brain (hemorrhage), which is quoted in the literature to be around 3%. The severity of the bleeding can vary, ranging from negligible to a sizeable amount of blood. In the former case, the patient or the doctors may not even notice any symptoms and the bleeding is only seen on MRI. However, when the amount of bleeding is large, the patient will present just like having a stroke, possibly with weakness, numbness, speech difficulties, and in the extreme case, death can ensue. Other risks include infection which may or may not be treatable by antibiotics delivered through an intravenous solution. This risk can be as high as 10%. At times, the hardware will have to be removed and the deep brain stimulator reimplanted after the infection is completely healed. The current target for dystonia (globus pallidus internus, or GPi) seems to carry less risk for cognitive impairment or psychiatric impairment, although they are still possibilities.
Is DBS for cervical dystonia covered by insurance?
The use of DBS in dystonia, including generalized, segmental, or focal such as cervical dystonia, was granted in 2003 under the Humanitarian Device Exemption (HDE) by the U.S. Food and Drug Administration (FDA). In most states, Medicare would cover the procedure, but it may require a petition or a letter explaining the situation from the neurologist or neurosurgeon. The coverage with private insurance is more variable, and most of the time, letters of petition will be required as well in order for the surgery to be covered.
What happens during the surgery?
After a patient is determined to be an appropriate candidate for surgery, a surgery date will be booked. The patient may come to the hospital the day prior to surgery, or in some cases, the morning of the surgery. His or her head would be shaved, the skin cleaned before a frame is secured on the head. (At some hospitals, a “frameless system” is used in which a device smaller than a smoke detector is secured on the head and instead of a full frame around the head. Some patients find that the frameless system creates less discomfort.) Further imaging will be done so that the images can be superimposed on the planning MRI. This is all done to plan the trajectory and target of the electrodes. The patient will then be sedated when the Burr hole is drilled on the head for the insertion of the electrode. However, after the electrode is inserted, the patient will then be awakened for the intraoperative monitoring. Intraoperative monitoring is another way to ensure the optimal positioning of electrodes. Different brain cells generate different distinct patterns and frequencies of signals, and using these signature signals, the location of the electrode can be ascertained. The reason why the patient needs to be awake is that the signals the brain cells generate are dampened when the patient is asleep, thus making recording and monitoring more difficult. During the intraoperative monitoring, the patient will be asked to perform various tasks and report unusual feelings or sensations. Multiple passes will have to be made in order to map out the area of interest accurately to ensure a good placement of the stimulating electrode. After the intraoperative monitoring is completed, the recording electrode will be inserted with some testing done in the operating room before the electrode is secured. The duration of surgery varies, but on average a procedure done on one side would take anywhere between 2-4 hours whereas bilateral procedure will take 3-6 hours. Depending on the practice of the neurosurgeon, the distance the patient has to travel to get the procedure done and other factors, the battery may be inserted under the skin below the clavicle on the same day or at a later date.
What happens immediately after surgery?
There are some differences among different hospitals but in general, right after surgery, the patient will be admitted to the intensive care unit for overnight observation. If the patient is awake enough, he or she can probably eat dinner that night. Pain medications and anti-nausea medications are given to ensure the comfort of the patient as some people do experience some discomfort. Some patients may stay in the hospital for another day prior to discharge. In general, the hospital stays for this procedure are quite short, around 2 days. If the battery was not inserted during the initial surgery, the patient will then return to the hospital a week or so later for the battery implantation. This is a same-day surgery, and the patient will be discharged that day.
When does the programming start? What happens during programming of the stimulator?
For dystonia, the programming can start after the micro-lesion effect has subsided. During the surgery, due to the passing of the recording electrode, the patient may experience a transient improvement in the dystonia immediately after surgery. This is called the micro-lesion effect. However, usually this improvement is short-lived. If the programming were to start before the micro-lesion effect subsided, then it would be difficult to tell whether the improvement is indeed due to the stimulation or whether the improvement is still a residual micro-lesion effect. It may take days or weeks for the micro-lesion effect to completely subside.
During programming, there are several parameters that can be changed in order to maximize the benefit. On each stimulating electrode, there are four contacts that can be used to send current through. One or more of the contacts can be used at the same time. Once the contact is picked, voltage, pulse width and frequency are the remaining parameters that can be put into different combinations.
Unlike other movement disorders that are improved by deep brain stimulation (e.g. Parkinson’s disease and essential tremor), the effect of deep brain stimulation may not be evident immediately. Sometimes it takes days for the patient to experience the improvement from the increasing stimulation. That makes programming more difficult and time consuming. There are different ways of programming patients with cervical dystonia. At some centers, based on the post-operative imaging and previous experience, the contact with the highest success rate in previous patients will be chosen and the remaining parameters will be set according to side effect threshold. At other centers, each contact is examined to determine the threshold of the side effect. Then each contact will be tested and a particular setting with that contact will be left on for a week or so before checking the next contact. After checking all four contacts on each side, the best contact will be chosen for further manipulation of parameters. The latter way of programming usually takes a longer period of time, and in a lot of cases, the former way will be tried first, and if the results are suboptimal, then the latter way will be undertaken. It may take months to find the best contact with the best parameters of stimulation for each patient as each and every patient is quite different and the programming has to be tailored to the individual patient. It has been reported that for the same parameters, the patient may not reach peak benefit until a year later.
The key to success for programming for dystonia, cervical dystonia included, is patience and close communication with the programming neurologist.
Do we know how long the benefit is going to last?
DBS for dystonia has not had as long a history as DBS for Parkinson’s disease and essential tremor, so patients have not been followed for as long a period as the other diseases. However, it seems like, from the case series in the literature, the benefit lasts at least 2+ years. At some centers, small numbers of patients have been followed for up to 5 years, and the benefits still persist. We will have to wait and see and follow the patients who have had this procedure done for longer periods of time in order to be able to tell more.
If I am interested in DBS for cervical dystonia, what should I do?
It is very important to find a center that is experienced in doing DBS in dystonia. There are a limited number of centers in the United States that are currently performing this procedure. Talk to your neurologist and find out more.
My mom and I wanted to thank you for hosting such a great symposium this year. This was our third year and we are looking forward to next years. E. Mathews