Deep brain stimulation (DBS) involves implanting stimulating electrodes into selected targets in the brain in order to mimic the effects of lesioning. Surgeons began using DBS in place of lesioning for Parkinson’s disease patients in the mid-1990s. DBS also has applications to tremor and pain. Whereas DBS has been used to treat thousands of persons with Parkinson’s disease, the procedure began being applied to dystonia less than 10 years ago. It is estimated that just under 1,000 dystonia patients have been treated with DBS.
Bilateral pallidal DBS produces significant benefit in dystonia with average improvements of about 50-60% in the Burke-Fahn-Marsden dystonia rating scale. Some primary generalized patients have been reported to have up to 90% improvement. DBS has also been performed on persons with secondary dystonias, cervical dystonia, segmental dystonia, and myoclonic dystonia with encouraging results.
The complete DBS apparatus includes the DBS electrode, a connecting wire, and a pulse generator (a.k.a. “brain pacemaker” or stimulator) that contains a battery. The initial procedure to implant DBS is identical to that of the pallidotomy and thalamotomy. Once the brain target is mapped and identified, instead of creating a lesion, the surgeon places the DBS electrode into the target. The wire and pulse generator may be implanted at the same time as the electrode or at a later date. The generator is implanted under the collarbone, and the wire is tunneled up the neck, behind the ear, and to the site of the electrode (the patient is under general anesthesia for this part of the procedure). The wire is connected to the electrode, and the incisions are closed. Most DBS procedures involve the implantation of two generators and are done in two surgeries. It is possible to implant both generators in a single surgery, and surgical centers vary in their preferred approach. Immediately after the operation, the patient may temporarily resume medications. The patient may be discharged the next day.
Once the generator is implanted, the patient must wait a week or two before the batteries are activated. This waiting period is necessary to allow the swelling that normally occurs with the surgery to diminish. The DBS electrode conveys electrical pulses into the brain using power produced by the battery in the generator. A series of visits to the hospital are required to adjust the voltage settings to the needs of the individual. It may take several weeks or months to achieve the correct settings. The patient can check the status of the generator using a handheld device that resembles a TV remote control. Using this device, the patient can determine if the generator is on or off, and can turn it back on in the event that it shuts down unexpectedly. (Certain phenomenon such as magnetic fields caused by security devices may cause the battery to temporarily stop working.)
The expected life span of a battery at a typical voltage is about four years. At a very high voltage, the battery may need to be replaced after a year; at a very low voltage, perhaps up to seven years. Replacing a battery can be done under general or local anesthesia as an outpatient procedure.
Dystonia does not respond to DBS in the same as other movement disorders do. For example, persons treated for tremor will generally improve within seconds of turning the generator on. In patients with dystonia, improvement may be delayed for days, and weeks or months may pass before the full extent of the benefit is reached. DBS does not necessarily eliminate the possibility of subsequent drug or botulinum toxin treatments.
Side effects are minimal, but no procedure is without risks. The main risk in DBS is a fatal hemorrhage. However 99-99.5% of patients do not have significant bleeding. Despite vigorous efforts to avoid it, infection is a risk in approximately 2% of patients. Infection can be serious and warrant the removal of the hardware. If this happens, it may be possible to re-implant the hardware once the infection is treated. Hardware failure is also a concern, though this is rare and precautions are in place in the event of situations such as a battery failing. It is estimated that in 5% of DBS procedures for dystonia some complication may arise, most of which can be addressed without removing the hardware.
Although no longer considered “investigational” for dystonia by the United States Food & Drug Administration, DBS is in its relatively early stages as a treatment for this disorder. The preliminary results are quite positive, and the procedure is expected to evolve over time as more patients are treated and more data is collected.