Deep Brain Stimulation
Deep Brain Stimulation (DBS) has been used to treat intractable pain for several decades. More recently, use of this technology has proven to be a safe and effective treatment for essential tremor, as well as tremor and involuntary movements associated with Parkinson’s disease, dystonia and multiple sclerosis, with more than 35,000 DBS implants worldwide. The applications for DBS therapy are expanding rapidly.
The procedure is comparable to that of a cardiac pacemaker in which the pacemaker helps maintain an appropriate cardiac rhythm. DBS is presumed to help modulate dysfunctional circuits in the brain so that the brain can function more effectively. This is accomplished by sending continuous electrical signals to specific target areas of the brain, which block the impulses that cause neurological dysfunctions. These targets are the ventralis intermediate nucleus of the thalamus (Vim), the globus pallidus pars interna (GPi), and the subthalamic nucleus (STN).
The DBS system consists of three components:
- The lead (also called an electrode) is a thin, insulated wire inserted through a small opening in the skull and implanted in the brain.
- The extension is an insulated wire that is passed under the skin of the head, neck, and shoulder, connecting the lead to the internal pulse generator (IPG).
- The IPG or neurostimulator is the third component and is usually implanted under the skin near the collarbone. In some cases it may be implanted in the chest or under the skin over the abdomen.
A small opening is made in the skull under a local anesthetic. The patient is awake during the DBS surgery to allow the surgical team to assess his or her brain functions. While the lead (electrode) is being advanced through the brain, the patient does not feel pain because of the human brain’s unique inability to generate pain signals. Computerized brain-mapping technology is utilized to pinpoint the precise location in the brain where nerve signals generate the tremors and other symptoms. Highly sophisticated imaging and recording equipment are used to map both the physical structure and the functioning of the brain. The electrodes are connected via wires to an internal pulse generator (IPG) that is placed in the chest wall.
A magnet is used with the IPG to adjust the stimulation parameters so that the appropriate level of stimulation is applied at the electrode tip. The patient is provided with an access control device or handheld magnet to turn the IPG on and off at home. Depending on the application, the battery can last three to five years. When the battery needs to be replaced, the IPG is also replaced, usually under local anesthesia as an outpatient procedure.
DBS Surgery Advantages
- Surgery can be performed on both sides of the brain for control of symptoms affecting both sides of the body.
- The effects are reversible and can be tailored to a patient’s clinical status.
- Stimulation parameters can be adjusted to minimize potential side effects and improve efficacy over time.
- The device can provide continuous symptom control 24 hours a day.
- Patients who have undergone DBS are still candidates for other treatment options such as stem cell or gene therapy when they become available.
DBS Surgery Risks
In properly selected patients, DBS is quite safe and effective, but there are some risks. There are also potential side effects, although they are generally mild and reversible. There is an estimated 2-3 percent risk of brain hemorrhage that may either be of no significance, or may cause paralysis, stroke, speech impairment or other major problems. There is a small risk of leakage of cerebrospinal fluid, which can lead to headaches or meningitis. There is a 15 percent risk of a minor or temporary problem associated with implantation, including infection. While treatment of infection may require removal of the electrodes, the infection itself does not cause lasting damage.
Side effects may include the following:
- Temporary tingling in the face or limbs
- Temporary pain/swelling at implantation site
- Allergic reaction to the implant
- Slight paralysis
- Speech or vision problems
- Jolting or shocking sensation
- Loss of balance
- Reduced coordination
- Concentration difficulties
The electrodes and electrical systems that provide stimulation are generally very well tolerated with no significant changes in surrounding brain tissue. Migration of the electrode from the original implantation site may occur. There also may be temporary rebound worsening of the tremor when stimulation is stopped. Surgery risks increase in people age 70 and older, and in those with other health conditions such as cerebrovascular disease and high blood pressure. The benefits of surgery should always be weighed carefully against its risks. Although a large percentage of patients report significant improvement after DBS surgery, there is no guarantee that surgery will help every individual.
Early in Parkinson’s disease (PD), there is a loss of brain cells that produce the chemical dopamine. Normally, dopamine operates in a delicate balance with other neurotransmitters to help coordinate the millions of nerve and muscle cells involved in movement. Without enough dopamine, this balance is disrupted, resulting in tremor (trembling in the hands, arms, legs and jaw); rigidity (stiffness of the limbs); slowness of movement; and impaired balance and coordination – the hallmark symptoms of PD.
DBS of the STN has increasingly been recognized as an effective treatment for patients with medically intractable PD because of its demonstrated safety and efficacy. It provides consistent clinical benefit and can reduce dopamine replacement therapy requirements by 50 to 70 percent. While DBS provides symptomatic relief, it does not slow or reverse the underlying neurodegenerative process of PD.
Appropriate candidates for DBS should have moderate to severe medically intractable Idiopathic PD, as diagnosed by a neurologist experienced in movement disorders. The disease should be present for at least three years with two or more of the four hallmark symptoms mentioned above before DBS is considered. Other indicators for DBS are when there are motor response complications or medication side effects from multiple medical therapy options including levodopa, and medication adjustments have not alleviated the complications/side effects.
Current research demonstrates that DBS at the GPi significantly improves symptoms of torsion dystonia in the majority of patients treated. DBS appears to be more effective in patients with primary dystonia than secondary dystonia, most likely due to the absence of structural brain abnormalities. Unlike PD, which responds soon after the onset of stimulation, dystonia may require weeks of stimulation before an improvement is evident. Moreover, the full benefit of stimulation may not be realized for 12-18 months after the onset of therapy. Complications thus far have been minor and few.
The main goal of performing DBS in multiple sclerosis (MS) patients is to control arm tremor. While tremor of the head and body may be helped, the decision to perform DBS should be aimed at decreasing arm tremor. Other MS symptoms such as loss of vision, sensation or strength are not helped by DBS, nor will this cure, reverse or slow the progression of the disease.
Severe Psychiatric Disorders
Preliminary research has demonstrated that DBS results in significant improvement in mood, memory recall, as well as reductions in anxiety, obsessions and compulsions in select patients with both OCD and treatment resistant depression (TRD).To date, this treatment has been undertaken on a small number of patients in clinical trials and is not widely available. However, findings are promising enough to indicate the need for more extensive studies to further understand how DBS enables these improvements.