Deep brain stimulation for patients with Parkinson’s disease
(This Q&A by John W. Henson, M.D., FAAN, editor of SNI’s newsletter BrainWaves, was published in Physicians Practice, September 2009)
Deep brain stimulation (DBS) functions like a pacemaker for the brain, restoring neurological function by delivering electrical impulses to precise, tiny regions of the brains of patients with Parkinson’s disease (PD). The DBS program at the Swedish Neuroscience Institute treats dozens of PD patients each year. In the following Q&A, three of the leaders of the SNI program describe several promising new indications for this remarkable technique. Susie Ro, M.D., is a movement disorders specialist who determines patient eligibility for DBS. SNI neurosurgeon Pete Nora, M.D., performs the exacting neurosurgical procedure in which electrodes are introduced into a targeted region deep within the brain. Peggy Shortt, M.N., ARNP, and her nurse practitioner colleagues, perform microelectrode recording and intra-operative testing during the DBS electrode implantation, and direct the programming of the fully implanted neurostimulation system in the weeks following surgery.
Q: How would you describe the ideal DBS candidate with PD?
Ro: A clear diagnosis of PD is the foremost criterion for the DBS candidate. Patients with parkinsonism due to causes other than Parkinson’s disease, such as progressive supranuclear palsy (PSP) or multiple system atrophy, for example, do not do well with DBS. Ideal candidates should have a robust response to levodopa, because symptoms that improve with levodopa (i.e., tremors, stiffness and slowness) also tend to improve with DBS. In addition, patients who have severe dyskinesias (abnormal movements caused by levodopa) or “wearingoff” phenomenon (needing doses more often than every three to four hours) can have less severe ups and downs, and more “on” time with DBS. Some patients who cannot tolerate the side effects of high doses of medication are also potential candidates. The best candidates are usually in the middle stage of their disease (5-15 years) and are functioning well when their medications are working. Realistic expectations, a good social support system and access to expert programming are also crucial. We are cautious about patients approaching 80 years of age. Although there is no set age cutoff, younger patients do better in general.
Q: Which symptoms do not improve with DBS?
Ro: Symptoms that do not improve with levodopa, including some types of balance, speech and memory problems, do not improve with DBS. If a patient cannot walk on their best “on-medicine” day, DBS will not fix that problem. DBS is not a last resort treatment for end-stage PD. Patients with uncontrolled depression, anxiety, memory loss or severe medical problems are at high risk for complications following surgery.
Q: What percentage of PD patients are good candidates for DBS?
Ro: Even though only 10-15 percent of PD patients eventually become good DBS candidates, it is a markedly underutilized treatment. Many patients are never referred for screening at all, or are referred too late. As a surgical referral center, we get a fairly high percentage of DBS referrals who turn out to be good candidates for surgery. Our selection guidelines are fairly strict, but they are only guidelines. We consider each patient individually. Because we are very selective, the patients who have surgery in our program tend to have excellent outcomes.
Q: Are there conditions other than PD for which DBS is emerging as an accepted therapy? Do you treat patients with these conditions at SNI?
Ro: DBS is a well-established treatment for essential tremor and primary generalized dystonia. We also treat other forms of cerebellar outflow tremor following stroke, trauma and multiple sclerosis, as well as certain types of dystonia.
We are expanding into other movement disorders, including severe Tourette’s syndrome. Neuropsychiatric disorders, such as obsessive-compulsive disorder and depression, is an exciting new area for DBS.
Q: The target area for the electrode tip is very deep in the brain. How do you place the electrode with a high degree of accuracy?
Nora: Several days before surgery we obtain a high resolution MRI scan of the brain, which we use for targeting and to confirm the absence of structural abnormalities. We use these MRI images and a stereotactic CT scan just prior to surgery to select the appropriate target for the electrode tip. During the procedure we perform microelectrode recordings of the selected target nuclei. Then the electrode is temporarily activated during surgery to ensure the patient obtains expected benefits without unwanted side effects.
Q: What is the structure of the electrically active tip of the electrode?
Nora: There are four electrical contacts along the axis of each electrode. This allows for the safest and simplest surgical placement while providing the maximum programming options for our patients.
Q: Is there a significant complication rate?
Nora: Nationally, the complication rate for DBS is approximately 5 percent and includes hemorrhage, infection and neurological injury. The most concerning of these are hemorrhage and neurological injury, which makes up only about 1 percent of all complications. Thus, the rate of significant complications is very low.
Q: What is the microlesion effect?
Nora: The microlesion effect refers to transient clinical improvement seen in patients after their electrodes have been placed but not yet activated. It is a sign the electrode is in excellent position, although it is not seen in every patient that does well.
Q: What is the programming process following electrode implantation?
Shortt: The DBS system is programmed during the patient’s “medication-off” state without the influence of medications usually taken to suppress the same symptoms we are planning to treat with stimulation. We can change many parameters using a radio-frequency device we hold over the patient’s implant, including electrical polarity, voltage, frequency, pulse width and rate. We select the field of stimulation by choosing the best symptom improvement for the patient’s needs.
Q: What is the waiting time between electrode implantation and programming?
Shortt: In general, the patient has an appointment with the DBS clinic about two weeks after surgery. We perform initial programming with stimulation mapping to determine the best benefit for the patient with the least side effects.
Q: Do you see immediate changes in neurological function during the programming process?
Shortt: Immediate improvement is often noted. It may take weeks or months of follow-up programming, however, to maximize motor benefits through reduced tremor, rigidity, bradykinesia, dyskinesia or dystonia. Patients with essential tremor may have the most immediate improvement with fewer programming sessions. In patients with PD, the brain stimulation titration is gradual because of the importance of balancing the dosing of medicines and stimulation. The patient will notice optimal improvement in three to six months. In dystonia patients, programming visits are monthly and the full benefit of stimulation may take up to a year following DBS implantation.