The United States Food and Drug Administration approved the use of deep brain stimulation (DBS) in the subthalamic nucleus (STN) and globus pallidum (Gpi) in March of 2002 for the treatment of medically refractory Parkinson's disease (PD). In contrast to the thalamic DBS, which controls only the tremor of PD, both STN and Gpi DBS stimulation are able to ameliorate all cardinal symptoms (tremor, bradykinesia, and rigidity) of PD. There is an impression that the STN stimulation appears to be superior to the Gpi stimulation, but thus far, no prospective randomized data exist for comparison of the two sites.
Not all people with P.D. require surgery. In fact, the vast majority do not require surgical intervention. Prospective candidates must have a diagnosis of P.D., have undergone optimization of medication regimen or who are intolerant to medications due to side effects, not experience significant disability or who have moderate to severe dementia..
Improvements are seen in disabilities related to either "off" period symptoms (tremor, rigidity, bradykinesia, muscle cramps associated with off-dystonia etc) that are responsive to Sinemet, or "on" period symptoms (e.g., dyskinesia) that are induced by dopaminergic drugs. When such symptoms threaten one's independence or livelihood, the risks associated with surgical interventions are often justified.
DBS surgery is a time consuming and tedious procedure that requires extensive cooperation from an awake patient during the surgery. Often the benefits of surgery are delayed and require more frequent postoperative visits for stimulator adjustments. Thus, prospective patients should be in good medical, physical, and mental condition to tolerate the surgery and postoperative care.. Optimal outcome requires significant effort from the patients. Therefore those patients with untreated or under-treated mental illnesses (e.g., depression, schizophrenia, etc.) are excluded from the surgery.
STN DBS surgery is often performed bilaterally. Both sides are usually implanted at the same time. In somewhat frail patients, each side is performed separately often months apart for recovery from the initial surgery.
On the day of surgery, a stereotactic frame is placed on the patient's head under local anesthesia. The patient then undergoes MRI and CT examination of the head with the frame in place. The surgeon will use the information obtained from the imaging studies to plan a surgical target. This imaging step takes approximately 1 hour (it may be variable depending on the surgeon). Following the studies, the patient will be moved to the operating room. The patient will be placed in lounge chair position in the operating room. Hair will be shaved and under a heavy sedation, two small burr holes will be placed on the skull. Microrecording system will be mounted to the head frame and the surgeon will perform mapping of the brain to accurately localize the brain target. This process may take 2 to 3 hours. During this part, patient is awake and will be asked to report various sensations and movements. Once the localization is completed, then permanent electrodes are placed into the brain targets. The electrodes are then anchored to the skull and the wounds are closed. The frame is then removed and the patient discharged from the operating room. The patient usually spends 1 or 2 days in hospital for test stimulation and postoperative MRI imaging. The patient is readmitted after 1 week and under general anesthesia, battery packs will be placed under the collarbones. After an overnight stay, the patient will be discharged for convalescence. Programming of the DBS will begin 1 month after the surgery. Adjustments of electrical stimulation and medications are usually made on a monthly basis until optimum setting is achieved. The implanted batteries usually last 5 years depending on stimulation parameters.
Outcomes from STN DBS
The surgery has been shown to be effective for all of the "off" symptoms of PD that were responsive to preoperative Sinemet. Rigidity, bradykinesia, tremor and gait difficulties improve by 40 -60 % in many studies. There is often a marked decline in "on/off" fluctuations, total duration of "off" periods, and "off" dystonia or painful leg spasms. The surgery also decreases the severity of "on" dyskinesia. Most patients experience approximately 50% reduction in PD medication intake. It is generally ineffective in improving "on" state function (i.e., If a patient was wheelchair bound before the surgery even at the best of times, then one would not be walking independently after a successful surgery).
Outcomes from Gpi DBS
The benefits of the surgery are similar to those of STN DBS. The degree of improvement appears to be somewhat less than that of STN. The "off" symptoms have been shown to decrease from 20 - 45%. Improvement in "on" dyskinesia appears to be greater with Gpi than STN DBS. Patients generally require the same amount of medications after the surgery as before the surgery. Also the battery use appears somewhat greater with Gpi stimulation than STN. The only real advantage of Gpi stimulation over STN DBS appears to be in the postoperative DBS programming, which is less problematic with Gpi than STN.
Risks of Surgery
Most DBS procedures are associated with a 1 - 2% chance of devastating intracranial hemorrhages. These hemorrhages are usually lethal or, if one survives, lead to permanent severe neurological deficit including coma, hemiplegia and language impairment. The surgeries are also associated with a 5 - 10% rate of less severe complications including those related to hardware (e.g., infections and breakage). One of the most common transient side effects of surgery is postoperative confusion. This is present in up to 40% of the patients in the immediate postoperative period. It is frightening to unprepared family members, because the patient can be quite agitated, confused and hallucinating. This is short-lived usually lasting 2- 3 days but can last up to weeks. Most patients experience some degree of tingling, numbness, muscle contractions, visual blurring, or lightheadedness associated with stimulation. These stimulation-induced side effects are usually well controlled by adjustments in stimulation parameters. Rarely, a patient will show severe sensitivity to stimulation manifested by violent involuntary movements of extremities, similar to dopa-induced dyskinesia but more severe (hemiballism). Again, this side effect is usually stimulation-induced and can be controlled with alteration in stimulation parameters. These patients will require a slower increase in stimulation parameters than the usual PD patients.
Rarely, DBS stimulation has been shown to worsen existing depression - it is usually associated with stimulation of the electrode in the deeper brain structure and corrected by using an alternate electrode. Permanent cognitive decline is rare except in those with existing dementia or in the most elderly patients. Temporary blunting of affect and a slightly withdrawn personality are often seen in the first 3 months of surgery but permanent changes are rare.
Other Considerations Family and social supports
For the most successful surgical outcome, a strong and committed family and social support is mandatory. Patients are often elderly and frail and require close supervision and assistance postoperatively. Temporary rehabilitation or nursing home facilities may be necessary. Also in contrast to other surgeries, the beneficial effects of surgery are obtained with resumption of electrical stimulation. Optimization of electrical stimulation of DBS requires multiple monthly visits to the physician's office for programming sessions. These sessions are usually very short visits where various electrical stimulation parameters are adjusted but can last several hours especially the very first programming. Medication adjustments are usually made at each programming session. Since the patients are usually debilitated, extensive family or social support are needed to realize the postoperative care.
STN and Gpi DBS procedures are approved by the FDA and covered by Medicare and thus by other US insurers. Due to the significant costs associated with the medical devices implanted, in excess of $30,000.00, the insurance co-payments can be significant and should be investigated before the surgery. Also expenses associated with frequent trips to the physician's office associated with programming should be considered before the surgery.
The most important consideration is the patient's expectation of the surgical benefit. It is important to have a realistic expectation of the surgery to avoid postoperative disappointments despite a successful surgery. It is important to recognize that no two patients are the same and therefore postoperative benefits are not the same. Equally important is recognizing the risk associated with surgery. Too often patients are only concerned with the anticipated benefits and ignore the risks. For this reason and others, a frank discussion of surgical benefit and risks should take place with the medical team and the patient and his or her family.
Taken from MPF The Messenger Newsletter, June 2002
Frederick Junn, M.D., Neurosurgeon, Oakwood Hospital - Dearborn, MI
Member, MPF Professional Advisory Board