Deep brain stimulation (DBS) is an advanced therapy for patients with Parkinson disease (PD) suffering from complications of carbidopa/levodopa treatment. It has been FDA approved for use in PD since 2002 and for tremor prior to that. DBS involves the surgical implantation of a device with electrodes that deliver electrical signals to specific areas within the brain. Once the electrodes are placed, they are then connected to an implanted pulse generator (battery) which is placed under the skin, typically in the chest. When the device is activated, it delivers regular electrical pulses to that area of the brain and results in improvement of PD symptoms. The exact mechanisms of how DBS improves symptoms are not known. However, we do know that it disrupts pathological signals that occur within the brain of PD patients.
Currently, DBS is approved for those patients with a diagnosis of idiopathic PD, who have had symptoms for four or more years and suffer from motor complications that are not controlled with medications. Motor complications refer to the medications not lasting as long (wearing off), levodopa induced dyskinesias (extra, abnormal and involuntary movements) and dose failures.
Individuals who would not benefit from DBS are those with atypical forms of PD, those with signs of dementia and those whose symptoms do not improve with levodopa. Depression and anxiety do not preclude someone from receiving DBS, but these should be addressed, treated and well controlled prior to proceeding.
The process of implanting DBS for patients is a lengthy process. It involves careful pre-surgical screening, two or three surgeries and many follow up programming appointments. The first step is what is called an “Off/On Test.” For this test, the patient comes to an appointment with the neurologist after not taking PD medications from the night before. The patient is then examined in this “Off” medication state. Then, the patient receives a higher than usual dose of carbidopa/levodopa and then re-examined once those take effect.
The next step is to have a formal neuropsychological evaluation performed. This evaluation typically takes about a half of a day and includes extensive testing of memory, language and other cognitive abilities. Once these two preliminary evaluations are complete, most DBS centers hold a multi-disciplinary case conference to discuss these results and the patient’s candidacy for DBS surgery. If there are no contraindications to surgery, the patient will meet with the neurosurgeon who reviews the procedure and the potential risk of surgery. Often times, an additional pre-operative medical evaluation is also required to screen for other medical conditions that could pose additional surgical risks or potential complications. The patient also receives a pre-surgical MRI of the brain to assist with placement of the DBS electrodes.
Most centers perform DBS implantation in two or three individual surgeries. After the DBS device is implanted, the patient then returns to the clinic to turn the device on, typically after three or four weeks. The number of programming appointments needed varies from one patient to the next but can take 6-12 months to reach optimal settings. The battery is checked at routine follow-up appointments and depending on which device is implanted, the battery will need to be replaced from time to time.
Not all symptoms of PD will improve from DBS therapy. The general rule of thumb is if particular symptoms improve after taking carbidopa/levodopa then those symptoms can be expected to improve with DBS. The caveat to this rule are refractory tremors. Tremor in PD can often be resistant to carbidopa/levodopa, but responds well to DBS. In addition, DBS can significantly reduce problems with medication wearing off and dyskinesias. Walking difficulties in PD can be varied and complex. Some of these may respond to DBS but many do not, including balance. Therefore, patients should consult with their DBS physician prior to surgery in regard to their specific walking issues.
Symptoms that are unlikely to improve with DBS are those symptoms that worsen with levodopa, balance, memory problems, speech and swallowing difficulties. DBS can also allow the reduction of some of the PD medications, although it is not realistic to expect to stop all PD related medications after surgery.
It is important to understand that DBS is not a cure however, it is very effective at treating many motor symptoms of PD and improving quality of life.
Ryan T. Brennan, D.O. is an assistant professor in the Department of Neurology at Medical College of Wisconsin.