- by Vickie L. Wheelock, MD
Reprinted with permission from the Parkinson Association of Northern California
As worldwide experience with deep-brain stimulation for Parkinson's disease advances and long-term follow-up increases, a number of important questions have arisen about the side effects and complications of DBS. Some commonly asked questions about this increasingly common procedure:
1) Does DBS have a differential effect on PD symptoms?
The evidence shows that rigidity and muscle stiffness are significantly relieved by DBS, as is slowness. Effects on tremor are generally quite good, but some patients with especially strong tremor may still experience some symptoms of tremor after DBS. The benefit of DBS for dyskinesia may be largely because of the reduction in medication that follows DBS.
2) Can DBS make any PD symptoms worse?
Some patients have significant difficulty with speech following DBS. This side effect generally occurs after bilateral subthalamic nucleus (STN) DBS, and appears to be a direct effect of stimulation. Reduction in stimulation parameters on one or both sides can improve speech. The effect ranges from a commonly noted slight decrease in vocal volume or slight slurring, to significant voice problems that can, in rare instances, make communication much more challenging.
Some patients seem to fall more often after DBS. This side effect is more common in patients with advanced PD, and may be the result of an "increased opportunity to fall" when "off" symptoms and freezing of gait are improved by DBS. Some of these falls are unpredictable and potentially serious—surgical patients should be especially careful in the first days and weeks after surgery to avoid falls.
Another rare side effect of DBS is called "apraxia of eyelid opening." While rare in North America, the French report that up to 30 percent of patients with STN DBS have this problem. The symptoms: difficulty opening the eyes or keeping the eyes open. Eyelid-opening difficulties are usually fairly subtle, but for some patients it can be very troubling, requiring DBS and medication adjustment, and sometimes, botulinum toxin ("botox") injections.
3) Is there a difference between the STN and the globus pallidus (GPi) target for DBS in PD?
STN DBS has become by far the most common surgical target. There have been only limited comparisons of the outcomes of STN versus GPi targets. The reason for the popularity of the STN target is the relative ease of intraoperative mapping, the immediacy of results during programming, and the reduced need for medication. The GPi is a larger, more complex target; results of programming take weeks to emerge, and patients generally require the same amount of medication after DBS.
Recently published studies of long term follow up of DBS performed in nonrandomized fashion show that both targets are quite effective for reducing PD symptoms, but the incidence of side effects is considerably lower with the GPi target. A randomized study of STN versus GPi DBS is under way, and the results are eagerly anticipated.
The above concerns aside, the first randomized trial of DBS versus best medical therapy for advanced PD was recently published in the New England Journal of Medicine. This multicenter European study demonstrated clear benefits for motor symptoms and quality of life in the group who underwent DBS surgery versus best medical therapy. While the risk of serious complications such as brain hemorrhage was higher in the surgical group, patients in the medical treatment group experienced a higher number of complications because of their advanced disease.
4) Does DBS affect behavior and/or cognition?
A series of papers published last summer in the journal Neurology raised a number of important concerns about this. Despite improvements in motor symptoms, some patients develop the onset of depression or of elevated mood (mania) after DBS. Others may become much more apathetic. Many DBS patients had social and professional adjustment difficulties, and sometimes personal relationships suffered. Furthermore, studies of cognition after DBS consistently show mild declines in language fluency, attention, and word recall. For these reasons, detailed multidisciplinary cognitive and behavioral assessment as well as adequate education for patients and families before and after surgery are strongly recommended.
Dr. Vicki L. Wheelock is a movement disorder specialist and associate clinical professor of neurology at UC Davis. Without seeing you and examining you, Dr. Wheelock cannot make specific diagnoses and recommendations. Any suggestions given in this article are for general information only.
