In properly selected patients, deep brain stimulation is remarkably safe and effective, although not completely without risk. Beneficial effects have been demonstrated to last for several years. Patients who initially responded well to medications, but over time have developed sides effects, can experience between 60 to 80 percent improvement in such symptoms as tremor and slowness of movement. Patients on average report a 50 percent improvement in their walking and balance. Similarly, patients with involuntary movements (dyskinesia) due to their medications, experience over 80 percent reduction in their involuntary movements. Most patients are able to significantly reduce their medications following deep brain stimulation.
Regarding Parkinson's disease in particular, an important indicator of the effectiveness of any treatment is the duration of "on-time" without dyskinesia. This means the patient is mobile, can perform everyday tasks without experiencing the involuntary movements. On average, deep brain stimulation doubles the amount of "on-time" without dyskinesia.
As with any surgery, the procedure is not entirely risk free. There is approximately a two to three percent chance of brain hemorrhage that may be of no significance, or may cause paralysis, stroke, speech impairment or other major problems. This means that for every 100 patients who undergo surgery, two or three will experience a permanent or severe complication. However, this also means that many patients will have no complications. There is a 15 percent chance of a minor or temporary problem. Rarely, infections can occur. While treatment of infection may require removal of the electrode, the infections themselves have not caused lasting damage.
The electrode that is implanted in the brain, and the electrical systems that provide stimulation, are generally very well tolerated with no significant changes in brain tissue around the electrodes.