The major benefit of DBS surgery for Parkinson’s disease is that it makes movement in the off-medication state more like the movement in the on-medication state. In addition, it can reduce levodopa-induced dyskinesias, either by a direct suppressive effect or indirectly by allowing some reduction in anti-parkinsonian medication. Thus, the procedure is most beneficial for Parkinson's patients who have prominent motor fluctuations, that is that they cycle between states of immobility ("off" state) and states of better mobility ("on" state). DBS can smooth out these fluctuations so that there is better function during more of the day. Any symptom that can improve with levodopa (slowness, stiffness, tremor, gait disorder) can also improve with DBS. Symptoms that do not respond at all to levodopa usually do not improve significantly with DBS. Following DBS, there may be a reduction, but not elimination, of anti-Parkinsonian medications. At present, we believe that DBS only suppresses symptoms and does not alter the underlying progression of Parkinson's disease.
The most serious potential risk of the surgical procedures is bleeding in the brain, producing a stroke. This risk varies from patient to patient, depending on the overall medical condition, but the average risk is about 2-3%. If stroke occurs, it usually occurs during, or within a few hours of, surgery. The effects of stroke can range from mild weakness that recovers in a few weeks or months to severe, permanent weakness, intellectual impairment, or death. The second most serious risk is infection, which occurs in about 4-5% of patients. If an infection occurs, it is usually not life threatening, but it may require removal of the entire DBS system. In most cases, a new DBS system can be re-implanted when the infection is healed. Finally, hardware may break or erode through the skin with normal usage, requiring it to be replaced.
In the first few days after surgery, it is normal to have some temporary swelling of the brain tissue around the electrode. This may produce no symptoms, but it can produce mild disorientation, confusion, sleepiness, or personality changes that may last for up to 1-2 weeks.