Not everyone is a good candidate for a deep brain stimulation (DBS) implant. The procedure is expensive and potentially risky. Good candidates are healthy and can withstand the stresses that a major surgery causes.
It is important, too, to be sure that DBS will have a good chance to be effective. One indication of that is how the patient's symptoms are responding to drug therapy. If drugs are having a good effect then DBS might be helpful, too, since drug therapies and DBS act on some of the same brain pathways.