Guidelines for Referring Neurologists: Deep Brain Stimulation for Parkinson's Disease
Who is a good candidate for deep brain stimulation for Parkinson's Disease? The criteria that we use for offering patients DBS surgery for Parkinson's disease are as follows:
1. Clear diagnosis of idiopathic PD. Patients with atypical parkinsonism or "parkinson's plus" syndromes do not respond to DBS. If there are features in the history and physical that are suggestive of atypical parkinsonism (such as very rapid progression of symptoms, autonomic failure or postural instability as early features of the disease, signs of cerebellar or pyramidal dysfunction) or an MRI suggesting an atypical syndrome, surgery is contraindicated.
2. Intact cognitive function. A good screening test is the mini-mental status test. A score of >26 is ideal, < 24 an absolute contraindication. Patients with cognitive dysfunction have difficulty tolerating awake surgery, may have permanent worsening of cognitive function postoperatively, deal poorly with the intrinsic complexity of DBS therapy, and realize little overall functional gain even if motor performance is improved. In borderline cases, we obtain formal neuropsychological evaluation.
3. Clear evidence of motor improvement with Sinemet, with good motor function in the best on-medication state. A good screening test is the Unified Parkinson's Disease Rating Scale (UPDRS) part III, performed after 12 hours off of medication and repeated following a supratherapeutic Sinemet dose. We require at least a 30% improvement in this score with Sinemet. The patient should be ambulatory in the best on state without much assistance. In general surgery makes the "off" states more like the "on" states but rarely does better than the best "on" state, so a patient with poor function in best "on" (for example, nonambulatory in best "on") is a poor surgical candidate. Patients who fluctuate between good motor function while "on" and poor motor function while "off" are usually good surgical candidates.
4. Lack of comorbidity. Serious cardiac disease, uncontrolled hypertension, or any other major chronic systemic illness increases the risk and decreases the benefit of surgery.
5. Realistic expectations. People who expect a sudden miracle are disappointed with the results, and become frustrated with the complexity of the therapy.
6. Patient age. The benefits of DBS for PD decline with advancing age, and the risks go up. Patients over 75 are informed that their benefits are likely to be modest. We have rarely implanted PD patients who are over 80.
7. Screening MRI of the brain should be free of severe vascular disease, atrophy that is out of proportion to age, or signs of atypical parkinsonism.
8. Degree of disability. DBS is a poor procedure to rescue someone with end stage PD, although these are the most desperate patients. It is also not appropriate for early PD when the symptoms are very well controlled on medical therapy. Patients should have an off-medication UPDRS-III score of > 25. The best time to intervene surgically is when the patient is just beginning to lose the ability to perform activities meaningful to him/her, in spite of optimal medical therapy. Often, this is associated with the development of significant motor fluctuations, dyskinesias, or both. In a patient who is still working, the time to intervene is before the patient is forced to retire on disability.
9. Ability to remain calm and cooperative during awake neurosurgery lasting about 2-3 hours per side of brain. A helpful "screening test" for this is how well the patient tolerates an MRI scan. For patients who are otherwise excellent candidates but could not tolerate being awake for part of the surgery, it is possible to have the DBS implantation under general anesthesia in our interventional MRI suite.
10. Willingness and ability to be seen for follow-up visits. Programming the DBS to find the optimal stimulation settings is very much a trial-and-error process, and the patient will need to be seen approximately once a month for at least the first few months after surgery.