Careful patient selection is the first and perhaps the most important step for success of DBS. There are no standardized criteria for choosing candidates, and criteria may differ depending on the targeted symptom or disorder. We will discuss the important aspects of patient selection that should be considered in PD, essential tremor, dystonia, and OCD/Tourette.
PD, which is a slowly progressive neurodegenerative disorder (cardinal manifestations- resting tremor, bradykinesia, rigidity, gait disorder), presents many challenges for the practitioner who is considering offering DBS. Although there are no set criteria for surgical candidacy, recently we developed and validated a screening questionnaire for this purpose. The Florida Surgical Questionnaire for Parkinson’s Disease(7)or FLASQ-PD is a 5-section questionnaire that includes: (A) criteria for the diagnosis of “probable” idiopathic PD, (B) potential contraindications to PD surgery, (C) general patient characteristics, (D) favorable/unfavorable characteristics, and (E) medication trial information subscores. The scoring system was designed to assign higher scores to better surgical candidates. The highest/best possible FLASQ-PD score is 34 with 0 red flags, and the lowest/worse possible FLASQ-PD score is 0 with 8 red flags. A red flag is a sign or symptom that would automatically put a patient at high risk for a complication of surgery. A score of approximately 25 without red flags indicates a potentially good surgical candidate. This questionnaire can be filled out and scored by your general neurologist, general practitioner, or other qualified health professional.
Potential candidates who score well on this questionnaire will require medical optimization with a movement disorders specialist (if possible), a neurosurgery consultation, a special MRI for targeting, and a full neuropsychological evaluation. Some patients may additionally require a speech and swallowing evaluation, and psychiatric evaluation for treatment of active affective disorders.
Parkinson’s Disease Candidates
In general the best PD surgical candidates have idiopathic Parkinson’s (not parkinsonism which includes other diagnoses such as multiple system atrophy, progressive supranuclear palsy, Lewy body disease, corticobasal degeneration), tend to be younger (below age 69, but may be older), have a great response to medication (at least 30% improvement, but preferably higher), be medication refractory to symptoms (wearing off of medications prior to the next dose, on-off fluctuations, dyskinesias, etc.), and have no or little cognitive dysfunction. Perhaps the most controversial aspect of patient selection often involves defining unacceptable cognitive dysfunction, especially since many PD patients suffer from frontal and memory deficits, but are quite functional in their daily lives. A general rule is that PD patients with a lot of memory or cognitive problems, and those who get disoriented frequently are poor candidates and can be made worse from surgery.
Essential Tremor Candidates
In ET, patients suffer from postural (holding the hands and arms in a fixed position) and action tremor (tremor when they attempt tasks) which often disrupts the simple but important daily tasks such as handwriting or drinking. ET candidates for DBS must have medication refractory tremor defined as having failed maximal titrations and preferably combinations of a beta blocker, primidone, and possibly a benzodiazepine. There are other medications that have been found effective in some patients with ET and these may be tried as well. The tremor must be interfering with the quality of life to consider surgery. There are no available questionnaires to screen for good ET surgical candidates, however the same interdisciplinary workup is necessary (as was discussed in PD), and it is important that the tremor be diagnosed correctly as ET can be confused with other tremor subtypes. Again, the most difficult criteria to interpret for the ET surgical candidate is the neuropsychological screening data, especially since it has recently been appreciated that ET can be associated with frontal lobe and memory dysfunction(9, 10).
Other disorders which may be addressed by DBS have been less studied in terms of selection criteria. In general the best dystonia (a twisting disease where agonist and antagonist muscles co-contract and leave the sufferer in abnormal postures which may be worsened by action) surgical candidates suffer from generalized disease (multiple body regions) which may or may not be the result of an identified genetic defect. This criteria is a generality based on a limited experience, however as more reports of DBS for focal dystonia emerge, the criteria may be expanded. So far at the University of Florida we have been successful with other more focal dystonias. Secondary dystonia, or dystonia due to other causes such as trauma, toxin, birth defect, or metabolic disorder seems to be less responsive to DBS, although the best surgical target remains to be defined for these cases, and there has been some successes reported. The dystonic patients need to fail maximal doses of appropriate medications and preferably combinations of medications including anticholinergics, muscle relaxants, and benzodiazepines, and should also undergo the same workup as for PD patients. It is helpful in dystonia if the operation is performed before abnormal joint postures become fixed or contracted. Patients with generalized dystonia may be normal on detailed neuropsychological testing, although recently it has been shown that they may suffer from impairments in complex learning(11, 12). It remains unknown whether the neuropsychological profile in dystonia patients effects surgical outcome.
DBS for OCD or Tourette remain investigational at this time. All potential candidates should be refractory to standard medical therapies, and informed consent should be obtained from an institutional review board before offering the procedure. The profile of the best candidates with these and similar syndromes remains unknown, although all candidates should undergo the same vigorous testing described above, and should be medication refractory. We are currently testing patients with refractory OCD under a National Institutes of Health grant, but the results are not yet available.
If you have questions or would like a consultation to see if you are a candidate please call 352-294-5400 or use our Contact Form.