1. Surgery For Parkinson’s Disease Current Practice and Future Directions
Emad Eskandar, MD
Alice Flaherty, MD, PhD
Leslie Shinobu, MD, PhD
G. Rees Cosgrove, MD FRCS (C)
Department of Neurosurgery &
Department of Neurology
Massachusetts General Hospital
Boston, MA

2. Pathways 1 Motor Cortex Premotor Cortex + Glutamate Putamen Gpe Gpi +
- GABA
Dopamine -
Motor
Thalamus
SNpc
STN

3. Pathways 2 Motor Cortex Premotor Cortex + Glutamate Putamen Gpe Gpi +
- GABA
Dopamine -
Motor
Thalamus
SNpc
STN

4. Pathways 3 Motor Cortex Premotor Cortex + Glutamate Putamen Gpe Gpi +
- GABA
Dopamine -
Motor
Thalamus
SNpc
STN

5. Current Surgical Targets
Thalamotomy/ Thalamic Stimulation
Mainly used for tremor - essential, MS
Other targets preferred for PD
Pallidotomy/Pallidal Stimulation
Effective for all cardinal features Considerable experience
Subthalamic Stimulation
Most recent addition
Several theoretical advantages
Currently most popular therapy

6. Patient Selection Movement Disorders Team Evaluation
- Initial screening
- Insure that medical therapy is optimized
- Neurologic evaluation using validated clinical rating scales
- Psychiatric Evaluation
- Neuro-psychologic Evaluation
- Neurosurgical Evaluation
- Consensus opinion at weekly conference
Inclusion Criteria
- Idiopathic Parkinson's Disease
- Symptoms for four or more years
- Documented response to levodopa therapy
- Medically refractory disease?
Exclusion Criteria
- Patients unable to communicate
- Patients unable to cooperate for surgery
- Dementia
- Abnormalities on pre-operative MRI
- Medical contraindications to surgery

7. MGH Pallidotomy Experience
247 patients referred as possible candidates for posteroventral pallidotomy (PVP)
158 surgical candidates identified on the basis of initial reviews
85 individuals eventually accepted for stereotactic pallidotomy
Mean age 61 (range 38-79)
109 Pallidotomies
19 Bilateral Operations

8. Pallidotomy MRI and CT stereotactic localization
Typical target coordinates
mm lateral to midline
2 - 4 mm anterior to mid AC/PC point
4 - 6 mm inferior to AC/PC plane
Physiologic Localization
Micro-electrode recordings
High frequency stimulation(75 hz) for amelioration of symptoms and neurologic side-effects - proximity to optic tract
Low frequency stimulation (2 hz) for assesment of motor thresholds - proximity to internal capsule
Lesion generation
Initial lesion 75º for 60 sec
Higher lesions 85º for 60 sec

9. Stereotactic Localization of STN
Subthalamic nucleus is small (5 x 7 mm) and difficult to visualize using current MRI and CT technology
Approximate location is determined relative to Anterior Commissure (AC) and Posterior Commissure (PC)
Standard coordinates are:
11-13 mm lateral to midline
4-5 mm posterior to mid AC/PC point
4-6 mm inferior to AC/PC plane
We use a combination of MRI and CT imaging to minimize error
STN

10. Physiologic Localization of STN
Optimal localization requires isolating the activity of single neurons by using micro-electrodes
Micro-drive moves the electrodes in small steps
Signal passed through preamplifier, amplifier, and filter
Signal displayed on oscilloscope or digitally on a computer monitor and, as audio signal
On-line display of signal, isolated spikes, and firing rates
Current system is FDA approved and combines all of these functions
We use 3 para-sagittal microelectrodes to increase efficiency
Frederick Hare - FDA approved
Stereotactic Localization
Micro-Electrodes
Physiology Computer
Micro Drive

11. Physiologic Localization
1 sec 9 10 1 2 3 4 6 7 8 11 12 5
Electrode
Trajectory
Thalamus
Zona
Incerta
Depth in (mm)
Tremor
Cell
Subthalamic
Nucleus
Para-sagittal Section - 12 mm lateral

12. Electrode Implantation in STN
Once optimal location is determined then DBS electrode is placed
Electrode is tested
If all is well, electrode is secured and placed in subgaleal pocket
Patient is placed under general anesthesia and pulse generator is implanted in infraclavicular area
Patient allowed to recover
Stimulator turned on after 2 weeks
Stimulator and medication adjustments by movement disorders team

13. STN Stimulation Pros Cons Adjustable and reversible
Greater improvement in “OFF” period motor scores than unilateral pallidotomy
Some improvement in “ON” period motor scores whereas most pallidotomy studies show no improvement
Reduction in l-dopa requirements
Well tolerated bilaterally except perhaps in older patients
Cons
No direct effect on dyskinesias
Longer and more complicated surgery
Problems associated with long-term implant: infection, migration, malfunction, and battery replacement

14. Unilateral Pallidotomy
Pros
Significant improvement in “OFF” period scores
Significant reduction in dyskinesias
Relatively well-established and standardized technique
Surgery is shorter and less difficult
No need for implanted hardware
Relatively few complications
Cons
Irreversible lesion
Smaller effect during “OFF” period
No effect during “ON” period
No change in l-dopa dosage
Potential for side-effects with bilateral lesions

15. Thalamic Stimulation for Tremor
Primary indications are essential tremor, MS-related tremor and in rare cases tremor-predominant PD
Target is Vim nucleus of thalamus
Stimulation appears to be as effective as thalamotomy
90% of patients with ET have good response
60% of patients with MS have good response
In recent prospective randomized trial patients with thalamic stimulators reported a better functional outcome than patients with thalamotomy
Long-term effects not well-known

16. Conclusions
Currently, there are a number of effective and relatively safe surgical techniques for the treatment of PD
Factors to consider include patient age, primary source of disability, and patient's wishes
Pallidotomy may be preferable for patients who suffer from dyskinesia as the major source of disability and in cases where frequent stimulator adjustments are impractical
STN stimulation may be suitable for patients with significant OFF period disability and in younger patients in whom it may be desirable to maintain intact circuitry