Parkinson's Disease | Pallidotomy

Pallidotomy

In the early 1900's before the advent of modern anti parkinsonian drugs, surgical treatment of Parkinson's disease was most common. A variety of operations aimed at destroying certain areas of the brain were carried out in an attempt to relieve severe tremor and rigidity. In 1952, Dr. Lars Leksell performed pallidotomy and showed that it was effective in relieving parkinsonian symptoms. At that time, the preferred surgical target for Parkinson's disease surgery was thalamus. However, after the introduction of Levodopa, pallidotomy took the back seat. Uncontrolled dyskinesias appeared as a side effect of prolonged levodopa treatment. Alternative drugs provided only temporary relief for this disabling side effect. This forced the surgeons to rethink about the surgical treatment for Parkinson's disease. In 1985 Dr. Lauri Laitinen from Sweden demonstrated that the pallidotomy described by Dr. Leksell could be effective in treating advanced Parkinson's disease patients. He modified the surgical target within the pallidum and achieved the better control of the symptoms. Many of his patients suffered from severe bradykinesia, rigidity, tremors and other unusual involuntary movements. These patients had long standing severe Parkinson's disease and suffered from drug-induced dyskinesias. He reported his first pallidotomy series of 38 patients in January 1992 and claimed that 80% to 90% of the patients had a long lasting relief of symptoms. This encouraging experience prompted other specialists to re-examine the role of pallidotomy in Parkinson's disease. Pallidotomy has been found to be most effective in controlling drug induced dyskinesias, dystonia and other associated with off phase symptoms.

The surgical target for pallidotomy is the most vetro-medial part of the globus pallidum known as Globus pallidum internus (Gpi). This part of the Gpi is located in close relationship to the internal capsule and optic tract. Internal capsule carries nerve fibers that are responsible for motor function and any damage to these fibers can cause weakness on the opposite side of the body whereas the optic tract carries the fibers for the vision and any damage to these fibers can cause visual field defect. These side effects can be avoided by using the expertise and experience of a functional neurosurgeon.

Fig. 1. Drawing showing the relationship of the pallidal target to the internal capsule and optic tract

Candidates for Pallidotomy

We currently advocate pallidotomy for the following group of patients

Patients who have predominantly unilateral Parkinson's disease with drug-induced dyskinesias.
The patients who have marked motor fluctuations such that the significant portion of the day is spent in functionally impaired state. This includes dyskinesia and off period symptoms.
Patients suffering from severe pain related to off medication period which cannot be improved upon by drug adjustments. Severe painful off phase dystonia is also an indication for surgery.
The patients who have unpredictable symptomatic relief that prevent establishment of a consistent medical regime.
Patients suffering from primary idiopathic dystonia

Surgical protocol

The patient is evaluated by the movement disorder neurologist prior to surgery. The patient is admitted two days prior to surgery. On the preoperative day the patient undergoes UPDRS, H&Y and Schwab and England activities of daily living assessment in "off" medication condition. A video recording is also performed at this stage. The same protocol of assessment and video recording is performed in "on" condition. Patient is observed in neurosurgical intensive care for one day after surgery and discharged on the third postoperative day. Follow up visits are scheduled at 1, 3, 6 and 12 months after surgery.

Surgical technique of Pallidotomy

We perform pallidotomy using CRW Stereotactic apparatus and macrostimulation. The stereotactic frame is fixed to the patient's head with the help of four pins. The area of fixation is numbed with the help of local anesthetic. The stereotactic frame is placed in a plane parallel to the orbitomeatal line. Following this the patient is taken to the CT scan department where an axial CT scan is performed. The scanner gantry is angled in a plane to include the anterior commissure (AC) and posterior commissure (PC) in one plane. These are fixed landmarks in the brain to which the target can be related. For high degree of accuracy the CT slices are 2mm thick and contiguous. The length of the AC-PC is measured. The pallidal target is 2mm in front of the mid point of AC-PC line at a laterality of 21-22mm and a depth of 4-6 mm. A inversion recovery, coronal, MRI scan is performed perpendicular to the AC-PC plane. The pallidal target is on a slice that passes through the mamillary body. The correct laterality and depth of the pallidal target is confirmed on this MRI and the CT target refined accordingly. Once the target is defined the patient is taken back to the operation theatre and made to comfortably lie down on the operation table. A small opening (burr hole) is made in the skull after infiltrating local anesthetic at the operative site. The target is reached with the help of stereotactic arc system.

The physiological exploration is performed using an electrode with an exposed tip of 2 x 2 mm. This is introduced through a precoronal burr hole. The exploration starts 6 mm above the target and the electrode is advanced in increment of 2 mm using micro drive. At each level stimulation is performed using 5 Hz. and 100 Hz. frequencies. Impedance, which is a measure of resistance of various tissues, is also noted at each level to discriminate between nuclei and fiber tracts. Motor evaluation to check for weakness, dysarthria and fasciculation's in tongue is performed at 5 Hz. Sensory evaluations is performed at 100Hz. frequency. During sensory stimulation there are some dyskinetic movements and decrease in rigidity. Patient is also asked to report any flashes of light or visual disturbances, indicating close proximity to the optic tract. If there are any motor or sensory side effects the electrode position is adjusted. If there are no side effects than a test lesion of 42 C for 60 seconds is made at this point, and if there is no deficits than a final lesion of 70C for 60 seconds is made. Similar procedure is repeated at a level 4mm, 2mm and at 0 target level.(Fig.2)

Fig. 2. Postoperative MRI a: Axial and b: Coronal, following pallidotomy. Note the relationship of the lesion to internal capsule and the optic tract

Pallidal stimulation is performed using similar technique. We mainly restrict the use of pallidal stimulation for the treatment of dystonia. We feel that STN stimulation is better than pallidal stimulation in the treatment of advanced Parkinson's disease.

Following the surgery the patient is observed in intensive care unit for 24 hours. In case of thalamic stimulation the IPG (Implantable pulse generator) is implanted on the next day and the programming of the electrode is commenced the day after. The usual hospital stay for thalamotomy is four days, whereas that for the thalamic stimulation is 10 days.

Untoward side effects resulting from a physiologically guided selective Vim thalamotomy are minimal. The most common complications of thalamotomy are pyramidal weakness, dysesthesia, cognitive and speech deficits. The cognitive and speech deficits are more commonly seen in left sided and bilateral thalamotomy. Due to increased incidence of morbidity, bilateral thalamotomy is not performed any more. The risk of intracerebral hemorrhage and infection is less than one per cent.

Results
Pallidotomy is a useful surgery in the armamentarium of Parkinson's disease treatment. When performed in a carefully selected group of patients it provides a significant improvement in the quality of life. The risk of major complications and mortality is less than 2%. It is at present the most acceptable form of surgical treatment for the idiopathic dystonia. Pallidal stimulation has proven to be superior than any other treatment in primary dystonia.