This surgery is based on the assumption that people with PD experience an overactivity of their globus pallidus on each side of the brain. In order to qualify for this surgery, the patient must be disabled by the disease and experience little or no relief with medication. Before the surgery, the patient must go through neurological and neuropsychological testing, a motor test, and a physical evaluation. Magnetic resonance imaging is also done.
Procedure
A computerized tomography scan is performed to identify the globus pallidus and other vital structures in the nearby area. A stereotactic head frame is attached under a local anesthetic. The patient must be conscious so that the surgeon can test alertness, vision, and speech. A burr hole is made, and a computer guided lesioning probe is inserted into the target area, which was previously specified by the CT and MRI scans. Electrical stimulation is applied, and a series of heat lesions are used to ablate an area of the globus pallidus. This interrupts the pathway responsible for rigidity, akinesia, and tremors.
This procedure poses some risks, and is only effective for 5-10% of patients. About 5% of patients experience some sort of complication from the surgery, the most severe of which is a stroke, caused by insertion of surgical implements into the brain. For those who respond well to L-dopa and dopa decarboxylase inhibitor, who have major tremors or an advanced case of PD, pallidotomy is not the best option. Although there has been a great deal of positive press attention to this, the bottom line is that it is a last-ditch treatment, and its greatest benefit is that the effects of L-dopa are extended for some time. (Gilbert, 1998)
Until the creation of L-dopa in 1967, this surgery was the treatment of choice for many patients with severe PD. With no drugs available, the only option was to destroy the part of the brain responsible for the uncontrollable tremors. Even though the surgery seemed successful in decreasing tremor, there was no effect on akinesia. Also, as the disease progressed, a second contralateral lesion was usually made. This often resulted in a high incidence of severely impaired speech and swallowing difficulties. (Quinn, 1998)
Procedure
The procedure for the thalamotomy is very similar to that of the pallidotomy. Actually, this procedure led to another type of surgical treatment, Deep Brain Stimulation.