The place of surgery in the treatment of Parkinson's disease

Summarized by Robert W. Griffith, MD
November 23, 2000 (Reviewed: February 16, 2003)

Introduction

Although medications are helpful in most Parkinson's patients, there are some in whom they only work well at doses that are accompanied by disabling side effects. Recently, more of these patients have turned to surgical treatment. In fact, destructive surgical lesions in the brain were used in the 40s and 50s as a form of treatment, but the introduction of L-dopa in the '60s led to reduced interest in surgery as a treatment option. However, there has been a revival of the use of surgery, as good results without complications have been reported more frequently. Dr. Kenneth Follett of the University of Iowa Neurosurgery Division has reviewed the various surgical approaches in use today.

In Parkinson's disease there is increased activity of the nerve cells in one part of the brain (the subthalamic nucleus), which causes a parallel increase in activity in two other parts - the globus pallidus and the substantia nigra. These areas are suitable for targeting surgically. The increased activity at these sites causes a suppression of activity in the mid-brain (the thalamus) and the brain stem, as well as in the surface areas of the brain controlling movement (the cortex), all of which is responsible for the symptoms of Parkinson's.

The Surgery

Surgical treatment can mean making a small destructive injury (a lesion) in one or other of the over-active areas, or by regular electrical stimulation of an over-active area, or an under-active area, such as the thalamus.

Who is able to benefit from surgery? People with disabling symptoms that cannot be controlled by medication, or those in whom the medication causes intolerable side effects, are the best candidates. To be sure that surgery is likely to help, they should have at least a slight response to L-dopa medication, to show that the necessary pathways in the brain are functioning. Candidates should not have dementia or severe medical conditions.

The surgery is usually done under local anesthesia, with the subject awake. The surgeon finds his way to the target area using coordinates obtained from a brain scan (a CT scan or an MRI); these are similar to map coordinates, but are, of course, 3-dimensional. When a narrow probe wire has reached the target area, a small electrical stimulus is sent, which produces a movement or a slight sensation that the patient can report. This shows the surgeon that the probe is correctly placed.

Interrupting the over-active signals

In order to produce a small area of destruction (a lesion), an intense radiofrequency is generated at the target site by the probe; this causes a heat-burn of the tissues measuring several millimeters across (about 1/4 inch diameter). Sometimes intense cold or radiation is used to produce the destructive lesion. The globus pallidus on one side can be partially destroyed in this way, which improves tremor, rigidity and bradykinesia (slowing of intentional movements) in most patients. It also improves the movement difficulties caused by L-dopa. Most of the benefits are seen on the side of the body opposite to that of the surgery, with the improvements in tremor lasting for 3 years or more. In some cases both sides of the brain are operated on at the same time, in others the second side is operated on later, if necessary.

Complications are seen in about 5% of cases treated by 1-sided globus pallidus lesions. If the damage spreads beyond the original target area, there may be some loss of vision, paralysis of the face, changes in speech and memory. If both sides are operated on at the same time, there is an increased risk of these complications.

Electrical stimulation

Because of a risk of complications in making permanent lesions, surgeons have resorted to another technique called deep brain stimulation (DBS). This has proved to be safer and more effective than the destructive procedures outlined above. A permanent electrode is passed through the hollow probe to the target site in the brain. A small generator, similar to a cardiac pacemaker, is implanted under the skin below the collarbone, and connected to the stimulating wire, using another wire passed under the skin of the neck, up behind the ear. This part of the procedure is done under general anesthesia. The stimulation values (frequency, amplitude, etc) are adjusted from outside the body, using radio signals. Once the stimulation characteristics have been set up, the patient can activate the system, as needed, using a small hand-held magnet.

As with the destructive lesions, doing DBS placement on both sides is highly effective, and it doesn't have the high rate of complications seen with 2-sided destructive lesions. The stimulation pattern can be reprogrammed fairly easily, which usually eliminates side effects of stimulation. DBS of the pallidum has been shown to be as effective as the corresponding destructive procedure - rigidity, tremor, slow movements, gait, the amount of "on" time, L-dopa movement disorders, and Activities of Daily Living scores are all improved.

The future

DBS of other areas (e.g. the substantia nigra) is been used on an experimental basis in some centers, both within and outside the USA. Doubtless further progress with this technology will be made, paralleling progress in the development of new medications. To date, transplantation of tissues from various organs have yielded disappointing results, compared with those of the surgical approaches described here.

The future for Parkinson's disease treatment is looking better all the time. And in the more distant future, we can expect gene therapy to be used in re-setting or replacing the brain cells that are not functioning properly, so that the basic mechanism underlying the disease can be restored to normal.

Source

• The surgical treatment of Parkinson's disease. KA. Follett, Annu Rev Med, 2000, vol. 51, pp. 135--147

Related Links
The American Parkinson Disease Association (APDA) Worldwide Web

Related Books
Parkinson's Disease & the Art of Moving

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