What techniques are used to treat Parkinson's?
At present there are four main areas of interest in surgery for Parkinson's:
-
Lesioning (pallidotomy, thalamotomy and subthalamotomy)
-
Gamma knife surgery
-
Deep brain stimulation (thalamic, pallidal and subthalamic stimulation)
-
Brain implants using foetal brain tissue.
Lesioning
These techniques involve making selective damage (a lesion) to certain cells within specific areas of the brain. The target site is located with the aid of computer technology. An electrode is then inserted with its tip at the optimum point. A small destructive lesion is then made by passing an electric current through the tip. These lesions are known to have a beneficial effect on some of the symptoms of Parkinson's.
The main target sites for lesioning are:
Thalamotomy involves making a lesion in a part of the thalamus. This technique is now used mainly to treat drug-resistant tremor. It is usually done on one side only as thalamotomy on both sides is thought to be too risky.
Pallidotomy is regaining popularity as a procedure and is now the most common form of lesioning technique used. The target site is located in the part of the brain known as the globus pallidus. Pallidotomy is most important for its dramatic effect on rigidity and akinesia (slowness of movement) and reductions in the sudden, involuntary movements (dyskinesia) that can result from drug therapy. Some bilateral pallidotomies are being performed for optimum symptom control. However, these carry increased surgical risks.
Subthalamotomy has been performed by neurosurgeons at a few centres. This procedure involves making a destructive lesion in the subthalamic nucleus rather than implanting an electrode as is the case with subthalamic stimulation (see below). Subthalamotomy is still experimental. However, if it can be shown to be as safe and effective as deep brain stimulation (see below), it might become the treatment of choice for the future; particularly as it may be more cost effective and will not require specific life-long monitoring and follow-up as deep brain stimulation does.
Gamma knife surgery
Gamma knife surgery is a development in the application of lesioning. It is a form of radiotherapy that focuses one dose of gamma radiation through the skin and skull. The effects of gamma knife surgery may take weeks or months to be seen, and its' risks relative to other surgical procedures are not yet known.
The difference between gamma knife surgery and traditional lesioning techniques is that gamma knife surgery is non-invasive, and it cannot be monitored during the procedure by testing the person with Parkinson's response to an internal electrode. Therefore, gamma knife surgery is, at present, usually only offered to people with Parkinson's who are not fit enough for conventional surgery. It is only availably privately or as part of a clinical trial.
Deep brain stimulation
Deep brain stimulation works by implanting a wire electrode into one of three target sites: the thalamus (thalamic stimulation), the globus pallidus (pallidal stimulation) or the subthalamic nucleus (subthalamic stimulation). The stimulator mimics the effect of a lesion, but it is reversible. The wire is connected to an Implantable Pulse Generator (IPG), which is implanted under the skin in the chest, rather like a pacemaker.
The IPG contains the battery and electronics necessary to generate the electrical signals for the stimulation. On a day-to-day basis the stimulation can be switched on and off by the person with Parkinson's using a hand-held programmer or small magnet.
Deep brain stimulation of the subthalamic nucleus is the current site of choice for stimulation, for it is effective on all the symptoms of PD. It can also enable drug dosages to be substantially lowered with consequent reduction of drug-related dyskinesias. The long-term outcome of deep brain stimulation is not known.
A separate information sheet on Deep Brain Stimulation (Code FS12) is available from the PDS.
Implantation of foetal brain tissue
For several years research has been carried out into the possibility of replacing the dead and dying dopamine-producing cells with transplanted brain tissue from human foetuses. The hope is that the foetal tissue will produce dopamine and hopefully correct the problems concerned with dopamine deficiency. Results so far have been very mixed and the treatment is still very experimental. Researchers estimate that it will probably remain so for at least 5-10 years.
What are the risks?
Each form of surgery for Parkinson's carries its own risks and these should be discussed with the consultant. However, some of the general risks associated with these techniques and which need to be considered include increased risk of a stroke leading to paralysis, cognitive changes, speech problems, and very rarely to death.
Who is suitable for surgery?
Surgery is not suitable for everyone. It is generally used to treat people who have had Parkinson's for some time and who are finding that their symptoms are not controlled effectively by medication and/or are experiencing very troublesome dyskinesias. The risks of surgery may be increased in very elderly people and those with other conditions, which might cause complications. Most surgeons would not perform surgery on someone who is experiencing confusion or psychosis, or who has severe depression.
Is further information available?
The main source of information and advice is the consultant who can refer on to a neurosurgeon if appropriate. Each person with Parkinson's will have his or her own questions and concerns about surgery. It is important for people who are considering surgery to ensure that they understand fully the procedure involved, the possible benefits and potential risks. It may be helpful to ask how many of the proposed procedures the neurosurgeon has performed and what results they have achieved so far.
What does the future hold for surgery?
There are currently many unanswered questions concerning surgical techniques for Parkinson's and further research is necessary. At the present time researchers are unsure as to how long beneficial results may last or if any procedures may delay the progression of Parkinson's. There is also some debate over the benefits of lesioning against stimulation.
The relative merits of surgery and medical treatment have never been assessed in a clinical trial until now, so all information is anecdotal and could potentially be biased. The UK Medical Research Council and the PDS are funding a large clinical trial to address this, called PD SURG. If you are referred to a neurosurgeon, he or she might ask you if you would like to participate in the trial.
Another possibility is that the best symptom control may be obtained from using a combination of surgical techniques. The questions need to be addressed in further clinical trials. Future surgical therapeutic options, which currently remain experimental, are aimed at replacing and/or restoring the dying dopamine cells.
There have been many exciting developments in surgical treatment for Parkinson's in recent years and the future looks promising. However, it is unlikely that surgery will ever be the most appropriate treatment for everyone.
We are indebted to the Parkinson's Disease Society for their help in compiling this section.
