There has been a recent resurgence in surgery for Parkinson's disease due to advanced diagnostic imaging techniques like CT scanning and MRI scanning.

Surgery to destroy a tiny part of the brain responsible for sending incorrect messages to the movement control centre of the brain began in the 1950s, but the operations were extremely risky and when the drug levodopa was discovered in the 1960s, interest in the operations waned.

However, since the late 1980s, new diagnostic techniques have brought fresh interest in brain surgery. New imaging techniques have helped to reduce the risk of the operation, providing surgeons with more precision. These operations are known as "stereotactic lesional surgery", and are suitable for certain groups of patients.

Surgery is not a cure for Parkinson's disease and surgeons are very selective on who they operate to ensure they get a good result.

It is still not known how the surgery works, but it is very successful for some patients.

There are three different operations used to treat Parkinson's disease: "Pallidotomy" and "Thalamotomy" which have been used in the past, and recently a new technique known as "Deep Brain Stimulation" has been developed.

Thalamotomy:

This operation involves making a cut in the deep part of the brain, known as the thalamus, which is responsible for the tremors in Parkinson's disease.

This operation is effective for tremors, and drug-resistant tremors. The ideal candidate is a young patient, with a shake as the predominant feature on one side that has not responded to drugs.

Complications include weakness down the same side of the body which is being treated, softer speech, and difficulty swallowing. Sometimes these unwanted effects disappear but in some patients they remain.

If the operation is performed on both sides the risk of complications is greater and few surgeons will operate on both sides at the same time or within a short timeframe. Normally they require a space of some years.

Pallidotomy:

The operation also involves destroying part of the brain responsible for Parkinson's disease, but this time the region known as the globus pallidis is damaged. This part of the brain is responsible for the stiffness, slow movements and tremors seen in Parkinson's disease.

This operation helps ease most symptoms of Parkinson's disease. The most dramatic benefit is for patients with drug-induced dyskinesia (involuntary movements), and can reduce these abnormal movements by 90 percent or more. The operation also helps to reduce tremors, slowness of movement and stiffness. Patients are often able to reduce their dose of levodopa following the operation.

The best candidate for this operation would preferably be a young patient who has been on levodopa for sometime but the effects are wearing off and has significant involuntary movements on one side of the body.

Complications include weakness down one side, problems with vision, speech, and an exaggeration of psychiatric problems if the patient has a mental illness.

In Auckland, so far 27 pallidotomy operations have been performed since 1996, with success rates similar to overseas results.

The procedure:

A large metal frame is fitted firmly over the patient's head, and a CT scan or MRI scan is used to determine the correct measurements of the area to be destroyed. The measurements are checked twice, and a probe that is fitted on the frame is placed in the correct position.

Then, with the patient still awake, a mild electric current is passed down the probe to the part which will be destroyed to test the patient's reactions to the current. If the patient gets tingling in the arm or sees flashing lights, it means the measurements may be slightly out.

Once the measurements are absolutely correct, the probe is then placed through the skull and a larger electric current is passed down the probe which heats the tip and destroys the target area.

Deep Brain Stimulation:

This operation is the most recent advance in brain surgery for Parkinson's disease. It involves placing fine wires deep in the brain to the same positions used for either pallidotomy or thalamotomy operations, and attaching them to a small electrical stimulator, similar to a pacemaker, which is inserted in the collar bone.

The stimulator can be turned on and off by the patient with the use of a magnet rubbed over the device, and to alter the amount of electrical current being used to stimulate the brain.

The operation can be carried out on both sides of the brain at the same time, and is believed to work by causing a paralysis of the brain cells involved in the tremor and symptoms of Parkinson's disease.

Surgeons need to be careful to get the balance right in this operation. However, the risks with deep brain stimulation are less than with thalamotomy and pallidotomy, and it can be turned off if necessary.

The operation is expensive and is not yet widely available in New Zealand. It is hoped it will become more accessible in future.

This article is based on a speech to the New Zealand Parkinson's Disease conference by Auckland neurologist Dr David McAuley.

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