Surgery

Ablation surgery:

• The procedure to locate, target and then lesion or ablate the area of the brain which produces the abnormal impulses that result in tremors and other associated Parkinson's disease symptoms. The lesion therefore targets the basal ganglia. Surgeries involving lesioning of the thalamus, subthalamus and globus pallidus are respectively named thalamotomy, subthalamotomy and pallidotomy. In all of the following surgeries a surgical lesion is made by insertion of a small electrode resulting in electrocoagulation of the target. MRI imaging is used before surgery in order to prevent damage of vital structures.

• Thalamotomy: Primarily helps patients who are experiencing severe disabling tremor. Involves lesioning of the ventral intermediate nucleus of the thalamus and can also improve rigidity. In doing so this surgery is also thought to worsen bradykinesia and gaiting stance and is therefore rarely used.  This is the oldest of the surgeries used to treat Parkinson's disease.

• Subthalamotomy: This involves the lesioning of the subthalamic nucleus. This nucleus is known to have an excitatory effect on the internal part of the globus pallidus, and can be associated with Parkinson's disease symptoms when overactivated. This target here is considered to be a method of alleviation of these symptoms, such as improvement of akinesia, tremor and rigidity. However, there are thought to be complications associated with this method of treatment that are seen to result in ballismus or large flailing limb movements. Finally, this method of treatment shows no alleviation of dyskinesias and its safety is a controversial matter.

• Pallidotomy: This is the most common form of ablative surgery used in the treatment of Parkinson's disease. A reduction of dopamine in the substantia nigra results in an increase of activity seen in the globus pallidus. It is this which results in an inhibitory effect on the thalamus, brainstem and cortex and therefore leads to bradykinesia as observed in Parkinson's disease. Through the use of levodopa the inhibitory effects of the globus pallidus can be initially restored, however, as previous stated, the extensive use of levodopa in the treatment of Parkinson’s disease can lead to severe dyskinesias. It it this dyskinesia that pallidotomy works to improve by ablation of the internal part of the globus pallidus, and has been seen to have significant effect in drug induced dyskinesias. Pallidotomy has also been shown to reduce dystonia.

Deep Brain Stimulation (DBS):

• This procedure is thought to be comparative to ablative surgery and is used to treat the slowness and tremors which may be seen in Parkinson’s disease, in doing so improving the symptoms. The procedure involves the insertion of a pulse generator subcutaneously in the chest. From this a wire runs under the skin to a small stimulating electrode which is inserted deep within brain. The insertion of this electrode into such a small target requires 1-2mm precision. High frequency electrical currents produced by the pulse generator are sent to the brain therefore acting as a brain stimulator.

• The process acts to temporarily disable overactive cells which may be causing the symptoms of Parkinson’s disease. The process therefore, stimulates the same effect as a lesion without permanently destroying any brain tissue. The usual sites for treatment via this method are the internal part of the Globus pallidus (therefore mimicking the effects of pallidotomy surgery) or the subthalamic nucleus (same effect as subthalamotomy).

Therapy through surgery has been seen to provide greater relief of symptoms with fewer side effects than most other available treatments.  It has been shown that this procedure, when undertaken via the subthalamic nucleus, can provide significant improvement of bradykinesia and tremor, and with this improving the patients number of ‘on’ days where mobility is not a problem and dyskinesias are limited.

Finally, DBS has also been shown to improve mobility during the ‘off’ phases therefore producing a reduction in the fluctuations experienced in Parkinson’s.

Transplantation or restorative surgery:

• This method of treatment is one that is relatively new and one who’s effect in Parkinson’s disease remains in question. The procedure involves the implantation of dopamine producing cells or tissues into the brain of patients with advanced Parkinson’s disease. Some work has involved the transplantation of tissue from the adrenal gland into to striatum. However, results in this method have been shown to be unsuccessful due to the transplanted tissues being unable to survive.

A current study focuses on human embryonic tissue transplants, however, the results to this again are variable. Pig embryo tissue transplantation has also been investigated however, there are many concerns involving how ethical and dangerous such a procedure may be. Stem cell therapy may therefore be an option for the future through the use of adult neural stem cells, embryonic stem cells, embryonic neural stem cells and through xenograft of specially reared pig embryos.

Image Courtesy of Andrew Gillies user of Wikimedia Commons under the terms of the GNU Free Documentation License.