Invasive intervention to alter the functions of brain structures involved in movement that become dysfunctional in Parkinson’s disease. Surgeries may involve the creation of lesions, or scars, through a technique called ablation (burning a very small segment of tissue, often just selective neurons) to interrupt the flow of nerve signals, the installation of deep brain stimulation electrodes to remodulate pathologic patterns of neuronal output, the implantation of tubes for the infusion of neurotrophic factors, the implantation of dopamine producing cells, or other possible interventions to improve Parkinson’s symptoms such as TREMORS, BRADYKINESIA, AKINESIA, and other dyskinesias. Because the risks associated with any surgery of the brain are relatively high, surgery to treat Parkinson’s typically becomes an option only when anti-parkinson’s medications no longer suppress motor symptoms. The most common surgical procedures are:
• deep brain stimulation (dbs), which is temporary and modifiable
• pallidotomy, which creates a lesion in the pal-lidus to relieve bradykinesia, akinesia, and other dyskinesias
• thalamotomy, which creates a lesion in the thalamus to relieve tremors
Researchers are exploring other surgical treatments that are still investigational, too, such as subthalamotomy stem cell implant, fetal dopaminERGIC CELL TRANSPLANT, and FETAL PORCINE BRAIN CELL TRANSPLANT.
Neurosurgeons use stereotactic frames, structures that attach to the skull, to assure precise placement of electrodes for these surgeries. This procedure allows computer-guided probe advancement, minimizing the risk of damage to adjacent tissues and to cells along the path of the probe. magnetic resonance imaging (MRI) helps neurosurgeons to locate and reach the sites within the brain where they wish to place the macroelectrodes to create the ablations or to implant macroelectrodes for deep brain stimulation. Microelectrodes are often inserted prior to the macroelectrode so that the electrical activity of target cells can be determined to see if they match the expected activity of the target (for example, cells firing in synchrony with the tremor in the thalamus, or cells that fire with passive movement of the involved limb in the globus pallidus) in a technique known as microelectrode recording. The person is mildly sedated for relaxation during the surgery but awake so the electrophysiology remains optimal for microelectrode recording and he or she can respond to questions and instructions from the neurosurgeons. The person’s responses help the surgeon ensure proper placement of the microelectrodes and test the effectiveness of the ablation or stimulation by using a brief test stimulation to ensure both efficacy and lack of side effects. Many results from ablative procedures are immediately apparent, although during the recovery period of eight to 10 weeks most people notice fluctuations in their symptoms as the tissue surrounding the ablated lesion first swells and then recedes, as a normal aspect of the healing process.
Benefits of Surgery
Surgical procedures can provide long-term relief from the most troublesome symptoms of Parkinson’s. As with medical treatments for Parkinson’s, it is difficult to predict exactly how a person’s symptoms will respond, partly because the physiology of the brain is unique from individual to individual and partly because the surgery disrupts only the consequences of Parkinson’s and cannot stop its progression. Eventually the disease progresses and symptoms will likely return and worsen. Most people continue to take anti-Parkinson’s medications after surgery although some surgeries are associated with significant expected reductions in the amount of medication required, which improves dopaminergic side effects.
Risks of Surgery
The risks of surgery for Parkinson’s disease are substantial, as they are for any procedure that enters the brain. Even with impeccable sterile technique it is impossible to rid the surface of the skin of bacteria completely; surgical instruments can carry bacteria into the brain, where they can cause infection. As well, bleeding can occur within the brain and cause damage to neurons. The consequences of such side effects can be minimal or catastrophic, depending on the areas of the brain that they affect and whether neurosurgeons can intervene to treat them.
A key risk of the surgeries for Parkinson’s is damage to adjacent tissues and structures during the placement of the microelectrodes and the macroelectrodes; these structures are not clearly delineated or consistent in terms of their physical location and structure. The pallidus and thalamus are very close to the optic tract, the path of nerve structures that manage vision. The neurosurgeon repeatedly asks the person whether he or she sees flashes of light or any other visual representations, which are a clear sign that the probe is very near the optic tract. Damage to the optic tract can result in permanent vision problems. It also is possible for the probe used to guide electrode placement to cause damage along the path of its progression into the thalamus or globus pallidus, with potential to cause temporary or permanent movement dysfunctions other than those of the Parkinson’s, including localized, regional, or extensive paralysis. Although many complications are obvious immediately, others do not appear until weeks or even months after the surgery.
Determining Whether and When Surgery Is Appropriate
Perhaps only 20 percent of people with Parkinson’s are likely to benefit from current surgery options. Those who experience the greatest level of success
• Are younger than age 70. People who are older have a more difficult recovery from the stress of surgery and seem to experience less substantial effects from surgical interventions.
• Have been taking anti-Parkinson’s medications and have reached the point at which they have significant fluctuations with good on-states and either severe on-dyskinesias or significant off-state symptoms.
• For subthalamic or pallidal targets, have primarily bradykinesia and akinesia.
• For thalamic targets have only tremors.
People who generally do not benefit significantly from surgery for Parkinson’s
• Derive reasonable control of symptoms through anti-Parkinson’s medications, with minimal off-state episodes.
• Have a Parkinson’s plus syndrome or rapidly advancing, severe Parkinson’s symptoms that do not respond well to anti-Parkinson’s medications.
• Have other significant health problems such as hypertension (high blood pressure), heart disease, or diabetes.
• Have dementia or significant cognitive impairment.
It is important that the person to have appropriate expectations and a full understanding of the potential benefits and risks. Surgery cannot cure Parkinson’s disease; nor can it eliminate the need for, at a minimum, levodopa. It is not possible to know how an individual will respond, or how long the effects will last. Each person must consider his or her unique circumstances.