Deep Brain Stimulation
Surgical therapies may be considered during the course of Parkinson's disease (PD), especially if symptoms cannot be adequately controlled with medication. Similar to all of the presently available Parkinson's drugs, surgical options offer symptomatic benefit. They can ease symptoms but have not been proven to change the underlying course of disease. Older surgeries (e.g., pallidotomy and thalamotomy) involve the targeted destruction of brain cells contributing to symptoms. While these procedures are still done in certain situations, they have largely been replaced by deep brain stimulation (DBS), which delivers electrical pulses to brain cells to decrease symptoms.
BENEFITS OF DEEP BRAIN STIMULATION
DBS is the most commonly performed surgical treatment for Parkinson's, but it's not for everyone. It is usually done in people who have had Parkinson's for at least four years and still get a benefit from medication but have motor complications, such as significant "off" time (periods when medication isn't working well and symptoms return) and/or dyskinesia (uncontrolled, involuntary movements). DBS typically works best to lessen motor symptoms like stiffness, slowness and tremor. It doesn't work as well for imbalance, freezing when walking or non-motor symptoms. DBS may even exacerbate thinking or memory problems so it's not recommended for people with dementia.
A general rule is that DBS will likely improve Parkinson's symptoms that respond to medication. (The opposite is also true: symptoms that don't get better with medication probably won't respond to DBS.) In the appropriately selected person, DBS can be very beneficial to lessen symptoms and medication requirements, as well as to decrease side effects that can accompany drug therapy.
THE EVALUATION PRIOR TO DBS SURGERY
A team of experts, including a movement disorder specialist (a neurologist with extra training in Parkinson's) and a neurosurgeon (a doctor who performs DBS procedures), conduct an extensive assessment when considering DBS for someone. The evaluation consists of medication and symptom review, examination both on and off Parkinson's drugs, brain imaging, and oftentimes also detailed memory/thinking testing (to detect any problems that could worsen after DBS). If DBS is offered, it's important to discuss the expected benefits (e.g., decreased tremor, fewer medications, etc.) as each person's experience is unique. It's also critical to discuss the potential surgical risks, including bleeding, stroke and infection.
THE DBS PROCEDURE AND DEVICE PROGRAMMING
In DBS surgery, thin wires called electrodes are placed into one or both sides of the brain in specific areas (either the subthalamic nucleus or the globus pallidus interna) that control movement. Usually a person remains awake during surgery so that he or she can answer questions and perform certain tasks to make sure that the electrodes are positioned correctly. However, some medical centers now are using brain imaging to guide the electrodes to the right spot while a person is asleep. Each method has its pros and cons and may not be suitable for everyone or available everywhere.
Once the electrodes are situated, they are connected to a battery-operated device (similar to a cardiac pacemaker) that is typically placed under the skin below the collarbone. This device, called a neurostimulator, delivers continuous electrical pulses through the electrodes to decrease Parkinson's symptoms.
A few weeks after surgery, a movement disorder specialist uses a handheld programmer to set parameters, tailored to each individual's unique symptoms, into the neurostimulator. The DBS settings are gradually tweaked over time and medications are simultaneously adjusted. Most people are able to decrease (but not completely discontinue) Parkinson's drugs after DBS. Determining the optimal combination of drugs and DBS settings -- that which gives the most benefit and the least side effects -- can take several months and even up to a year.
HOW DEEP BRAIN STIMULATION WORKS
Exactly how DBS works is not completely understood, but many researchers and specialists believe that DBS regulates abnormal electrical signaling patterns in the brain. In order to control normal movement and other functions, brain cells communicate with each other using electrical signals. In Parkinson's disease, these signals become irregular and uncoordinated and lead to motor symptoms. DBS basically interrupts the atypical signaling patterns in a way that allows the cells to communicate more smoothly and thereby lessens symptoms.
RESEARCH ON DBS AND PARKINSON'S
Researchers are working to improve upon the existing DBS devices and surgical methods with the goal of making the therapy beneficial for more symptoms and therefore for a greater number of people. Some researchers are targeting DBS to a different area of the brain -- the pedunculopontine nucleus (PPN) -- to treat walking and balance problems that don't typically improve with present-day DBS strategies. Others are developing so-called "smart" DBS, in which devices record a person's unique brain signals and deliver electrical stimulation only when needed, such as when symptoms return, rather than continuously, as the current systems do.
Advances in the understanding of DBS mechanisms and improvements in the devices and surgical approaches may eventually make the therapy effective for more symptoms and, as a result, for a wider variety of people at different stages of Parkinson's.