Parkinson's Disease Parkinson's disease is a progressive neurological disease that affects movement. The condition occurs when a group of cells in an area of the brain, called the substantia nigra, become impaired or die. These brain cells are normally responsible for production of the brain chemical, dopamine, which aids in transmission of messages in the parts of the brain that control smooth movement and coordination. In patients with Parkinson's, these brain cells die off at a faster rate, causing a drop in the production of dopamine.

According to the Parkinson's Disease Foundation, about one million Americans have Parkinson's disease; 40,000 new cases are diagnosed every year. The condition usually develops after 65, but can occur at younger ages. About 15 percent of Parkinson's patients are under 50.

Symptoms of Parkinson's don't appear until a patient has lost about 80 percent of his/her dopamine-producing cells. The earliest sign is usually a tremor on one side of the body, typically in the hand. At first, the tremor is apparent while the limb is at rest and commonly subsides when the limb is in motion. Eventually, the tremor becomes more apparent and spreads to the other side of the body. Other major signs of Parkinson's disease include rigidity (stiffness caused by increased muscle tone), bradykinesia (slowness of movement) and impaired balance and coordination. Some people with Parkinson's disease also experience changes in speech, problems with swallowing, depression, sleep disturbances, memory problems, personality changes, loss of facial expression or sexual dysfunction.

Treating Parkinson's Disease There is currently no cure for Parkinson's disease. Treatments are aimed at improving symptoms and quality of life. One common therapy is a combination of the drugs levodopa and carbidopa. Nerve cells use levodopa to make dopamine, increasing the supply of the chemical to the brain. The drug, carbidopa, delays the conversion of levodopa by the body until it reaches the brain. Levodopa is most helpful for reducing signs of rigidity and bradykinesia.

Some Parkinson's patients may benefit from a treatment called deep brain stimulation. In this procedure, tiny electrodes are implanted into target areas of the brain. The electrodes are connected to a battery-operated pacemaker-like device (called a neurostimulator) that is implanted under the skin near the collarbone or chest. Once in place, the neurostimulator sends electrical impulses to the electrodes, blocking the signals from the areas causing the Parkinson's symptoms.

Targeting the Brain The electrodes used in deep brain stimulation must be placed in a precise position to effectively treat the symptoms. Traditionally, the planning and surgery is done using a fixed stereotactic frame placed on the patient's head. The metal frame is attached to the patient's skull using surgical screws and pins. With the head frame attached, the patient undergoes brain imaging. The images from the brain scan are combined with calibration points on the head frame to create a computerized map of the brain. That information helps doctors plan the potential locations for the electrodes.

The patient is taken to the surgical suite and the head frame is mounted to the operating table. The patient remains awake during the implantation. After placing a local anesthetic on the head, a small hole is drilled into the skull. Using the brain map for guidance, tiny electrodes are placed on target areas of the brain. As the electrodes are placed in various areas, the patient is asked to respond and report any changes in symptoms or sensations. The process helps to confirm the target location for the implantable electrodes. Once the appropriate area has been located, a permanent electrode is placed in the brain.

The fixed frame system is an important tool in helping doctors place the electrodes in the correct area of the brain. However, the frame is very heavy and a patient is unable to move his/her head once it is locked onto the operating table.

Anant Patel, M.D. a neurosurgeon at North Austin Medical Center, is using a new, frameless system for placement of electrodes in deep brain stimulation. The day before surgery, five tiny markers are implanted into the scalp. These markers serve as reference points. Then, a CT scan is done. On the day of the surgery, a plastic device (about the diameter of the palm of the hand) is mounted into the skull with three tiny screws. With the frameless system, a patient doesn't have to lie with his/her head completely still. The plastic unit is locked onto the skull, so the reference points don't change, even if the patient moves.

Patel says the frameless system is much more comfortable for the patient than using the fixed head frame. The surgery goes a lot faster, and he believes, is more precise.

For information on Parkinson's Disease: American Parkinson Disease Association, http://www.apdaparkinson.org National Institute of Neurological Disorders and Stroke, http://www.ninds.nih.gov The National Parkinson Foundation, http://www.parkinson.org Parkinson's Disease Foundation, http://www.pdf.org