Parkinson's disease is a progressive neurological disorder that results from the loss of neurons in a region of the brain that controls movement. This creates a shortage of the brain-signaling chemical (neurotransmitter) known as dopamine, causing movement problems characteristic of Parkinson's disease. The exact cause of Parkinson's is not currently known.
Although early symptoms of Parkinson's disease
may be subtle, people will eventually develop a characteristic tremor (trembling or shaking) of a limb, especially when the body is at rest. As the disease progresses, symptoms may worsen and new ones may appear.
Although carbidopa-levodopa is an effective Parkinson's medication, its benefits are often limited to about five years of use, at which time the drug may start to cause intolerable side effects and may begin to lose its effectiveness. It is not currently known why this might occur; some people think it is simply a manifestation of the worsening of the disease that normally happens over time.