Parkinson's disease is a disorder of certain nerve cells in the brain that normally produce a chemical called dopamine, which helps the brain direct and control movement. In Parkinson's disease, these dopamine-producing nerve cells break down, causing dopamine levels to drop and affecting the brain signals that direct movement.
The classic symptoms of Parkinson's disease are shaking (tremor), stiff muscles (rigidity), and slow movement (bradykinesia). A person with fully developed Parkinson's disease may also have a stooped posture, a blank stare or fixed facial expression, speech problems, and problems with balance or walking. He or she may also have confusion and memory loss.
The cause of the disease is unknown. Parkinson's disease usually begins in middle or late life, rarely before age 50—except in cases where genetic causes are suspected. The disease usually progresses gradually over many years, often at different rates in different people. There is no cure for Parkinson's disease, but medicine and in some cases surgery can help relieve symptoms.
Multiple sclerosis (MS) is a chronic disease of the central nervous system. It is thought to be an autoimmune disorder. It is an unpredictable condition that can be relatively benign, disabling or devastating. Some individuals with MS may be mildly affected, while others may lose their ability to see clearly, write, speak or walk when communication between the brain and other parts of the body becomes disrupted.
Myelin is a fatty tissue that surrounds and protects the nerve fibers. Myelin is lost in multiple areas with MS. This loss of myelin forms scar tissue called sclerosis. These areas are also called plaques or lesions. When damaged in this way, the nerves are unable to conduct electrical impulses to and from the brain.
There are many possible causes of MS, including the following:
- Autoimmune disorders
- Infectious agents, such as viruses
- Environmental factors
- Genetic factors
However, not enough is known about the role these factors play to definitively describe why a particular patient develops MS. The symptoms of MS are erratic. They may be mild or severe, of long duration or short. They may appear in various combinations, depending on the area of the nervous system affected.