Parkinson disease is a disorder of the central nervous system that affects different parts of the brain. More than one million people in North America and more than four million people worldwide have the disease. As the general population ages, the number of cases of Parkinson disease increase.
Parkinson disease is known as late onset if symptoms begin after the age of fifty and early onset if symptoms begin before the age of fifty. If symptoms appear before the age of twenty, the disease may be called juvenile onset Parkinson disease. Most cases of Parkinson disease occur in people with no family history of the disease. Approximately fifteen percent of people with Parkinson disease do have a family history of the disease.
Several different areas of the brain are affected by Parkinson disease, including those that regulate blood pressure and heart activity and other involuntary functions. Parkinson disease also affects the substantia nigra — the area of the brain that controls balance and movement. When nerve cells in the substantia nigra die or become impaired, the brain has trouble controlling muscle movement. In a healthy brain, nerve cells produce dopamine, which helps transmit signals to make movement smooth. When the nerve cells that make dopamine die off or become impaired, the communication between the brain and the muscles is weakened.
In many cases of Parkinson disease, protein deposits appear in the dead or impaired nerve cells. Experts aren’t sure whether the protein deposits are responsible for the damage or if they are part of the body’s defenses.
The first (and most familiar) symptom of Parkinson disease is the tremor (shaking) of a limb, especially when the person is resting. The tremor usually begins on one side of the body, and often in one hand; however, tremors can affect the arms, legs, feet, and face. Other symptoms include rigidity or stiffness of limbs and body, slow movement known as bradykinesia, inability to move known as akinesia, loss of coordination, and impaired balance.