Definition of Parkinson's disease:

Parkinson's disease is a disorder of the brain that leads to shaking (tremors) and difficulty with walking, movement, and coordination.

Causes, incidence, and risk factors:

Parkinson's disease most often develops after age 50. It is one of the most common nervous system disorders of the elderly. Sometimes Parkinson's disease occurs in younger adults. It affects both men and women.

In some cases, Parkinson's disease occurs in families. When a young person is affected, it is usually because of a form of the disease that runs in families.

Nerve cells use a brain chemical called dopamine to help control muscle movement. Parkinson's disease occurs when the nerve cells in the brain that make dopamine are slowly destroyed. Without dopamine, the nerve cells in that part of the brain cannot properly send messages. This leads to the loss of muscle function. The damage gets worse with time. Exactly why these brain cells waste away is unknown.

Parkinson's in children may occur because the nerves are not as sensitive to dopamine. Parkinson's is rare in children.

The term "parkinsonism" refers to any condition that involves the types of movement changes seen in Parkinson's disease. Parkinsonism may be caused by other disorders (such as secondary parkinsonism) or certain medications.