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 was first described in England in 1817 by Dr. James Parkinson. The disease affects approximately 2 of every 1,000 people and most often develops after age 50. It is one of the most common neurologic disorders of the elderly. Sometimes Parkinson's disease occurs in younger adults, but is rarely seen in children. It affects both men and women.

In some cases, Parkinson's disease occurs within families, especially when it affects young people. Most of the cases that occur at an older age have no known cause.

Parkinson's disease occurs when the nerve cells in the part of the brain that controls muscle movement are gradually destroyed. The damage gets worse with time. The exact reason that the cells of the brain waste away is unknown. The disorder may affect one or both sides of the body, with varying degrees of loss of function.

Nerve cells use a brain chemical called dopamine to help send signals back and forth. Damage in the area of the brain that controls muscle movement causes a decrease in dopamine production. Too little dopamine disturbs the balance between nerve-signalling substances (transmitters). Without dopamine, the nerve cells cannot properly send messages. This results in the loss of muscle function.

Some people with Parkinson's disease become severely depressed. This may be due to loss of dopamine in certain brain areas involved with pleasure and mood. Lack of dopamine can also affect motivation and the ability to make voluntary movements.

Early loss of mental capacities is uncommon. However, persons with severe Parkinson's may have overall mental deterioration (including dementia and hallucinations). Dementia can also be a side effect of some of the medications used to treat the disorder.

Parkinson's in children appears to occur when nerves are not as sensitive to dopamine, rather than damage to the area of brain that produces dopamine. Parkinson's in children is rare.

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