Parkinson's Disease

What Is It?

Parkinson's disease is a disease of the central nervous system that causes problems with body motions, including tremor (shakiness), rigidity (muscle stiffness), slowed body movements, unstable posture and difficulty walking. It happens when nerve cells (neurons) in a part of the brain called the substantia nigra gradually die. These cells normally produce dopamine, a chemical that helps to relay messages between areas of the brain that control body movement. The death of cells in this area of the brain leads to abnormally low levels of dopamine, which makes it difficult for a person with Parkinson's disease to control muscle tension and muscle movement, both at rest and during periods of activity.

Parkinson's disease affects about 1 million people in the United States, with approximately 50,000 new cases diagnosed each year. It usually occurs in middle age, typically beginning around age 60. However, about 5 percent of patients have early-onset Parkinson's disease and are younger than 40 years old when symptoms begin. Internationally, Parkinson's disease affects about one to two of every 1,000 people. It affects Europeans and North Americans more frequently than Asians or Africans. It is more common in men than in women.

So far, scientists have not determined the reason why some people develop Parkinson's disease and others do not. The genetics are complex and the influence of family history depends upon the age of onset. A person who has a parent or sibling that was diagnosed with the disease at a younger age is at higher risk of getting Parkinson's, but not if the affected family member was older when diagnosed.

Symptoms

Parkinson's disease usually begins as a slight tremor or stiffness involving the arm or leg on one side of the body. The tremor is prominent at rest and is regular, typically occurring at a rate of three to six times per second. The Parkinson's disease tremor usually worsens under stress, improves when the arm or leg is moved voluntarily, and may disappear entirely during sleep. In the earliest stages, Parkinson's disease may be evident only as a tremor involving the thumb and index finger. This tremor sometimes is called "pill-rolling" tremor because it looks as if the person is manipulating a small object such as a pill.

As the illness progresses, the tremor may become more widespread, and eventually affect limbs on both sides of the body. Handwriting may become small, shaky and eventually illegible. In addition to the classic tremor, Parkinson's disease often causes stiffness or rigidity in the muscles of the arms or legs and a slowing of body movements (bradykinesia).

The rigidity and bradykinesia can be the most disabling aspects of the disease. They can impair the person's ability to walk and to perform activities of daily living, such as washing, dressing or using eating utensils. Problems with unsteady balance and posture may make it hard for a person with Parkinson's disease to sit down in a chair or to rise from one. Walking is accomplished with small, shuffling steps and a stooped posture, usually without the normal arm-swinging motions. Bradykinesia can affect the facial muscles, decreasing spontaneous facial expressions and normal eye blinking.