Overview and Facts

Parkinson's disease

(Also known as Parkinson disease, Parkinson's, idiopathic parkinsonism, primary parkinsonism, PD, hypokinetic rigid syndrome/HRS, orparalysis agitans)

Parkinson's disease is a disorder of the brain that leads to shaking (tremors) and difficulty with walking, movement, and coordination. The disease is named after the English doctor James Parkinson, who published the first detailed description in An Essay on the Shaking Palsy in 1817. (Please click here for related article)

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 runs 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 is rare in children. It may occur because the nerves are not as sensitive to dopamine.

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 (called secondary parkinsonism) or certain medications.

About 1.5 million Americans have Parkinson's disease and 60,000 more are diagnosed with it each year [source: National Parkinson Foundation]. Most people who get the disease are older than 60, but about 15 percent are diagnosed before age 50 [source: National Parkinson Foundation].

Although doctors don't know what exactly causes Parkinson's, they think it stems from a combination of genetic and environmental factors. In about 5 to 10 percent of patients, there is a strong family history of the disease [source: National Parkinson Foundation]. Parkinson's may affect the same generation (siblings), or two different generations (parent and child) in this small percentage of familial cases.

Other possible causes of Parkinson's (and conditions like it) include:

Toxins: Scientists have linked exposure to manganese, carbon monoxide, cyanide and some pesticides and herbicides with a higher Parkinson's risk [sources: National Parkinson Foundation, Mayo Clinic]. However, most people with the disease haven't been exposed to these substances.

­­A virus: In the early 1900s, people who came down with a form of the encephalitis virus became stuck in a trancelike state in which they couldn't move or speak. When neurologist Dr. Oliver Sacks treated these people with levodopa, the same medication used to treat Parkinson's, they briefly came "back to life." (These "Awakenings" were depicted in the 1990 movie starring Robin Williams.)

Head trauma: Boxer Muhammad Ali, one of the most famous Parkinson's sufferers, developed the disease when he was only in his 40s. Researchers have been studying whether trauma to the head may play a role in the development of the disease.

Structural problems: Strokes and hydrocephalus (fluid buildup in the brain) are two conditions that may lead to an increased risk of parkinsonism.

** Parkinson's Clusters

When Canadian actor Michael J. Fox was just starting his career back in the 1970s, he worked at a television studio in Vancouver, British Columbia. Years later, four of the 125 people he worked with on the crew had developed Parkinson's disease -- a percentage far higher than normal. Scientists have found similar clusters of Parkinson's cases within companies and neighborhoods. ­Although there is a chance that these cluster cases are purely coincidental, researchers are looking at whether exposure to a common toxin might have triggered the disease in these cases.