What is Parkinson’s disease?

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Parkinson's is a degenerative, neurological disorder that predominately affects movement. According to the National Parkinson Foundation, between 50,000 and 60,000 people are diagnosed with Parkinson's every year.

Parkinson's, also known as PD, is named after English doctor James Parkinson, who published the first description of the brain disease in an essay in 1817.

The exact cause of the disease is unknown and PD is a very heterogeneous disease.  "Although symptoms may be similar in different individuals, there may be important differences in the underlying cause of the disorder," said neurologist and Ohio State professor Sandra Kostyk.

Parkinson's can be caused by genetics, outside factors (such as head injury or pesticide exposure) and, most often, a mixture of both. Men have a greater chance of contracting the disease than women.

Parkinson's is the result of cell loss in a few areas of the brain, especially the substantia nigra, which is responsible for the production of dopamine, which transmits signals within the brain that coordinate movement. Dopamine loss causes neurons to fire haphazardly, decreasing the control one has over his or her movements.

The cardinal symptoms of Parkinson's are the most evident to an observer. They include resting tremor (when a limb moves uncontrollably at rest but stops during voluntary movement), bradykinesia (slow voluntary movement), balance problems and rigidity, according to the Michael J. Fox Foundation for Parkinson's Research.

Other "non-motor" symptoms include cognitive impairment, memory loss, dementia, low blood pressure, constipation, depression, anxiety, insomnia, anosmia, sleep problems and drooling. Although cognitive difficulties can occur, most of time when someone with Parkinson's halts his or her speech, it is not a mental symptom but a physical one.

PD is difficult to diagnose, especially during the early stages. No definitive tests exist yet, but patients are usually diagnosed after providing their medical history to a doctor and taking a neurological exam. A diagnosis will usually follow if a few of the cardinal symptoms are present.

After Michael J. Fox went public with his PD diagnosis, he became one of the world's most prominent figures in the battle against PD and established the Michael J. Fox Foundation for Parkinson's Research in 2000. The foundation is the largest funder of Parkinson's-based research, after the federal government.

In interviews, Fox has often used the analogy that PD diagnosis is like standing in the middle of a road with cement shoes on, hearing a bus approaching. One doesn't know how large the bus is or how fast it is going, but you know it will hit you.

PD is currently untreatable. Therapy aims to treat the symptoms that are more difficult for people with the disease. Since reactions to Parkinson's are not uniform or standard, there is no one treatment regimen that is best suited for everyone. Aside from support groups, physical and speech therapy and lifestyle changes, treatment can include medication and surgery. Some therapies can slow PD's progression.

Some PD drugs are dopaminergic, meaning they attempt to replenish an individual with the dopamine he or she lacks (Levodopa, Carbidopa). Other PD drugs are dopamine agonists, meaning they mimic the effect of dopamine on the brain (Pramipexole, Ropinerole, Bromocriptine). MAO-inhibitors (Selegiline, Rasagilene) and COMT-inhibitors (Entacapone, Tolcapone) increase the power and quantity, respectively, of Levodopa in the brain, raising dopamine levels.

Doctor Peter LeWitt, director of the Henry Ford Parkinson's Disease and Movement Disorders Program, reports that new medications are being developed for improving motor functions and slowing the progression of PD, as are gene therapy studies.

For more information, visit the Parkinson Disease Foundation, the Michael J. Fox Foundation for Parkinson's Research or the National Parkinson Foundation.