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What is Parkinson's Disease?

Parkinson's Disease (PD) belongs to a group of conditions called motor system disorders. It is a neurodegenerative disease which is the most common cause of parkinsonism, or the akinetic-rigid syndrome.

There are many causes of parkinsonism, and although there is a specific pathology under the microscope associated with Parkinson's disease, its cause appears to involve multiple factors and there may in fact be more than one cause or etiology.

Parkinson's disease is recognized by the presence of at least three of four cardinal signs:

  • resting tremor,
  • cogwheel rigidity,
  • bradykinesia/akinesia, and
  • postural reflex impairment.

Parkinson's disease affects at approximately 1.5 million people in the United States. Although Parkinson's disease most commonly affects people over age 60, it can occur as early as age 20.

The basic problem in Parkinson's disease is loss of dopamine-producing nerve cells in a region of the brain called the substantia nigra pars compacta. The loss of the dopamine these cells release in a region of the brain called the striatum produces the symptoms of the akinetic-rigid syndrome. Everybody has a gradual loss of these dopamine-producing nerve cells as they age, but patients with Parkinson's disease have lost more of them than other people. Why these cells die in Parkinson's disease is unclear, and the focus of much research. Studies of identical twins show that most Parkinson's disease is not inherited, and epidemiological studies support a multifactorial model in which both genetic and environmental factors play a role. Familial forms of Parkinson's disease are known but are uncommon and atypical, most often presenting at an earlier age.

The other causes of parkinsonism, or the akinetic-rigid syndrome, include other neurodegenerative diseases besides typical Parkinson's disease, such as the Parkinson's Plus diseases, familial forms of Parkinson's disease, Wilson's disease and Huntington's disease in children (these diseases cause different symptoms in adults), poisons including carbon monoxide, manganese and MPTP (a rare contaminant in synthetic drugs of abuse, i.e. "designer drugs"), injuries to the basal ganglia including strokes ("vasculogenic Parkinson's"), acute or chronic ("pugilistic Parkinson's") head trauma, post-encephalitic (Von Economo's disease) and drug-induced parkinsonism.

The risk factors for Parkinsonism are increasing age (especially after age 60), family history (particularly of early onset Parkinsonism), and a rural as opposed to an urban environment. The occurrence of Parkinson's disease is thought to vary with race, but recent studies show that in the U.S.A. the incidence in African-American men and women and in Asian-American men is similar to the incidence in Americans of European origin.

How is Parkinson' Disease Diagnosed?

There are currently no blood, laboratory or radiological tests to diagnose Parkinson's disease (PD). In early Parkinson's, the symptoms are often vague, such as minor tremor in a hand, a change in handwriting, pain in the neck or back, or occasional stumbling. The physician may need to observe the person over time prior to making an accurate diagnosis. Generally, when two of the four cardinal signs occur (tremor at rest, bradykinesia, rigidity or problems with balance), a diagnosis may be made and treatment initiated.

Contributed by:

Edwin B. George, MD, Ph.D., Wayne State University School of Medicine. Chairman, Michigan Parkinson Foundation Board of Directors, Member MPF Board of Directors, and Past Chairman.