WHAT IS PARKINSON'S DISEASE?



Parkinson's disease 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.

GLOSSARY


Underlined terms are defined elsewhere in the glossary

Akinetic-rigid syndrome: A syndrome, or collection of systems, consisting of lack of movement (akinesia) or reduced movements (hypokinesia), slow movements (bradykinesia), and stiffness or rigidity (involuntary resistance to movement). The rigidity is of a type called cogwheel rigidity.

Basal ganglia: A group of nuclei, or clusters of nerve cells, near the base of the brain that is important in regulating both movements and emotions.

Bradykinesia, hypokinesia & akinesia: Bradykinesia means slow movements. Hypokinesia means reduced movements and generally refers to making smaller movements than intended, such as the small steps seen when a Parkinsons patient walks, or the small size of a Parkinsons patient's handwriting (called micrographia). Akinesia means lack of movement.

Cogwheel rigidity: " A type of rigidity in which, when a patient's limb is moved by the examiner, it resists and gives way in small, step-like movements as if it was being controlled by a cog-wheel.

Dopamine: One of a number of chemicals used by nerve cells as neurotransmitters. Messages are carried electrically along individual nerve cells but signaling from one nerve cell to another is usually accomplished by releasing a neurotransmitter chemical. Dopamine is the main neurotransmitter of the nerve cells which die off in Parkinson's disease.

Epidemiological studies: Statistical studies of the occurence of diseases in populations and environments.

Familial Parkinsons: Some unusual forms of Parkinson's disease run in a few families. Abnormal genes have been identified in some of these families, but abnormalities in these genes are NOT found in most patients with Parkinson's disease. Alpha-synuclein and parkin are the proteins coded for by genes identified as being abnormal in some familial forms of atypical Parkinson's disease. Normal alpha-synuclein is also the major protein in Lewy bodies, the pathologic inclusions found in typical Parkinson's disease. The normal functions of alpha-synuclein and parkin are not yet clearly established.

Neurodegenerative Disease: A disease in which nerve cells in the brain or spinal cord (central nervous system, CNS) progressively die or degenerate.

Parkinson's Plus diseases: These are neurodegenerative diseases which cause the akinetic-rigid syndrome or parkinsonism PLUS additional symptoms not usually seen in Parkinson's disease. These diseases are progressive supranuclear palsy or PSP, corticobasilar ganglionic degeneration or CBGD, and multiple system atrophy or MSA, which includes Shy-Drager Syndrome, olivopontocerebellar atrophy or OPCA, and striato-nigral degeneration.

Postural reflexes: Postural reflexes are the involuntary movements people automatically make to maintain their balance when standing and walking. Impairment of the postural reflexes causes poor balance and a tendency to fall.

Resting tremor: Tremor is a rhythmic movement or shaking of any part of the body. The tremor of Parkinson's disease is called a "resting tremor" because it is present when a limb is at rest and may be reduced or go away when the limb is held up or otherwise used by the patient. Most other types of tremor are reduced or absent when the limb is at rest and relaxed.

Striatum: A region of the brain made up of two nuclei, or clusters of nerve cells, the globus pallidus (which means "white ball") and caudate (which means "tailed"). These two nuclei are part of a group of nuclei called the basal ganglia, which is important in regulating both movements and emotions.

Substantia nigra: This literally means "the black substance" and is a region in the brainstem (where the spinal cord joins the brain) where there is a group of dopamine-producing nerve cells, which appear darker than the surrounding tissue. The dopamine-producing nerve cells are in the pars compacta (meaning "compact or dense part"). There is another part called the pars reticulata ("speckled part").

Contributed by: Edwin B. George, MD, Ph.D., Wayne State University School of Medicine. Chairman, Michigan Parkinson Foundation Professional Advisory Board, Member MPF Board of Directors