General Characteristics of Parkinson's Disease
Parkinson's disease, sometimes referred to as "shaking palsy," affects approximately half a million people in the United States. It is a disorder that results from the degeneration of certain brain cells, and its most characteristic feature is defective message transmission from the brain to various portions of the body. This results in uncontrollable movement, which may be manifested as tremor, muscular rigidity or sluggishness.
Causes and Types of Parkinsonism
The most common form of the disease is called idiopathic parkinsonism and has no known cause. It has no known hereditary component, nor is it contagious. Parkinsonism affects women and men in equal proportions.
There is also drug-induced parkinsonism, which is caused mostly by drugs to treat severe mental illness. This form of parkinsonism is usually reversed when the drug is discontinued or its dosage decreased. Parkinsonism also may be caused by disorders such as encephalitis and hardening of the arteries (arteriosclerosis), or following certain brain injuries, including those caused by a stroke.
Mechanism of Parkinsonism
Parkinsonism is believed to be related to the substantia nigra (black substance) of the nerve cells, which produce and store a chemical substance called dopamine--one of several neurotransmitters. (A neurotransmitter relays messages from the brain across a small open space--or synapse--at the junction of the nerves.) Parkinson's disease apparently interferes with dopamine storage and/or production, which causes disturbances in nerve message transmission. This, in turn, leads to shaking or other defective motor responses. In addition to dopamine depletion, parkinsonism also seems to involve an excess of cholinergic activity. Treatment, therefore, entails either increasing the concentration of dopamine or decreasing the concentration of acetylcholine, another neurotransmitter that causes symptoms of Parkinson's disease when dopamine levels are reduced. Both treatments are often used.
