PARKINSON'S DISEASE
DEFINITION
Parkinson's disease (PD) is a chronic, progressive disorder of the nervous system. A chronic disorder continues for long periods of time, usually many years. Parkinson's disease affects a person's muscular coordination. Symptoms of PD include tremor (shaking), rigidity in some muscles, slow movements, and problems with maintaining normal posture. The disease is caused by the death of cells in one of the movement control centers of the brain. These nerve cells control body movement.
DESCRIPTION
Parkinson's disease affects about five hundred thousand people in the United States. It occurs with equal frequency in men and women. About fifty thousand new cases appear each year. The disease usually develops when a person is in his or her late fifties or early sixties. It develops gradually over a matter of months and years. A PD patient slowly loses control over the muscles that control movement. About 15 percent of people between the ages of sixty-five and seventy-four show some signs of PD. The rate among those in the age group between seventy-five and eighty-four is about 30 percent.
CAUSES
The immediate cause of Parkinson's disease is the destruction of brain cells in a part of the brain known as the substantia nigra (SN). The substantia nigra controls many types of muscular movement by releasing a neurotransmitter called dopamine. A neurotransmitter is a chemical that transports electrical signals between brain cells. Dopamine is needed to carry nerve messages from one brain cell to another.
Parkinson's Disease: Words to Know
- Chronic:
- Recurring frequently or lasting a long time.
- Dopamine:
- A neurotransmitter that helps send signals that control movement.
- Neurotransmitter:
- A chemical that helps transmit electrical signals from one brain cell to another.
- Substantia nigra:
- A region of the brain that controls movement.
When brain cells die in the substantia nigra it doesn't release enough dopamine. Without dopamine, signals cannot travel from SN brain cells to cells in other parts of the brain. The "instructions" that brain cells need to move muscles do not reach their targets. Eventually, walking, writing, reaching for objects, and other basic movements do not occur correctly. Muscular movement becomes weaker and more erratic.
Researchers have not yet discovered the basic cause of Parkinson's disease. They do not know why SN brain cells lose the ability to produce dopamine. Some scientists think that the disease is hereditary. They believe that PD can be passed down from generation to generation. Other researchers think that environmental factors may be to blame. They suspect that certain chemicals in the world around us get into the human body and damage SN brain cells.
So far, a few chemicals have been found that cause the symptoms of PD. One chemical known to cause symptoms of PD is called MPTP. MPTP is sometimes found as an impurity in illegal drugs. A person who accidentally ingests (eats) MPTP begins to show signs of PD within hours. These symptoms become permanent.
JAMES PARKINSON
"Shaking palsy" was a disease well known to physicians for hundreds of years. Patients with the disorder gradually became worse over a period of years. They slowly lost control over their limbs, and eventually lost the ability to dress and care for themselves.
The first scientific description of this disease was written in 1817 by Dr. James Parkinson (1755–1824). Parkinson was a man of many interests. Not only did he describe the nature of "shaking palsy," but he also provided the first explanation of appendicitis. Parkinson was also interested in the study of geology and paleontology (fossils), and was a social reformer. He fought for reform of the English parliamentary system and for better treatment of mental patients.
Parkinson also went one step beyond describing "shaking palsy." He conducted an autopsy on a patient who died of the condition. He found a swelling of the medulla, a part of the brain, which he said might be the cause of the disorder. For his research on this disease, "shaky palsy" was eventually renamed Parkinson's disease in his honor.
SYMPTOMS
The symptoms by which PD can be identified include:
- Tremor (shaking), usually beginning in the hands. The classic tremor associated with PD is called "pill-rolling tremor." The movement is like rolling a pill between the thumb and forefinger. The movement occurs about three times per second.
- Slowing down of movements. A person may slow down or even stop in the middle of familiar movements, such as walking, eating, or shaving.
- Muscle rigidity (stiffness). A PD patient's movements may be jerky rather than smooth.
- Problems with posture and balance. A person may change the way he or she walks to keep from falling over.
- "Masked face." This condition gets its name from the fact that the patient seems to have no facial expression. He or she may even have a greatly reduced rate of eye blinking.
Parkinson's disease may also be accompanied by one or more other symptoms, including:
- Depression
- Changes in the way a person speaks
- Sleep problems, including restlessness and nightmares
- Emotional changes, including increased fear, irritability, and feelings of insecurity
- Incontinence (loss of bladder control)
- Constipation
- Changes in handwriting
- Dementia (increased problems with mental functions)
DIAGNOSIS
There are no laboratory tests for the diagnosis of Parkinson's disease. The condition is fairly easy to diagnose based on the presence of the characteristic symptoms listed above. A person suspected of having PD will have a complete neurological (nervous system) examination. Tests may be conducted to rule out other conditions with similar symptoms. PD can also be diagnosed after a person has died. Characteristic structures in the brain are taken as proof of the disease.
TREATMENT
There is no cure for Parkinson's disease. One drug, selegiline (trade name Eldepryl) may slow the destruction of SN brain cells. However, there are a number of treatments for the symptoms of PD.
Exercise, Nutrition, and Physical Therapy
Regular, moderate exercise can improve motor (muscular) control. It improves a person's circulation and appetite and frees up stiff muscles. A physical therapist can help a patient design an exercise program for his or her special needs.
Good nutrition is also important. PD patients often lose interest in food. They may simply lose their appetite, or they may have nausea from drugs they are taking for treatment. Also, as their bodies begin to move more slowly, they may become irritated by how long it takes to eat. Food may digest slowly as well, causing the person to feel full much of the day.
These problems can be partially solved by including more fiber in a person's diet. Soft foods also go down more easily and are digested more quickly. Certain types of drugs can also increase the movement of food through the digestive system.
There is currently no evidence that vitamins, minerals, or other nutritional supplements have any effect on the symptoms of PD.
Drugs
Researchers have discovered a number of drugs that can help relieve the symptoms of Parkinson's disease. The effectiveness of the drugs depends on many factors. These factors include the patient's body chemistry, the rate at which the disease is progressing, and the length of time the drug has been used. Each PD drug also has side effects. In some cases, those side effects may limit the use of a drug by some patients.
There are presently five classes of drugs used to treat Parkinson's disease.
DRUGS THAT REPLACE DOPAMINE. The symptoms of the disease develop because SN brain cells do not produce enough dopamine. One solution, then, would be to give dopamine to the brain.
The problem with this solution is that the body's blood-brain barrier (BBB) gets in the way. It stops certain toxins and chemicals from entering the brain. In most places in the body substances can pass easily in and out of the blood vessels. This is how the cells of the body get the things they need to function properly. In the BBB, the walls of the blood vessels are much less permeable (open to penetration). The blood-brain barrier is very important because it protects the brain from harmful chemicals and helps maintain a safe, stable environment for sensitive brain tissues. But sometimes helpful chemicals are also kept from entering the brain.
The BBB doesn't allow neurotransmitters or hormones from elsewhere in the body to enter the brain. Dopamine, the chemical needed by Parkinson's patients, is a neurotransmitter. This is a problem for doctors. A person cannot be treated for Parkinson's by being given a pill or an injection of dopamine. The chemical in the pill or injection cannot get through the blood-brain barrier into the brain.
One solution is to "fool" the blood-brain barrier. A patient can be given a drug that looks to the blood-brain barrier like a material it should let through. Researchers have had some success attaching medicines to elements that can pass through the BBB.
In the case of Parkinson's doctors found that they could inject the body with levodopa or L-dopa, a substance that the BBB lets pass into the brain and then turns into dopamine. L-dopa treatments often work for five years or longer. Then the drug begins to lose its effectiveness. It may also begin to produce side effects that are as bad as the symptoms of PD itself.
ENZYME INHIBITORS. Dopamine does not stay in the brain forever. Instead, it is attacked by other chemicals that break it down into other substances. These chemicals are known as enzymes.
Another way to relieve the symptoms of PD, then, is to prevent enzymes from acting on dopamine—that is, to inhibit them from breaking it down. If the enzymes are inhibited, more dopamine will remain in the brain. The drugs given to PD patients often contain L-dopa and one or more enzyme inhibitors.
DOPAMINE AGONISTS. A dopamine agonist is a drug that acts in the brain in much the same way that dopamine does. Patients with Parkinson's disease can take dopamine agonists to make up for missing dopamine. Like other drugs used to treat PD, dopamine agonists can have serious side effects, including confusion and hallucinations at higher doses.
ANTICHOLINERGIC DRUGS. Dopamine is only one of many neurotransmitters in the brain. Brain function depends on a balance of all neurotransmitters. This balance changes as the amount of dopamine decreases. One way to restore this balance is with anticholinergic drugs. These drugs reduce the
amount of other neurotransmitters in the brain. They help maintain the correct balance of all neurotransmitters.
DRUGS WHOSE MODE OF ACTION IS UNCERTAIN. Sometimes drugs will work with PD patients, but researchers don't know why. The drug known as amantadine (pronounced uh-MANT-uh-deen, trade name Symmetrel) is an example. Amantadine is used to treat the symptoms of a variety of mental disorders. No one knows exactly how the drug relieves these symptoms, but it does, at least to a modest degree.
Surgery
Some symptoms of Parkinson's disease occur because one part of the brain receives too much stimulation or another part receives too little. These problems can sometimes be helped by surgery. In one surgical procedure, a long thin needle is inserted into a certain part of the brain. The cells in that part of the brain are then killed with heat or electricity. This procedure prevents that region of the brain from becoming overactive.
A similar procedure can be used to make another part of the brain more active. A needle is inserted into the correct region of the brain. A mild electric current is then sent into the brain through the needle. The electric current may cause that region of the brain to become more active.
Surgery is used when patients do not respond to drugs or when drugs no longer work. Surgical procedures are often effective in helping people recover some of their normal muscular movement.
A third surgical procedure involves transplanting SN cells from the brain of a fetus. The brain cells in a fetus are in an early stage of development. When implanted into the brain of a PD patient, they sometimes take over the job of making dopamine. They begin to function in place of the patient's own SN cells that have lost the ability to produce dopamine. This procedure is still in an experimental stage.
Alternative Treatment
Alternative treatments have limited promise for treating Parkinson's disease. Acupuncture, massage, and yoga may help relieve some symptoms of the disease by loosening tight muscles. Some alternative practitioners recommend the use of herbs and nutritional supplements, such as vitamins A, B, C, E, and the minerals calcium, selenium, and zinc. These supplements can sometimes have harmful side effects when used with drugs, however.
PROGNOSIS
There is no cure for Parkinson's disease. Drugs may help relieve symptoms for a few or many years. Those symptoms eventually get worse, however. Drug therapy becomes less successful. During the late stages of the disease, psychiatric symptoms become most troubling. These symptoms include problems with sleeping, increasing dementia, hallucinations, and loss of contact with reality.
PREVENTION
There is no known way to prevent Parkinson's disease.
FOR MORE INFORMATION
Books
Atwood, Glenna Wotton. Living Well With Parkinson's. New York: John Wiley & Sons, 1991.
Biziere, Kathleen, and Matthias Kurth. Living with Parkinson's Disease. New York: Demos Vermande, 1997.
Hauser, Robert, and Theresa Zesiewica. Parkinson's Disease : Questions and Answers, 2nd edition. Chicago: Merit Publishing International, 1998.
Williams, Frank L. Parkinson's Disease : The Complete Guide for Patients and Caregivers. New York: Fireside, 1993.
Organizations
National Parkinson Foundation. 1501 NW Ninth Ave., Bob Hope Road, Miami, FL 33136. http://www.parkinson.org.
Parkinson's Disease Foundation. 710 West 168th St., New York, NY 10032. (800) 457–6676. http://www.apdaparkinson.com.
Worldwide Education and Awareness for movement Disorders. Mt. Sinai Medical Center, 1 Gustave Levy Place, New York, NY 10029. (800) 437–MOV2. http://www.wemove.org.
Web sites
About Parkinson's Disease. [Online] http://www.parkinsonsinfo.com/about_parkinsons/ (accessed on October 27, 1999).
"Ask NOAH About: Parkinson's Disease." NOAH: New York Online Access to Health. [Online] http://www.noah.cuny.edu/neuro/parkin.html (accessed on October 27, 1999).
AWAKENINGS. [Online] http://www.parkinsondisease.com (accessed on October 27, 1999).
"Parkinson's Disease." Health-Center.com [Online] http://www.healthguide.com/english/brain/pd/default.htm (accessed on October 27, 1999).
The Parkinson's Web. [Online] http://pdweb.mgh.harvard.edu (accessed on October 28, 1999).