What is Parkinson's Disease?
Parkinson's Disease is a complex neurological disorder. Low levels of dopamine, an important chemical agent in the brain, lead to a motor-system disorder and the following symptoms:
- trembling in hands, arms, legs, jaw, and face
- stiffness of the limbs and trunk
- slowness of movement
- impaired balance and coordination
These symptoms are both chronic, persisting over a long period of time, and they are progressive, getting more severe over time.
Parkinson's disease is the most common form of parkinsonism. Parkinsonism is a group of disorders with similar features - such as the symptoms listed above and the low levels of dopamine in the brain. The other forms, however, have either known or suspected causes; while the root causes of Parkinson's Disease are still not known.
What Causes Parkinson's Disease?
While the root causes of Parkinson's disease are not known, scientists have found several causes of the symptoms.
Certain nerve cells, called neurons, in an area of the brain called the substantia nigra die or become impaired. The cause of this impairment is not known, but these cells are the primary producers of dopamine, a chemical messenger responsible for transmitting muscle activity signals to the next "relay station" of the breain called the striatum.
Parkinson's patients have a loss of 80 percent or more of these dopamine-producing cells - and without the dopamine agent nerve cells in the striatum begin firing out of control, leaving patients unable to direct or control their movements.
There are several theories as to what kills or disables the dopamine-producing neurons:
- Free Radicals. Free radicals are unstable molecules generated by normal chemical reactions in the body. Some evidence seems to suggest that these free radicals are causing damage in their ensuing chemical reactions.
- Toxins. Some scientists suggest that toxins in pesticides, foods, or other agents might lead to Parkinson's. This theory is based on the fact that certain toxins in drugs have caused other parkinsonism disorders.
- Genetic Factors. A relatively new theory is exploring the role of certain genes and mutations. After finding that one of the toxins related to parkinsonism impairs mitochondria, scientists have been exploring the roles of mitochondrial DNA defects in Parkinson's Disease.
- Accelerated aging. Some believe that the decay of these neurons is simply an accelerated aging, brought about by another unknown cause.
Many also believe that Parkinson's, in fact, will be found to be caused by a combination of these four elements.
Who Gets Parkinson's Disease?
About 50,000 Americans are diagnosed with Parkinson's disease each year, with more than half a million Americans affected at any one time. Getting an accurate count of the number of cases may be impossible however, because many people in the early stages of the disease assume their symptoms are the result of normal aging and do not seek help from a physician. Also, diagnosis is sometimes difficult and uncertain because other conditions may produce some of the symptoms of Parkinson's disease. People with Parkinson's disease may be told by their doctors that they have other disorders or, conversely, people with similar diseases may be initially diagnosed as having Parkinson's disease.
Parkinson's disease strikes men and women in almost equal numbers and it knows no social, economic, or geographic boundaries. Some studies show that African-Americans and Asians are less likely than whites to develop Parkinson's disease. Scientists have not been able to explain this apparent lower incidence in certain populations. It is reasonable to assume, however, that all people have a similar probability of developing the disease.
Age, however, clearly correlates with the onset of symptoms. Parkinson's disease is a disease of late middle age, usually affecting people over the age of 50. The average age of onset is 60 years. However, some physicians have reportedly noticed more cases of "early-onset" Parkinson's disease in the past several years, and some have estimated that 5 to 10 percent of patients are under the age of 40.
What are the symptoms of the disease?
The four main symptoms of Parkinson's, as discussed above, are:
- Tremor. The tremor associated with Parkinson's disease has a characteristic appearance. Typically, the tremor takes the form of a rhythmic back-and-forth motion of the thumb and forefinger at three beats per second. This is sometimes called "pill rolling." Tremor usually begins in a hand, although sometimes a foot or the jaw is affected first. It is most obvious when the hand is at rest or when a person is under stress. In three out of four patients, the tremor may affect only one part or side of the body, especially during the early stages of the disease. Later it may become more general. Tremor is rarely disabling and it usually disappears during sleep or improves with intentional movement.
- Rigidity. Rigidity, or a resistance to movement, affects most parkinsonian patients. A major principle of body movement is that all muscles have an opposing muscle. Movement is possible not just because one muscle becomes more active, but because the opposing muscle relaxes. In Parkinson's disease, rigidity comes about when, in response to signals from the brain, the delicate balance of opposing muscles is disturbed. The muscles remain constantly tensed and contracted so that the person aches or feels stiff or weak. The rigidity becomes obvious when another person tries to move the patient's arm, which will move only in ratchet-like or short, jerky movements known as "cogwheel" rigidity.
- Bradykinesia. Bradykinesia, or the slowing down and loss of spontaneous and automatic movement, is particularly frustrating because it is unpredictable. One moment the patient can move easily. The next moment he or she may need help. This may well be the most disabling and distressing symptom of the disease because the patient cannot rapidly perform routine movements. Activities once performed quickly and easily - such as washing or dressing - may take several hours.
- Postural instability. Postural instability, or impaired balance and coordination, causes patients to develop a forward or backward lean and to fall easily. When bumped from the front or when starting to walk, patients with a backward lean have a tendency to step backwards, which is known as retropulsion. Postural instability can cause patients to have a stooped posture in which the head is bowed and the shoulders are drooped. As the disease progresses, walking may be affected. Patients may halt in mid-stride and "freeze" in place, possibly even toppling over. Or patients may walk with a series of quick, small steps as if hurrying forward to keep balance. This is known as festination.
Other symptoms of Parkinson's appear in varying degree, such as:
- Depression
- Emotional changes
- Difficulty swallowing and chewing
- Speech changes
- Urinary problems or constipation
- Skin problems
- Sleep problems
What are the other forms of Parkinsonism?
- Postencephalitic parkinsonism - a movement disorder developed by some after the acute phase of encephalitis lathargica
- Drug-induced parkinsonism - a reversible form of parkinsonism sometimes resulting from use of certain drugs prescribed for patients with psychiatric disorders. Also may develop with drugs prescribed for stomach disorders or high blood pressure.
- Striatonigral degeneration - a variant of parkinsonism with areas of damage different than Parkinson's disease
- Arteriosclerotic parkinsonism - develops when blood vessels are damaged in multiple small strokes
- Toxin-induced parkinsonism - certain toxins can induce a form of parkinsonism very close to Parkinson's disease
- Parkinsonism-dementia complex of Guam - localized to the Chamorro populations of Guam and the Mariana Islands, this form of parkinsonism accompanies Lou Gehrig's disease and is very aggressive
- Parkinsonism accompanying other conditions - many other neurological conditions generate parkinsonian symptoms
How is Parkinson's Disease diagnosed?
There are no specific tests that can be performed for Parkinson's disease. Instead, the physician may need to observe the patient for some time until it is apparent that the tremor is consistently present and is joined by one or more of the other classic symptoms.
How is the disease treated?
Drugs
There are several drugs that have been found to provide relief from the symptoms of Parkinson's disease. Unfortunately, many of them have mild to severe side effects. In addition, the results vary on patient to patient, and often treat some symptoms while leaving others.
Levodopa is the most widely effective and versatile drug in use today. Nerve cells can use levodopa to create the dopamine needed in the brain. Dopamine cannot be directly given, because it doesn't cross the blood-brain barrier, the elaborate meshwork of fine blood vessels and cells that filters blood reaching the brain. It is often matched with other drugs to minimize side-effects, multiply efficiency, and prolong the effects of the drug. Although levodopa is a very effective drug for treatment of systems, it does not stop the progression of the disease; and it can have side effects. In addition, after a period of time, levodopa can begin to lose effectiveness.
There are other drugs which can work alongside Levodopa to maximize the effects or target specific needs of the patient, but none which have shown such dramatic results.
Surgery
Surgery has been, and can be, used to treat Parkinson's disease. In general, it is currently regarded as a backup treatment to drugs. There are several procedures, for varying intended results. Further research is still being done on the value of these techniques, as well as new procedures being explored.
Exercise
Exercise is often used to treat Parkinson's. While it doesn't stop disease progression, it can help improve mobility, body strength, and range of motion; as well as target certain muscles to improve speech or eating.
Support Groups
Because of the drastic changes in their life, support groups are often encouraged to help patients adjust to their new lifestyle.
What is happening in Parkinson's Disease Research?
As yet, there is no way to predict or prevent the disease. However, researchers are now looking for a biomarker - a biochemical abnormality that all patients with Parkinson's disease might share - that could be picked up by screening techniques or by a simple chemical test given to people who do not have any parkinsonian symptoms.
Positron emission tomography (PET) scanning may lead to important advances in our knowledge about Parkinson's disease. PET scans of the brain produce pictures of chemical changes as they occur in the living brain. Using PET, research scientists can study the brain's dopamine receptors (the sites on nerve cells that bind with dopamine) to determine if the loss of dopamine activity follows or precedes degeneration of the neurons that make this chemical. This information could help scientists better understand the disease process and may potentially lead to improved treatments.
In addition, the last decade of research has led to many promising new clinical trials, technologies, and drug treatments. Parkinson's disease research focuses on many areas, such as the motor system and brain functions, the roles of toxins in triggering the disorder, genetic factors, and new drugs. Scientists continue to study the roles of DNA in the disease formation, as well as regenerative techniques through drugs and implants.