|
Pathology => Human Diseases => Parkinson's Disease
Parkinson's Disease
Parkinson's Disease, progressively disabling neurological disease marked by tremor and increasing stiffness of the muscles. The onset of this disease is gradual, which makes it difficult to diagnose in its early stages. Tremor usually begins in one or both hands; eventually the thumb and forefinger may show a rapid repetitive movement described as "pill rolling." In addition to muscular rigidity, other symptoms include slow body movement, poor coordination, and faulty balance. A shortening of muscles along the front of the neck tends to bend the head and spine forward, while the lack of animation in the face creates a masklike expression. As these symptoms worsen, chronic fatigue, mental confusion, and speech impairment may develop and the person with Parkinson's may find it impossible to walk unassisted.
This disease, which occurs in all parts of the world, affects roughly equal numbers of men and women and is most likely to develop after the age of 50. According to the National Parkinson's Foundation, doctors diagnose about 50,000 new cases annually in the United States, and an estimated 1.5 million Americans suffer from the illness at any one time.
The symptoms of Parkinson's disease appear when neurons (nerve cells) located in the substantia nigra, a part of the brain stem, either die or lose their ability to function properly. The chief neurotransmitter-or carrier of nerve signals-in this area of the brain is dopamine, which is deficient in people who have Parkinson's. The cause of this deficiency is not known, but research suggests that several factors may reinforce each other to produce Parkinson's disease. There may be a genetic predisposition for some forms of the disease-between 15 and 20 percent of people with Parkinson's are closely related to an individual who displays the disease's characteristic symptoms. In 1996 scientists identified a gene associated with a rare form of Parkinson's disease. Genetic predisposition may be limited only to rare forms of the disease, however. A 1999 study found that the most common form of Parkinson's disease is not inherited, suggesting that exposure to certain environmental agents may be a primary cause. Although the identity of these agents remains unknown, candidates include harmful pesticides or toxins in food; and free radicals, which are unstable molecules that may contribute to neuron damage by reacting with other molecules-especially metallic elements such as iron-in the basic chemical process known as oxidation.
Introduction of the drug L-dopa, or levodopa, in the mid-1960s led to the relief of Parkinson's symptoms in many people with the disease. L-dopa stimulates the production of dopamine in surviving neurons in the substantia nigra. L-dopa becomes less effective over time in relieving symptoms, at which point a substitute drug such as pergolide or bromocriptine may be prescribed. In 1997 the drugs pramipexole (sold under the brand name Mirapex) and ropinirole, (brand name Requip) were approved by the Food and Drug Administration (FDA) for use in the treatment of Parkinson's disease. These drugs appear to have fewer side effects than some of the older medicines. Other drugs that affect the action of central nervous system neurotransmitters have proven useful in relieving tremors.
Brain surgery, a common method for treating Parkinson's before the discovery of L-dopa, is coming back into favor for patients with severe tremors. Surgeons use various procedures to destroy tissue in regions of the brain believed to play a role in Parkinson's disease, such as the substantia nigra. These procedures have positive effects for some people, but experts caution that they do not work for everyone. Additional surgical treatments are under investigation. Such experimental treatments include a pacemaker-like device to prevent tremors, and more recently, replacing damaged neural tissue with healthy fetal neural tissue.
Back
|
