Multiple sclerosis is a chronic, progressive disease of the nervous system. While it is still not fully understood, MS is believed to be an autoimmune disorder in which the body's immune system mistakenly attacks and destroys the tissue of the central nervous system.
In the central nervous system—the brain, optic nerve, and spinal cord—nerves act as messengers, communicating feelings and responses from the body to the brain and the brain to the body. Each nerve is covered by a fatty substance called myelin, which insulates the nerve and helps conduct electrical impulses quickly and efficiently. In MS, the myelin sheath is injured, disrupting or halting communication between brain and body and affecting muscle coordination and vision, for example. Myelin can be regenerated, but not quickly enough to outpace the deterioration caused by the disease. MS gets its name from the buildup of scar tissue (sclerosis) in multiple areas of the brain, optic nerve, or spinal cord.
In the United States, about 1 in 1,000 people has multiple sclerosis. Women are more likely than men to get the disease—about two thirds of people with MS are women. Symptoms generally first appear between the ages of 20 and 40, but onset can occur earlier or later.
The progression of the disease varies from person to person, and there is no way to predict how and when symptoms will unfold in a particular individual. Some people with MS experience acute attacks followed by long periods of partial or even full recovery. Others steadily progress in disability. There is no cure for multiple sclerosis, but there are many treatments, and people can live long, productive lives with the disease. While some people become severely disabled by the disease, about half of people with MS are still able to walk unassisted 15 years after they have been diagnosed.
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The central nervous system, which includes the brain, optic nerve, and spinal cord, is made up of nerves that act as the body's messenger system. The nerve fibers are covered by a fatty, protein-rich substance called myelin, which insulates the nerves and helps in the transmission of impulses, the messages between the brain and other parts of the body. In multiple sclerosis, the myelin sheath is destroyed, in a process called demyelination. Without the myelin, signals transmitted throughout the central nervous system are disrupted or halted. The brain becomes unable to send and receive messages, and muscle coordination, bodily sensations, and vision are affected.
The course of multiple sclerosis varies widely from person to person, and there is no way to predict on an individual level how or when the disease will progress. However, researchers have defined four basic types of MS progression:
Relapsing-remitting: This form of MS is characterized by acute attacks ("exacerbations") lasting at least 24 hours, which are followed by full or partial recovery. During remission periods, which can last from months to years, the disease does not worsen. The vast majority of people who suffer from the condition are diagnosed with this type.
Primary progressive: This less common type is characterized by a gradual, steady progression of disability, without obvious relapses or remissions. Onset tends to be later than age 40.
Secondary progressive: This type of MS begins with a relapsing-remitting period but then evolves into a steady deterioration.
Progressive relapsing: This rare form is characterized by a steady progression in disability accompanied by acute attacks that may or may not be followed by recovery.
The underlying cause of multiple sclerosis is currently unknown. The disease is thought to result from a combination of factors, including genetics, environmental triggers (such as viruses, trauma, vitamin deficiency, or exposure to heavy metals), and a malfunction of the immune system.
The many symptoms of MS are believed to be caused by the immune system's attack on the protective myelin sheaths that insulate the nerves of the central nervous system, in both the spinal cord and the brain. The myelin becomes inflamed and destroyed, scar tissue forms, and the signals that ordinarily travel through the nervous system controlling muscle action and sensations are interrupted.
Multiple sclerosis may be more likely to occur in certain people because of an inherited predisposition. Those with a relative who has MS have a 10 to 15 percent higher risk of developing the disease than the population as a whole, for example, and the disease is more common in people of northern European heritage.
But it also seems clear that other factors are at work. An environmental trigger such as a common viral infection may also explain MS in people who already are at higher risk because of their genetic makeup. Women are more likely than men to get the disease: About two thirds of people with MS are women. MS is more likely to occur in temperate zones such as northern Europe, the northern United States, southern Australia, and New Zealand. Low levels of vitamin D are associated with an increased risk of MS, although it is unknown whether vitamin D supplements can prevent the disease.
Last reviewed on 03/19/2007
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