Multiple Sclerosis (MS) Quick Facts
What Is Multiple Sclerosis (MS)?
Multiple sclerosis (MS) is a chronic disease that affects different parts of the central nervous system at different points in time. The central nervous system is made up of the brain and spinal cord (see the central nervous system). The brain controls bodily activities, such as movements and thoughts. The spinal cord serves as a pathway for messages between the brain and various parts of the body. These messages participate in most bodily actions. Because MS affects different parts of the central nervous system, it can affect the functioning of many parts of the body.
Many researchers consider MS an autoimmune disease of the central nervous system. With an autoimmune disease that affects the brain or spinal cord, the body's immune system, its defense system against infection and disease, treats normal central nervous system tissues as if they are foreign and attacks them. When the immune system attacks tissues in the central nervous system, as in MS, the messages the brain sends get interrupted.
The central nervous system. Click to view larger image.
Who Gets Multiple Sclerosis?
- The onset of MS typically occurs between the ages of 20-50 years. MS is the most common, disabling neurologic disorder in young adults.
- Women are about 2 times more likely than men to develop MS.
- The disease is more common in people who live farther from the equator, although the strength of this association has recently been questioned.
- MS occurs more frequently in whites with northern European ancestry. People living in North America, Europe, and Australia are more likely to develop MS than those living in Asia.
- Genetic factors play a role in MS. If a parent or a sibling has MS, the risk of developing MS is 3%. If an identical twin has MS, the risk of the other twin is 25-40%.
- Endocrine factors are also thought to play a role in MS. For instance, there is a decrease in the number of MS attacks during pregnancy. Within the 3 months that follow pregnancy, the chance of new MS attacks is higher. This fluctuation in disease severity is thought to be a response to hormonal changes that occur during the pregnancy and the postpartum period.
What Causes This Disease?
White blood cells called T cells, which fight disease and infection, instead attack myelin, the fatty substance that surrounds and protects the nerves of the central nervous system. This attack damages the protective myelin sheath and either partially or completely strips the myelin off the nerve fibers (see Multimedia file 2). Because the myelin is supposed to help speed and direct the transmission of impulses along nerve cells, whenever any part of the myelin sheath is damaged, the nerve impulses are distorted. The messages the nerves try to send are delayed and usually misinterpreted by the brain, if the messages get through at all. This interruption of messages is what causes multiple sclerosis (MS) symptoms. Often, the T cells also damage the nerve fibers themselves, causing increased MS symptoms and increased disability over time. (See Myelin and the Central Nervous System.)
It is important for patients to realize that the immune system is not underactive in MS and that it does not predispose them to infections. Rather, the immune system in MS is overreactive to certain environmental agents and responds irregularly by attacking the central nervous system.
Medically Reviewed by a Doctor on 11/17/2017
Carmel Armon, MD, MHS, MSc
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