What is Multiple Sclerosis (MS)?
MS is a neurological disease that occurs when the insulating material (“myelin”) around nerve cells in the central nervous system is damaged. The word sclerosis comes from the Greek word “skleros,” meaning hard. In multiple sclerosis, hard areas called “plaques” develop along a neuron’s axon. “Multiple” refers to the many different areas of the nervous system that may have damaged myelin. People with MS can experience symptoms such as difficulties in walking, visual problems, and pain.
MS is NOT contagious and it is not fatal. However, because MS disrupts the way messages are sent through the nervous system, the symptoms of MS can be serious and disabling. MS is considered to be an autoimmune disease. This means that a person’s immune system attacks its own tissue. In MS, the immune system attacks myelin.
The Immune System
Your body is always on the look-out for foreign invaders such as bacteria and viruses. If these invaders get into your body they may make you sick. However, your body has defense mechanisms to fight these microorganisms and prevent infections. These defense mechanisms make up your immune system. Some immune cells can remove the invaders themselves and others cause extra blood to be directed to the site of infection and produce inflammation. Other immune cells produce chemicals or “antibodies” to find and eliminate harmful invaders. The cells that produce antibodies are located in the lymphatic system (see picture on the left), a group of organs including the bone marrow, thymus, spleen, lymph nodes, tonsils and appendix. These cells travel into other parts of the body when they detect an invader or some foreign matter. The organs of the lymphatic system are connected by a series of lymphatic vessels that eventually empty into the bloodstream.
Sometimes, the immune system sees parts of its own body as foreign and attacks them in what is called an “autoimmune response.” In the case of MS, the immune system attacks the myelin around nerve cells in the brain and spinal cord.
What Causes MS?
Although the exact cause of MS is not known, several environmental and genetic factors probably contribute to the autoimmune response.
Researchers have discovered that the risk of MS is greater with increasing distance from the equator. Even in the United States, MS is more common in northern states than it is in southern states. According to the National Multiple Sclerosis Society, the rate of MS in the United States below the 37th parallel is 57 to 78 cases per 100,000 people. Above the 37th parallel, the rate of MS is 110 to 140 cases per 100,000 people — approximately twice the rate as below the 37th parallel. However, the reason for this distribution of MS is unknown. It is possible that something (e.g., a virus) in the environment triggers the autoimmune response.
Susceptibility to MS probably has a genetic component. If a person has MS, there is an increased risk that a close relative, such as a child or sibling will have MS. The identical twin of a person with MS has about a 33% chance of developing MS. However, because this chance is not 100%, MS is not strictly an inherited disorder.
What Happens to the Nervous System?
MS affects neurons in several ways:
Patches of inflammation may occur in the myelin that surrounds axons in the brain and other parts of the nervous system. This inflammation can damage the myelin.
Myelin around axons may deteriorate and be lost. This is called “demyelination.”
Axons may be damaged and destroyed.
When myelin is damaged, the transmission of electrical signals along axons is impaired. It is possible that the body can repair damaged myelin after inflammation is reduced. This process is called “remyelination.” Normal Neuron
Neuron Affected by MS
Who Gets MS? What are the Symptoms?
People usually develop symptoms of MS when they are 20 to 40 years old; MS is two to three times more common in women than in men. The National Multiple Sclerosis Society estimates that 250,000 to 350,000 people in the US have MS.
Somatosensory (touch) problems such as numbness or tingling of the hands and feet
Loss of muscle strength and dexterity
Problems with walking, balance and coordination
Visual problems due to inflammation of the optic nerve Other possible symptoms:
Bladder and bowel problems
Cognitive (e.g., thinking, memory) problems
Symptoms of MS vary from person to person. There are several courses that the disease may take.
Relapsing-Remitting MS: people show symptoms of the disease, but then seem to recover. After a period of time, the symptoms appear again. The cycle of symptoms-to-recovery continues over time. This is the most common type of MS.
Primary Progressive MS: people show gradual worsening of symptoms without recovery.
Secondary Progressive MS: people first show periods of recovery, but later enter a stage of gradual worsening of symptoms without recovery.