What Is Multiple Sclerosis? MS Symptoms, Causes, Diagnosis
Reviewed By: Charles Patrick Davis, MD, PhD
What Is MS?
Multiple sclerosis (MS) is an autoimmune disease in which the body's immune system attacks its own central nervous system (the brain and spinal cord).
Multiple sclerosis (MS) is an autoimmune disease in which the body's immune system attacks its own central nervous system (the brain and spinal cord). In MS, the immune system attacks and damages or destroys myelin, a substance that surrounds and insulates the nerves. The myelin destruction causes a distortion or interruption in nerve impulses traveling to and from the brain. This can result in a wide variety of symptoms.

Who Can Get Multiple Sclerosis?
Multiple sclerosis is estimated to affect 2.8 million people worldwide.
Multiple sclerosis is estimated to affect 2.8 million people worldwide. Most people are diagnosed between the ages of 20 and 50, though it can also occur in young children and the elderly.

MS in Women
Multiple sclerosis is three times more common in women than in men. In addition, nearly all women afflicted with MS get the condition before menopause. This could mean that hormones play an important role in the disease’s development.

MS in Men
Usually, MS in men is more severe than it is in women. They typically get MS in their 30s and 40s, just as their testosterone levels begin to decline.

Although MS is more common in women than men overall, one form of the disease contradicts this pattern. People with primary progressive (PP) MS are about as likely to be male as female. (The four main types of MS are described later).

Multiple Sclerosis and Smoking
People who smoke are more likely to develop MS, and to develop it more severely and with a faster progression.

MS is more prevalent among Caucasians than other ethnicities. MS is believed to have a genetic component as people with a first-degree relative with the disease have a higher incidence than the general population.

Multiple Sclerosis Causes
Some theories have been proposed, though there is not enough evidence to establish any one cause.
We don't know exactly what causes multiple sclerosis, but it is believed to be some combination of immunologic, environmental, infectious, and/or genetic factors. Some theories have been proposed, though there is not enough evidence to establish any one cause. Theories as to what causes MS include:

Exposure to mercury and other heavy metals
Allergies, including pet allergies
Exposure to chemical solvents such as amines, esters, ethers, and ketones
Viruses such as Epstein-Barr virus (EBV) and human herpes virus 6 (HHV-6)
How MS Attacks the Body
By attacking myelin, the immune system in a person with MS causes inflammation and degeneration of the myelin that can lead to demyelination.
Multiple sclerosis (MS) is an autoimmune disorder in which the immune system mistakenly perceives its own myelin (the protective sheath around the nerves) as an intruder and attacks it, as it would a virus or other foreign infectious agent. To understand how this harms the body, it helps to understand how nerves work.

Nerve Anatomy
A nerve can be seen by the naked eye, but it is made up of hundreds or even thousands of microscopic nerve fibers wrapped by connective tissue. Nerves conduct messages to and from the brain by way of electrical impulses.

Often the nerve fibers that make up a nerve are all individually wrapped in myelin, a protective sheath that causes electric impulses to conduct down the nerve much faster than fibers that lack myelin. (The same principle is used to improve electric wires by covering them with a plastic outer layer.)

How Does MS Destroy Myelin?
In multiple sclerosis, the immune system's T cells attack the myelin sheath. By attacking myelin, the immune system in a person with MS causes inflammation and degeneration of the myelin that can lead to demyelination, or stripping of the myelin covering of the nerves. It can also cause scarring (the "sclerosis" in the name “multiple sclerosis”). This causes electrical impulses to travel more slowly along the nerves resulting in deterioration of function in body processes such as vision, speech, walking, writing, and memory.

Is Multiple Sclerosis Inherited?
While multiple sclerosis is not hereditary, genetics are believed to play a role.
While multiple sclerosis is not hereditary, genetics are believed to play a role. In the U.S., the chances of developing MS are one in 750. Having a first-degree relative (parent, sibling) increases the risk to up to 5%. An identical twin of someone with MS has a 25% chance of being diagnosed with the disorder. It is thought there is an outside trigger, as genetics only makes certain people susceptible to getting MS, which is why the disease is not considered hereditary. Genes may make a person more likely to develop the disease, but it is believed that there still is an additional outside trigger that makes it happen.

Types of MS
There are four different types of multiple sclerosis that have been identified and each type can have symptoms ranging from mild to severe.
There are four different types of multiple sclerosis that have been identified and each type can have symptoms ranging from mild to severe. The different types of MS can help predict the course of the disease and a patient's response to treatment. The four types of MS are discussed on the next four slides.

Relapsing-Remitting (RR) MS
Relapsing-remitting multiple sclerosis (RR-MS, RRMS or RMS) is the most common type of MS.
Relapsing-remitting multiple sclerosis (RR-MS, RRMS or RMS) is the most common type of MS, affecting about 85% of MS sufferers. RR-MS is defined by inflammatory attacks on the myelin and nerve fibers causing a worsening of neurologic function. Symptoms vary from patient to patient, and symptoms can flare up (called relapses or exacerbations) unexpectedly, and then disappear (remission).

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