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Demyelination and Multiple Sclerosis

Learn how an abnormal immune response damages the central nervous system and causes MS symptoms.


In this article

Multiple sclerosis: An immune-mediated disease

Normally, your immune system protects you from disease and infection. It attacks germs that get into your body, such as viruses and bacteria. In MS, the immune cells attack the central nervous system (CNS) by mistake. This is why MS is known as an immune-mediated disease.

Within the CNS, the immune system in someone with MS primarily attacks:

  • The myelin coating, or sheath, around nerves
  • Nerve fibers (axons)
  • Cells that make myelin (oligodendrocytes)

The damaged areas develop scar tissue, or sclerosis. This gives the disease its name — multiple areas of scarring, or “multiple sclerosis.” This damage to different areas of the CNS produces a range of neurological symptoms that vary among people with MS in type and severity.

We don’t fully understand what causes the immune system to attack the nervous system in MS. We believe that genetics, infectious disease and environmental factors combine to trigger the disease.

What is demyelination?

In MS, the immune system primarily attacks the myelin sheath that surrounds the nerve fibers, also known as axons. Axons are the long, threadlike parts of a nerve cell. The sheath protects these axons much as insulation around an electrical wire protects the wire. The illustration below shows how the attack damages the myelin sheath.

two diagrams, one showing a healthy nerve and the other one showing damage from multiple sclerosis

two diagrams, one showing a healthy nerve and the other one showing damage from multiple sclerosis

In addition to the myelin, the attack also damages the oligodendrocytes. This makes it harder for the CNS to replace the damaged myelin. All of this leads to a loss of myelin, or demyelination. Without the myelin insulation, the axons also get damaged.

For a more detailed description of this process, visit our myelin page.

Effects of axon damage

Without the protective myelin sheath, the axons, or nerve fibers, can be damaged and even completely severed. When the axon is severed, messages no longer travel efficiently between the brain and the body.

Myelin has some ability to repair itself, and researchers are looking for ways to restore what has been lost in people with MS. However, axons cannot be repaired. And damage to axons can occur even in the earliest stages of the disease. That’s why early treatment with a disease-modifying medication should be considered by anyone with a confirmed diagnosis of MS. Learn more about these medications below.

Therapies for MS that help prevent demyelination

Researchers have developed medications called disease-modifying therapies or DMTs that target the parts of the immune response in MS that cause inflammation and damage. There are now many different DMTs available that help modify the MS disease process and prevent the demyelination that causes MS symptoms, disease progression and disability.


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