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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. The central nervous system includes the brain, spinal cord and optic nerves and controls everything that we do.

Because the damage in MS is done by the immune system, it 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 central nervous system in MS. We believe that genetics, infectious disease and environmental factors combine to trigger the disease.

What is demyelination and demyelinating disease?

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

The immune system also attacks and causes damage to 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, or nerve fibers, also get damaged. They can even be completely severed.

A disease that causes this process is called a demyelinating disease. For a more detailed description of demyelination, visit our myelin page.

Effects of axon damage

When the axon is damaged or severed, messages no longer travel efficiently between the brain and the body. This causes the symptoms of MS, including vision problems, walking or gait difficulties and cognitive changes.

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 therapy should be considered by anyone with a confirmed diagnosis of MS. Learn more about these therapies below.

Demyelinating lesions

Lesions are damaged areas in the brain and spinal cord caused by the immune-system attack. The exact type and severity of the symptoms that results depends on the number of lesions and the area of the central nervous system that’s damaged.

Disease-modifying therapies have all been shown to reduce the accumulation of new demyelinating lesions. Scientists have also discovered that the body heals some lesions naturally. It does this by stimulating oligodendrocytes in the area or by recruiting young oligodendrocytes from further away. This allows the body to begin making new myelin at the damaged site. However, this natural repair process is slow and incomplete. More studies are needed to understand the remyelination process and develop treatments to repair damage.

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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