What to Know About Demyelination, the Driving Force of MS

If you’re unfamiliar with the word demyelination, we don’t blame you. Unless you have a health condition like multiple sclerosis (MS), you may not be totally clear on what it means or what kind of role it might play in your health. Simply put, demyelination causes demyelinating diseases, which are characterized by various neurological symptoms.

Understanding demyelination starts with understanding myelin, which is a protective coating of cells that acts as insulation around the nerve fibers (also called axons) in your brain and spinal cord, according to the Mayo Clinic. Nerve fibers are important because they carry vital information that facilitates muscle movements and sensory input (such as sights, sounds, and smells) to and from your central nervous system, according to the National Library of Medicine (NLM).

“Think of a copper wire, which has kind of a sheath around it—in some ways, myelin does the same thing,” Tyrell Simkins, DO, PhD, an associate professor in the department of neurology at the University of California-Davis who specializes in researching myelin, tells SELF. “Myelin protects the axons. But what’s most important about myelin is that it actually makes the information transmitted by our nerves go faster.” Basically, myelin helps ensure that as soon as you think about moving your arm, it moves as you intend it to.

So, what happens during demyelination, and how does it lead to diseases of the nervous system like MS? SELF spoke to experts to break it all down.

What is demyelination?

Demyelination means the protective myelin around your nerve cells has become damaged, making it hard for the signals between your brain and the rest of your body to communicate, according to the NLM. When myelin is damaged, your nerves either transmit information more slowly or not at all, which can then lead to the neurological symptoms associated with demyelinating diseases such as multiple sclerosis.

In fact, demyelination and multiple sclerosis are inextricably linked. “If you don’t have evidence of demyelination, we cannot diagnose you with multiple sclerosis,” Dr. Simkins says. Before someone even learns they have MS, demyelination is already happening—but you may not have symptoms in the early stages because not enough myelin has been damaged.

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What causes demyelination in people with multiple sclerosis?

There are a few types of demyelination, and each one develops for different reasons1. Inflammatory demyelination is associated with multiple sclerosis. In this case, your immune system mistakenly attacks your myelin and damages the myelin sheath. “The immune system gets turned around, and instead of attacking bacteria or a virus, for example, it recognizes myelin as something foreign,” Dr. Simkins explains. “Then it starts doing the things that it would do to bacteria or viruses to the myelin, which is trying to break them down and trying to remove them.”

“What causes those immune cells to inappropriately target the central nervous system? That’s one thing we don’t know,” Ari Green, MD, medical director of the Multiple Sclerosis and Neuroinflammation Center at the University of California, San Francisco, tells SELF. “One of the prevailing theories is that the onset of this might be related to exposure to the Epstein-Barr virus, which is the virus that causes mono2,” Dr. Simkins says. The connection is still a bit unclear, but people who have had Epstein-Barr are more likely to later develop MS compared to people who have never had the virus, according to Dr. Simkins. That’s not to say that contracting Epstein-Barr causes MS directly, but the association is being further studied.

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What are the different types of demyelination?

The other types of demyelination are rare, and experts are still trying to understand them better. Here is a little more about the different types of demyelination:

  • Viral demyelination occurs when someone comes into contact with a virus that can eventually lead to demyelination. It may sound similar to what happens with the Epstein-Barr virus, but in this case, it is often caused by the JC polyomavirus1. Typically, this virus doesn’t cause problems in most people who contract it unless their immune system becomes very weak—say, because they needed to have surgery. In that case, the JC polyomavirus may become active and destroy the cells that make myelin, according to the National Organization of Rare Diseases (NORD).
  • Acquired metabolic demyelination is another rare form of demyelination that happens alongside an acquired metabolic disorder. These are metabolic conditions resulting from an environmental trigger, such as drinking heavy amounts of alcohol over a long period of time or having a blood infection, according to Houston Methodist.
  • Hypoxic-ischemic demyelination happens if the brain is deprived of oxygen (hypoxia) or blood (ischemia) for a significant period of time. Usually, your brain tissue dies1 if your brain is deprived of blood or oxygen, so this rarely happens.
  • Compression-induced demyelination is very rare but typically happens after brain trauma1. In this scenario, experts theorize that chronic nerve compression changes myelin structure, leading to demyelination.