Demyelination: What Is It and Why Does It Happen?

Written by Christine Case-Lo | Published on March 27, 2014
Medically Reviewed by George T. Krucik, MD, MBA on March 27, 2014

Demyelination: Bare Nerves

Nerves do amazing things, sending and receiving messages from every part of your body and processing them in your brain. They allow you to speak, see, feel, and think.

Nerves are protected in the body by a coating called myelin. When myelin is worn away or damaged, nerves don’t work as well. They can deteriorate, causing problems inside the brain and throughout the body.

Damage to the myelin sheath around nerves is called demyelination. Demyelination plays a part in several chronic diseases. Researchers are working to find ways to prevent or reverse demyelination.

The Stuff That Nerves Are Made Of

Nerves are made up of cells called neurons. Neurons are composed of a cell body, dendrites, and an axon. The axon is the long part of the cell that sends messages from one neuron to the next. Axons also connect neurons to other cells, such as muscle cells.

Some axons are microscopically short. Some are very long—even up to three feet! Some axons are covered in myelin, an insulating material to protect the axons and to carry their messages as quickly as possible.

What Is Myelin?

Myelin is made of layers of membranes that shield the axon underneath. This is just like an electrical wire with coating to protect the metal underneath. This insulation allows the signal to travel faster. In unmyelinated neurons, a signal can travel along the nerves at about one meter per second—that’s jogging speed. In a myelinated neuron, the signal can travel 100 meters per second, the speed of a racecar.

Certain diseases can cause damage to myelin, slowing down messages sent along axons. The damage can lead to deterioration of the axon. Depending upon the location of the damage, axon loss can cause problems with feeling, moving, seeing, hearing, and thinking clearly.

Causes of Demyelination

Inflammation is the most common cause of myelin damage. Other causes include:

  • inflammation
  • infection with certain viruses
  • metabolic problems
  • loss of oxygen
  • physical compression

Inflammatory and Viral Demyelination

Inflammatory demyelination occurs due to the body’s immune system attacking myelin. Multiple sclerosis (MS), optic neuritis, and acute-disseminated encephalomyelitis (ADEM) are types of demyelination caused by inflammation in the brain and spinal cord. Guillain-Barre syndrome (GBS) involves inflammatory demyelination of peripheral nerves in the body (those not in the brain or spinal cord).

Viral demyelination occurs with progressive multifocal leucoencephalopathy (PML). PML is caused by infection with the JC virus. Metabolic damage to myelin can occur with alcoholism, liver damage, and electrolyte imbalances. Hypoxic-ischemic demyelination occurs due to oxygen deprivation or vascular disease in the brain.

Vaccines and Demyelination

Vaccination activates long-term immunity toward a disease by administering a form of a virus or bacteria. It’s possible that activating the immune system could trigger an autoimmune reaction. This occurs only in a few individuals with hypersensitive immune systems. Some children and adults experience “acute demyelinating syndromes” after exposure to certain vaccines such as those for influenza or HPV. However, there have only been 77 documented cases since 1979.

MS is not an “acute demyelinating” disease, but a chronic one. A 2003 review concluded that there was no increased risk of MS from a wide variety of common vaccines. There is little risk of MS due to the hepatitis B vaccine.

Effects of Demyelination

Demyelination prevents nerves from being able to conduct messages to and from the brain. The effects of demyelination can occur very rapidly. In Guillain-Barre syndrome (GBS), a demyelinating inflammation of peripheral nerves, it may only take a few hours for symptoms to appear once myelin is under attack.

For chronic illnesses like MS, symptoms can come and go, and will progress over years. Nerves are a key part of how your body functions. A wide range of symptoms can occur when nerves are compromised by demyelination.

Symptoms of Demyelination

Symptoms of demyelinating diseases can include:

  • numbness
  • loss of reflexes and uncoordinated movements
  • poorly controlled blood pressure
  • blurred vision
  • dizziness
  • racing heart beat or palpitations
  • memory problems
  • pain
  • loss of bladder and bowel control
  • fatigue

Multiple Sclerosis

MS is the most common demyelinating disease, with 2.3 million people affected worldwide. MS is a chronic disease where demyelination occurs in the white matter of the brain and in the spinal cord. In areas where myelin is under attack by the immune system, lesions or “plaques” form. These plaques are scar tissue. The name “sclerosis” means scar. Many of these plaques occur throughout the brain and over the course of years.

MS subtypes are:

  • relapsing-remitting MS
  • primary progressive MS
  • secondary progressive MS
  • progressive relapsing MS

About 85 percent of patients are initially diagnosed with relapsing-remitting MS.

Slowing Demyelination

There is no cure for demyelinating diseases. In some cases, new myelin growth can occur in areas of damage. However, the new myelin is thinner and not as effective. Research is underway to increase the body’s ability to grow new myelin.

Most treatment of demyelinating disease concentrates on reducing the immune response. This is done with drugs like interferon beta or glatiramer acetate. Vitamin D is also a potential treatment. People with low levels of vitamin D are more susceptible to developing MS or demyelinating diseases, so high levels of vitamin D may reduce inflammatory immune response.

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