What happens to myelin in multiple sclerosis?

With multiple sclerosis (MS), the body’s own system of defense, known as the immune system, malfunctions. It sends disease-fighting cells into the central nervous system (CNS) that may destroy the body’s own myelin. This occurs because the immune system is incorrectly identifying the myelin in the CNS as a foreign body. When the body’s own immune system attacks its own tissue, this is referred to as an “autoimmune disease,” and MS is believed to fall into this category. Examples of other autoimmune diseases include lupus and rheumatoid arthritis.

Lymphocytes are a type of white blood cell and play a strong role in the body’s defense system. Another type of white blood cell is the macrophage, and this works to ingest and destroy foreign substances.

White blood cells circulate in the blood and are produced when the immune system perceives a foreign body and instructs the cells to eliminate it, thereby “protecting” the body. In order to reach the nerves within the CNS, the immune system cells and molecules must cross a protective barrier that surrounds the blood vessels. Known as the blood-brain barrier (BBB), this layer of cells is designed to prevent damaging cells and other substances in the blood (including those that could cause disease) from entering the brain, optic nerves, and spinal cord of the CNS.

With MS, damaging immune-system cells (macrophages and other lymphocytes) are able to break through the BBB and enter the CNS, where they begin their attack on the myelin. This creates inflammation along the nerves where the myelin is being damaged. Areas of activity are known as lesions (or plaques). Lesions vary in activity levels, ranging from very active (acute), to chronic, to inactive.

Often, myelin that is damaged may be restored through a process called “remyelination,” particularly early in the disease. Oligodendrocytes are cells that produce and maintain myelin. Over time, however, oligodendrocytes may be lost and unable to repair the damaged myelin.

Remyelination is believed to occur in relapsing-remitting MS (RRMS) when a symptom flare-up subsides and goes into remission. The return of function is thought to result from not only myelin repair, but reduced inflammation as well. Eventually, the axon becomes exposed and damaged, and the myelin may no longer be repaired. With primary-progressive MS (PPMS) and other forms of progressive MS, the oligodendrocytes are unable to repair the myelin, and therefore symptoms do not remit.

Areas of damaged myelin become scarred and can no longer fully insulate the nerve – leaving unprotected areas, where the flow of nerve impulses is interrupted. This interruption in the communication between the brain and other parts of the body results in the symptoms experienced by individuals with MS.

Read The MS Process and Targets for Treatment.

Multiple sclerosis (MS) is a disease of the central nervous system (CNS). The CNS consists of the brain, optic nerves and spinal cord. With MS, areas of the CNS become inflamed, damaging the protective covering (known as “myelin“) that surrounds and insulates the nerves (known as “axons“). In addition to the myelin, over time, the axons and nerve cells (neurons) within the CNS may also become damaged.

The damage to the protective covering and also to the nerves disrupts the smooth flow of nerve impulses. As a result, messages from the brain and spinal cord going to other parts of the body may be delayed and have trouble reaching their destination – causing the symptoms of MS.

Common symptoms include:

Areas of inflammation and damage are known as “lesions.” The changes in size, number, and location of these lesions may determine the type and severity of symptoms. While individuals with relapsing forms of MS are believed to experience more inflammation than those with progressive forms of MS, lesions still occur for individuals with all forms of MS. However, the lesions in progressive forms of MS may be less active and expand more slowly.

In addition to symptoms, disease activity may be evaluated from changes in the size or number of lesions. Frequently, MS may be “clinically silent,” showing no increase in symptoms, yet continuing to show signs of disease activity within the CNS. For individuals with relapsing forms of MS, early and continued treatment with a disease-modifying therapy (DMT) can often slow the “clinically silent” disease activity in the brain, reducing the size and number of active lesions. This is why most neurologists, as well as the American Academy of Neurology, recommend that individuals with relapsing forms of MS begin treatment as soon as possible after the diagnosis is established. More recent FDA approvals have brought new DMTs that also treat active secondary-progressive MS and primary-progressive MS.

Additionally, areas of thick scar tissue may eventually form along the areas of permanently damaged myelin. These areas of scar tissue are referred to as “plaques.” The term “multiple sclerosis” originates from the discovery of these hardened plaques. Multiple refers to “many;” sclerosis refers to “scars.”

Lesions and plaques are viewed on a magnetic resonance imaging (MRI) scanner. This technology is used to help diagnose MS and evaluate its progress at various intervals.

Multiple sclerosis (MS) is a long-lasting (chronic) disease of the central nervous system. It is thought to be an autoimmune disorder, a condition in which the body attacks itself by mistake. MS is an unpredictable disease that affects people differently. Some people with MS may have only mild symptoms. Others may lose their ability to see clearly, write, speak, or walk when communication between the brain and other parts of the body becomes disrupted.

Myelin is the fatty tissue that surrounds and protects nerve fibers. In MS, the myelin is destroyed in many areas. This loss of myelin forms scar tissue called sclerosis. These areas are also called plaques or lesions. When the nerves are damaged in this way, they can’t conduct electrical impulses to and from the brain.

What causes multiple sclerosis?

There are many possible causes of MS, including:

• Autoimmune disorders

• Infectious agents, such as viruses

• Environmental factors

• Genetic factors

What are the symptoms of multiple sclerosis?

The symptoms of MS are often unpredictable. They may be mild or severe, short-term or long-lasting. They may appear in different combinations, depending on the area of the nervous system affected. The following are the most common symptoms of MS. But each person may have different symptoms.

First symptoms of MS

The following are often the first symptoms of MS:

• Blurred or double vision

• Red-green color distortion

• Pain and loss of vision because of swelling of the optic nerve (optic neuritis)

• Trouble walking

• An abnormal feeling or pain, such as numbness, prickling, or pins and needles (paresthesia)

Other symptoms of multiple sclerosis

• Muscle weakness in the arms and legs

• Trouble with coordination. You may have problems walking or standing. You may also be partially or completely paralyzed.

• Spasticity. The involuntary increased tone of muscles leading to stiffness and spasms.

• Fatigue. This may be brought on by physical activity, but it may ease with rest. You may have constant tiredness that doesn't go away.

• Loss of sensation

• Speech problems

• Tremor

• Dizziness

• Hearing loss

• Bowel and bladder problems

• Depression

• Changes in sexual function

About 50% of all people with MS have thinking (cognitive) problems linked to the disease. The effects of these problems may be mild. Your healthcare provider may only find them after much testing. The problems may be with:

• Focusing (concentration)

• Attention

• Memory

• Poor judgment

Symptoms of MS are grouped as primary, secondary, or tertiary as described below:

The symptoms of MS may look like other health conditions or problems. Always talk with your healthcare provider for a diagnosis.

How is multiple sclerosis diagnosed?

No specific test is available to diagnose multiple sclerosis. But a healthcare provider can make a diagnosis by following a careful process to rule out other causes and diseases. Two things must be true to make a diagnosis of MS:

1. You must have had 2 attacks at least 1 month apart. An attack is when any MS symptoms show up suddenly. Or when any MS symptoms get worse for at least 24 hours.

2. You must have more than 1 area of damage to the central nervous system myelin. Myelin is the sheath that surrounds and protects nerve fibers. This damage must have occurred at more than 1 point in time and not have been caused by any other disease.

Generally a single attack along with certain patterns of changes in brain tissue seen on an MRI scan of the brain performed with contrast can mean that you have MS.

An MS evaluation involves a complete health history and neurological exam. This includes:

• Mental functions

• Emotional functions

• Language functions

• Movement and coordination

• Vision

• Balance

• Functions of the 5 senses

The following may be used when evaluating a person for multiple sclerosis:

• MRI. A diagnostic test that uses a combination of large magnets, sound waves, and a computer to make detailed pictures of organs and structures within the body. It can find plaques or scarring caused by MS.

• Evoked potentials. These tests record the brain's electrical response to visual, auditory, and sensory stimuli. These tests show if you have a slowing of messages in the different parts of the brain.

• Cerebral spinal fluid analysis. This is also called a spinal tap or lumbar puncture. It looks at the fluid taken from the spinal column to make an evaluation or diagnosis. This test checks for cellular and chemical abnormalities seen with MS.

• Blood tests. These are done to rule out other causes for various neurological symptoms.

Evaluation and diagnosis of MS requires a variety of tools to rule out other possible disorders. It also requires a series of lab tests that, if positive, confirms the diagnosis.

How is multiple sclerosis treated?

Your healthcare provider will figure out the best treatment plan for you based on:

• Your age, overall health, and past health

• How sick you are

• How well you can handle certain medicines, treatments, or therapies

• How long your condition is expected to last

• Your opinion or preference

There is no cure yet for MS. But you can do things to help change the course of the disease, treat flare-ups, manage symptoms, and improve your function and mobility.

Treatments for the conditions seen with MS may include:

• Medicines (talk with your provider to see what medicines may be an option for you)

• Equipment such as canes, braces, or walkers

• Rehabilitation activities

Rehabilitation varies depending on your symptoms and how severe they are. MS rehabilitation may help you to:

• Get back functions that are important for daily living

• Be as independent as you can

• Involve your family

• Make the right decisions relating to your care

• Learn about equipment like canes, braces, or walkers that can make is easier to move around

• Set up an exercise program that builds muscle strength, endurance, and control

• Get back motor skills

• Speak more easily if you have weakness or a lack of coordination of face and tongue muscles

• Manage bowel or bladder incontinence

• Relearn thinking skills

• Change the way your home is set up to keep you safe but allow you to move about as easily as possible

What are the complications of multiple sclerosis?

The complications of MS range from mild to severe. They can range from fatigue to the inability to walk. Other problems include loss of vision, balance, and bowel or bladder control. Depression can result from the difficulty of living with a chronic condition.

Living with multiple sclerosis

It's important to take your medicines as directed. You may get help by taking part in a clinical trial. Using equipment like canes or walkers can help you get around as walking becomes more difficult. Rehabilitation activities can also help you keep or get back functioning. Changing the way your home is set up can help you stay independent. Talk with your family and healthcare providers about what you need.

Key points

• Multiple sclerosis (MS) is a chronic disease of the central nervous system.

• MS is unpredictable. Some people may be only mildly affected. Others may lose the ability to see clearly, write, speak, or walk.

• Early symptoms can include vision problems, trouble walking, and tingling feelings.

• MS affects people differently. But common problems are trouble with movement and thinking, and bowel and bladder incontinence.

• Medicines and rehabilitation can help to keep or restore functioning.