What is multiple sclerosis? An expert explains

Learn more from neurologist Oliver Tobin, M.B., B.Ch., B.A.O., Ph.D.

I'm Dr. Oliver Tobin, a neurologist specializing in multiple sclerosis at Mayo Clinic. In this video, we'll be covering the basics of multiple sclerosis. What is it? Who gets it? The symptoms, diagnosis, and treatment. Whether you're looking for answers about your own health or that of someone you love, we're here to provide you with the best information available. Multiple sclerosis is a disorder in which the body's immune system attacks the protective covering of the nerve cells in the brain, optic nerve and spinal cord, called the myelin sheath. And this sheath is often compared to the insulation on an electrical wire. When that covering is damaged, it exposes the actual nerve fiber, which can slow or block the signals being transmitted within it. The nerve fibers themselves might also be damaged. The body can repair damage to the myelin sheath, but it's not perfect. The resulting damage leaves lesions or scars, and this is where the name comes from: multiple sclerosis, multiple scars. Now everyone loses brain cells and spinal cord cells as they get older. But if part of the brain or spinal cord has been damaged by MS, the nerve cells in that area will die off faster than the areas around it that are normal. This happens very slowly, usually over decades and typically shows up as gradual walking difficulty happening over several years. When you read about multiple sclerosis, you may hear about different types -- the most frequent being relapsing-remitting multiple sclerosis. And this is characterized by attacks, or relapses.

We don't know what causes MS, but there are certain factors that may increase the risk or trigger its onset. So while MS can occur at any age, it mostly makes its first appearance in people between the ages of 20 and 40. Low levels of vitamin D and low exposure to sunlight, which enables our body to make vitamin D, are associated with an increased risk of developing MS. As people who have MS who have low vitamin D tend to have more severe disease. So people who are overweight are more likely to develop MS and people who have MS and are overweight tend to have more severe disease and a faster onset of progression. People who have MS and who smoke tend to have more relapses, worse progressive disease, and worse cognitive symptoms. Women are up to three times as likely as men to have relapsing-remitting MS. The risk for MS in the general population is about 0.5%. If a parent or sibling has MS, your risk is about twice that or about 1%. Certain infections are also important. A variety of viruses have been linked to MS, including Epstein-Barr virus, which causes mono. Northern and southern latitudes have a higher prevalence, including Canada, the northern US, New Zealand, southeastern Australia, and Europe. White people, especially of northern European descent, are at the highest risk. People of Asian, African, and Native American ancestry have the lowest risk. A slightly increased risk is seen if a patient already has autoimmune thyroid disease, pernicious anemia, psoriasis, type 1 diabetes, or inflammatory bowel disease.

Symptoms of a relapse usually come on over 24 to 48 hours, last for a few days to a few weeks and then improve in the region of 80 to a 100 percent. Those symptoms include loss of vision in an eye, loss of power in an arm or leg or a rising sense of numbness in the legs. Other common symptoms associated with MS include spasms, fatigue, depression, incontinence issues, sexual dysfunction, and walking difficulties.

There's currently no single test to make a diagnosis of MS. However, there are four key features which help to secure the diagnosis. Firstly, are there typical symptoms of multiple sclerosis? Again, those are loss of vision in an eye, loss of power in an arm or leg, or sensory disturbance in an arm or leg lasting for more than 24 hours. Secondly, do you have any physical examination findings consistent with MS? Next, is the MRI of your brain or spine consistent with MS? Now here it's important to note that 95 percent of people over the age of 40 have an abnormal brain MRI, just the same as many of us have wrinkles on our skin. Lastly, are the results of the spinal fluid analysis consistent with MS? Your doctor may recommend blood tests to check for other diseases that share the same symptoms. They may also recommend an OCT test or optical coherence tomography. This is a short scan of the thickness of the layers at the back of your eye.

So the best thing to do when living with MS is to find a trusted interdisciplinary medical team that can help you monitor and manage your health. Having a multidisciplinary team is essential for addressing the individual symptoms that you're experiencing. If you have an MS attack or relapse, your doctor may prescribe you corticosteroids to reduce or improve your symptoms. And if your attack symptoms do not respond to steroids, another option is plasmapheresis or plasma exchange, which is a treatment similar to dialysis. About 50 percent of people who do not respond to steroids have a significant improvement with a short course of plasma exchange. There are over 20 medications currently approved for prevention of MS attacks and prevention of new MRI lesions.

As learning to function with MS can be challenging, there are medical experts ready to work with you to help you manage it, so you can still live a full life. Consulting with a physiatrist, physical or occupational therapist can help you deal with physical difficulties. Physical activity is strongly recommended for all people with MS. Mental health is also an important consideration. So keeping up personal connections with friends and family and trying to stay involved with your hobbies is important. But also be kind to yourself and realistic about what you're up for. This can change from day to day, so it's okay to give yourself permission if something seems like too much or if you need to cancel plans. You may also find support groups helpful to connect with people who understand what you are going through and discuss your feelings and concerns with a doctor or a counselor. Meanwhile, scientists are hard at work, expanding our understanding of this disease and developing new treatments and medications which are ever more effective. If you want to learn more, watch more of our videos or visit mayoclinic.org. We wish you well.

Multiple sclerosis (MS) is a potentially disabling disease of the brain and spinal cord (central nervous system).

In MS, the immune system attacks the protective sheath (myelin) that covers nerve fibers and causes communication problems between your brain and the rest of your body. Eventually, the disease can cause permanent damage or deterioration of the nerve fibers.

Signs and symptoms of MS vary widely between patients and depend on the location and severity of nerve fiber damage in the central nevous system. Some people with severe MS may lose the ability to walk independently or ambulate at all. Other individuals may experience long periods of remission without any new symptoms depending on the type of MS they have.

There's no cure for multiple sclerosis. However, there are treatments to help speed the recovery from attacks, modify the course of the disease and manage symptoms.


Multiple sclerosis signs and symptoms may differ greatly from person to person and over the course of the disease depending on the location of affected nerve fibers.

Common symptoms include:

  • Numbness or weakness in one or more limbs that typically occurs on one side of your body at a time
  • Tingling
  • Electric-shock sensations that occur with certain neck movements, especially bending the neck forward (Lhermitte sign)
  • Lack of coordination
  • Unsteady gait or inability to walk
  • Partial or complete loss of vision, usually in one eye at a time, often with pain during eye movement
  • Prolonged double vision
  • Blurry vision
  • Vertigo
  • Problems with sexual, bowel and bladder function
  • Fatigue
  • Slurred speech
  • Cognitive problems
  • Mood disturbances

When to see a doctor

See a doctor if you experience any of the above symptoms for unknown reasons.

Disease course

Most people with MS have a relapsing-remitting disease course. They experience periods of new symptoms or relapses that develop over days or weeks and usually improve partially or completely. These relapses are followed by quiet periods of disease remission that can last months or even years.

Small increases in body temperature can temporarily worsen signs and symptoms of MS. These aren't considered true disease relapses but pseudorelapses.

At least 20% to 40% of those with relapsing-remitting MS can eventually develop a steady progression of symptoms, with or without periods of remission, within 10 to 20 years from disease onset. This is known as secondary-progressive MS.

The worsening of symptoms usually includes problems with mobility and gait. The rate of disease progression varies greatly among people with secondary-progressive MS.

Some people with MS experience a gradual onset and steady progression of signs and symptoms without any relapses, known as primary-progressive MS.

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The cause of multiple sclerosis is unknown. It's considered an immune mediated disease in which the body's immune system attacks its own tissues. In the case of MS, this immune system malfunction destroys the fatty substance that coats and protects nerve fibers in the brain and spinal cord (myelin).

Myelin can be compared to the insulation coating on electrical wires. When the protective myelin is damaged and the nerve fiber is exposed, the messages that travel along that nerve fiber may be slowed or blocked.

It isn't clear why MS develops in some people and not others. A combination of genetics and environmental factors appears to be responsible.

Risk factors

These factors may increase your risk of developing multiple sclerosis:

  • Age. MS can occur at any age, but onset usually occurs around 20 and 40 years of age. However, younger and older people can be affected.
  • Sex. Women are more than 2 to 3 times as likely as men are to have relapsing-remitting MS.
  • Family history. If one of your parents or siblings has had MS, you are at higher risk of developing the disease.
  • Certain infections. A variety of viruses have been linked to MS, including Epstein-Barr, the virus that causes infectious mononucleosis.
  • Race. White people, particularly those of Northern European descent, are at highest risk of developing MS. People of Asian, African or Native American descent have the lowest risk. A recent study suggests that the number of Black and Hispanic young adults with multiple sclerosis may be greater than previously thought.
  • Climate. MS is far more common in countries with temperate climates, including Canada, the northern United States, New Zealand, southeastern Australia and Europe. Your birth month may also affect the chances of developing multiple sclerosis, since exposure to the sun when a mother is pregnant seems to decrease later development of multiple sclerosis in these children.
  • Vitamin D. Having low levels of vitamin D and low exposure to sunlight is associated with a greater risk of MS.
  • Your genes. A gene on chromosome 6p21 has been found to be associated with multiple sclerosis.
  • Obesity. An association with obesity and multiple sclerosis has been found in females. This is especially true for female childhood and adolescent obesity.
  • Certain autoimmune diseases. You have a slightly higher risk of developing MS if you have other autoimmune disorders such as thyroid disease, pernicious anemia, psoriasis, type 1 diabetes or inflammatory bowel disease.
  • Smoking. Smokers who experience an initial symptom that may signal MS are more likely than nonsmokers to develop a second event that confirms relapsing-remitting MS.


People with multiple sclerosis may also develop:

  • Muscle stiffness or spasms
  • Severe weakness or paralysis, typically in the legs
  • Problems with bladder, bowel or sexual function
  • Cognitive problems, like forgetfulness or word finding difficulties
  • Mood problems, such as depression, anxiety or mood swings
  • Seizures, though very rare
Dec. 24, 2022
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