What is relapsing MS?

Understanding the details of relapsing MS can help

Relapsing multiple sclerosis (MS) is a progressive disease that causes damage to the central nervous system (CNS). Everybody experiences relapsing MS differently. The various ways the symptoms may evolve has been used to describe a few different forms of relapsing MS.

Forms of relapsing MS

  • Clinically isolated syndrome (CIS): CIS is the first episode of neurologic symptoms caused by inflammation and damage to the myelin in the central nervous system. The episode must last for at least 24 hours to be considered CIS. It is characteristic of multiple sclerosis but does not yet meet the criteria for a relapsing MS diagnosis. People who experience CIS may or may not go on to develop relapsing MS
  • Relapsing-remitting MS (RRMS): This is the most common form of relapsing MS. People with RRMS experience defined attacks of new or increasing neurologic symptoms. These attacks are known as relapses (or exacerbations) and are followed by periods of recovery called “remission.” While in remission, symptoms may continue and become permanent, or disappear. During remission, there is no obvious progression of the disease
  • Active secondary-progressive relapsing MS (SPMS): Relapsing MS can transition to SPMS, a condition in which the disease tends to progress more steadily. With active SPMS, you may still experience relapses

About 85% of people with MS have relapsing MS. Below, you will find more details about relapsing MS, its symptoms, and the treatment options available.

How many people have MS?

Estimates over 17 years suggest that the prevalence of MS in the US ranges from 851,749 to 913,925 people, based on health claims data. Please keep in mind these are estimates and not exact. MS is about 2-3 times more common in women than in men. People are usually diagnosed with MS between the ages of 20 and 50. However, diagnosis can also happen at other ages.

How relapsing MS affects the body

Relapsing MS is thought to be an autoimmune disease, which means that instead of defending the body against harmful invaders (such as viruses or bacteria), the immune system attacks the body itself. 

Specifically, relapsing forms of MS affect the cells of the CNS. Your brain contains nerve cells, which are called neurons. These neurons have nerve fibers (axons) that are protected and insulated by the myelin sheath. Myelin helps neurons send electrical signals to and from the brain, telling the body what to do.

With relapsing MS, immune cells cross the blood-brain barrier (BBB), cause inflammation within the CNS, and attack the myelin sheath. This is thought to interfere with the ability of neurons to send signals between the brain and the body. When your brain can’t properly communicate with nerves and muscles, various symptoms of relapsing MS can occur.

Understanding relapses, symptoms, disability progression, and lesions

As your disease progresses, existing relapsing MS symptoms may worsen, or new symptoms may appear during a flare-up. If you have any questions about relapsing MS symptoms, the best source of information is your healthcare provider.


Relapses, also known as flare-ups or exacerbations, are new symptoms or a worsening of existing symptoms. Their severity and duration are often unpredictable. Relapses can:

  • last from a few days to several months
  • cause permanent damage to the CNS
  • possibly lead to future disability

Even infrequent or mild relapses can cause permanent damage to the CNS and may lead to future disability. 

If you think that you might be having a relapse, be sure to talk with your healthcare provider.

Relapsing MS causes brain lesions that can be detected by MRI

Relapsing MS causes brain lesions that can be visualized with magnetic resonance imaging (MRI). MRIs are able to show both recent lesion development and previous lesion damage. Some common types of lesions that can be visualized with MRIs include:

  • Gadolinium-enhanced (Gd+) lesions: A dye containing gadolinium is used to show lesions that indicate active inflammation
  • T2 lesions: Lesions that show the long-term impact of inflammation on the brain
  • T1 lesions: Lesions that show damage that may be permanent

The exact relationship between MRI findings and the development of clinical symptoms is not clear. However, MRIs are commonly used to help you and your healthcare provider monitor disease activity in your body.

It’s important to talk with your neurologist about each one of your MRIs because that may help with working out a treatment plan moving forward. 

Finding the right relapsing MS treatment option for you

Whether or not you are experiencing any relapsing MS symptoms that you can feel on a daily basis, underlying relapsing MS activity could be damaging your CNS.

Studies have shown that nerve damage, which may contribute to physical disability progression, can happen during relapses or when new symptoms arise.

To help slow this progression, talk with your healthcare provider about starting on treatment as soon as you are diagnosed.

There are different types of treatments

Do your research. Look at the ways that different treatment options work. Find out about their clinical studies, side effects, effectiveness, dosing, and administration. Learning all you can empowers you to make a confident decision with your healthcare provider.

Treatment options
from Biogen

Biogen offers a number of treatment options for relapsing MS. Find out which could be right for you.

See relapsing MS treatment options

Relapsing MS glossary

Common relapsing MS terms are defined here. To learn more about these terms, talk with your healthcare provider. Your healthcare provider is the best resource you have for learning more about your disease.

  • Autoimmune disease: When your immune system mistakes your own cells for a foreign invader and attacks them
  • Blood-brain barrier: A cell layer around blood vessels that protects the brain from harmful substances
  • Infusion: The process of flowing a solution into the body, usually through a vein
  • Intravenous (IV): The passing of medicines into a vein through a needle attached to a tube
  • Magnetic resonance imaging (MRI): A method of creating images of the inside of the body. MRI uses powerful magnets and radio waves to produce these images. Along with other devices, MRI may help confirm or determine a diagnosis. MRI can be particularly helpful when diagnosing disorders of the brain or spine because it can provide detailed pictures of certain regions of the body that are difficult to see using other types of scanning devices
  • MRI brain lesions: Abnormal tissue in the brain detected by MRI
  • Multiple sclerosis (MS): A disease that affects the brain and spinal cord. It is thought to be an autoimmune disease, and it is characterized by the demyelination, or destruction, of myelin sheath. Myelin sheath is the protective covering for the nerve fibers of the central nervous system, and it helps the nerve fibers transmit electrical impulses between different parts of the body. When myelin sheath is destroyed in MS, messages between different parts of the body are not transmitted as effectively. After the myelin is destroyed, scar tissue called sclerosis is left behind in the damaged areas, which are referred to as lesions or plaques. This damage to the nervous system can result in a variety of symptoms, including vision problems and difficulty with muscle movement, coordination, and balance
  • Myelin sheath: The thick, soft, white, fatty layer of protective material around nerve fibers. This material is called myelin. If the myelin sheath around nerve fibers deteriorates or is destroyed, it can interfere with the fibers’ ability to transmit messages successfully from one part of the body to another
  • Nerves: A bundle of fibers that transmit messages between the nervous system and different parts of the body
  • Physical disability progression: Total or partial loss of a person’s bodily functions, as measured by the Expanded Disability Status Scale (EDSS)
  • Relapse: When new MS symptoms appear, or old symptoms reappear or become worse. Also called a “flare-up,” “attack,” or “exacerbation”

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