What Is a Multiple Sclerosis Relapse?

The Science Behind Your Relapses and How You May Prevent Them

In This Article

woman having eye pain

An MS relapse is either a worsening of symptoms that you already have or the appearance of new symptoms. It's caused by an MS lesion on your brain or spinal cord. Relapses are also referred to as exacerbations, attacks, bouts, or flares.


Relapses are caused by the inflammation that occurs when your immune system attacks the myelin surrounding nerves in your brain or spinal cord. More specifically, myelin is the protective coating that covers nerve fibers and helps them conduct signals among one another.

When the myelin is attacked by immune cells, a “lesion” or an area of inflammation and eventual damage (demyelination) occurs, making the nerves less efficient in conducting signals.

A person's MS symptoms then depend on the location of this lesion in the brain, spinal cord, or optic nerve. For instance, inflammation in the cerebellum may cause loss of balance and coordination, while inflammation of the optic nerves may cause decreased vision.

Signs and Symptoms

Some relapses are very obvious, for instance, losing your sight in one eye due to an attack of optic neuritis. However, other relapses may not be as sudden or dramatic. For instance, you may just feel extra “wobbly” or tired.

The way to really know if you are having a relapse is to have an MRI with gadolinium—which is contrast material that is injected during the MRI scan. Gadolinium is drawn to areas of inflammation and “lights up” when a lesion is “active.” In this case, demyelination is currently occurring, and you are having a true relapse, rather than feeling symptoms caused by older lesions.


A pseudoexacerbation is a temporary increase in symptoms that is brought on by an external factor. Most often they are caused by an increase in core body temperature due to heat from hot weather, exertion, or fever, and this is called the Uhthoff phenomenon. Once the body temperature returns to normal, the neurological symptoms subside.

How Long Will It Last? 

In order to be a true MS relapse, the symptoms have to last at least 24 hours. That being said, relapses usually last several weeks, although they can be as short as a couple of days, or as long as several months.

It's also important to note that a new relapse must be separated from a prior relapse by at least a month. This is to distinguish it from symptoms that may be from a previously active lesion, which can change as inflammation subsides, remyelination occurs, and/or scar tissue forms.


Many relapse symptoms can be treated with high-dose corticosteroids, usually Solu-Medrol. The decision is made to treat a relapse based on how much disability the symptoms are causing, and how much they interfere with a person's daily activities.

The steroid treatment may significantly shorten the duration of the more severe symptoms, allowing a faster return to normal activities. However, some symptoms may take a longer time to go away and may never quite clear up entirely, and this is means a person may have some residual disability.


The most important thing that you can do to prevent relapses is to begin using and adhering to one of the disease-modifying therapies. These therapies have been shown to reduce the number and severity of MS relapses, the development of new brain and spinal cord lesions, and delay a person's disability progression. The good news is that there are a number of options available now for treating MS, so together with your neurologist, you can find the best fit for you.

A Word From Verywell

MS relapses can be incredibly frustrating and anxiety-provoking for both patients and their loved ones, and it's common for people to question whether they are truly experiencing a new relapse, feeling symptoms from old relapses, or having a pseudoexacerbation. In the end, it's best to speak with your neurologist about your symptoms if you are not sure, especially if they are interfering with your daily activities or causing you discomfort.

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Article Sources

  • Birnbaum, M.D. George. 2013. Multiple Sclerosis: Clinician’s Guide to Diagnosis and Treatment, 2nd Edition. New York, New York. Oxford University Press. 
  • National MS Society. (2017). Disease-Modifying Therapies for MS.