Multiple sclerosis (MS) is a chronic condition with a variety of symptoms that come and go. Around 8 in 10 people have a type of MS called relapsing-remitting MS (RRMS). In RRMS, most of the damage to the central nervous system (CNS) occurs during short periods called “relapses” — also known as “exacerbations” and “flare-ups.” During these periods, new symptoms can appear or existing symptoms can worsen.

During periods of worsening MS symptoms, people living with MS often wonder whether they’re experiencing a true MS relapse or just a temporary worsening of symptoms known as a “pseudoexacerbation” or “pseudo-relapse.” Understanding the differences between a true MS relapse and a pseudoexacerbation can help you manage your health more effectively and guide you in knowing when to reach out to your health care team for help.

Here are six key differences between an MS relapse and a pseudoexacerbation to help you identify which one you might be experiencing.

1. Duration of Symptoms

A multiple sclerosis relapse involves the emergence of new symptoms or the return of old ones that last for more than 24 hours. Typically, an exacerbation will persist for longer periods — days, weeks, even months. A true exacerbation isn’t caused by other factors unrelated to MS, such as infections or increases in body temperature.

In contrast, a pseudoexacerbation is a temporary worsening of symptoms, typically lasting less than 24 hours. Usually, these are triggered by reversible factors such as heat, stress, or infection. Once the trigger is removed, these symptoms usually go away.

2. Cause of Symptoms

A true MS exacerbation is caused by new inflammatory damage in the central nervous system (the brain and spinal cord). This damage can lead to the worsening of existing lesions or the creation of new lesions. These lesions can sometimes be seen on MRI scans. Symptoms and disease progression correspond to the new inflammation and damage that can sometimes be seen on imaging.

MS relapses often occur without any clear external trigger. This can make them unpredictable as they can strike anytime, without warning, and they can’t be prevented.

In a pseudoexacerbation, external factors — rather than new disease activity — temporarily impair the nervous system. Pseudoexacerbations don’t cause any damage, so a scan wouldn’t reveal any new lesions. Usually, you can identify an external factor or trigger that causes symptoms.

Triggers for pseudoexacerbations can include the following:

• Fever
• Stress
• Physical exertion
• Infections
• Hot weather

The most common cause of pseudoexacerbation is a urinary tract infection (UTI). Another common cause is the heat, especially in people with heat-sensitive MS. If you are one of those people, it’s important to avoid saunas, hot tubs, and being outside on hot days.

3. Frequency and Patterns

MS relapses can vary widely in frequency. Some people may experience multiple relapses per year, while others may go years without one. The pattern can vary unpredictably and make managing your health during flare-ups difficult.

Pseudoexacerbations last for a shorter duration of time, but they occur more frequently than MS relapses. They tend to occur in response to known triggers. By avoiding these triggers, a person should experience these episodes less frequently and have an easier time managing them.

4. Impact on Long-Term Disability

An MS relapse can significantly contribute to your long-term disability and quality of life. Each relapse may leave damage. Over time, this residual damage to your brain and spinal cord may progressively affect your health and ability to function, leading to a progressive decline.

In contrast, pseudoexacerbations neither cause permanent damage nor contribute to long-term disability. Once the trigger is removed, your symptoms should start to resolve. People typically return to their baseline level of functioning shortly after a pseudoexacerbation goes away.

5. Symptom Severity

Symptoms of MS during a relapse can be severe and debilitating. These symptoms can greatly impact your life, both because of how long they last and their intensity. New symptoms may appear based on where new damage has occurred, or old symptoms may get worse.

Common symptoms during an MS relapse may include:

• Reduced mobility
• Vision problems (including optic neuritis, which is inflammation of the eye’s optic nerve)
• Difficulty with balancing
• Bladder control issues
• Pain or unusual sensations
• Fatigue and weakness
• Reduced concentration

The severity of your symptoms depends on a variety of factors. One study found that severe attacks are most likely to occur in people who are male, have a longer duration of relapse, and are not taking a disease-modifying therapy (DMT).

Symptoms of pseudoexacerbations are often similar to those of an MS relapse, but they’re usually less severe and have a lesser impact on a person’s life. Pseudoexacerbation can cause symptoms similar to those of a previous relapse, as areas of previous damage are more susceptible to stress. These mild symptoms should resolve quickly once the root cause is addressed.

6. Diagnosis and Treatment

If you think you’re experiencing an MS relapse, make an appointment with your neurologist as soon as possible. They will usually assess your function with a comprehensive physical exam to evaluate the severity of your impairment. They may sometimes recommend imaging, such as an MRI, to look for new or worsening lesions. MRIs are not necessary to diagnose a relapse, but they may be helpful for ruling out other potential causes for your symptoms.

After confirming that you’re experiencing an MS relapse, your doctor may adjust your medication regimen. Short courses of high-dose corticosteroids are commonly given during an MS relapse to reduce inflammation causing damage in your brain. They may give this medication in the hospital through an IV line, but it can also be administered at home in tablet form.

These medications, as well as rehabilitation, may reduce the duration of a relapse and reduce long-term consequences to your health. Some studies show that corticosteroids may also delay your next relapse, although this is still being studied.

Diagnosing a pseudoexacerbation entails ruling out external triggers. Physicians usually look for fever and signs of infection, then treat the underlying problem. If needed, your physician may recommend an MRI.

When To Seek Medical Attention

If you experience new or worsening MS symptoms that last more than 24 hours, it’s important to seek medical attention. It’s especially important to get medical help if your symptoms greatly impair your functioning, like your ability to walk or see.

Your neurologist can help determine if you’re experiencing a true relapse or a pseudoexacerbation. Early intervention of an MS relapse may help reduce the duration of your symptoms and prevent long-term disability.

Talk With Others Who Understand

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 213,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Have you experienced an MS relapse or a pseudoexacerbation? How did you and your doctor tell the difference? What advice do you have for other people living with MS? Share your tips and experiences in a comment below or post on your Activities page.