Multiple sclerosis (MS) is a chronic (long-term) 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 healthcare 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 true MS relapse involves new or returning symptoms that last longer than 24 hours. These changes often persist for several days, weeks, or even months. Relapses aren’t triggered by external factors like infections or changes 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 (areas of damage or scarred tissue) 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 (a flare-up of new or worsening symptoms), make an appointment with your neurologist as soon as possible. They will usually assess how you’re functioning through a comprehensive physical exam to evaluate the severity of your symptoms.

Your doctor may also recommend imaging, such as an MRI, to check for new or worsening lesions (areas of damage in the brain or spinal cord). While MRIs are not required to diagnose a relapse, they can help rule out other potential causes of symptoms.

Once your doctor confirms you’re having a relapse, they may adjust your treatment plan. A short course of high-dose corticosteroids is often used to reduce inflammation in the brain and spinal cord. These medications may be given in the hospital through an IV, or at home in pill form.

Steroids and rehabilitation therapies — like physical or occupational therapy —may shorten the relapse and help limit long-term effects on your health. Some research suggests that corticosteroids might also delay future relapses, but this is still being studied.

To diagnose a pseudoexacerbation, your doctor will first look for possible causes such as fever or infection. If necessary, they may recommend an MRI to help distinguish between a true relapse and a pseudoexacerbation.

When To Seek Medical Attention

If you experience new or worsening MS symptoms that last longer than 24 hours, it’s important to contact your doctor. This is especially urgent if your symptoms significantly affect daily activities, such as walking, seeing, or using your hands.

Your neurologist can help determine whether you're having a true relapse or a pseudoexacerbation. Getting medical care early may help shorten the relapse and reduce the risk of long-term disability.

Talk With Others Who Understand

On MyMSTeam, people share their experiences with multiple sclerosis, get advice, and find support from others who understand.

How do you manage the uncertainty of relapses or pseudoexacerbations? Let others know in the comments below.