Recognising a relapse of Multiple Sclerosis (MS) is a vital skill for effectively managing the condition and ensuring timely medical intervention. A relapse, also commonly referred to as an exacerbation, flare up, or attack, occurs when new neurological symptoms appear or old ones significantly worsen due to fresh inflammation in the central nervous system. Because MS is highly individual, no two relapses look exactly the same, and symptoms can range from mild tingling to more severe functional challenges. Understanding the clinical criteria that define a true relapse helps you provide accurate information to your healthcare team, allowing them to determine if treatment, such as steroids, is necessary to speed up recovery.
In the clinical world, we use specific benchmarks to separate a genuine inflammatory event from the temporary fluctuations that occur in daily life. Most people with relapsing remitting MS will experience these episodes periodically, followed by phases of recovery or stability. By learning the 24 hour rule and identifying potential triggers like heat or infection, you can gain better control over your health journey. This article provides a structured guide on what to look for, how to distinguish a relapse from a pseudo-relapse, and the practical steps to take when you suspect your MS is becoming active.
What We’ll Discuss In This Article
- The clinical definition of a true MS relapse
- Common neurological symptoms associated with flare ups
- The 24 hour and 30 day rules for diagnosis
- Distinguishing between a true relapse and a pseudo relapse
- Common triggers for temporary symptom worsening
- Emergency guidance for severe neurological changes
Defining a True MS Relapse
To be classified as a true relapse, a clinical episode must meet three primary criteria. These standards ensure that the medical team is reacting to new inflammatory activity in the brain or spinal cord rather than transient changes.
- The 24 Hour Rule: The symptoms must be present for at least 24 hours. Fluctuations that disappear within a few hours are usually not considered a true relapse.
- The 30 Day Rule: New symptoms must occur at least 30 days after the start of a previous relapse to be considered a separate event.
- Absence of Triggers: The symptoms must occur without an obvious external cause, such as a high fever, an active infection, or extreme heat exposure.
Common Symptoms of an MS Flare Up
While MS can affect any part of the central nervous system, certain symptoms are more frequently associated with relapses. These symptoms often develop over several hours or days, reach a peak, and then gradually subside over weeks or months.
Visual Changes
One of the most common signs is optic neuritis, which involves inflammation of the optic nerve. You might notice blurred vision, eye pain that worsens with movement, or a loss of colour vibrancy. Occasionally, double vision or involuntary eye movements may occur.
Sensory and Motor Issues
You might experience new or rising numbness, pins and needles, or a burning sensation in your limbs or face. Significant weakness in an arm or leg, difficulty walking, or a sudden loss of coordination and balance are also hallmark signs that the nervous system is under stress.
Other Relapse Indicators
Relapses can also present as severe fatigue that is out of proportion to your activity, bladder or bowel urgency, and cognitive changes such as difficulty concentrating or memory lapses.
Relapse versus Pseudo Relapse
It is essential to understand the difference between a true relapse and a pseudo relapse, often called a pseudo exacerbation. A pseudo-relapse is a temporary worsening of old symptoms that does not involve new inflammation or permanent damage.
The most frequent cause of a pseudo relapse is a rise in core body temperature, known as Uhthoff’s phenomenon. This can be caused by hot weather, a hot bath, exercise, or a fever. Other common triggers include stress, poor sleep, and systemic infections, particularly urinary tract infections (UTIs). Once the trigger is addressed, such as by cooling down or treating the infection, the symptoms typically return to their previous baseline within 24 hours.
| Feature | True Relapse | Pseudo Relapse |
| Duration | Lasts more than 24 hours (often weeks) | Usually resolves within 24 hours |
| Cause | New inflammation in the brain/spinal cord | External triggers like heat or stress |
| Damage | Can cause new lesions on an MRI | No new damage or MRI changes |
| Symptom Type | Often entirely new symptoms | Worsening of old, existing symptoms |
Steps to Take If You Suspect a Relapse
If you believe you are experiencing a relapse, taking a systematic approach can help your clinical team provide the best advice.
Rule Out Infection
The first step is often to check for an infection. Urinary tract infections are notorious for triggering MS symptoms. Many UK clinics recommend using a urine dipstick test or seeing your GP to rule out a UTI before starting any MS-specific treatments like steroids.
Track and Document
Keep a detailed diary of your symptoms. Note when they started, exactly what they feel like, and if anything makes them better or worse. This documentation is invaluable for your neurologist or MS nurse when they assess whether your current disease modifying therapy is still effective.
Contact Your MS Team
Once you have monitored the symptoms for 24 hours and ruled out infection, contact your specialist MS nurse or neurologist. They can decide if you need a clinical assessment or if your symptoms are non-disabling enough to be managed with rest and monitoring.
Emergency Guidance
While most MS relapses can be managed through your specialist team or GP, some situations require immediate medical attention. Seek emergency care by calling 999 or visiting an accident and emergency department if you experience:
- Sudden and complete loss of vision in one or both eyes
- Severe weakness that makes it impossible to stand or walk safely
- New and significant difficulty with breathing or swallowing
- Acute confusion, seizures, or a sudden loss of consciousness
- A rapid and severe loss of balance that leads to repeated falls
In these cases, immediate stabilization and assessment are necessary to rule out other serious conditions like a stroke.
To Summarise
Recognising an MS relapse involves applying the 24-hour rule and ensuring that no external triggers like heat or infection are present. True relapses involve new inflammatory activity and symptoms that last for days or weeks, whereas pseudo relapses are temporary fluctuations that resolve once the body cools or an infection is treated. By monitoring your symptoms closely and maintaining clear communication with your MS specialist team, you can ensure that each flare up is managed appropriately, protecting your long term neurological health and quality of life.
How long does a typical MS relapse last?
A relapse can last anywhere from a few days to several weeks or even months. Most people see a significant improvement within four to six weeks.
Will I always need steroids for a relapse?
No. Steroids are used to speed up recovery from a disabling relapse, but they do not change the long term outcome of the disease. Mild, non disabling symptoms are often left to resolve naturally.
Can stress cause a true relapse?
While stress is a common trigger for a pseudo relapse, chronic or severe stress can also impact the immune system and potentially contribute to a true relapse in some individuals.
What is Uhthoff’s phenomenon?
This is a temporary worsening of neurological symptoms caused by an increase in body temperature. It is a classic sign of a pseudo relapse and usually improves once you cool down.
Should I stop my medication during a relapse?
No. You should continue your disease modifying therapy unless specifically told to stop by your neurologist. DMTs are designed to prevent future relapses, not treat an active one.
Is every new pain a sign of a relapse?
Not necessarily. People with MS can still experience standard health issues like muscle strains or headaches. If a pain lasts more than 24 hours and feels neurological, contact your team.
How many relapses are considered normal per year?
There is no normal number, but the goal of modern treatment is NEDA (No Evidence of Disease Activity). If you are having more than one relapse a year, your team may suggest switching medications.
Authority Snapshot
This article was reviewed by Dr. Stefan Petrov, a UK-trained physician with extensive experience in general medicine, surgery, and emergency care. Dr. Petrov holds an MBBS and postgraduate certifications in life support and cardiac care. He has managed complex patient cases in both ward and intensive care settings and is dedicated to providing clear, evidence based health information. This guide follows the established 2026 clinical protocols for the identification and management of Multiple Sclerosis relapses in the United Kingdom.
