Multiple Sclerosis (MS) is a chronic disease that targets the central nervous system. It is characterized by an immune system attack against myelin, the protective sheath surrounding nerve fibers. This damage disrupts the electrical signals traveling between the brain and the rest of the body. A “flare-up,” also known as a relapse or exacerbation, represents a period when new symptoms appear or existing ones significantly worsen.
Defining an MS Relapse
A true MS relapse is clinically defined by a strict set of criteria that distinguish it from the temporary worsening of symptoms. For an episode to be classified as a relapse, the new or worsening neurological symptoms must persist for a minimum of 24 to 48 hours. Furthermore, this event must occur at least 30 days after the end of a previous relapse.
The underlying cause of a relapse is acute inflammation within the central nervous system. Activated immune cells invade the brain and spinal cord, causing damage to the myelin sheath and the nerve axons underneath. This demyelination slows or blocks the transmission of nerve impulses, which is what causes the new neurological symptoms experienced during the episode.
A distinction is made between a true relapse and a pseudo-relapse, which is a temporary worsening of symptoms. A true relapse reflects new inflammatory damage, while a pseudo-relapse is typically triggered by external factors like heat or fever and does not involve new damage. Therefore, a true relapse must occur in the absence of a fever or infection, as these can cause a temporary increase in core body temperature that makes old symptoms reappear without new inflammation.
Recognizing the Signs
The specific signs of a flare-up are highly variable because symptoms depend entirely on the location of the inflammatory damage in the brain or spinal cord. A relapse can manifest as a single symptom or a combination of multiple issues, reflecting a focal or multifocal event in the central nervous system. The most common manifestations involve sensory, motor, or visual systems.
Sensory changes are frequently reported, often presenting as numbness, tingling, or a pins-and-needles sensation in the limbs or torso. These sensory disturbances can also include Lhermitte’s sign, a brief, shock-like sensation that travels down the spine when the neck is bent forward. Motor symptoms often involve new or increased muscle weakness, difficulty walking, or spasticity, which is an uncomfortable stiffness and involuntary muscle tightening.
Visual disturbances are also a common presentation, most notably optic neuritis, which is inflammation of the optic nerve. This condition typically causes eye pain, often made worse by eye movement, and can lead to blurred vision, loss of color vision, or partial blindness in one eye. Other signs may include balance problems, dizziness, or issues with coordination, reflecting damage in the cerebellum or brainstem.
Common Flare-Up Triggers
While the exact event that precipitates any single relapse is often unclear, several environmental and physical factors are known to increase the likelihood of a true MS flare-up. Acute infections, whether viral or bacterial, are among the most frequently identified triggers. Infections like the flu, a cold, or a urinary tract infection activate the immune system, which can then mistakenly initiate a new attack on the central nervous system.
Physical or emotional stress is also considered a factor that can precede a relapse in some individuals. Severe stress can alter immune function, potentially leading to the inflammatory cascade characteristic of a new lesion. Lack of sufficient, restorative sleep can also stress the immune system, making a relapse more probable.
It is important to distinguish these true relapse triggers from factors that cause a temporary pseudo-relapse, such as extreme heat or fever. While an increase in core body temperature can temporarily worsen existing MS symptoms, this effect is due to the heat slowing nerve signal conduction in already damaged nerves.
Acute Management and Treatment
The goal of acute management for an MS flare-up is to reduce the inflammation quickly and shorten the duration of the relapse. High-dose corticosteroids are the first-line treatment for relapses that cause disability or interfere with daily functioning. These anti-inflammatory medications, most commonly intravenous methylprednisolone, are typically administered for three to five days.
Corticosteroids work by suppressing the immune system’s activity and reducing the inflammation and edema around the areas of nerve damage. This helps to restore nerve signal conduction more quickly, speeding up the recovery of neurological function. While they accelerate recovery from the acute attack, corticosteroids do not affect the long-term progression of the disease.
For severe relapses that do not show improvement after a course of high-dose corticosteroids, therapeutic plasma exchange (PLEX) may be considered. PLEX involves removing the plasma, the liquid part of the blood which contains harmful immune factors, and replacing it with a substitute solution. This treatment is typically reserved for highly disabling attacks and is thought to benefit roughly 40 to 60 percent of patients who are unresponsive to steroids.
Supportive care, including adequate rest, is also a component of managing a flare-up, as severe fatigue is a common symptom. Consulting a neurologist immediately upon recognizing new or worsening symptoms is necessary to confirm the diagnosis and determine if acute treatment is needed. Early intervention with appropriate acute therapies can improve the outcome of a relapse.