Multiple Sclerosis (MS) is a chronic condition of the central nervous system where the immune system mistakenly attacks the protective myelin sheath surrounding nerve fibers. This damage interferes with the transmission of electrical signals, leading to unpredictable neurological symptoms. The course of MS is characterized by periods of relative wellness (remission) interspersed with episodes of acute worsening of symptoms, commonly referred to as an MS flare-up.
Defining the MS Flare-Up (Relapse)
A true MS flare-up, also called a relapse or exacerbation, is a distinct episode of new neurological symptoms or a significant worsening of existing ones. It is caused by new inflammation and subsequent demyelination within the brain, spinal cord, or optic nerves. The clinical definition requires symptoms to persist for a minimum of 24 to 48 hours.
The symptoms must occur without a fever or underlying infection, as these can mimic a flare-up. To be considered a new relapse, the episode must be separated from any previous relapse by at least 30 days. These criteria help neurologists confirm a genuine inflammatory event that indicates active disease, often correlating with new lesions on a magnetic resonance imaging (MRI) scan.
Common Symptoms and Severity
The specific symptoms experienced during a relapse are determined by the location of the new inflammatory damage. For example, inflammation on the optic nerve causes optic neuritis, resulting in vision loss or pain upon eye movement. Damage in the spinal cord can lead to sensory changes (numbness, tingling, or electrical shock sensations) or motor symptoms like weakness and mobility issues.
Symptoms range from mild annoyances to severe, life-altering experiences. A severe relapse might cause significant difficulties with balance, coordination (ataxia), or profound fatigue that interferes with daily function. The severity determines if the flare requires observation or immediate medical intervention. While symptoms develop over hours or days, the relapse can last for several weeks or months before recovery begins.
Acute Management and Medical Intervention
When a true MS flare-up is suspected, contact a neurologist for an urgent evaluation. The goal of acute treatment is to quickly reduce inflammation and accelerate recovery from the attack, limiting permanent damage from the new lesion.
The standard intervention for a flare causing significant disability is a short course of high-dose corticosteroids. These powerful anti-inflammatory drugs, such as intravenous methylprednisolone, are typically administered for three to five days. Corticosteroids suppress the immune system and rapidly reduce central nervous system inflammation, shortening the relapse duration.
In cases where a severe, debilitating flare-up does not improve after the initial course of corticosteroids, more aggressive treatments may be necessary. Plasma exchange (PLEX) filters the patient’s blood to remove immune system components attacking the myelin. This procedure is reserved for the most severe attacks causing significant disability and often requires a hospital stay.
Differentiating True Flares from Pseudo-Flares
It is important to distinguish a true inflammatory relapse from a “pseudo-flare,” or pseudo-exacerbation. A pseudo-flare involves a temporary worsening of existing MS symptoms without new inflammation or damage. They are not caused by new lesions, meaning they do not indicate worsening underlying disease activity. Instead, they are triggered by external factors that temporarily impair nerve signal conduction in already damaged areas.
Pseudo-flares are often caused by an elevation in core body temperature, known as Uhthoff’s phenomenon, triggered by heat, fever, or strenuous exercise. Other frequent triggers include underlying infections, particularly urinary tract infections (UTIs), stress, and fatigue. The critical difference is that pseudo-flares resolve quickly, often within hours or a day, once the underlying trigger is addressed.
Since pseudo-flares do not involve new demyelination, they do not require treatment with high-dose corticosteroids. The appropriate course of action is identifying and treating the underlying cause, such as an infection or fever, which allows the symptoms to subside. This distinction is why healthcare providers always check for infection or fever when evaluating a potential MS flare-up.