What Is a Relapse?

A relapse is a clinically significant event (meaning that it has outward signs and/or symptoms) caused by an MS lesion in your CNS. It is either the appearance of new symptoms or the worsening of symptoms that you already have. Relapses are also referred to as “exacerbations,” “attacks,” or “flares.” Symptoms must last at least twenty-four hours and be separated from a previous relapse by at least one month to qualify as a true relapse.

Some relapses will be obvious to you. Losing feeling in your foot is an example of an obvious relapse. However, other relapses may not be as sudden or dramatic and you may just feel unusually tired. One way to truly identify a relapse is to have an MRI with gadolinium (a dye-like contrast material that is injected intravenously during the MRI). Gadolinium is drawn to areas of inflammation and “lights up” when a lesion is active. If you are having a definite relapse, inflammation is at work, and you are experiencing an attack, rather than feeling symptoms caused by older lesions.


In order for your neurologist to diagnose a relapse, your symptoms must show evidence of occurring in your CNS, and there must be no other possible cause of your symptoms, such as a fever or overheating. You and your doctor will also surmise whether or not your symptoms are disruptive to your daily life before he decides if treatment is necessary.

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