An exacerbation of MS (also known as a relapse, attack or flare-up) causes new symptoms or the worsening of old symptoms. It can be very mild, or severe enough to interfere with a person’s ability to function at home and at work. No two exacerbations are alike, and symptoms vary from person to person and from one exacerbation to another. For example, the exacerbation might be an episode of optic neuritis (caused by inflammation of the optic nerve that impairs vision), or problems with balance or severe fatigue. Some relapses produce only one symptom (related to inflammation in a single area of the central nervous system) while other relapses causes two or symptoms at the same time (related to inflammation in more than one area of the central nervous system).
To be a true exacerbation, the attack must last at least 24 hours and be separated from the previous attack by at least 30 days. Most exacerbations last from a few days to several weeks or even months.