MS relapses: the basics

Since about 85% of people with MS have relapses, you've probably had personal experience with relapses. A relapse is a period where MS symptoms get worse or new symptoms appear. These symptoms may include fatigue, vision problems, bowel or bladder problems, abnormal sensations, or difficulty walking.

In order to be considered a relapse, this period must last for at least 24 hours, and must occur at least one month after the last relapse. Otherwise, it is considered a pseudorelapse – see "MS pseudorelapses: smoke and mirrors?" in this health feature. Most relapses develop over about a week, and resolve slowly over weeks to months. Relapses are also known as exacerbations or flare-ups.

So what is happening in the body during a relapse? An area of brain tissue becomes inflamed, leading to the destruction of myelin, the protective coating of nerve cells. This is also known as demyelination, and leads to the worsening of neurological symptoms. It is not known exactly why relapses occur, but this is part of the underlying disease for people with relapsing forms of MS.

Once the relapse is over, MS symptoms return to their baseline level (the level they were at before the relapse started). This is known as a remission. "Remission" does not mean that all MS symptoms have disappeared, just that they have gone back to their pre-relapse levels.

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