What is a Relapse?

Reviewed by: HU Medical Review Board | Last reviewed: May 2015.

An MS relapse happens when new MS symptoms appear or old existing symptoms suddenly get worse in a patient who has been diagnosed with MS. To be considered a relapse, the new symptoms or worsening of symptoms must persist for at least 24 hours and it must have been at least 30 days since your previous relapse. A relapse may also be referred to as an attack, exacerbation, or flare-up.

The relapses and symptoms of MS differ from patient to patient and often vary in severity. They can be very mild and have little effect on your ability to function or they can be severe and interfere with your ability to carry out normal tasks at home and at work. The relapses and symptoms one person experiences may also change and fluctuate over time.

What happens during a relapse?

During an MS relapse or attack, immune cells that normally circulate harmlessly in your blood stream (until your body needs to fight invasion by some foreign substance or organism) attack and breakdown the blood-brain barrier (BBB).

The immune cells, of which there are many different types (T-cells, B-cells, antibodies, cytokines, chemokines) break through the BBB and cause inflammation that destroys myelin, the protective covering of nerve cells, exposing the nerve fiber or axon. Demyelination occurs when inflammation damages the myelin sheath covering the nerve cells.

Once demyelination occurs, the axon (nerve fiber) is exposed and can be damaged by inflammation. In places of demyelination, astrocytes (a type of nervous system cells) help to form scar tissue (sclerosis). In some places where the nerve fiber or axon is exposed, inflammation can lead to a complete break in the nerve fiber resulting in axonal loss.

Myelin functions as insulation around the nerve fiber, like the plastic covering on an electrical wire, and helps nerve impulses travel along the nerve fiber.  When demyelination occurs, impulses or signals that normally travel along nerve fibers are slowed or interrupted. This leads to a loss of communication between the CNS and various parts of the body, resulting in the symptoms associated with MS.

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