How do you define a relapse?

Many people with MS call a relapse an 'attack' because this can describe the period of time they experience new problems or begin to feel unwell. Medical staff define a relapse as the occurrence of new symptoms or the reoccurrence of old symptoms that last more than 24 hours.  

How long do relapses last?

In relapses, symptoms usually come on over a short period of time - hours or days. They often stay for a number of weeks, usually four to six, though this can vary from very short periods of only a few days to many months.

Relapses can vary from mild to severe. At their worst, acute relapses may need hospital treatment.

 

What causes a relapse?

In MS, relapses are caused by inflammation in the central nervous system (the brain and spinal cord). This inflammation is the body's reaction when immune cells mistakenly attack the protective layer (myelin) that surrounds nerve fibres. When messages are blocked in an area that has a specific function, such as the optic (visual) nerve, or the motor (movement) or sensory fibres in the spinal cord, then symptoms occur. When inflammation dies down, so too can the symptoms.

Inflammation may also damage some of the nerve fibres (axons) themselves. Although it does not always happen, studies have shown that axons can be damaged even in the earliest stages of MS.

 

Can we predict the outcome of a relapse?

Outcome from relapses is often very good, with complete remission. However, this is not always the case. If the damage to myelin is severe, then some symptoms remain, though there is the potential for them to improve over the following months if there is further effective repair to myelin. There may also be incomplete recovery when a critical number of axons are damaged or destroyed, and this may be irreversible. When people with MS have a relapse, the main process going on is inflammation. However, it is likely that during most relapses some damage also occurs to myelin and to the axons. If the axon dies, then repair cannot occur.

We can all lose quite a lot of axons without this affecting the way our bodies function. It is thought, however, there may be a threshold effect – a certain point where any further loss does have an effect. From then on, each time more axons are lost, there is a worsening in the level of function.

 

Do relapse outcomes get worse over time?

If a number of attacks affect one particular part of the central nervous system, it is less likely that recovery will be complete. This is probably the reason why recovery from relapses is less complete over time and why the response to steroid treatment tends to be less impressive the longer the condition has been present. 

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