What is a relapse?

In response to a previous comment.

"This is a very good question and is something neurologists have been grappling with for decades."

What is a relapse?

A relapse is defined as an episode of neurological symptoms that happens at least 30 days after any previous episode began, lasts at least 24 hours and is not attributable to another cause and occurs in the absence of an infection or fever.

In clinical trials the definition is more stringent and has to be accompanied by either new clinical signs, i.e. changes in the neurological examination,  or an increase in the disability (EDSS) score. This is why you may hear the term "protocol defined relapse"; the "protocol" refers to the definition of a relapse that is used in that particular trial. To confuse things two clinical trials may use slightly different definitions of a relapse, which makes it hard to compare results from different trials. 

Can relapses result in the appearance of old symptoms?

Yes. A relapse can result in the appearance of new symptoms, that you have not experienced before, or the recurrence or worsening of symptoms that have occurred in the past. 

"What about intermittent symptoms?"

It is important not to confuse intermittent symptoms from a previous relapse with a new relapse. Intermittent symptoms occur when a damaged nerve pathway recovers, but the recovery is incomplete. The partially recovered nerves then become susceptible to heat and/or fatigue, which results in symptoms coming and going. For example, if you have previously had an episode of loss of vision or pins and needles you may find when you exercise, or get tired, or experience hot weather, your vision blurs or the pins and needles return. In this situation the symptoms usually resolve on rest or cooling and rarely last more than a few hours. This is not a relapse. 

What causes a relapse?

A relapse is caused by an area of inflammation and demyelination (loss of the nerve's insulation) in a particular pathway in the brain an spinal cord. The pathological and MRI correlate of this is the so called MS lesion or MS plaque.

Are there other names for a relapse?

Yes. Relapses are also referred to as attacks, exacerbations, flare-ups, acute episodes or clinical events.