Although the effects of multiple sclerosis can vary greatly from person to person, the condition is often categorised into one of three broad groups:
- Relapsing remitting MS
- Secondary progressive MS
- Primary progressive MS
Relapsing remitting MS
The majority of people with MS are diagnosed with the relapsing remitting form. This means they will have periods when symptoms flare up aggressively - known as a relapse, an attack or an exacerbation - followed by periods of good or complete recovery - a remission.
A relapse is the appearance of a new symptom or the reappearance of old symptoms that lasts more than 24 hours. A relapse can last for considerably longer than that and may persist for weeks or months. The frequency of relapses, the severity of symptoms experienced and the length of the gap between attacks are unpredictable. Similarly, it may sometimes be difficult to determine what is a fluctuation in symptoms (a day to day worsening or improvement) and what is a relapse.
On average, people with relapsing remitting MS have one or two attacks a year. Although recovery from relapses may become less complete, the level of disability will remain largely stable between relapses.
Rapidly evolving severe relapsing remitting MS
The term rapidly evolving severe relapsing remitting MS (RES) is used in relation to the drugs natalizumab (Tysabri) and fingolimod (Gilenya). This is a less common form of relapsing remitting MS in which someone has two or more disabling relapses in one year and evidence of increasing lesions on two consecutive MRI scans.
The term benign MS is sometimes used. This is a version of relapsing remitting MS with very mild attacks separated by long periods with no symptoms.
The phrase is sometimes used inaccurately to describe a period with few or no symptoms following diagnosis. However, as the defining characteristic of benign MS is the long-term absence of symptoms, it can only be diagnosed retrospectively after ten or more years. It is estimated that about 15-20% of people with MS have this experience of the condition. The term should be used with caution and can only describe an individual's past experience of MS.
Secondary progressive MS
Many people who are initially diagnosed with relapsing remitting MS find that over time the frequency of relapses decreases but disability gradually increases. As this follows and initial (primary) relapsing remitting phase, this is known as secondary progressive MS. People's experience of secondary progressive MS can vary widely. Some people find that the increase or progression of disability is very gradual, whilst for others it can occur more quickly.
Studies that have monitored people with MS over a long period of time suggest that after 19 years, half those people who were diagnosed with relapsing remitting MS will have developed secondary progressive MS.
A small number of people are diagnosed with secondary progressive MS from the outset, rather than becoming secondary progressive after having relapsing remitting MS. In hindsight, they may have experienced relapses in the past but these may have been mild or their significance was missed. Alternatively, there may have been lesions (small patches of damage caused by MS) but they were in areas of the brain or spinal cord that did not give rise to any symptoms.
Some people may have been given a different diagnosis (not MS) to begin with. This will have been changed to a diagnosis of MS once the pattern of symptoms became clearer or because later tests were able to detect damage due to MS.
Primary progressive MS
About 10% of people with MS are diagnosed with a form in which disability increases from the outset. This is known as primary progressive MS (or, less commonly, chronic progressive MS). Again, there is a variety of experience of primary progressive MS. Some people can have a persistent increase in disability whilst others may experience plateaux or a more gentle worsening of symptoms.
Some people whose MS has been progressive from onset will also experience occasional relapses. This is sometimes referred to as progressive relapsing MS.
In 2014, an international committee suggested revisions to the classification of multiple sclerosis types to take into account better ways of monitoring the condition. This included classifying MS based on disease activity seen in MRI scans, eg someone whose scan showed recent new areas of damage might be classed as relapsing remitting-active. Someone whose scan remained largely unchanged might be relapsing remitting-non-active. Progressive relapsing MS would be reclassified as progressive MS-active.
The committee also suggested that clinically isolated syndrome (CIS), someone's first episode of neurological symptoms, be classed as a type of MS.
- Neurology 1996;46(4):907-911. Summary Defining the clinical course of multiple sclerosis: results of an international survey.
- Multiple Sclerosis 2008;14(3):314-324. Summary Natural history of secondary-progressive multiple sclerosis.
- Neurology 2014;83:1-9. Full article (pdf 472kb) Defining the clinical course of multiple sclerosis: the 2013 revisions.
Last updated: 13 August 2014
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