The course of MS is unpredictable. Some people may feel and seem healthy for many years following diagnosis, while others may be severely debilitated very quickly. Most people fit somewhere between these two extremes.
Although every individual will experience a different combination of MS symptoms, and it is hard to predict how MS will affect a person over their lifetime, there have been four basic types of MS identified relating to the course of the disease.
Clinically Isolated Syndrome
Clinically Isolated Syndrome (CIS) is the first episode of neurological symptoms experienced by a person, lasting at least 24 hours. The person may experience a single sign or symptom, or more than one at the same time. As with MS, it is caused by inflammation and demyelination in the central nervous system. Not everyone who experiences CIS goes on to develop MS, but CIS can be an indicator for it. Researchers don’t yet know why CIS turns into MS for some people but not others. If someone with CIS also has lesions (as seen on a brain MRI) that are similar to those seen in MS, then they are at higher risk. Research suggests that early treatment of CIS can delay conversion to MS for people at high risk.
In relapsing MS (sometimes called relapsing-remitting MS), people experience attacks or exacerbations of symptoms (‘relapses’), which then fade or disappear (‘remission’). The symptoms may be new, or existing symptoms may become more severe. Relapses can last for varying periods – from a few days up to months – and then the disease may then be inactive for months or years. About 85 per cent of people with MS are initially diagnosed with relapsing MS.
Relapsing MS can also be categorised by whether it is active or not active (someone who has active MS experiences relapses and/or evidence of new MRI activity). It can also be classified as worsening (a confirmed increase in disability over a specified period of time following a relapse) or not worsening.
Secondary progressive MS
Secondary progressive MS (SPMS) is a secondary phase of relapsing MS that may develop years or even decades following diagnosis with relapsing MS. Most people who have relapsing MS will transition to SPMS. In SPMS there is progressive worsening of symptoms over time with no definite periods of remission.
SPMS can also be categorised by whether it is active or not active (someone who has active MS experiences relapses and/or evidence of new MRI activity). It can also be classified as with progression (evidence of disease worsening over time, with or without relapses) or without progression.
Primary progressive MS
About 10 to 15 per cent of people with MS are diagnosed with primary progressive MS (PPMS). People with PPMS have steadily worsening symptoms and disability from the start, rather than sudden attacks or relapses followed by recovery.
PPMS can also be categorised by whether it is active or not active (someone who has active MS experiences relapses and/or evidence of new MRI activity). It can also be classified as with progression (evidence of disease worsening over time, with or without relapses) or without progression.
Additional classification of types of MS
For useful descriptions of what active, worsening and progression looks like in relapsing MS, primary and secondary progressive MS, see the graphs on the National MS Society’s web page here. These characterisations are important as they can affect whether a certain type of treatment will be effective or not.