Types of MS
Initially, most people with MS experience symptom flare-ups, which are also known as relapses, exacerbations, or attacks. When people experience a relapse, they may be having new symptoms or an increase in existing symptoms. These usually persist for a short period of time (from a few days to a few months) and afterward they may remain symptom-free for periods of months or years. This type of MS is referred to as relapsing-remitting MS (RRMS). Approximately 80% to 85% of people with MS are initially diagnosed with this form of the disease.
Over time, RRMS may advance to secondary-progressive MS (SPMS). This form of MS does not have the dramatic variations in symptoms that RRMS does, but rather has a slow, steady progression – with or without relapses. If relapses do occur, they usually do not fully remit. Without treatment, approximately half of individuals with RRMS convert to SPMS within 10 years. However, with the introduction of long-term disease-modifying therapies (DMTs), fewer individuals advance to this latter form of the disease.
Multiple sclerosis (MS) affects each person differently. MS has long been divided into the following three main categories:
- Relapsing-Remitting MS (RRMS)
- Secondary-Progressive MS (SPMS)
- Primary-Progressive MS (PPMS)
Individuals who are not initially diagnosed with RRMS may experience a more steady progression of the disease from the onset. Approximately 10% of the MS population is diagnosed with primary-progressive MS (PPMS), where individuals experience a steady worsening of symptoms from the start, and do not have periodic relapses and remissions.
The remaining 5% of individuals are diagnosed with less-common forms of MS, such as progressive-relapsing MS, where an individual may experience a more steady progression of the disease, but may also experience symptom flare-ups. However, not all experts agree on this form of MS, and the term is not often used. As researchers and clinicians learn more about MS – including how the disease progresses differently between patients, how the effectiveness of different treatments varies between patients, and how the internal disease processes differ – the three main types of MS, as well as any other less-common type – will continue to be evaluated and possibly reclassified in the future.
In addition, prior to an MS diagnosis, individuals with “possible MS” may often fall under the parameters of one of two syndromes. The first is clinically isolated syndrome (CIS), where someone may have experienced symptoms of MS for the first time, and an MRI may show evidence of MS, but a diagnosis cannot be confirmed at that time. Disease-modifying therapies are often used to treat CIS in an effort to delay or prevent the eventual diagnosis of MS.
The second syndrome is radiologically isolated syndrome (RIS), which is the term used when someone has an MRI performed for an unrelated reason, and shows evidence of MS on the MRI scan, but does not have any signs of MS symptoms. Recent studies are defining which patients with RIS are at an increased risk of MS – and beginning to explore whether therapeutic intervention is warranted.