Multiple sclerosis (MS) manifests in different patterns depending on how it first appears and then progresses. Each course represents a different type of MS. It is common to be diagnosed with one type, and later, if the course of the disease progression changes, to be given a new diagnosis based on those changes.

MS is an autoimmune disease that affects the central nervous system. Doctors identify the different types of MS based on the results of MRI scans. These images show lesions (also called plaques or scars) on the brain and spinal cord resulting from demyelination (the loss of myelin, the fatty substance that insulates nerves in the brain and spinal cord).

Scores on the Expanded Disability Status Scale (EDSS) are also taken into account as a measure of disease progression. There is some controversy among doctors and researchers about how to classify different types of MS.

Clinically Isolated Syndrome

Clinically isolated syndrome (CIS) is not a type of MS but a condition that may or may not progress into MS. Many people who go on to develop MS are initially diagnosed with CIS.

CIS means that a person has had one episode of neurological symptoms lasting at least 24 hours and caused by demyelination. The episode may be monofocal, with one sign or symptom caused by a single lesion, or multifocal, with several signs or symptoms caused by multiple lesions.

If older lesions are found during an MRI on someone with CIS, a diagnosis of MS may be made without waiting for additional episodes to occur. Some people with CIS never experience another episode of symptoms and never have another lesion — they remain diagnosed with CIS.

At the time CIS is diagnosed, the doctor will assess the risk of developing MS. People with CIS who have lesions similar to those seen in people with MS are at higher risk for developing MS within the next few years than people without MS-like lesions. People with lower risk may be treated temporarily with corticosteroids, and those at higher risk may be recommended to begin disease-modifying therapy (DMT) to avoid developing MS.

Read more about clinically isolated syndrome.

A related term is radiologically isolated syndrome (RIS). In those with RIS, a lesion is found during an unrelated MRI scan, but there are no MS-like symptoms. Like in CIS, a person with RIS is not diagnosed with MS but may be at risk for developing MS at some point.

Relapsing-Remitting Multiple Sclerosis

Relapsing-remitting MS (RRMS) is the most common form of MS. About 85 percent of people with MS are diagnosed with this type. People are most often diagnosed in their 20s and 30s, and women are two to three times more likely to have RRMS than men. RRMS tends to cause more brain lesions than spinal cord lesions, resulting in increased cognitive and visual symptoms.

People with RRMS have a clear pattern of relapses (also called flare-ups or exacerbations) and remissions. During relapses, disease activity flares, causing new or more intense symptoms. New lesions may appear. During remission, people with RRMS may recover fully or partially, and symptoms of MS may lessen, disappear, or remain permanent. The disease does not appear to progress during remission.

RRMS may be further described as being “active” or “not active” based on MRI scans and “worsening” or “not worsening” based on disability testing. These descriptions help doctors decide whether treatment is effective and whether to recommend more aggressive treatment.

People diagnosed with RRMS are encouraged to immediately begin long-term maintenance treatment with a DMT to reduce the frequency and severity of flares and delay disease progression.

Some people with RRMS may eventually transition to secondary progressive MS (SPMS) many years after the initial diagnosis.

Read more about relapsing-remitting MS.

Primary Progressive Multiple Sclerosis

About 15 percent of people with MS have primary progressive MS (PPMS). PPMS affects men and women at equal rates and is most often diagnosed in adults in their 40s and 50s.

In people with PPMS, the condition generally progresses without clear relapses or periods of remission. Neurological function and disability worsen over time. PPMS tends to cause more spinal cord lesions than brain lesions, resulting in increased motor symptoms such as difficulty walking. Over time, PPMS may be further described as being “active” or “not active” based on MRI scans, and “with progression” or “without progression” based on disability testing.

Currently, Ocrevus — a formulatin of ocrelizumab — is the only medication approved by the U.S. Food and Drug Administration (FDA) to treat PPMS.

An older, related term is progressive-relapsing MS (PRMS). PRMS was previously considered to be a separate diagnosis, but since 2013, it has been viewed as a subset of PPMS. In PRMS, there are clear periods of acute relapse, but the disease progresses between relapses without remission.

Read more about primary progressive MS.

Secondary Progressive Multiple Sclerosis

Some people may be initially diagnosed with RRMS and then have their disease course transition to a pattern of progressive worsening, resulting in increased disability. When this happens, they may be rediagnosed with SPMS. Individuals with SPMS may continue to experience disease flares associated with demyelination as with RRMS, or flare-ups may give way to a more steadily progressive course.

Like PPMS, SPMS may be further described as being “active” or “not active” based on MRI scans, and “with progression” or “without progression” based on disability testing. In cases when SPMS is active and progressing, doctors may recommend more aggressive treatment.

DMTs approved by the FDA to treat SPMS include Mavenclad (a formulation of cladribine), Mayzent (siponimod), and Novantrone (mitoxantrone).

Benign MS

The concept of benign MS (BMS) is controversial. Some people with MS experience a comparatively mild disease course, developing little or no disability. If this lasts for 10 to 15 years, the disease type can be referred to as “benign” based on EDSS scores. BMS is not given as the initial diagnosis but rather is an assessment of the disease pattern after many years.

BMS appears to correlate to a milder disease course for those with RRMS. Doctors differ in their opinion of the value of a BMS diagnosis. Some may feel that a benign diagnosis means it is safe to stop treatment with DMTs after a certain number of years without progression. Other doctors feel that it is not a meaningful basis for treatment decisions.

A related term occasionally used is “burned-out MS.” A person whose disease progression significantly slows after many years may be described as having burned-out MS.

Rare Types of Multiple Sclerosis

Tumefactive MS is a rare form of the disease with signs and symptoms similar to those caused by brain tumors. Tumefactive MS is often misdiagnosed as a type of brain tumor called an astrocytoma. People who experience an episode of tumefactive MS often go on to develop RRMS. People with tumefactive MS can be treated with some DMTs.

Pediatric MS (diagnosed in people under 18) is extremely rare, accounting for 3 percent to 5 percent of MS diagnoses. The disease course in pediatric MS is similar to that of RRMS in adults. On average, children with MS experience relapses two to three times more frequently than adults with early-stage RRMS. Children with MS are treated with DMTs.

Some researchers use the terms “fulminant MS,” “malignant MS,” and/or “Marburg variant MS” to describe particularly severe, rapidly progressing courses that cause MS symptoms. Some doctors do not consider this rare condition to be a type of MS at all but rather a distinct disease. The Marburg course is seen mainly in children and younger adults and often causes death within one year.

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