There are four main types of multiple sclerosis, each defined by how far the disease has progressed. Determining the type can help inform treatment decisions and long-term prognosis.

Multiple sclerosis (MS) is thought to be an autoimmune, inflammatory disease affecting the central nervous system and peripheral nerves. MS can be unpredictable and, in some cases, disabling. But not all forms of MS are the same.

In 1996, the National Multiple Sclerosis Society (NMSS) created an advisory committee that described four distinct categories. These course definitions were updated in 2013 to reflect advances in research.

The four main types of MS are:

• clinically isolated syndrome (CIS)
• relapsing-remitting MS (RRMS)
• primary-progressive MS (PPMS)
• secondary-progressive MS (SPMS)

The medical community at large now uses these four categories when diagnosing and treating MS. The types are defined by how far the disease has progressed in each patient.

Determining the type of MS you have can help guide treatment decisions. Understanding the types of MS can also help you know what to expect throughout the course of the disease.

Clinically isolated syndrome (CIS) is a single episode of neurologic symptoms that lasts 24 hours or more. CIS symptoms can’t be tied to fever, infection, or other illnesses. Rather, symptoms are the result of inflammation or demyelination in the central nervous system.

You might have only one symptom (monofocal episode) or several (multifocal episode).

If you have CIS, you may never experience another episode. Or this episode could be your first MS attack.

If an MRI detects brain lesions similar to those found in people with MS, there’s a 60%–80% chance that you’ll have another episode and a diagnosis of MS within the coming years.

When undergoing testing for CIS, you may receive a diagnosis of MS if an MRI detects older lesions in a different part of your central nervous system. That would mean you’ve had a previous attack, even if you weren’t aware of it.

Your doctor might also diagnose MS if your cerebrospinal fluid contains oligoclonal bands.

The most common type of MS is relapsing-remitting MS (RRMS). Approximately 85% of people with MS have RRMS at the time of diagnosis.

RRMS is marked by periods where symptoms increase (relapses) followed by periods of partial or complete recovery (remission).

Common symptoms of RRMS include:

• fatigue
• numbness
• motor and muscle weakness
• changes in vision
• spasticity
• bowel issues
• bladder issues
• cognitive problems

With RRMS, disease activity is usually marked by inflammation and new lesions on the brain. However, RRMS can also involve the development of new lesions without symptom activity. It’s also possible for RRMS to be stable with no new MRI activity or worsening symptoms.

RRMS is typically diagnosed earlier on in the course of the disease. Most people diagnosed with this type of MS are in their 20s and 30s. RRMS also affects more women than men.

Around 10%–15% of people with MS are initially diagnosed with this progressive form of MS.

PPMS progresses slowly yet steadily from the time of its onset. It can have periods of active disease as well as periods of remission. However, even in periods of remission, there’s still continued accumulation of disability and deterioration. In essence, people living with PPMS experience a fairly continuous worsening of their condition.

There can be variations in the rate of progression over the course of the disease — as well as the possibility of minor improvements (usually temporary) and occasional plateaus in symptom progression.

Symptoms of PPMS can overlap with symptoms of RRMS. However, PPMS is typically marked by walking troubles, worsening mobility, and increasing disability.

PPMS tends to involve less inflammation than RRMS. PPMS lesions are also more likely to appear on the spinal cord, whereas RRMS lesions occur more in the brain.

On average, PPMS is diagnosed 10 years later than RRMS. PPMS also affects women and men equally.

SPMS is another progressive form of MS. It’s thought of as the second phase of RRMS. That’s because it initially follows the relapsing-remitting disease course, with symptom flare-ups followed by recovery periods.

As such, SPMS symptoms can overlap with RRMS symptoms. However, SPMS involves nerve damage or loss that leads to more steady disease progression.

However, with SMPS, the disability of MS doesn’t disappear between cycles. Instead, this period of fluctuation is followed by a steady worsening of the condition. People with SPMS may experience minor remissions or plateaus in their symptoms, but this isn’t always the case.

Without treatment, 50% of people with RRMS go on to develop SPMS within a decade, and 90% of RRMS cases progress to SPMS within 25 years.

These statistics may improve with the use of newer disease-modifying therapies (DMTs). However, more research needs to be done to fully understand how DMTs may affect MS progression long-term.

A rare type known as fulminate MS is considered the most severe form of the disease. It’s a rapidly progressive form of MS marked by severe relapses within 5 years of diagnosis.

Also known as malignant MS or Marburg MS, fulminate MS may require more aggressive treatment compared to other forms of MS.

Benign MS is considered to be the mildest form of the disease. It’s thought of as a type of RRMS marked by long periods of remission, or little to no attacks of MS symptoms. The longer someone with benign MS remains in this state, the better the long-term outcomes.

However, benign MS is also rare.

Early MS can be challenging for doctors to diagnose. However, identifying MS early at the relapsing-remitting stage can help ensure prompt treatment to avoid developing more progressive forms of the illness.

Early, aggressive treatment with DMTs may help slow or prevent the progression of MS.