Understanding Different Types of MS

Multiple sclerosis (MS) is a disease that affects the brain, spinal cord, and optic nerve (the nerve of the eyes). In people with MS, the immune system mistakenly attacks the protective covering of nerves (myelin). This leads to disruption in nerve signals between the brain and the body. MS can cause many different symptoms, including fatigue, muscle weakness, balance problems, and trouble thinking clearly.¹

MS can be grouped into different types based on how the disease progresses over time. These are:^1-3

• Relapsing-remitting MS
• Progression independent of relapse activity
• Secondary progressive MS
• Primary progressive MS
• Progressive-relapsing MS

There are also other categories that doctors may use when possible signs or symptoms of MS first appear. These are:²

• Clinically isolated syndrome
• Radiologically isolated syndrome

Relapsing-remitting MS

Relapsing-remitting MS (RRMS) is the most common form of MS. About 70 to 85 percent of people with MS have RRMS. People with RRMS experience on-and-off symptoms of MS.^1,4,5

When new neurologic symptoms occur, this is called an episode or a relapse. During a relapse, new symptoms of MS typically develop over a few hours to a few days. The symptoms may be new or similar to ones you have experienced before.^1,4

Usually, people with RRMS experience remission after a relapse. This is when the symptoms become less severe or go away completely. This improvement can happen over weeks or months. People who do not make a full recovery between episodes may notice that some MS symptoms get worse over time.^1,4

Progression independent of relapse activity

Progression independent of relapse activity (PIRA) is a term referring to when neurologic symptoms of MS slowly get worse even during periods of remission. There is no new damage to the brain or spinal cord seen on current imaging during remission. But people with PIRA may notice that their MS symptoms are getting worse over several months or years, and they may slowly develop new symptoms.^3,6

PIRA can happen with several types of MS. Experts estimate that between 4 and 24 percent of people with MS may have PIRA. Researchers are currently trying to find out what causes PIRA.^3,6

One possible cause is that there is some leftover inflammation that remains in the brain even after treatment. This inflammation can be hard to see using imaging tests like MRI. This hidden inflammation is sometimes called “smoldering MS.” It is possible that the worsening of symptoms in PIRA is a result of this untreated inflammation.³

Secondary progressive MS

People with RRMS may eventually progress to secondary progressive MS (SPMS). This usually occurs about 10 to 15 years after being diagnosed with RRMS. More than half of people with RRMS develop SPMS.^1,2

In people with SPMS, the neurologic symptoms of MS continue to get worse at a steady pace between relapses. This means that a slow worsening of current symptoms or slow development of new symptoms can occur during periods of remission (PIRA). People with SPMS may still experience relapses in which MS symptoms suddenly get worse in a short period of time.^1,2,4,5

Primary progressive MS

Primary progressive MS (PPMS) occurs in about 15 to 20 percent of people with MS. With PPMS, cycles of relapses and remissions are less common. Instead, people with PPMS have symptoms that slowly and steadily get worse over time independent of any relapses (PIRA).^1,4

PPMS can be active or nonactive. With active PPMS, new areas of damage (lesions) appear in the brain or spinal cord during relapses. In nonactive PPMS, there are no new areas of damage or relapses. People with nonactive PPMS may experience a gradual worsening of symptoms despite not having any relapses (PIRA).⁷

Both active and nonactive types of PPMS can occur with or without progression of disability. Progression of disability is when symptoms of MS get noticeably worse over time.⁷

Progressive-relapsing MS

About 5 percent of people with MS have progressive-relapsing MS (PRMS). Just like with PPMS, people with PRMS experience MS symptoms that steadily get worse over time. PRMS also causes relapses in which the symptoms suddenly get worse over a short time.¹

Clinically isolated syndrome

Doctors may use the category of clinically isolated syndrome (CIS) to describe the first episode of symptoms that look like those of MS. People with CIS do not meet the full requirements for an MS diagnosis. Some people with CIS will develop MS in the future, while others will not. So, it is important for people with CIS to be examined and monitored by a neurologist.^1,2,4,5

Those with CIS who show nerve damage on an MRI scan and have certain markers of inflammation in their spinal fluid are more likely to develop MS. For some people with CIS, getting treatment can help delay or prevent an MS diagnosis.^1,2,4,5

Radiologically isolated syndrome

Radiologically isolated syndrome (RIS) is when people who do not have clinical symptoms of MS have lesions on their brain or spinal cord that look similar to lesions in people with MS. More than half of people diagnosed with RIS develop MS within 10 years.⁵