Clinically Isolated Syndrome (CIS)

Reviewed by: HU Medical Review Board | Last reviewed: May 2021.

MS-like symptoms can be caused by many things. Infections, injuries, vitamin deficiencies, and more can lead to neurological symptoms. But the symptoms of MS are caused by demyelination of nerves. This is most likely due to the body mistakenly attacking its own tissues. Conditions like this are called autoimmune conditions. Clinically isolated syndrome (CIS) is the first episode of MS-like symptoms caused specifically by demyelination.1,2

Is Clinically Isolated Syndrome (CIS) the same as MS?

Both CIS and MS are caused by the same underlying issue. However, it is possible for a person to have CIS and not MS. In some cases, symptoms may resolve and CIS remains the diagnosis. In other cases, another episode of MS-like symptoms occurs later on. At this point, an MS diagnosis is made. It is also possible to be diagnosed with MS during the first onset of symptoms if certain criteria are met.

CIS tends to affect the same group of people MS does. Women between 20 and 40 years old are the most likely to have CIS.1

Types of CIS

CIS can be classified based on the number of symptoms you have. If you have 1 symptom, that is a monofocal episode of CIS. This may occur if a person has vision issues (optic neuritis) only. A multifocal episode of CIS occurs when a person has multiple symptoms. For example, you could have vision changes plus numbness in the arms. When multiple symptoms occur, it is likely a person has demyelination in several parts of the central nervous system (CNS).1

Most people will experience at least a partial, if not complete, recovery from CIS symptoms.1

This or That

Have you been diagnosed with CIS?

Transition from CIS to MS

Making a diagnosis of MS requires multiple episodes of symptoms. These episodes must last for at least 24 hours and be separated over time. MS is a clinical diagnosis. This means, there is no 1 test that confirms it. A doctor can make the diagnosis based only on symptom history and a physical exam. However, other tests can be helpful, too.
The McDonald criteria are a set of guidelines that take into account symptoms, magnetic resonance imaging (MRI) findings, and cerebrospinal fluid (CSF) studies to help make a diagnosis.

With the 2017 criteria, it is possible to get an MS diagnosis at the onset of symptoms rather than waiting for more episodes to occur. A diagnosis of MS can also be made if you have multiple brain lesions on MRI that are of different ages. Lesions that are in different areas of the brain can also point toward MS. Finally, a diagnosis can be made if you have a protein in your CSF called oligoclonal bands (O-bands).1-3

Each person’s situation is unique. The transition from CIS to MS can vary and depends on different factors.

Who has the highest risk of progression?

A person with MS-like brain lesions on MRI has a higher risk of progressing to MS. This risk may be as high as 60 to 80 percent. But the next episode of symptoms may not be for several years.1

On the other hand, people who do not have MS-like lesions on their brain MRI have a lower chance of progressing to MS. In this group, there may be about a 20 percent chance of developing MS over the next several years.1

Treating CIS and preventing further symptoms

If you fall into the higher-risk group you may need to start treatment. In this case, treatment is aimed at preventing or delaying another episode of symptoms. Several disease-modifying drugs are approved for CIS. If you have CIS and are concerned about your risk of progression, talk with your doctor to see if treatment may be helpful.1

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