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Clinically Isolated Syndrome (CIS)


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What is clinically isolated syndrome (CIS)?

In multiple sclerosis, the immune system attacks the brain, spinal cord and optic nerves. These make up the central nervous system, which controls everything we do. Damage from the attack disrupts signals to and from the brain and causes the symptoms of MS.

Clinically isolated syndrome (CIS) is one of the 4 multiple sclerosis disease courses. CIS refers to a first episode of neurologic symptoms like those in MS. If you experience CIS, you may or may not go on to develop MS.

To be considered CIS, the episode must:

  • Last at least 24 hours
  • Be caused by inflammation and demyelination (loss of the myelin that covers the nerve cells) in the central nervous system

An episode can include one or more than one symptom. It usually has no associated fever or infection and is followed by a complete or partial recovery.

CIS symptoms

In CIS, your symptoms are linked to where the damage to the myelin occurred in the central nervous system. You may have:

  • Vision problems, including optic neuritis, blurred vision, poor contrast or color vision and pain on eye movement
  • Numbness or tingling of the face, body or extremities (arms and legs)
  • Walking difficulties
  • Spasticity
  • Fatigue
  • Weakness
  • Bladder and/or bowel problems
  • Dizziness
  • Sexual problems

If you are currently experiencing these symptoms, see your healthcare provider. An MS Navigator can help you locate a provider if you don’t already have one.

Who gets CIS, and when?

Like MS, CIS is not directly inherited, and it is not contagious. CIS is 2 to 3 times more common in women than men. Seventy percent of people diagnosed with CIS are between the ages of 20 and 40 years (the average age is 30). But people can develop CIS at older or younger ages.

How is CIS different from MS?

Based upon clinical symptoms alone, CIS and MS may appear the same. In both, damage to the myelin sheath (demyelination) interferes with the way nerve impulses travel to and from the brain, resulting in neurologic symptoms.

  • A person with CIS, by definition, is experiencing the first episode of symptoms caused by inflammation and demyelination in the central nervous system. A person with MS has experienced more than one episode.
  • With CIS, an MRI may demonstrate damage only in the area responsible for the current symptoms. With MS, there may be multiple lesions on MRI in different areas of the brain and spinal cord.

CIS progression to MS

If you have experienced CIS, you may or may not go on to develop MS. Your healthcare provider will do their best to determine the likelihood of this happening. Here are the criteria they use to make that determination:

  • High risk of developing MS: If a provider sees brain lesions similar to those in MS on magnetic resonance imaging (MRI), they predict that you have a 60% to 80% chance of a second neurologic event and diagnosis of MS within several years.
  • Low risk of developing MS: If CIS is not accompanied by MRI-detected brain lesions, you have about a 20% chance of developing MS over the same period of time.
  • Diagnosis of MS: If CIS is accompanied by MRI findings of old lesions or scars that confirm an earlier episode of damage in a different location in the central nervous system, then an MS diagnosis is confirmed. The presence of oligoclonal bands in a person’s cerebrospinal fluid can also help make the diagnosis.

As MRI technology becomes more advanced, it is likely that the diagnosis of MS will be made more quickly and there will be fewer people diagnosed with CIS. A quicker diagnosis also allows people to get treatment earlier and to slow their disease course.

For those whose CIS does turn into MS, how long does it take?

Not everyone who has an episode of CIS goes on to receive an MS diagnosis. Only 63% of those who experience an episode of CIS go on to receive an MS diagnosis. It is impossible to predict who will and in what period of time. Many factors contribute to this — including some that have not been identified yet.

In addition, many people with CIS are using disease-modifying therapies to delay (and in some cases prevent) MS. If you have had an episode of CIS and are not using a DMT, talk to your healthcare provider about treatment.

What factors influence whether or not CIS turns into MS?

Researchers have recognized multiple variables and risk factors that play a role in the potential for CIS to convert to MS. These include:

  • Younger age of disease onset
  • Male gender
  • The number of MRI lesions
  • Oligoclonal bands in cerebrospinal fluid

This list is not exhaustive. (For more details, see a 2021 study about MS biomarkers.) Also, the items in this list do not always apply to each person with CIS. For instance, all men with CIS are not guaranteed to get MS. Finally, there are also a number of risk factors associated with MS, like vitamin D deficiency and smoking, that you can control. If you’d like to learn more about how you can promote your overall health, see the Diet and Nutrition page.

Treatment for clinically isolated syndrome

Treatment with a disease-modifying therapy (DMT) may delay or prevent a second neurologic episode and, therefore, the onset of MS. In addition, early treatment may minimize future disability caused by further inflammation and damage to nerve cells, which can sometimes occur without any noticeable symptoms. If you have CIS, discuss starting a DMT with your healthcare provider if both things are true:

  1. You have had one event of MS-like symptoms
  2. You have two or more brain lesions on an MRI scan

You and your healthcare provider can take into account your specific risks and benefits and decide whether or not you should start a DMT.


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