What Is Clinically Isolated Syndrome?

Medically Reviewed by Christopher Melinosky, MD on November 14, 2021

When your body attacks your nervous system, it’s often diagnosed as multiple sclerosis. But when it happens just one time, that’s considered clinically isolated syndrome.

The two conditions have the same symptoms -- including muscle weakness and problems with balance. But people with MS have had two or more episodes of symptoms. Those with CIS have had only one.

Until a few years ago, doctors told people who had one flare that they had “possible MS.” While CIS can develop into multiple sclerosis, that doesn't always happen. Treatments can ease your symptoms or help you in other ways.


CIS symptoms can happen in one part of your body or in different areas at the same time. Common ones include:

If the symptoms last for at least 24 hours, and other conditions are ruled out, a doctor is likely to diagnose you with CIS. Stroke, Lyme disease, and blood vessel problems also have similar symptoms.

Your doctor might take a sample of your spinal fluid and do an MRI test to find out if there’s been any damage to your central nervous system.

What Causes It?

When you have CIS, your body attacks and damages the protective coating around your nerves, called myelin. That keeps your nerves from sending signals the way they should. It's what causes your symptoms.

Doctors aren't sure why the body attacks itself this way. Some think a virus could be to blame, but the exact cause of CIS is unknown.

Women and people between the ages of 20 and 40 have a higher risk of getting the condition.

Will It Turn Into MS?

There’s no way to know for sure, but an MRI can give your doctor a better idea. If the scan shows brain lesions, your chances of getting MS in the next few years are higher. If the MRI shows no lesions, your risk is small.

Is Treatment Needed?

The symptoms of a CIS flare don’t last long. Your doctor may prescribe steroids or other medications for relief. They may want to do another MRI 3 or 6 months after your diagnosis to check for new lesions.

If you have lesions and your doctor thinks you’re likely to eventually have MS, they might prescribe you medication to treat multiple sclerosis. Some are pills, and others are drugs you inject. They have side effects, so talk to your doctor about what’s right for you.

When started early, meds can help cut the number of brain lesions you have or how many attacks you’ll have in the future. Research suggests these drugs may also help delay or prevent MS.

Show Sources


National Multiple Sclerosis Society: “What is MS? Related conditions: Clinically isolated syndrome (CIS).” National Multiple Sclerosis Society: “Symptoms & diagnosis: MS symptoms.”

National Institute of Neurological Disorders and Stroke: “NINDS multiple sclerosis information page.” National Multiple Sclerosis Society: “Symptoms & diagnosis: Clinically isolated syndrome (CIS).”

Kuhle J Multiple Sclerosis Journal, February 2015.

National Multiple Sclerosis Society: “Treating MS: Medications: Adherence.”

National Multiple Sclerosis Society: “Symptoms & diagnosis: Possible MS.”

Multiple Sclerosis Trust: “Clinically isolated syndrome (CIS).”

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