CIS and MS: What's the Difference?

Medically Reviewed by Dany Paul Baby, MD on February 24, 2023
3 min read

If your doctor says you have clinically isolated syndrome (CIS)—a condition with some of the same symptoms as multiple sclerosis (MS)—you may have a lot of questions because it's easy to get CIS and MS mixed up.

For many people, the neurological symptoms of CIS go away and don't return. But for others, it's the first sign of what may turn out to be MS, a lifelong condition.

CIS is the onset of certain neurological issues that last at least 24 hours. Your symptoms may be caused by inflammation and demyelination (damage to the myelin sheath, the cover that protects nerve fibers in your brain) in your central nervous system.

CIS symptoms may look different for everyone, but they may include:

  • Vertigo (dizziness)
  • Vision problems (optic neuritis)
  • Loss of sensation in your face
  • Weakness in your limbs (one side of your body might be affected more than the other)
  • Bladder issues
  • Loss of control of bodily movements (ataxia)

Most people fully or partially recover from CIS. Moreover, you don't get a fever or an infection as part of CIS. Your doctor will order a brain scan (for example, an MRI) to rule out MS. 

CIS and MS cause the same kind of damage to the coating on the nerves of your brain and spinal cord. That leads to problems in the normal flow of brain signals in your body.

Because of that, CIS and MS can also have the same symptoms. You might get things such as numbness or tingling, vision problems, trouble with walking and balance, dizziness, and bladder issues. Like an MS flare-up, CIS symptoms last at least 24 hours.

Women are more likely to get both conditions, and they typically show up in adults below the age of 50 years.

When your body attacks your nervous system, you may have MS. But when it happens just one time, that’s considered CIS. MS, on the other hand, stays with you your whole life and may get worse with time. You'll need ongoing treatments to manage it.

It's possible that what looks like CIS is the beginning of MS. Your doctor won't know for sure unless your symptoms come back and an MRI shows signs of MS. Until a few years ago, doctors told people who had one flare that they had “possible MS.”

CIS and MS look different on an MRI. With MS, you may have multiple lesions on different parts of your brain. In case of CIS, an MRI may show damage only in the area of your brain linked to the symptoms you're having.


There's currently no way to know for sure, but an MRI of your brain and spinal cord can give you some clues.

If you have an MRI that looks like the kind you get with MS, your chances may be high that you'll develop MS. If your MRI doesn't look like the ones of MS, your risk is lower.


It depends. With MS, you should start treatment as soon as you find out you have it.

In case of CIS, the decision to start treatment can vary. Your symptoms may go away on their own, or you might get a steroid to help improve them. But then you have the question of whether to have a long-term treatment.

If your risk of getting MS is higher, your doctor may suggest starting the same treatment you'd get for MS. It's called disease-modifying therapy. Some studies show that it can delay the start of MS and possibly help prevent serious disabilities.

It can be a tough decision because you don't know for sure your CIS will lead to MS, and the drugs used for treatment have side effects. It is helpful to find a doctor with a lot of experience with MS. Together, you can weigh the pros and cons.

You can ask them questions like:

  • What are the odds I'll get MS?
  • What drugs might work best?
  • What are the risks and side effects?
  • Who can help me decide?

When CIS does turn into MS, how much it affects you varies. In the long run, about a third of people will have only minor, if any, disabilities. But half of them will have a severe effect.