Have you or a loved one ever had strange neurological symptoms, like vision problems or weakness that came on suddenly then disappeared?
They could be caused by clinically isolated syndrome (CIS). CIS is a single episode of nerve-related symptoms. These symptoms could be caused by inflammation in or damage to your brain or spinal cord.
While CIS can go away on its own, it might also be an early sign of a more serious condition like multiple sclerosis (MS). Here’s what to know about CIS, what it means for your health and when to get medical care.
What is clinically isolated syndrome (CIS)?
Clinically isolated syndrome is a single episode of neurological symptoms that lasts for at least 24 hours. It happens when the immune system mistakenly attacks the central nervous system, which includes the brain, optic nerve and spinal cord.
These symptoms may come on suddenly and then disappear, sometimes completely. CIS is an early phase of MS and it can be the first warning sign of the condition.
“CIS is considered the first attack before a diagnosis of MS. It is often diagnosed when a patient has a typical attack of MS but does not yet meet the criteria to be diagnosed,” said Lamees Alzyoud, MD, a neurologist with Banner - University Medicine.
If your doctor suspects CIS, they will usually order tests to rule out other causes and see if there’s a risk of developing multiple sclerosis in the future.
“New criteria, introduced in 2024, gave us more tools to use when assessing people with CIS. Those criteria can lead to an earlier MS diagnosis, so more people previously diagnosed with CIS might fulfill the MS criteria now,” Dr. Alzyoud said.
Common symptoms of CIS
Symptoms of CIS depend on which part of the central nervous system is affected. These one-time neurological episodes often include:
- Blurry vision or pain when moving one eye (optic neuritis)
- Numbness, tingling or loss of sensation affecting one side of your body or below a certain point in your spine, such as from the waist down
- Muscle weakness in the arms or legs
- Trouble with balance or dizziness
- Less commonly, difficulty speaking or bladder problems
If you notice any of these symptoms, especially if they appear suddenly and last more than a day, it’s important to see a health care provider..
How is CIS diagnosed?
“A CIS diagnosis is based on symptoms, a clinical exam and what we see on MRI,” Dr. Alzyoud said. “It’s important to have a thorough evaluation to make a diagnosis and to rule out other diseases with similar symptoms.”
There isn’t a single test for CIS, so your doctor will look at what’s happening in your nervous system with:
- Neurological exam: Checks your strength, reflexes, vision and coordination
- MRI scan: Looks for lesions in the brain or spinal cord
- Lumbar puncture (spinal tap): Tests spinal fluid for signs of inflammation or MS
- Blood tests: Help rule out other conditions
These tests also help your doctor estimate the risk that CIS may turn into MS.
Is CIS an early sign of multiple sclerosis?
CIS can be an early sign of MS. “It should be thought of as the first attack of MS as the majority of people with CIS go on to develop MS in the next five to 10 years,” Dr. Alzyoud said.
Your risk depends on what doctors find during testing, especially MRI scans. If you have lesions (areas of damage or inflammation) on your brain or spinal cord, you’re more likely to be diagnosed with MS later.
However, if your MRI and other tests are clear, you have a lower risk of MS after CIS.
What happens after a CIS diagnosis?
Some people need treatment with MS medications if they are diagnosed with CIS, but not everyone. If your symptoms go away and no new lesions appear, your doctor may recommend regular checkups and follow-up MRIs to watch for any changes.
“If you don’t yet fulfill the criteria for MS but you had CIS, we will usually discuss starting medications called disease-modifying therapies (DMT) to prevent the progression from CIS to MS,” Dr. Alzyoud said.
Even if you don’t need to start treatment, making healthy choices like staying active, managing stress and avoiding smoking can help protect your brain health.
When to see a doctor for neurological symptoms
Don’t wait to seek medical care if you have sudden neurological symptoms like blurry vision, numbness, dizziness or muscle weakness. Even if these symptoms go away, they could be a warning sign of MS.
“See a doctor for any new symptoms that last more than 24 hours,” Dr. Alzyoud said.
Your doctor may ask:
- When did the symptoms start?
- How long did they last?
- Did they affect one or both sides of the body?
- Have you had similar symptoms before?
Seeing a doctor early can make a big difference in your care plan and your future health.
How Banner Health can help
At Banner Health, our expert neurologists and MS specialists understand complex conditions like CIS. With our advanced diagnostic testing, personalized monitoring and long-term support, you can feel confident in your care every step of the way.
Whether you’ve just had your first episode or are seeking a second opinion, we’re here to help you move forward. If you’ve had a sudden neurological episode or been told you may have CIS, schedule a visit with a Banner neurologist today.
