What Is Clinically Isolated Syndrome?

Patient Expert

Multiple sclerosis is a disease in which the body experiences episodes of neurological symptoms caused by inflammatory or demyelinating attacks within the central nervous system at different points in time.

Relapsing-remitting multiple sclerosis is characterized by individual episodes that last more than 24 hours and may improve afterward. Primary-progressive MS is characterized by a steady worsening of neurological symptoms without significant remission.

When someone experiences a single demyelinating or inflammatory attack of the central nervous system that causes neurological symptoms resembling MS, it is called clinically isolated syndrome, or CIS. Here are some common questions about CIS and how it is distinguished from other forms of MS.

Is CIS the same as MS?

According to updated recommendations redefining the phenotypes of MS made in 2014, CIS is considered an official form of MS. However, not everybody who experiences an episode of CIS will go on to develop full-blown multiple sclerosis.

How does CIS resemble other forms of MS?

An episode of CIS includes neurological symptoms that last for 24 hours or longer and are caused by inflammation or demyelination within the central nervous system (CNS). Myelin is the fatty substance that surrounds and protects nerves. Myelin helps to speed messages along nerves, and a loss of myelin serves to slow down the messages or keep them from getting through in the first place. A place where inflammation has attacked the myelin is called a lesion. The effects of demyelination are the same for each form of MS.

An attack of CIS can be monofocal — involving a single symptom related to a single lesion — or multifocal — involving more than one symptom caused by lesions in different locations in the CNS. The CNS includes the brain, spinal cord, and optic nerves. An episode of CIS is often followed by complete or partial recovery.

How is CIS diagnosed?

Similar to other diseases of the central nervous system, diagnosis of CIS may include laboratory tests to eliminate other potential causes of symptoms, a complete neurological exam to access function of the nerves, a thorough medical history, and magnetic resonance imaging (MRI) to look for evidence of inflammation or demyelination within the CNS. Depending upon symptoms, the recommended MRI given at this stage of diagnosis may only include the brain and not the spinal cord.

During the MRI, a contrast agent, called gadolinium, may be injected into a vein. This helps to identify current inflammation and “active” lesions where the blood-brain-barrier is compromised. An MRI can also show older lesions that indicate damage occurred at a different point in time.

According to 2010 revised McDonald diagnostic criteria for MS, when a case of CIS is accompanied by MRI evidence of a prior episode of demyelination — whether or not it caused noticeable symptoms at the time, and is in an area of the CNS not associated with the current attack — a diagnosis of MS can be made.

How likely is CIS to progress to MS?

It is challenging to make an accurate diagnosis of CIS or MS and even more difficult to predict whether CIS will to progress to MS. For example, optic neuritis is a common neurological event that might be determined to be CIS; however, not every person who experiences optic neuritis will develop MS. On a personal note, I was eventually diagnosed with MS five years after I experienced a temporarily blinding case of optic neuritis.

When a person with CIS who has brain lesions detected by MRI that resemble those that are more commonly seen in MS, the person has an increased risk of developing MS. According to the National MS Society, this person has a 60 to 80 percent chance of experiencing another neurological event within several years and thus be diagnosed with MS.

People diagnosed with CIS who do not have MS-like brain lesions at the time of attack have a significantly lower risk — about 20 percent chance — of developing MS over several years. How my MS developed after several years fits into this lower risk category.

Can CIS be treated?

The goal in treating CIS would be to delay or prevent a second neurological attack and to reduce future disability. Disease-modifying therapies (DMTs) used for MS that are also FDA approved for use in cases of CIS include Avonex, Betaseron, Copaxone, Extavia, and Glatopa. As with MS, early treatment is encouraged to protect against inflammation in the CNS and subsequent damage to nerve cells.