The term “clinically isolated syndrome” (CIS) is used to describe a first episode of neurologic symptoms that lasts at least 24 hours and is caused by inflammation and demyelination in one or more sites in the central nervous system (CNS). CIS can be either monofocal or multifocal:
- Monofocal episode: The person experiences a single neurologic sign or symptom — for example, an attack of optic neuritis — that’s caused by a single lesion.
- Multifocal episode: The person experiences more than one sign or symptom — for example, an attack of optic neuritis accompanied by weakness on one side — caused by lesions in more than one place.
Individuals who experience a CIS may or may not go on to develop MS. In diagnosing CIS, the physician faces two challenges: first, to determine whether the person is experiencing a neurologic episode caused by damage in the CNS, and second, to determine the likelihood that a person experiencing this type of demyelinating event is going to go on to develop MS.
- High risk of developing MS: When CIS is accompanied by MRI-detected brain lesions that are similar to those seen in MS, the person has a high likelihood of a second neurologic event and diagnosis of MS within several years.
- Lower risk of developing MS: When CIS is not accompanied by MRI-detected lesions, the person has a lower likelihood of developing MS than the high-risk individual over the same time period.
The 2010 revisions to the diagnostic criteria for MS say that the diagnosis of MS can be made when CIS is accompanied by MRI findings (old lesions or scars) that confirm that an earlier episode of damage occurred in a different location in the CNS. 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.
An accurate diagnosis at this time is important because people with a high risk of developing MS are encouraged to begin treatment with a disease-modifying medication in order to 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 are sometimes silent (occurring even if no symptoms can be observed). Several medications are now approved by the U.S. Food and Drug Administration (FDA) for CIS: Avonex®, Betaseron®, Extavia® and Copaxone®.
Read more about CIS.