According to the National MS Society, clinically isolated syndrome (CIS) refers to an initial case of neurological symptoms that continue for at least a day. These symptoms are the result of demyelination or inflammation in the central nervous system. The syndrome is either monofocal, in that the person only experiences one symptom such as optic neurosis, or multifocal, where they may experience more than one symptom during the episode.
Those who experience CIS generally have no fever or infection during the episode and partially or completely recover afterwards.
If a person has a CIS, they have an elevated risk of developing multiple sclerosis. If an MRI scan detects lesions similar to those seen in MS patients, there is a 60 percent to 80 percent chance the person will develop MS over the next few years. These patients are considered high-risk. If no lesions are detected on the MRI, the person has a 20 percent chance of developing MS. These patients are considered low-risk.
Incidents of CIS are (like MS) much higher in women than men, with women twice to three times as likely to have an episode. Seventy percent of those who have a CIS are between 20 and 40 years old.
CIS differs from MS in that CIS is a single neurologic episode whereas MS is multiple neurologic episodes. An MRI scan will show damage in the area of the brain responsible for the symptoms for those with CIS but MS patients will have lesions in several areas. However, if other lesions are found on an MRI scan, it shows that there’s been more than one episode and the person will be diagnosed with MS.
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