Like multiple sclerosis (MS), clinically isolated syndrome (CIS) itself is not fatal. However, it may increase the risk of certain complications, like pneumonia, that can be life-threatening in certain circumstances. On average, people with CIS live for more than 45 years after their first episode of symptoms, meaning that the disease has little impact on life expectancy.
Although most people with clinically isolated syndrome (CIS) will eventually progress to multiple sclerosis (MS), some CIS patients will never go on to develop MS. Studies suggest that about 80% of CIS patients will develop MS within two decades of disease onset, but modern multiple sclerosis treatments are likely to reduce those percentages.
During the initial acute attack, symptoms of clinically isolated syndrome (CIS) may cause substantial impairment in day-to-day life — for example, limiting vision or causing paralysis. Symptoms generally ease after the initial episode, though this recovery is not always complete and some symptoms may persist or become permanent.
The initial attack of neurologic symptoms in clinically isolated syndrome (CIS) is often mild enough that it doesn’t require immediate treatment, though anti-inflammatory medications like glucocorticoids may be given if symptoms are causing substantial problems in daily life. Disease-modifying therapies that can reduce the risk of conversion from CIS to multiple sclerosis (MS) are available, and are generally recommended for those at high risk of progressing to MS. People diagnosed with CIS should talk to their healthcare team to define a treatment strategy that is appropriate to their unique situation.
Similar to a relapse in multiple sclerosis, the initial acute episode of clinically isolated syndrome must last at least 24 hours. It usually lasts a few weeks, though attacks can vary in length from days to months.
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