What Is Clinically Isolated Syndrome? Key Facts About This MS Subtype

Learn how doctors diagnosis this “silent MS.”

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Typically, when people discuss multiple sclerosis, they focus on the two most common types: relapsing-remitting MS and primary progressive MS. Another type of very early MS, called clinically isolated syndrome, or CIS, is lesser known.

The best way to understand MS is to think of it as a continuum. “We have patients who have almost silent MS where their MRI would show MS, but they haven’t had symptoms yet,” says Michelle Fabian, MD, a neurologist at The Mount Sinai Hospital.

In many cases, patients may have an MRI for something else and the results will show inflammation or loss of myelin somewhere in the central nervous system—the nerves for the brain, spinal cord, or optic nerve. Despite not experiencing typical symptoms of MS, the lesion suggests an MS-like episode. This could be clinically isolated syndrome.

However, if the MRI shows evidence of more than one MS attack, the patient is considered to have multiple sclerosis, not CIS. “We usually [diagnose] most people [with] MS from the first attack,” says Dr. Fabian, “but some [patients] don’t have enough lesions on their MRI that we can give them the full diagnosis.” These patients are diagnosed with CIS.

Clinically isolated syndrome may progress to MS, or it may not. If an MRI shows new lesions on a different spot of the central nervous system (or old lesions that had gone undetected), the diagnosis will advance to MS, according to the National Multiple Sclerosis Society. (Find out how doctors test and diagnose MS here.)

If CIS is caught early, doctors treat it with the same disease-modifying therapy (medications to help prevent episodes) they use to treat cases of MS. “If we treat a person with clinically isolated syndrome, they are less likely to develop further manifestations of MS, and they do better,” says Dr. Fabian. “The goal is that once we put a patient on a treatment, we don’t want them to have any more lesions or any new relapses.”

Even if CIS does progress to MS, it does not necessarily mean the patient’s life will have to change significantly. Learn how new treatments have changed the outlook for MS.