Isolated demyelinating syndromes of the central nervous system

**Definition:** Isolated demyelinating syndromes of the central nervous system (also known as Clinically isolated syndrome (CIS)) is the first clinical inflammatory demyelinating event of the central nervous system, lasting more than 24 hours. CIS is now recognised as the first clinical presentation of a disease that shows characteristics of inflammatory demyelination that could be Multiple sclerosis (MS), but has yet to fulfill criteria of dissemination in time.

**Long definition:** Possible presentations of Isolated demyelinating syndromes of the central nervous system (also known as clinically isolated syndrome (CIS)) include optic neuritis, a brain stem and/or cerebellar syndrome, a spinal cord syndrome, or uncommonly cerebral hemispheric symptoms. Natural history studies and clinical trials of MS disease modifying therapies have shown that CIS coupled with brain MRI lesions carries a high risk for meeting diagnostic criteria for MS. Use of the 2010 revisions to the McDonald MS diagnostic criteria allows some patients with a single clinical episode to be diagnosed as MS based on the single scan criterion for dissemination in time and space. Clinically isolated syndrome is distinct from radiologically isolated syndrome (RIS), in which patients have incidental magnetic resonance image (MRI) white matter lesions in regions suggestive if demyeliantion in the absence of clinical symptoms.