Abstract
Clinically isolated syndrome (CIS) is a central nervous system demyelinating event isolated in time that is compatible with the possible future development of multiple sclerosis (MS). Early risk stratification for conversion to MS helps with treatment decisions. Magnetic resonance imaging (MRI) is currently the most useful tool to evaluate risk. Cerebrospinal fluid studies and evoked potentials may also be used to assess the likelihood of MS. Four clinical trials evaluating the benefits of either interferon β (IFN-β) or glatiramer acetate (GA) within the first 3 months after a high-risk CIS demonstrate decreased rates of conversion to clinically definite MS (CDMS) and a lesser degree of MRI progression with early treatment. In the 3-, 5-, and 10-year extension studies of 2 formulations of IFN-β, the decreased conversion rate to CDMS remained meaningful when comparing early treatment of CIS to treatment delayed by a median of 2 to 3 years. Diagnostic criteria have been developed based on the clinical and MRI follow-up of large cohorts with CIS and provide guidance on how to utilize clinical activity in combination with radiographic information to diagnose MS. The most recent 2010 McDonald criteria simplify requirements for dissemination in time and space and allow for diagnosis of MS from a baseline brain MRI if there are both silent gadolinium-enhancing lesions and nonenhancing lesions on the same imaging study. The diagnostic criteria for MS require special consideration in children at risk for acute disseminated encephalomyelitis (ADEM), in older adults who may have small vessel ischemic disease, and in ethnic groups that more commonly develop neuromyelitis optica (NMO).