Multiple sclerosis is a chronic inflammatory immune-mediated disorder of the central nervous system.Diagnosis requires the combination of clinical signs and symptoms with paraclinical findings obtained by magnetic resonance imaging and cerebrospinal fluid analysis .which are componants of the 2017 McDonald criteria .So far, the gold standard for demonstrating intrathecal IgG synthesis is represented by selective oligoclonal bands in cerebrospinal fluid by isoelectric focusing (IEF), alongside an elevated IgG index .However, the detection of oligoclonal bands in cerebrospinal fluid has several limits as , it requires a time-consuming and expensive laboratory technique, with about three hours needed to obtain results Furthermore, it only provides aqualitative information about the presence of IgG in CSF .During CNS inflammation , kappa free light chain are secreted in the CSF and their concentration reflect the degree of intrathecal B cells and plasma cells activation .Measurement of KFLC could help diagnosis of OCB negative MS and identify intrathecal immunoglobulin synthesis in patient presenting with one isolated band on isoelectric focusing , and it is fully automated,rater independent, stable against preanalytical errors . Thus, the intrathecal synthesis of free light chains are more sensitive, less costly, and less time-consuming compared To OCB detection .The most reliable parameter used to assess FLC diagnostic value in MS is the k-index, .So κ-FLC index predicted the time to conversion to MS as well as disability progression . So patients with early MS and high κ-FLC index is an independent risk factor for conversion from CIS to MS
