MM Voortman, T Stojakovic et al. Figure 1. CSF FLC levels of CIS/MS patients and controls. Comparisons between patients with CIS (n = 48), MS (n = 13) and controls (n = 60) of CSF levels of (a) KFLC, (b) LFLC and (c) the KFLC/LFLC CSF ratio. Significantly elevated levels of KFLC and LFLC and KFLC/LFLC ratio were found for both CIS and MS patients compared to controls (all p < 0.001) by applying Kruskal-Wallis test with post hoc Dunn's multiple comparison test. No significant differences were found between CIS and MS patients. Horizontal bars represent median values. CIS: clinically isolated syndrome; CSF: cerebrospinal fluid; KFLC: free light chain kappa; LFLC: free light chain lambda; MS: multiple sclerosis. higher risk of conversion from CIS to CDMS. This suggests a prognostic role of this variable despite our failure to find significant correlations of FLC metrics with cross-sectional and longitudinal MRI measures of brain damage. There is a large body of evidence that B cell and antibodies play a central role in the immunopathogenesis of MS.27 Detection of intrathecal Ig production either by quantitative or qualitative means is a supportive criterion in the diagnosis of MS.1 Since years the gold journals.sagepub.com/home/msj standard to verify intrathecal Ig synthesis is the detection of OCB in the CSF by isoelectric focusing followed by immunoblotting.28 The downside of this qualitative measure is that it is a rather timeconsuming procedure and that the interpretation of the results is rater dependent.28 Subsequent to B-cell activation, plasma cells not only produce intact immunoglobulins but also an excess of light chains,29 which can be found as FLC in the circulation and in the CSF in case of intrathecal immune activation. Different from OCB, FLC can easily be determined 1501https://journals.sagepub.com/home/msj