Background: Cerebrospinal fluid (CSF) kappa free light chains (KFLC) are gaining increasing interest as markers of intrathecal immunoglobulin synthesis. The main aim of this study was to assess the diagnostic accuracy (AUC) of the kappa index (CSF/serum KFLC divided by the CSF/serum albumin ratio) compared to CSF oligoclonal IgG bands (OCB) in predicting Multiple Sclerosis (MS) or a central nervous system infectious/inflammatory disorder (CNSID). Methods: We enrolled patients who underwent a diagnostic spinal tap throughout two years. KFLC levels were determined using a Freelite assay (Binding Site) and the turbidimetric Optilite analyzer. Results: Of 540 included patients, 223 had a CNSID, and 84 had MS. The kappa index was more sensitive (0.89 versus 0.85) and less specific (0.84 versus 0.89), with the same AUC (0.87) as OCB for MS diagnosis (optimal cut-off: 6.2). Adding patients with a single CSF IgG band to the OCB-positive group slightly increased the AUC (0.88). Likewise, the kappa index (cut-off: 3.9) was more sensitive (0.67 versus 0.50) and less specific (0.81 versus 0.97), with the same AUC (0.74) as OCB, for a CNSID diagnosis. Conclusion: The kappa index and CSF OCB have comparable diagnostic accuracies for a MS or CNSID diagnosis and supply the clinician with useful, complementary information.

Hypogammaglobulinemia (HG) is a known side effect of treatment with anti-CD20 monoclonal antibodies, and it is associated with the risk of infections. Aim of this retrospective multicentre study was to assess the frequency of HG in Multiple Sclerosis (MS) and Neuromyelitis Optica Spectrum Disorder patients treated with Ocrelizumab or Rituximab and its association with the occurrence of severe infections (SI). Furthermore, predictors of HG and SI were sought. We included 556 patients (190M, 366F, mean age: 47 years) with a mean follow-up of 28 months (range 12-90 months). IgG HG occurred in 20% and IgM HG in 34% of patients. At multivariable analysis, the risk of IgG HG was influenced by an older age (≥50 years) (OR 1.64, 95%CI: 1.06-2.54, p=0.027), and by the number of treatment cycles (OR: 1.20, 95%CI: 1.09-1.33, p<0.001). A total of 25 SI occurred (100 person-years rate: 1.8), with a disease phenotype other than relapsing-remitting (OR 1.50, 95%CI: 1.02-2.20; p=0.039) and IgG HG (OR 2.65, 95%CI: 1.15-6.12; p=0.022) increasing its risk. IgG and IgM HG occurred in a considerable proportion of patients. IgG HG increased the risk of SI, which were, nevertheless, relatively infrequent. Our results highlight the importance of monitoring immunoglobulin levels during treatment with anti-CD20 agents, to personalize treatment strategies.

The kappa index is a well-established marker of intrathecal synthesis (IS) of immunoglobulin (Ig). Routinely used for diagnostic aims, IgG IS, which can be assessed quantitatively (ad hoc formulas) or qualitatively (oligoclonal bands, OCBs), may fail in detecting a humoral immune response within the central nervous system (CNS). The main aim of this study was to evaluate the kappa index for its ability to detect the presence of CNS humoral immunity and to associate it with a distinct group of disorders, in the absence of IgG IS/OCBs. Within the kappa index-positive, IgG OCB-negative (Kappa+OCB-) patient group, we also examined whether IgM/IgA IS, determined with the IgM/IgA index and CSF IgM OCBs, could contribute to disease group stratification. Diagnoses were classified as multiple sclerosis (MS), or other inflammatory (INFL), infectious (INFECT), or non-inflammatory (Other) central/peripheral nervous system disorders. Sixty-nine Kappa+OCB- patients and 50 controls (24 Kappa-OCB- and 26 Kappa+OCB+ patients) were included in this study. The most frequent diagnosis in the Kappa+OCB- group was MS (27/69), followed by INFECT (16/69). Additional evidence of IS was demonstrated through an elevated IgG/IgM/IgA index or by the presence of IgM OCBs in 59%, and through only IgM/IgA IS in 52% of cases. In INFECT patients, the median IgM/IgA indexes were higher (p < 0.001) than in other groups, with 18 patients (95%) presenting an elevated IgM index, 11 patients (58%) presenting CSF IgM OCBs, and 10 patients (53%) presenting an elevated IgA index. The vast majority of all INFECT (16/19) belonged to the Kappa+OCB- group. Our data confirm that the kappa index performs at the highest level in assessing intrathecal humoral immunity and supporting the diagnosis of both MS and CNS infectious disorders, which are also characterized by the intrathecal production of IgM and IgA.

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative autoimmune disorder of the central nervous system characterized by demyelination and neurodegeneration. Traditionally considered a T-cell-mediated disease, the crucial role of B lymphocytes in its pathogenesis, through different mechanisms contributing to inflammation and autoreactivity, is increasingly recognized. The risk of long-term disability in MS patients can be reduced by an early treatment initiation, in particular with high-efficacy therapies. The aim of this review is to provide an overview of the mechanisms of action of high-efficacy therapies for MS, with a focus on their impact on B cells and how this contributes to the drugs’ efficacy and safety profiles. Anti-CD20 monoclonal antibodies, Alemtuzumab, Cladribine and sequestering therapies encompassing Natalizumab and S1P receptors modulators will be discussed and emerging therapies, including Bruton’s Tyrosine Kinase inhibitors, will be presented.