1 Introduction Immunoglobulin G (IgG) is synthesized intrathecally by B-cell–derived plasma cells in both infectious and immune-mediated central nervous system (CNS) inflammation [1]. The traditional method to detect intrathecal IgG synthesis, oligoclonal bands (OCB) by isoelectric focusing (IEF), is positive in 88%–95% of multiple sclerosis (MS) patients [2, 3] and it has been part of the 2017 McDonald criteria of MS diagnosis [4].