The majority of the studies exploring the measurement of FLCs as an alternative marker of intrathecal immunoglobulin synthesis have focused on MS.
MS is an autoimmune inflammatory disease of the CNS, characterised by myelin loss, axonal pathology, and progressive neurologic dysfunction . The majority of patients will first present with what is termed a clinically isolated syndrome (CIS): a single episode of symptoms and objective findings, reflecting a focal or multifocal inflammatory demyelinating event in the CNS, lasting at least 24 hours . Over a period of 20 years, about 60% of CIS patients will suffer a second demyelinating event and progress to a diagnosis of clinically definite MS . The diagnosis of MS relies on the integration of clinical, magnetic resonance imaging (MRI) and laboratory findings to demonstrate that damage to the CNS is disseminated in both time (DIT) and space (DIS) . The latest revisions to international MS diagnostic guidelines (the 2017 McDonald criteria) place a strong emphasis on CSF examination, particularly when clinical and MRI evidence is insufficient to confirm a diagnosis of MS . When patients present with a typical CIS, but clinical or MRI findings only demonstrate DIS, the detection of CSF-specific OCB allows a diagnosis of MS to be made. The impact of the 2017 McDonald criteria was assessed in a retrospective study by Beesley et al. . They concluded that the revised criteria allow earlier diagnosis of MS, without affecting diagnostic accuracy. In another study by van der Vuurst de Vries et al. , it was reported that the 2017 McDonald criteria had greater sensitivity but lower specificity for a second attack than the 2010 criteria. The new MS diagnostic guidelines enable identification of more patients with less active disease course.