CSF biomarkers in multiple sclerosis: beyond neuroinflammation

For many years, quantifiable biomarkers in neurological diseases have represented a hot topic. In multiple sclerosis (MS), cerebrospinal fluid biomarkers have played a diagnostic role since the introduction of Poser’s criteria in 1983, with IgG oligoclonal bands playing a supporting role in an epoch prior to magnetic resonance imaging and a complementary one after the introduction of McDonald criteria in 2001. Nowadays, that supporting role has turned into a main one in substituting for dissemination in time and defining the diagnosis of MS in patients with a first clinical event, according to the 2017 revised McDonald criteria. Possibly kappa free light chains, N-CAM, chitinase 3-like protein 1 and IgM oligoclonal bands, not yet implemented in clinical practice, could similarly gain importance in the near future. Furthermore, the increasing knowledge of molecular mechanisms leading to chronic inflammation has enhanced interest in looking for biomarkers of disease activity, better defining the MS phenotype and patients with highly active disease. Accordingly, myelin proteins, intermediate filaments, metalloproteinases and other molecules involved in the inflammatory cascade, are currently under investigation. Finally, it has long been known that axonal loss occurs from the early phases, leading to a progressive neurological deterioration. Since established criteria to assess treatment failure and transition to progressive forms are still lacking, both treatment response and prognostic biomarkers would be useful to predict MS course, and neurofilaments seem to have this potential. The purpose of this review article was to illustrate biomarkers that have been already validated or require further validation after proving to be useful in exploratory studies and potentially could prove useful in clinical practice in the coming years.