Neurofilament light chain as an indicator of exacerbation prior to clinical symptoms in multiple sclerosis

•CSF NfL increase is significantly elevated and precedes clinical symptoms by many weeks.•CSF NfL increase correlates with clinical symptoms despite no change in MRI suggesting more sensitive and relevant biomarker for an exacerbation than MRI.•CSF NfL returns to baseline consistent with clinical improvement.•Although baseline CSF NfL is elevated as can be found in patient's age group, it is a reliable marker when use as the individual patients own baseline. Biomarkers may be a sensitive measure of disease activity in patients with multiple sclerosis (pwMS). A pwMS had a marked increase of neurofilament light chain (NfL) in CSF 9-weeks prior to a clinical exacerbation. Brain MRI, CSF, EDSS were measured at baseline, 6 weeks and 28 weeks. The patient had an exacerbation at week 15 of study but the NfL measured at week 6 were found to show a nearly 3-fold increase of CSF NfL levels prior to symptoms when the NfL levels were later measured. This is an example supporting the usefulness of NfL in monitoring disease activity in pwMS which may predict disease activity prior to a clinical exacerbation.