NEFL and multiple sclerosis: Besides these imaging markers with good spatial resolution, serum neurofilament light chain (sNfL) is an emerging fluid biomarker of neuro-axonal injury in many neurological conditions.12–14 In multiple sclerosis, sNfL levels are elevated during clinical relapses and correlate with an increase in T2-hyperintensive, as well as new gadolinium-enhancing lesions and brain atrophy.15–20 Thus, sNfL represents a marker for neuro-axonal damage and predicts disability progression.14,15 Nonetheless, little is known about the association of sNfL levels and cognitive decline in multiple sclerosis.