NEFL and multiple sclerosis: It has already been discussed before that CSF as well as blood NfL remains high for 2–3 months after a relapse and then drops to lower levels in multiple sclerosis patients [15, 17] and that serum levels in chronic inflammatory demyelinating polyneuropathy significantly decrease after 1 month of treatment and in remission periods [32, 34]; this could also affect the diagnostic accuracy of sNfL in patients with SFN, as there are no clear signs of relapses or the exact timing of fiber loss and degeneration.