NEFL and myeloid sarcoma: NfL is exclusivelyexpressed in neurons and is released into the extracellular space upon axonal damage.1 In MS, serum NfL (sNfL) concentrations are associated with increased risk ofrelapses, higher neurological disability scores, increased magnetic resonanceimaging (MRI) disease activity and with more severe brain and spinal cord volumeloss.2, , , , , –8 Serum NfL concentration isassociated with short-term clinical outcomes,9 but the association with long-term clinical outcomes is less clear.10