NEFL and primary central nervous system vasculitis: Methods: NfL in serum and CSF was measured in 33 PACNS patients (25 active [aPACNS], 8 in remission [rPACNS]) enrolled between 2014 and 2022 and compared to controls (serum: n = 303; CSF: n = 68); Results: Serum NfL was significantly elevated in aPACNS (median: 45.77 pg/mL) versus rPACNS (6.68 pg/mL; p < 0.001) and healthy controls (6.05 pg/mL; p < 0.001).