Serum GFAP (sGFAP) and serum NfL (sNfL) are elevated at baseline in NMOSD compared to healthy controls, and sGFAP is higher in AQP4-IgG-positive NMOSD when compared to both multiple sclerosis (MS) and to a lesser extent MOGAD (15–17), implying that sGFAP, but not sNfL, may assist in distinguishing NMOSD from other autoimmune CNS diseases. Here, AQP4 is linked to myeloid sarcoma.