It is clear that the use of discriminatory models on plasma metabolites or conventional MRI can distinguish patients with relapsing-remitting MS (RRMS) from those with aquaporin-4 antibody (AQP4-Ab) NMOSD and RRMS from myelin oligodendrocyte glycoprotein antibody (MOG-Ab) disease remarkably accurately.2, –, 4 Thus, we aim to use these methods to tackle the diagnostic difficulties in antibody-negative patients who have features overlapping NMOSD and MS. Here, AQP4 is linked to myeloid sarcoma.