AQP4 and myeloid sarcoma: With a greater understanding of NMOSD and MOGAD, there has been an increasing reliance on the AQP4-IgG and MOG- IgG tests.10,12,23,24 Under suspected Neuromyelitis optica (NMO) or in cases with features atypical for MS-ON, testing for AQP4-IgG and MOG - IgG is advised, as the seropositivity has specific diagnostic and prognostic implications.