AQP4 and myeloid sarcoma: The principal values and outcomes of this study were: to act as an aid for diagnosis of demyelinating disease in the acute setting prior to availability of antibody results which may influence acute treatment (e.g. plasma exchange); to aid confirmation of MS diagnosis, which by definition is antibody negative; and to assist with potential identification of true seronegative AQP4-related NMOSD and MOGAD.