AQP4 and myeloid sarcoma: Special investigations performed, included serology and an urgent magnetic resonance imaging (MRI) of the brain and spinal cord, which exhibited a diffuse demyelinating disease of the brain and spinal cord without the typical features of multiple sclerosis (MS) and laboratory findings, which were positive for the AQP-4 antibody, confirming the diagnosis of neuromyelitis optica (NMO).