AQP4 and transverse myelitis: Neuromyelitis optica (NMO, formerly known as Devic disease) is an inflammatory antibody- mediated CNS disease that is associated with serological testing of autoantibody marker directed against AQP4, a water channel on astrocytes (AQP4-IgG), and typically presents with optic neuritis, transverse myelitis, and variable, if any, brain involvement.