AQP4 and neuromyelitis optica: The diagnosis of NMOSD has been based on clinical manifestations and magnetic resonance imaging at the optic nerve, spinal cord, brainstem, diencephalic and cortical regions, in addition to detection of the AQP4 antibody (AQP4-Ab) as in the cell-based assay (CBA) recommended by the International Panel for NMO Diagnosis1,8.