AQP4 and demyelinating disease: Although multiple sclerosis and AQP4 antibody NMOSD may present with overlapping clinical and radiological features, their pathology is distinct.8,9 In particular, multiple sclerosis is defined as a primarily demyelinating disease, while AQP4 antibody NMOSD is an astrocytopathy with secondary damage to oligodendrocytes and neurons related to disease attacks.