Neuromyelitis Optica is an inflammable, incurable autoimmune disease of the central nervous system, which causes demyelination and can lead to severe disabilities, like blindness and paralysis. Because of its similar neurologic symptoms and radiologic findings, it was often misdiagnosed with multiple sclerosis. Since one specific antibody against the protein aquaporin-4 has been found in patient blood, the disease is declared as an independent and different disease than multiple sclerosis. The finding of a specific antibody enabled the understanding of pathogenic mechanisms in neuromyelitis optica. Because of their different immunopathogenesis, the development of specific treatment strategies is crucial. Especially in the therapy with interferon-β, the therapy outcome differs a lot between the two diseases. This thesis deals with the differential diagnosis of neuromyelitis optica and multiple sclerosis and its importance for successful therapy.