The spectrum of idiopathic inflammatory-demyelinating disorders of the CNS is classified based on clinical symptoms and signs, clinical severity, lesion distribution, neuroimaging features and cerebrospinal fluid characteristics. There is a wide variety of conditions in this broad spectrum. In some cases, the dissemination in the CNS is limited to the optic nerves and spinal cord. Neuromyelitis optica (NMO) and the NMO spectrum disorders have a predilection for the optic nerves and spinal cord. Clinical, MRI, cerebrospinal fluid and neuropathological features show that NMO could be considered as a distinct disease rather than as a variant of multiple sclerosis. Accurate and early diagnosis is critical to facilitate initiation of immunosuppressive and/or immunomodulatory therapy to prevent attacks and disability progression.