Neuromyelitis optica, also known as Devic disease (DD), is a chronic disorder of nerve tissue characterized by inflammation of the optic nerve (optic neuritis) and inflammation of the spinal cord (myelitis). There appear to be two forms of this disease. In the classical, but less common type, there is a series of attacks over a short period of time (days or weeks) but, after the initial outburst, there are seldom repeat incidents. The second form is more common and is characterized by repeated attacks separated by periods of remission. In this form, the interval between attacks may be weeks, months or years. In its early stages, Devic disease may be confused with multiple sclerosis.