For a long time it was thought that neuromyelitis optica (NMO) – or Devic's disease – was a particular form of MS. It has become clear over recent years, however, that it is a separate disorder. Patients with NMO also have relapses but these are usually characterised by inflammations of the optic nerves and the top part of the spinal cord. Lesions in the brain occur less frequently. Symptoms of a relapse are normally more severe than for MS. Recovery is also often not as good. A progressive phase of the disease has not yet been described.

The majority of patients with NMO (70%) have a specific and pathological antibody in their blood: aquaporin 4 antibodies. Some patients with these antibodies develop a disease that is however less typical than described above. The term NMO spectrum disorder is therefore being used more and more frequently.

In order to prevent new relapses, patients are almost always given medication that suppresses the immune system function (e.g. Imuran®). Without treatment, the risk of recurrence is great. Classic maintenance treatments for MS do not work for NMO and can sometimes even be harmful. It is therefore very important to make the best possible diagnostic distinction between the two disorders.