Neuromyelitis optica (NMO) causes attacks of optic neuritis and transverse myelitis, as does MS. In MS, optic neuritis typically causes visual impairment in one eye at a time, while both eyes may be affected simultaneously in NMO.
Transverse myelitis causes weakness and loss of sensation in the legs and, depending how high on the spinal cord the inflammation occurs, occasionally in the arms. Transverse myelitis can also affect bowel and bladder function. The attacks tend to be more severe in NMO than in MS, causing more severe symptoms — although that is not always the case.
A new blood test that measures antibodies to aquaporin-4 detects this condition in about 70% of cases. This test may identify that a person has NMO even before he or she experiences all the symptoms that lead to a confident diagnosis. The treatment options for NMO differ significantly from those for MS, so making the correct diagnosis is very important.
Acute attacks of NMO are generally treated with intravenous methylprednisolone. Following the initial episode, a combination of prednisone and azathioprine (or, on occasion, some other immune suppressing medication) is used to prevent future attacks.
No controlled clinical trials have demonstrated the effectiveness of any long-term treatment. Some recent research has suggested that plasma exchange may be an effective treatment for severe attacks that have not responded to intravenous methylprednisolone. The disease-modiyfing therapies that have been approved for use in MS are not effective in NMO.