Differential diagnosis There is in addition to the myelitis described earlier a progressive and sometimes saltatory subacute necrotic myelopathy without optic neuritis that shares the features of Devic disease but not the optic neuropathy and, in our view, they probably represent the same entity (Katz and Ropper). The differential diagnosis is broader and includes vascular malformations of the cord or dura and infarction or neoplasm of the cord. The cord in the cases we have studied was swollen on MRI in the early stages, often with edema extending many segments above and below the area of primary disease, and later became atrophic, similar to what has been reported in Devic disease. Up to 50 cells are typical in the CSF and the protein is elevated but the spinal fluid may be normal during periods of clinical stability. Several, but not all, of these cases have had positive NMO IgG antibodies (see above), further supporting the notion that most of these aggressive, purely spinal cases are allied with Devic disease.
Treatment Although no adequate randomized treatment trials have been conducted, retrospective and open-label uncontrolled data permit several tentative conclusions about the use of immunomodulating therapies for acute attacks and prevention of future relapses. Acute exacerbation of confirmed or suspected NMOSD have been treated promptly with high-dose intravenous corticosteroids. A subsequent corticosteroid taper for several months may be considered. Plasma exchange (PLEX) is often recommended for severe attacks, either concomitantly or immediately following a course of glucocorticoids. Its use is supported by results of a randomized, sham-controlled double-masked clinical trial by Weinshenker and colleagues (1999) in 22 patients with demyelinating disease, of whom 2 had NMO. Retrospective studies have also shown that acute treatment PLEX yields better visual outcomes than corticosteroids alone (Merle). Treatment with intravenous immunoglobulin also appears to have benefit, although possibly less so than PLEX.
Chronic immunosuppressive treatment is considered possibly valuable to reduce the occurrence of relapses in NMO. The main agents that have been evaluated in retrospective studies and prospective open label series include azathioprine, mycophenolate mofetil, and rituximab (Mealy et al). Medications that have also been used, less commonly, include methotrexate, mitoxantrone, and cyclophosphamide. Accurate diagnosis of NMO is important to guide optimal treatment decisions, since several disease-modifying agents that are used for treatment of MS, including interferon-beta (IFN-β), natalizumab, and fingolimod, may have a deleterious effect on the relapse rate in NMO patients. The course of NMO across individual patients can be unpredictable, and recommendations regarding the optimal duration of preventative treatment have not been established.