Diagnosis and classification of neuromyelitis optica

Neuromyelitis optica (NMO), is an autoimmune disorder of the central nervous system (CNS), mainly affecting the spinal cord and optic nerves. NMO is more prevalent in women than men, with a female predominance usually higher than observed in MS. The median age of onset is also higher than MS, with a median of 35–45 years. Cases of NMO are more prevalent in areas of non-Caucasian populations, especially in Asian countries.

In 2004 Lennon et al. described a circulating IgG auto-antibody (NMO-IgG) in patients with NMO, that was absent in those with multiple sclerosis. This NMO-IgG target was identfied as the astrocyte water channel protein aquaporin 4 (AQP4). Pathological changes attributed to NMO occur mostly in the spinal cord and optic nerve, and to a lesser extent in the brain. Pathogenesis occurs by complement-mediated astrocyte damage, cascading to leukocyte infiltration, oligodendrocyte death and neuronal cell damage. The result is necrosis of major CNS cell types, explaining the poor recovery and major neurological deficits.

Revised diagnostic criteria for NMO of Wingerchuk et al in 2006 defined definite NMO as consisting of optic neuritis and acute myelitis, with two of three additionally supportive criteria, consisting of longitudinally extensive spinal cord lesions, brain MRI not meeting the diagnosis of MS and seropositive NMO. NMO-IgG seropositivity predicts relapse and conversion to NMO in patients with recurrent optic neuritis and a single attack of longitudinally extensive transverse myelitis.

Reports show that seropositive NMO differs from seronegative disease both clinically and epidemiologically, reflecting strong predominance in women, frequent association with other autoimmune disorders, more frequent and severe attacks and higher spinal cord lesion load. Whether seronegative disease represents optico-spinal MS or reflects pathogenic diversity in NMO, such as seronegative myasthenia gravis, is still unknown.

Authors: Drori T, Chapman J
Source: Autoimmun Rev. 2014 Apr-May;13(4-5):531-3. doi: 10.1016/j.autrev.2014.01.034. Epub 2014 Jan 11.
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