- Last Update On : 2017-02-20
Neuromyelitis optica (NMO), also known as Devic's disease or opticospinal multiple sclerosis, is a severe autoimmune inflammatory demyelinating disease that selectively affects optic nerves and the spinal cord. Brain lesions occur in less than 60% of cases. Within 5 years, approximately 30% of patients lose vision in at least 1 eye and 10% are unable to walk independently. In North America, the proportion of nonwhite individuals is higher among patients with NMO than among those with classic multiple sclerosis.
Many patients with NMO are misdiagnosed as having multiple sclerosis. Accurate diagnosis is important because prognosis and treatment for the two diseases differ. NMO attacks are often severe resulting in early onset of blindness and paraplegia. NMO is treated with immunosuppression while multiple sclerosis is treated with immunodulation. Plasmapheresis is more beneficial for patients with acute attacks of NMO than for those with multiple sclerosis.
Patients with NMO produce an antibody to aquaporin-4, a water channel protein located in astrocytes. NMO is now classified as an autoimmune AQP4 channelopathy. Seropositivity for aquaporin4 IgG allows early diagnosis of NMO. Sensitivity is 80% and specificity is 99%. Aquaporin4 IgG is uniformly negative in patients with classical multiple sclerosis. A positive value is consistent with an NMO spectrum disorder and justifies initiation of early immunosuppressive therapy to prevent severe disability.
Seropositive patients are much more likely to relapse or progress within 2 years than seronegative patients. Seronegativity does not exclude the diagnosis of NMO. Patients already treated with immunosuppressive therapy may not have detectable antibody.
Aquaporin4 IgG autoantibody is synthesized by peripheral lymphoid tissues and is not synthesized intrathecally. Serum autoantibody must reach a significant concentration before autoantibody is detected in cerebrospinal fluid. The optimal specimen for detection of aquaporin4 IgG is serum and not cerebrospinal fluid. Followup testing is recommended within 3 to 6 months after initiation of therapy.
Reference value is negative. This autoantibody is not detected in healthy individuals.
Specimen requirement is a red top tube of blood.
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