Role of NMO-IgG in Distinguishing the Type of Optic Neuritis

PURPOSE: To emphasize the importance of neuromyelitis optica (NMO)-immunoglobulin G (IgG) antibodies testing in patients with typical optic neuritis (ON) refractory to steroid treatment. METHODS: Two patients were evaluated with ON refractory to steroid therapy and poor visual acuity; they were tested for NMO-IgG antibodies. RESULTS: Brain magnetic resonance imaging was normal in both patients. The serum and cerebrospinal fluid were positive for NMO-IgG antibodies. Magnetic resonance imaging of the cervical and thoracic spine revealed lesions longer than three vertebral segments and the diagnosis of NMO was confirmed. Treatment with plasma exchange and immunosuppressive therapy resulted in marked improvement of visual acuity. This improvement was sustained. CONCLUSIONS: The testing for NMO-IgG antibodies is important for distinguishing ON in NMO from multiple sclerosis in cases of ON refractory to steroid treatment. These cases suggest that testing for NMO-IgG antibodies should be performed in comparative trials on a larger series.