Objective Neuromyelitis optica (NMO) is an inflammatory disease that affects the optic nerve and spinal cord. Optic neuritis and longitudinally extensive myelitis associated with systemic autoimmune disease have been recently defined as NMO spectrum disorder (NMOSD). In this study, we report the efficacy of intravenous cyclophosphamide (IVCY) therapy for NMOSD. Methods Four patients diagnosed with NMOSD were enrolled in this study. The expanded disability status scale (EDSS) score was used to

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... aluate the degree of severity. All of the patients received intravenous methylprednisolone (IVMP; 1 g/day for three days), and two patients also received plasmapheresis (PP). All of the patients were administered IVCY treatment. Results Anti-AQP4 antibodies were present in the sera of all patients. All patients exhibited longitudinally extensive transverse myelitis (LETM). Only one patient who fulfilled the criteria for a diagnosis of NMO exhibited optic neuritis. Two patients developed relapse under treatment with low-dose prednisolone (PSL) before the administration of IVCY. The patients in this study exhibited a median improvement in the EDSS score following IVCY treatment from 8.0 to 5.75. Adverse effects were observed in only one patient. Conclusion This study, despite its retrospective design, demonstrated the therapeutic efficacy of IVCY for NMOSD in both the acute and chronic phases of the disease and determined the IVCY dosage for Japanese women with NMOSD. Additionally, this study provided evidence that for NMOSD patients with severe disabilities, IVCY added to IVMP and PP may be a useful therapeutic modality.