Objective: To compare the clinical features of our sero-negative and sero-positive neuromyelitis optica (NMO) patients. Methods: Thirty-nine patients with NMO were recruited and analyzed retrospectively. Serum aquaporin 4 (AQP4) antibody status was determined by a cell-based assay. For the sero-negative patients, cerebrospinal fluid (CSF) and serum samples were re-tested using the cell-based assay and an indirect immunofluorescence assay. Results: By the cell-based assay, 30 patients (76.92%, 30/39), were positive for AQP4 antibodies in serum and 37 patients (94.9%, 37/39), had a CSF-positive antibody status. Seven NMO patients (17.9%, 7/39) were sero-negative by the cell-based assay but demonstrated positive CSF results. By indirect immunofluorescence, the remaining two patients, who had no AQP4 antibodies in serum or CSF by the cell-based assay, were positive for IgG antibodies in serum, which selectively targeted the central nervous system microvessels, pia, subpia, Virchow-Robin space, kidney, and stomach. There were no significant differences between the sero-positive and sero-negative NMO groups among their demographic and clinical data. Conclusions: Repeating the test using a different assay or CSF is helpful to clarify whether sero-negative NMO patients do in fact carry AQP4 antibodies.
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