Detection of Aquaporin-4 antibody in cerebrospinal fluid in neuromyelitis optica spectrum disorder.

Neuromyelitis optica spectrum disorder is an astrocytopathy associated with aquaporin-4 immunoglobulin G (AQP4-IgG). Although live cell-based serum assays have improved antibody detection, the diagnostic value of cerebrospinal fluid (CSF) AQP4-IgG testing remains uncertain. To assess its incremental utility, we retrospectively identified patients who underwent paired serum and CSF AQP4-IgG testing using live cell-based assays. Among 606 paired serum-CSF samples, 7 were serum-positive. Of these, 5 of 7 were also CSF-positive. The two remaining serum-positive patients were CSF-negative. No CSF-restricted cases were identified. Despite a low number of serum-positive cases, our findings add to an existing body of evidence supporting limiting routine CSF AQP4-IgG testing.