Persistent anti-argonaute antibody positivity despite clinical remission in AQP4-IgG–positive neuromyelitis optica spectrum disorder: a case report

Background The clinical significance of anti-Argonaute antibodies (Ago-Abs) in neuromyelitis optica spectrum disorder (NMOSD) remains unclear. Case presentation We report a 49-year-old woman with AQP4-IgG–positive NMOSD who experienced recurrent, severe longitudinally extensive transverse myelitis (LETM). During clinical remission, serum Ago-IgG was positive at 1:100 in May 2024 and remained positive at the same reported dilution on repeat testing in January 2026. Other CNS autoantibodies, including MOG-IgG, GFAP-IgG, and CV2/CRMP5-IgG, were consistently negative. Magnetic resonance imaging showed resolution of the previous spinal lesions. Conclusion This case demonstrates persistent Ago-Ab positivity on two measurements approximately 20 months apart during clinical remission in AQP4-IgG–positive NMOSD. Because Ago-Ab was not measured during active relapses, its relationship with disease activity remains uncertain.