Paraneoplastic neuromyelitis optica spectrum disorder with dual AQP4-IgG and CRMP5 antibodies following thymectomy: a case report.

We present a rare case of paraneoplastic neuromyelitis optica spectrum disorder (NMOSD) in a 50-year-old woman with a history of B3 thymoma, marked by dual positivity for AQP4-IgG and CV2/CRMP5 antibodies. The patient developed sequential bilateral optic neuritis, with orbital MRI revealing enhancement of the left optic nerve. Serological analysis showed a high AQP4-IgG titer (1:320) and positive CV2/CRMP5 antibodies, while other paraneoplastic markers were absent. Treatment with glucocorticoids and mycophenolate mofetil led to substantial visual recovery. This case underscores the association between thymoma and paraneoplastic NMOSD and suggests a potential interaction between AQP4- and CRMP5-related autoimmune responses. Although CV2/CRMP5 antibodies are typically linked to lung cancer and thymoma, their coexistence with AQP4-IgG in NMOSD points to a distinct paraneoplastic mechanism. These findings support the need for thorough tumor screening in NMOSD patients with atypical features, particularly those with CV2/CRMP5 seropositivity.