A Rare Overlap of <scp>AQP4</scp> and <scp>MOG</scp> Seropositivity in Neuromyelitis Optica Spectrum Disorder: A Case Report

ABSTRACT Background Neuromyelitis optica spectrum disorder (NMOSD) is an immune‐mediated disorder of the central nervous system associated with autoantibodies against aquaporin‐4 (AQP4). This is distinct from myelin‐oligodendrocyte glycoprotein antibody‐associated disease (MOGAD), defined by anti‐MOG antibodies. The coexistence of AQP4 and MOG antibodies is rare and remains incompletely understood. Case Presentation We present a rare case of a 53‐year‐old woman with dual AQP4 and MOG antibodies in serum and a clinical presentation of recurrent myelitis. She presented with four discrete episodes of bilateral lower limb sensory deficits and mild weakness. Cerebrospinal fluid analysis demonstrated lymphocytic pleocytosis without oligoclonal bands. An MRI spine demonstrated high T2 signal in the right anterior hemicord; MRI brain demonstrated nodular enhancement within the posterior horn and atrium of the right lateral ventricle. High‐titre anti‐AQP4 and anti‐MOG antibodies were detected in serum and remained positive on serial cell‐based assays. Despite maintenance intravenous immunoglobulin, she relapsed and was commenced on rituximab, achieving subsequent clinical stability. Conclusions Dual anti‐AQP4 and anti‐MOG seropositivity is rare and presents diagnostic and therapeutic challenges. This case highlights overlapping clinical features of NMOSD and MOGAD and the need for further research to guide classification and management.