Double Seronegative Neuromyelitis Optica Spectrum Disorder with Longitudinally Extensive Transverse Myelitis and Optic Neuritis: A Challenging Case Report.

Neuromyelitis optica spectrum disorder (NMOSD) is a rare antibody-mediated neuroinflammatory disease of the central nervous system, typically manifesting in the optic nerves, spinal cord, and other regions of the central nervous system. We hereby report a case of a 16-year-old girl who presented with a six-month history of transverse myelitis with an acute episode of bilateral retrobulbar optic neuritis. MRI revealed patchy contrast enhancements over bilateral retrobulbar intraorbital optic nerves together with long-segment spinal cord hyperintensities (C2 to T2 level). Visual evoked potential testing during the acute presentation showed the absence of P100 bilaterally. However, both serum AQP4-IgG and MOG-IgG were reported to be negative. Despite remarkable improvement in bilateral optic nerve functions, she continued to have disabling bilateral lower limb spasticity, contractures, and loss of bilateral lower limb sensation after five cycles of plasma exchange. This case summarizes the challenges to diagnosing double seronegative NMOSD and its immediate therapeutic significance.