Double-negative NMOSD: from case report to a proposed diagnostic and therapeutic algorithm

Background: Double seronegative neuromyelitis optica spectrum disorder (DN-NMOSD) is a rare autoimmune disease of the central nervous system, typically involving the optic nerve and spinal cord, characterized by negativity for anti-AQP4 and anti-MOG antibodies. Objectives and methods: A 35-year-old man with optic neuritis and recurrent myelitis, negative for AQP4 and MOG antibodies, was diagnosed with double seronegative NMOSD (DN-NMOSD). Initial treatment with Rituximab led to temporary stability, but relapses in 2021 and 2022 prompted a switch to Satralizumab (anti-IL-6R), achieving two years of clinical and radiological stability. Discussions and conclusions: This case underscores the therapeutic potential of anti-IL-6 drugs for DN-NMOSD, especially when anti-CD20 therapies fail. It highlights the heterogeneity of DN-NMOSD and the need for novel biomarkers, such as GFAP, tau, and IL-6, to better understand disease mechanisms and guide targeted treatments. A structured therapeutic approach, starting with anti-CD20 drugs and progressing to anti-IL-6 agents if ineffective, may optimize outcomes in this poorly understood condition.