Dysthyroid Optic Neuropathy Complicated by Neuromyelitis Optica Spectrum Disorder: A Case Report

Introduction: Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune disorder that principally targets the central nervous system, specifically the spinal cord and optic nerves. NMOSD is often associated with thyroid pathologies such as Graves' disease or Hashimoto's thyroiditis. Thyroid eye disease (TED) is an autoimmune condition characterized by inflammation and hypertrophy of the extraocular muscles. Dysthyroid optic neuropathy (DON), a critical complication of TED, may lead to irreversible visual loss. We report a case of DON complicated by NMOSD. Case Presentation: We report a case of an autoimmune disease presenting as DON in a 44-year-old Japanese woman with a history of Graves' disease, who experienced reduced visual acuity and orbital pain. Brain magnetic resonance imaging disclosed hypertrophy of the rectus muscles, compressing the optic nerve bilaterally. Consequently, she was diagnosed with DON and underwent three courses of steroid semi-pulse therapy and left orbital decompression surgery, alleviating optic nerve compression. Nevertheless, the visual prognosis remained poor. A subsequent serological test showed positive for aquaporin-4 antibody. Treatment with satralizumab, an interleukin-6 receptor monoclonal antibody, was initiated in conjunction with steroids to suppress the autoimmune response and reduce NMOSD relapse risk. Following this treatment, no NMOSD recurrences were reported. Conclusion: This case highlights the necessity of considering the possible coexistence of DON and NMOSD in patients with autoimmune diseases.