Aquaporin-4-IgG-positive neuromyelitis optica spectrum disorder in an adolescent with inflammatory polyarthritis and Sjögren-related features: a case report

Neuromyelitis optica spectrum disorder (NMOSD) is a severe immune-mediated astrocytopathy most commonly associated with aquaporin-4 immunoglobulin G (AQP4-IgG). Optic neuritis is a common phenotype in pediatric NMOSD, but diagnosis may be delayed when early magnetic resonance imaging (MRI) is unrevealing or when visual loss occurs in the setting of systemic autoimmune disease. A 15-year-old Chinese girl with chronic symmetric inflammatory small-joint symptoms and Sjögren-related features presented with severe right visual loss. At the first documented presentation, the right eye had hand-motion vision and a relative afferent pupillary defect, whereas the left eye, despite preserved visual acuity, already showed mild optic disc pallor and marked peripapillary retinal nerve fiber layer (pRNFL) thinning. A non-contrast brain and optic-nerve MRI performed approximately 5–6 weeks after symptom onset was reported as unrevealing. Rheumatoid factor (RF) was positive on two occasions more than 3 months apart, anti-cyclic citrullinated peptide antibody was negative, and hand MRI showed rheumatoid-arthritis-like inflammatory changes. The rheumatologic phenotype was therefore described as chronic RF-positive inflammatory polyarthritis, with RF-positive polyarticular juvenile idiopathic arthritis considered in the pediatric differential diagnosis. Four months later, she developed painful left visual loss. Serum AQP4-IgG was positive by fixed cell-based assay at a titer of 1:320, whereas serum MOG-IgG was negative. She fulfilled the 2015 International Consensus Diagnostic Criteria for AQP4-IgG-positive NMOSD. She received intravenous methylprednisolone for the acute attack, followed by an oral prednisone taper, while methotrexate was continued for the rheumatologic disease. Plasma exchange could not be performed because of local resource limitations, and left-eye visual recovery remained limited. During irregular follow-up, severe bilateral visual impairment developed. Incomplete interval documentation precluded distinction between relapse-related injury and chronic post-inflammatory axonal loss. This case illustrates that a nondiagnostic initial non-contrast optic-nerve MRI and normal-range pRNFL thickness in the symptomatic eye do not exclude optic neuritis. Early serum AQP4-IgG testing should be considered in adolescents with severe optic neuritis and systemic autoimmune features. Sustained specialist follow-up and appropriate relapse prevention are required after diagnosis.