Clinical pitfall: false-positive aquaporin-4 IgG leading to misdiagnosis of neuromyelitis optica spectrum disorder in patient with spinal arteriovenous fistula.

INTRODUCTION: We report the cases of a 68-year-old male with a filum terminale arteriovenous fistula (AVF) who was initially misdiagnosed with neuromyelitis optica spectrum disorder (NMOSD) based on imaging findings and false-positive aquaporin-4 IgG (AQP4-IgG). CASE
PRESENTATION: A 68-year-old male presented with slowly progressive weakness and numbness in his bilateral lower extremities. He was initially diagnosed with NMOSD and treated with immunosuppressive therapy based on findings of extensive spinal cord edema on magnetic resonance imaging (MRI) and initial negative spinal angiography as well as positive AQP4-IgG. Despite immunosuppressive treatment, his symptoms progressed slowly. He repeated MRI that showed persistent abnormal signal within the spinal cord. Second spinal angiography revealed filum terminale dural arteriovenous fistula (AVF). Finally, he underwent surgical disconnection of the fistula. Repeated AQP-IgG was reported negative. DISCUSSION: Although NMOSD and spinal AVFs can share imaging findings on spinal cord MRI, typical clinical features of each disorder are distinct. Identification of AQP4-IgG is the hallmark to confirm a clinical diagnosis of NMOSD; however, different assays can vary in sensitivity and specificity. Although it is rare, false positives can occur especially at low titers. A misdiagnosis of NMOSD and delayed diagnosis of spinal AVF had significant clinical implications because the treatment of spinal AVF is surgical disconnection or endovascular embolization, whereas the treatment for NMOSD includes long-term immunosuppressive therapy. Clinicians should be aware of the potential technical issues in detecting AQP4-IgG especially in the context of patients with atypical presentations for NMOSD.