Neuromyelitis optica spectrum disorder and autoimmune glial fibrillary acidic protein astrocytopathy overlap syndrome mimicking a pontine mass: The utility of brainstem biopsy

Abstract Objective Diffuse intrinsic pontine gliomas (DIPG) are high‐grade tumors with a dismal prognosis and are classically diagnosed by radiologic features. DIPG is a critical differential consideration for a pediatric patient presenting with an infiltrative brainstem mass. However, inflammatory and infectious etiologies must also be considered, especially in individuals with atypical radiographic features. In a carefully selected clinical scenario, biopsy can be employed to quickly diagnose and direct treatment for patients with brainstem masses. Results This 10‐year‐old girl presented with acute onset of dysarthria, ataxia, left‐sided weakness, hypertonicity, and dysmetria. Magnetic resonance imaging revealed an infiltrative pontine lesion with atypical features for that of DIPG or specific inflammatory disease. Due to rapid clinical deterioration, stereotactic brainstem biopsy was performed for diagnostic clarity and showed inflammation but no malignant cells. She was then treated for a presumed antibody‐mediated autoimmune etiology with evaluation later revealing neuromyelitis optica spectrum disorder (NMOSD) and autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy overlap syndrome. Interpretation We present a novel example of pediatric NMOSD and autoimmune GFAP astrocytopathy overlap syndrome originally presenting as an infiltrative pontine mass. Our report highlights the safety and utility of brainstem biopsy for brainstem masses atypical for DIPG.