Hydrocephalus as an Initial Presentation of Myelin Oligodendrocyte Glycoprotein (MOG) Antibody-Associated Disease: A Case Report and Review of Tumor-Mimicking Demyelination.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is a demyelinating disease of the central nervous system (CNS) that manifests as optic neuritis, transverse myelitis, acute disseminated encephalomyelitis, and cortical encephalitis. Some patients with MOGAD present with tumor-like brain lesions. However, hydrocephalus as an initial presentation is rare. We present the case of a 23-year-old Japanese man with an acute onset of headache, nausea, and diplopia, who was initially suspected of having a germinoma but was later diagnosed with MOGAD. Brain magnetic resonance imaging (MRI) revealed a tumor-like lesion with hyperintensity on fluid-attenuated inversion recovery (FLAIR) imaging and contrast enhancement on T1-weighted postcontrast images, extending from the midbrain to the thalamus with obstructive hydrocephalus. Neuroendoscopic third ventriculostomy and brain biopsy were performed. Histopathological analyses revealed demyelination, perivascular lymphocytic infiltration, and MOG loss. MOG antibody tests were positive, confirming MOGAD. The patient was treated with pulse steroid therapy (methylprednisolone 1,000 mg/day) and seven sessions of plasmapheresis, resulting in significant neurological improvement. He was discharged approximately two months after symptom onset, and at the six-month follow-up from discharge, he remained relapse-free with only mild diplopia. In this case, early diagnosis via pathological brain analysis and anti-MOG antibody testing allowed for timely treatment. We emphasize the importance of including MOGAD in the diagnostic workup of tumor-mimicking CNS lesions that can cause hydrocephalus.