We report the case of a patient with myelin oligodendrocyte glycoprotein (MOG)- antibody-associated disease presenting with tumefactive demyelinating lesion. Neurological examination showed aphasia, acalculia, agraphia, alexia, left-right disorientation, and right hemiplegia. Brain magnetic resonance imaging revealed a large monofocal lesion with mild brain edema and ring enhancement. Stereotactic brain biopsy was performed, and neuropathological findings showed inflammatory demyelination and preserved axons without tumor cells. A cell-based assay detected anti-MOG antibody in the cerebrospinal fluid. Neurological symptoms gradually improved after steroid pulse therapy. MOG-antibody-associated diseases should be considered in the differential diagnosis of tumefactive demyelinating lesion.

Keywords: Biopsy; Eosinophil; MOG; Pathological; Steroid therapy; Tumefactive demyelinating lesion.