Abstract
A preschool girl presented with sudden-onset bilateral painless loss of vision from 2 days prior. Child's examination showed light perception vision, sluggishly reacting pupils, otherwise normal anterior segment, healthy optic disc and retina in both eyes. MRI of brain and orbit with contrast revealed thickened left part of the optic chiasm with contrast enhancement extending proximally to bilateral optic tract and hyperintensities in the left thalamus and periventricular white mater. Considering the topographical distribution of lesions in the brain, neuromyelitis optica spectrum disorder was suspected. The child was started on intravenous methylprednisolone followed by tapering oral steroids. Serological testing was positive for myelin oligodendrocyte glycoprotein (MOG) and negative for aquaporin-4 antibodies. This case represents an unusual case of MOG associated demyelination disorder where the distribution of lesions showed chiasmal involvement along with optic tract, thalamus and deep white mater lesions.