When squint and proptosis signal more: A case of probable paediatric myelin oligodendrocyte glycoprotein antibody-associated disease presenting as optic neuritis.

Abstract

Background: Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is an inflammatory demyelinating disorder of the central nervous system affecting individuals of all age groups.^1,2 Although optic neuritis, acute disseminated encephalomyelitis, and transverse myelitis are typical presentations, paediatric patients demonstrate a distinct clinical phenotype with age-related variation in disease expression.² Orbital manifestations are uncommon and may lead to diagnostic uncertainty.

Case Presentation: A previously healthy 4-year-old boy presented with acute-onset outward deviation and apparent proptosis of the right eye following a recent episode of pneumonia. Visual acuity was 20/600 in the right eye and 20/40 in the left eye, with a right relative afferent pupillary defect and marked right optic disc swelling with perivascular sheathing. Initial evaluation focused on excluding orbital cellulitis, inflammatory orbital disease, orbital tumour, and orbital apex syndrome. Computed tomography of the orbit and brain was performed to exclude an orbital mass or infectious orbital pathology and demonstrated enlargement of the right optic nerve. Subsequent magnetic resonance imaging revealed optic nerve enhancement consistent with optic neuritis, along with large, poorly defined T2/FLAIR hyperintense lesions involving the bilateral frontal and parietal white matter and the hemicerebellum, suggestive of an inflammatory demyelinating process. Aquaporin-4 antibody was negative, while serum MOG-IgG was reported as borderline positive with a reference cut-off of 1:10 using indirect immunofluorescence antibody testing. However, the quantitative titre and specific criteria for borderline interpretation were unavailable. The patient was treated with intravenous methylprednisolone followed by intravenous immunoglobulin because of an inadequate initial response. Significant clinical improvement was observed at the three-week follow-up, with visual acuity improving to 20/40 in the right eye and resolution of ocular deviation, relative afferent pupillary defect, and optic disc swelling. The patient completed immunotherapy and remained free from ocular relapse or neurological deterioration during two years of follow-up.

Conclusion: This case highlights that optic neuritis associated with MOGAD may present with atypical orbital features, including proptosis and ocular deviation, mimicking primary orbital disease. Early recognition of inflammatory demyelinating optic neuropathy and appropriate neuroimaging are essential for timely diagnosis and treatment. Although definitive serological confirmation was limited by borderline MOG-IgG positivity, the clinical-radiological features and favourable response to immunotherapy supported a diagnosis of probable MOGAD.