RESUMEN
BACKGROUND: We observed a rare case of orbital myositis involving the optic nerve. CASE: A 52-year-old woman complained of visual disturbance, lid swelling, ocular pain, and conjunctival injection in her right eye. Her corrected vision was 0.15 in the right eye and 1.2 in the left eye. Relative afferent pupillary defect(RAPD) and central scotoma in visual field test were noted in the right eye. Ocular movement of her right eye was moderately disturbed in all directions. Although laboratory data showed elevation of erythrocyte sedimentation rate, other hematological data such as thyroid function, autoimmune antibodies, and viral infection antibodies were normal. Magnetic resonance imaging(MRI) findings showed compression of the optic nerve at the orbital apex by marked thickening of the right lateral rectus muscle and superior rectus muscle, and inflammation directly invading the optic nerve. Based on the above findings, we diagnosed the case as orbital myositis complicated with optic neuropathy, and started corticosteroid therapy. Her right corrected vision improved dramatically, and the RAPD, central scotoma, and lid swelling disappeared shortly after administration. Enlargement of the extraocular muscles was still present one month after corticosteroid therapy. CONCLUSION: MRI findings suggested that optic neuropathy in this case was induced not only by mechanical compression by the enlarged extraocular muscles at the orbital apex but also by direct inflammatory infiltration from the extraocular muscles.