Giant cell arteritis mimicking infiltrative leptomeningeal disease of the optic nerves

A 67-year-old man presented with several days of progressive, painless left eye vision loss. He reported mild jaw claudication but denied headache, scalp tenderness or constitutional symptoms. Examination revealed palpable temporal arteries, blurring of the left optic disc, and 20/100 vision in the left eye with mild relative afferent pupillary defect. Inflammatory markers were sent, and methylprednisolone was initiated for presumptive giant cell arteritis (GCA). Erythrocyte sedimentation rate was normal, however, and C reactive protein was only mildly elevated, prompting further investigation. Orbital MRI revealed nodular enhancement of the optic nerve sheaths bilaterally from optic nerve head to chiasm, raising concern for an infiltrative leptomeningeal process such as sarcoidosis or lymphoma. Methylprednisolone was temporarily stopped while a broad work up for inflammatory and neoplastic causes was pursued. Fluorodeoxyglucose-positron emission tomography ultimately revealed hypermetabolism in the temporal, ophthalmic and occipital arteries suggesting GCA, which was confirmed by temporal artery biopsy. Steroids were restarted, and the patient's vision stabilised.