A 17-year-old previously healthy girl presented with 3 months of decreased vision in the right eye associated with throbbing pain with eye movement. The patient had no history of weakness, incontinence, or severe headaches. Initial presentation was notable for hand motion visual acuity with a 2+ relative afferent pupillary defect on the right; fundus examination revealed grade IV disc edema with obscuration of all major vessels on the disc (Figure, A). A magnetic resonance image (MRI) of the brain with and without gadolinium contrast was degraded by motion and orthodontic artifact but was suggestive of optic nerve enhancement consistent with optic neuritis. Results of serology tests and cerebral spinal fluid analysis were negative for infectious and inflammatory etiologies, including syphilis, sarcoidosis, Lyme disease, viral etiologies, multiple sclerosis, and lupus.