Clinical Reasoning: An Immunocompetent Young Adult With Acute Vision Loss.

A 23-year-old male patient presented to the emergency department with several days of exacerbating headaches, bilateral retrobulbar pain, and blurred vision. Ophthalmologic evaluation was consistent with bilateral optic neuritis (ON). MRI, CSF analysis, and blood tests were normal except for elevated liver enzymes and elevated cytomegalovirus-immunoglobulin G titers. Prompt treatment with intravenous methylprednisolone for acute ON was initiated, despite the concern for an acute systemic viral infection, resulting in rapid improvement in vision. This case report highlights the key differentiating findings and management between demyelinating, infectious, and para-infectious ON.