A 28-year-old woman presents with acute monocular vision loss and pain on eye movement for 3 days. Examination reveals a relative afferent pupillary defect (RAPD) and the structure marked **A** in the fundus photograph shows swelling with blurred disc margins and hyperemia. MRI brain and orbits with gadolinium reveals enhancement of the optic nerve and two T2 hyperintense lesions in the periventricular white matter. Which of the following is the most appropriate initial management?

Explanation

## Why IV methylprednisolone followed by oral prednisone taper is correct The clinical presentation—acute monocular vision loss, pain on eye movement, RAPD, and disc edema (papillitis at structure **A**)—is pathognomonic for demyelinating optic neuritis. The MRI findings of optic nerve enhancement plus two periventricular white matter lesions satisfy dissemination in space and time criteria for multiple sclerosis. The Optic Neuritis Treatment Trial (ONTT) established that IV methylprednisolone 1 g daily for 3 days followed by oral prednisone 1 mg/kg with taper is the gold standard for typical demyelinating ON. This regimen speeds visual recovery and reduces the risk of recurrence. Critically, oral prednisone alone is contraindicated as it doubles recurrence risk (Yanoff Ophthalmology 5e, ONTT 1992). ## Why each distractor is wrong - **Oral prednisone alone**: The ONTT explicitly demonstrated that oral prednisone monotherapy doubles the recurrence rate of optic neuritis and is contraindicated. It must be preceded by IV methylprednisolone. - **IV methylprednisolone + plasmapheresis + rituximab**: This aggressive immunosuppressive approach is reserved for neuromyelitis optica spectrum disorder (NMOSD, AQP4-IgG positive) or MOG antibody disease with bilateral/severe disease. The clinical presentation and MRI pattern here are consistent with typical demyelinating ON associated with MS, not NMOSD. - **Observation alone**: Untreated optic neuritis carries risk of recurrence and progression to clinically definite MS. Corticosteroid therapy is indicated to accelerate visual recovery and reduce recurrence, even though final visual acuity at 1 year is similar with or without treatment. **High-Yield:** Papillitis (disc edema) in acute monocular vision loss + pain + RAPD = demyelinating ON; always use IV methylprednisolone first, never oral prednisone alone; check MRI for MS lesions and serum AQP4-IgG/MOG-IgG if atypical features present. [cite: Yanoff Ophthalmology 5e Ch 9.6; Optic Neuritis Treatment Trial 1992]