A 28-year-old woman with multiple sclerosis presents with acute unilateral vision loss and pain on eye movement. Fundoscopy shows optic disc swelling. MRI confirms demyelination of the optic nerve. Her visual acuity is 6/60 in the affected eye. What is the most appropriate immediate next step in management?

Explanation

## Clinical Diagnosis: Optic Neuritis The patient presents with acute unilateral vision loss, pain on eye movement (retrobulbar optic neuritis), optic disc swelling, and MRI-confirmed demyelination. This is optic neuritis — inflammation of the optic nerve, often associated with multiple sclerosis. ## Why High-Dose IV Methylprednisolone? **Key Point:** High-dose IV methylprednisolone is the evidence-based acute treatment for optic neuritis. The Optic Neuritis Treatment Trial (ONTT) demonstrated that IV methylprednisolone accelerates visual recovery and reduces the risk of MS conversion in the contralateral eye. **High-Yield:** IV steroids (not oral, not topical) are first-line for acute demyelinating optic neuritis. The regimen is typically 1 g IV daily for 3–5 days, followed by oral prednisone taper. **Clinical Pearl:** Pain on eye movement (pain with ocular motility) is pathognomonic for retrobulbar optic neuritis and indicates inflammation of the optic nerve sheath. This is NOT vascular (no amaurosis fugax) and responds to anti-inflammatory therapy. ## Treatment Timeline ```mermaid flowchart TD A[Acute optic neuritis diagnosis]:::outcome --> B[IV methylprednisolone 1g daily × 3-5 days]:::action B --> C[Oral prednisone taper over 2-4 weeks]:::action C --> D[Assess visual recovery at 1-2 weeks]:::decision D -->|Good recovery| E[Continue MS-modifying therapy]:::action D -->|Incomplete recovery| F[Consider plasma exchange]:::action E --> G[Reduced MS conversion risk]:::outcome ``` ## Why Other Options Are Wrong | Option | Why Wrong | |--------|----------| | **Carotid Doppler** | Optic neuritis is inflammatory/demyelinating, not vascular. Carotid stenosis causes amaurosis fugax (transient monocular vision loss), not acute painful vision loss with disc swelling. | | **Interferon-beta** | While appropriate for long-term MS management, it does NOT treat acute optic neuritis. Acute inflammation requires immediate high-dose steroids; interferon is secondary prevention. | | **Topical dexamethasone + acetazolamide** | Topical steroids do not penetrate the optic nerve adequately. Acetazolamide is for papilledema/raised ICP, not optic neuritis. This regimen is ineffective and delays proper treatment. |