A 28-year-old woman presents with sudden-onset unilateral vision loss and eye pain on movement. Examination reveals a relative afferent pupillary defect (RAPD), and fundoscopy shows optic disc swelling with blurred margins and flame-shaped hemorrhages at the disc border. Visual evoked potentials show delayed latency. MRI brain and orbits reveals T2 hyperintensity in the optic nerve. What is the drug of choice for this condition?

Explanation

## Clinical Diagnosis: Optic Neuritis (Papillitis) ### Key Distinguishing Features **Key Point:** Optic neuritis presents with **vision loss + eye pain on movement + RAPD + delayed VEP latency**, distinguishing it from papilloedema, which is asymptomatic and bilateral. ### Pathophysiology Optic neuritis is demyelinating inflammation of the optic nerve, often associated with multiple sclerosis (MS). The MRI finding of T2 hyperintensity in the optic nerve confirms demyelination. ### First-Line Treatment **High-Yield:** The Optic Neuritis Treatment Trial (ONTT) established that **intravenous methylprednisolone 1 g daily for 3 days** followed by oral prednisolone taper is the gold standard for acute optic neuritis. **Clinical Pearl:** IV methylprednisolone accelerates visual recovery and reduces the risk of MS conversion by ~30% over 2 years. It does not improve final visual acuity but hastens recovery. ### Mechanism of Action Corticosteroids suppress T-cell mediated demyelination and reduce inflammation in the optic nerve, promoting remyelination and recovery of conduction. ### Comparison: Papilloedema vs Papillitis | Feature | Papilloedema | Papillitis (Optic Neuritis) | |---------|--------------|-----------------------------| | **Vision** | Preserved initially | Loss (sudden, unilateral) | | **Pain** | None | Eye pain on movement | | **RAPD** | Absent | Present | | **Bilaterality** | Bilateral | Unilateral | | **VEP** | Normal latency | Delayed latency | | **Treatment** | Address ICP cause | IV methylprednisolone | **Mnemonic:** **ONIT** = **O**ptic **N**euritis = **I**V **T**herapy (methylprednisolone) ### Why IV Over Oral? IV methylprednisolone achieves higher CNS penetration and faster anti-inflammatory effect compared to oral corticosteroids, which is critical in acute demyelinating disease.