A 28-year-old woman presents with sudden-onset blurred vision in the left eye and pain on eye movements. Fundoscopy reveals hyperaemia and blurring of the optic disc margins with early exudates around the disc. Visual acuity is 6/36. Which is the most common cause of papillitis in this patient?

Explanation

## Papillitis: Definition and Aetiology **Key Point:** Papillitis is inflammation of the optic disc (optic neuritis involving the disc head), presenting with disc hyperaemia, blurring of margins, and early exudates. It differs from papilloedema, which is swelling due to raised intracranial pressure without primary inflammation. ## Most Common Cause **High-Yield:** Demyelinating disease, particularly multiple sclerosis (MS), is the most common cause of papillitis in young adults, especially women. The clinical presentation of acute vision loss with pain on eye movements and disc inflammation is classic for optic neuritis associated with MS. ## Distinguishing Features of Papillitis vs Papilloedema | Feature | Papillitis | Papilloedema | |---------|-----------|---------------| | **Onset** | Acute (hours to days) | Insidious (weeks to months) | | **Pain on eye movement** | Present (90%) | Absent | | **Visual acuity** | Markedly reduced early | Normal until late | | **Disc appearance** | Hyperaemic, blurred margins | Pale, swollen, blurred margins | | **Exudates** | Early peripapillary exudates | Late exudates | | **Aetiology** | Inflammatory (MS, syphilis, TB) | Raised ICP (tumour, IIH, CVST) | | **Pupillary defect** | Relative afferent pupillary defect (RAPD) | Normal | ## Clinical Pearl **Clinical Pearl:** The triad of acute vision loss + pain on eye movements + disc hyperaemia with early exudates strongly suggests **optic neuritis due to demyelinating disease**. MS is the most common association in young women in developed countries; in India, consider TB and syphilis as differential diagnoses. ## Why MS is the Top Cause 1. **Epidemiology:** MS affects young adults (20–40 years), with female predominance (2:1). 2. **Optic neuritis as presenting feature:** Occurs in 50% of MS patients at some point; 25% present with optic neuritis. 3. **Pathophysiology:** Demyelination of optic nerve fibres causes acute inflammation and conduction block. **Mnemonic:** **DIPS** — Demyelination, Infection (TB/syphilis), Papillitis, Systemic disease (sarcoidosis). ## Differential Considerations - **Intracranial mass (option B):** Causes papilloedema (raised ICP), not papillitis. Vision loss is gradual; pain on eye movement is absent. - **Idiopathic intracranial hypertension (option C):** Causes papilloedema. Affects obese women but vision is normal early; no pain on eye movement. - **Cerebral venous sinus thrombosis (option D):** Causes papilloedema via raised ICP. Acute presentation but associated with headache, seizures, focal deficits—not isolated optic neuritis. [cite:Neuro-Ophthalmology, Khurana 7e Ch 3]