A 28-year-old woman presents with sudden-onset unilateral vision loss and pain on eye movement. Fundoscopy reveals disc swelling with blurred margins, hyperemia of the disc, and peripapillary flame hemorrhages. Visual evoked potentials show delayed latency. All of the following are features consistent with papillitis EXCEPT:

Explanation

## Distinguishing Papillitis from Papilloedema ### Clinical Presentation of Papillitis **Key Point:** Papillitis is inflammation of the optic disc, typically unilateral, and is often the first manifestation of optic neuritis. **High-Yield:** The cardinal feature distinguishing papillitis from papilloedema is the presence of **RAPD (relative afferent pupillary defect)** — this is ALWAYS present in papillitis because there is direct damage to retinal ganglion cells and axons. ### Comparison Table: Papillitis vs Papilloedema | Feature | Papillitis | Papilloedema | | --- | --- | --- | | **RAPD** | Present (always) | Absent (unless late/severe) | | **Vision loss** | Marked, early | Mild, late | | **Pain with eye movement** | Yes, characteristic | No | | **Disc hyperemia** | Yes, prominent | No (pale, elevated) | | **Peripapillary hemorrhages** | Yes, flame-shaped | Rare | | **Bilaterality** | Unilateral (usually) | Bilateral | | **Pupil reactivity** | Sluggish (RAPD) | Normal (early) | ### Why Each Feature Fits Papillitis 1. **Visual acuity markedly reduced** — Papillitis causes direct axonal damage → severe vision loss early in the course. 2. **Pain with extraocular movements** — Inflammation of the optic nerve sheath causes retrobulbar pain that worsens with eye movement; this is pathognomonic for optic neuritis/papillitis. 3. **Disc margins hyperemic and blurred** — Active inflammation causes disc hyperemia and loss of margin definition; peripapillary flame hemorrhages are common. ### Why RAPD is Absent is WRONG **Clinical Pearl:** RAPD is the **single most reliable sign** that distinguishes papillitis (optic neuritis) from papilloedema. The presence of RAPD indicates direct damage to the optic nerve's afferent pathway and is present in virtually all cases of papillitis. Absence of RAPD would argue AGAINST papillitis and favor papilloedema or another diagnosis. **Warning:** A student might confuse papillitis with papilloedema and incorrectly think RAPD is absent in both — this is a common trap. RAPD is present in papillitis and absent (or very late) in papilloedema. [cite:Harrison 21e Ch 379]