Which corneal finding is pathognomonic for primary herpes simplex keratitis?

Explanation

## Herpes Simplex Keratitis — Epithelial (Dendritic) Ulcer **Key Point:** The **dendritic ulcer** with terminal bulbs is the pathognomonic finding of primary HSV-1 keratitis. It stains with fluorescein (central ulcer) and rose bengal or lissamine green (viral-infected epithelial cells at the margins). ### Morphology of the Dendritic Ulcer ``` Terminal bulbs (swollen ends) ↓ ●───● / \ ● ● ← Central branching ulcer \ / ●───● ↓ Stains with fluorescein ``` ### Stages of HSV Keratitis | Stage | Timing | Corneal Finding | Staining | Management | |-------|--------|---|---|---| | **Epithelial (Primary)** | Days 1–2 | Dendritic ulcer with terminal bulbs | Fluorescein (ulcer), rose bengal (margins) | Topical acyclovir 5× daily; avoid topical steroids | | **Stromal (Recurrent)** | Weeks–months | Stromal infiltration, edema, neovascularization | Minimal staining | Topical acyclovir + weak topical steroid (prednisolone 0.5%) | | **Endotheliitis** | Chronic recurrence | Descemet's folds, anterior chamber reaction, keratic precipitates | None | Topical steroid + systemic acyclovir | **High-Yield:** The **terminal bulbs** (swollen, club-shaped ends of the ulcer branches) are the single most specific feature distinguishing HSV dendritic ulcer from VZV pseudodendritic ulcer (which has rolled, heaped edges and no bulbs). **Mnemonic:** **DENDRITIC = Dendritic branches + Epithelial ulcer + Negative culture (viral, not bacterial) + Denies response to antibiotics + Responds to antivirals + Infectious (HSV) + Terminal bulbs + Immune recurrence + Corneal scarring (if recurrent)** **Clinical Pearl:** Rose bengal or lissamine green stains the **infected epithelial cells** at the ulcer margin (viral cytopathic effect), while fluorescein stains the **ulcer base** (denuded epithelium). This dual staining pattern is diagnostic. **Warning:** Do NOT use topical steroids alone in epithelial HSV keratitis — steroids suppress local immunity and allow the virus to spread, causing **geographic ulcer** (coalescence of dendrites into a large ulcer). Always combine with acyclovir.