A 28-year-old man with a history of recurrent HSV-1 keratitis presents with eye pain and photophobia. Slit-lamp examination shows a branching dendritic ulcer. Which finding best distinguishes recurrent HSV keratitis from primary HSV keratitis?

## Primary vs. Recurrent HSV Keratitis ### Comparison Table | Feature | Primary HSV Keratitis | Recurrent HSV Keratitis | |---------|----------------------|------------------------| | **Epithelial involvement** | Dendritic/geographic ulcers | Dendritic ulcers (less common) | | **Stromal involvement** | Rare, minimal | Common (stromal keratitis in 25% of recurrences) | | **Anterior uveitis** | Mild to moderate | Moderate to severe | | **Corneal scarring** | Minimal | Prominent from previous episodes | | **Corneal vascularization** | Absent | Present (neovascularization) | | **Systemic symptoms** | Common (fever, malaise, lymphadenopathy) | Absent or minimal | | **Unilateral involvement** | Can be bilateral | Usually unilateral | | **Recurrence rate** | N/A (first episode) | 50% within 2 years | **Key Point:** The presence of **stromal scarring and vascularization** from previous episodes is the single best discriminator between primary and recurrent HSV keratitis. These represent cumulative corneal damage from repeated viral reactivation. ### Pathophysiology of Recurrence 1. **Viral reactivation:** HSV lies dormant in the trigeminal ganglion and reactivates along sensory nerve endings 2. **Stromal inflammation:** Immune-mediated response to viral antigens in the stroma leads to: - Neovascularization (ingrowth of new blood vessels) - Stromal edema and haze - Progressive scarring with each episode 3. **Cumulative damage:** Unlike primary infection, recurrent episodes leave behind structural changes visible on slit lamp **High-Yield:** While primary HSV keratitis typically presents with epithelial dendritic ulcers and systemic prodrome, recurrent episodes are characterized by **stromal involvement, scarring, and vascularization** — signs of previous corneal damage. **Clinical Pearl:** A patient with clear corneal scarring and neovascularization who presents with a new dendritic ulcer has recurrent HSV keratitis, not primary infection. The history of recurrence is confirmed by the structural changes in the cornea. **Mnemonic: SCAR** — **S**tromal involvement, **C**orneal scarring, **A**nterior uveitis (severe), **R**ecurrent episodes → Recurrent HSV keratitis. [cite:Khurana 6e Ch 5]