A 32-year-old woman presents with vesicular rash on the lips and perioral region for 3 days. PCR confirms herpes simplex virus infection. Which is the most common site of recurrent HSV-1 infection?

Explanation

## Most Common Site of HSV-1 Recurrence **Key Point:** HSV-1 recurrent infection most frequently affects the **lips and perioral region** (herpes labialis), accounting for >90% of all HSV-1 reactivation episodes. ### Pathophysiology of Recurrence 1. **Primary infection** → viral replication in mucous membranes 2. **Retrograde axonal transport** → latency in trigeminal ganglion (CN V) 3. **Reactivation triggers** → stress, fever, immunosuppression, UV exposure 4. **Anterograde transport** → recurrence at dermatome supplied by CN V (lips, nose, chin) ### Site Distribution of HSV-1 vs HSV-2 | Site | HSV-1 Frequency | HSV-2 Frequency | Notes | |------|-----------------|-----------------|-------| | Lips/perioral | 90% | Rare | Most common HSV-1 site | | Genital | 10–15% | 80–90% | More common with HSV-2 | | Sacral/buttocks | <5% | 10–15% | Dermatomal distribution | | Ocular | <2% | <1% | Can cause keratitis | **Clinical Pearl:** Recurrent HSV-1 labialis is preceded by **prodromal symptoms** (tingling, burning) 12–48 hours before vesicles appear, allowing early intervention with topical acyclovir. **High-Yield:** The **trigeminal ganglion** is the primary site of latency for HSV-1; reactivation follows the sensory distribution of CN V (ophthalmic, maxillary, mandibular divisions). ### Why Lips Are Preferred - Trigeminal nerve (CN V) innervates the perioral region - Frequent minor trauma and UV exposure trigger reactivation - Mucocutaneous junction is a natural site of viral shedding - Cooler temperature at skin surface favors recurrence