Which clinical feature best distinguishes herpes zoster from herpes simplex virus (HSV) infection of the skin?

Explanation

## Distinguishing Herpes Zoster from HSV Infection ### Key Discriminating Feature **Key Point:** Dermatomal (unilateral, band-like) distribution is the hallmark distinguishing feature of herpes zoster and is virtually absent in primary or recurrent HSV infection. ### Comparison Table | Feature | Herpes Zoster | Herpes Simplex (HSV) | | --- | --- | --- | | **Distribution** | Dermatomal (unilateral, follows nerve root) | Random/non-dermatomal; often perioral, genital, or fingers | | **Bilaterality** | Rare (except immunocompromised) | Can be bilateral in recurrent disease | | **Vesicle morphology** | Vesicles on erythematous base | Vesicles on erythematous base | | **Tzanck smear** | Positive (multinucleated giant cells) | Positive (multinucleated giant cells) | | **Recurrence pattern** | Usually single episode; rare recurrence | Frequent recurrences at same site | | **Prodrome** | Dermatomal pain/paresthesia (1–3 days) | Burning/tingling at site | ### Why Dermatomal Distribution Matters **High-Yield:** The dermatomal pattern in zoster reflects reactivation of latent virus in a single dorsal root ganglion. This anatomical constraint is pathognomonic and is the single most reliable clinical discriminator. **Clinical Pearl:** In an immunocompromised patient (e.g., HIV/AIDS), zoster may become disseminated and lose its strict dermatomal pattern, but this is an exception and the patient's immune status would be evident from context. ### Why Other Features Are Not Discriminating - **Vesicles on erythematous base:** Both conditions present identically at the morphological level. - **Tzanck smear positivity:** Both HSV and VZV produce multinucleated giant cells; the test cannot distinguish between them. - **Recurrent episodes at same site:** While zoster recurrence is rare, HSV recurrence at the same site is common—but this is a *frequency* difference, not an absolute discriminator. Primary zoster is a single episode, but the question does not specify primary vs. recurrent.