Pain followed by erythematous papules in a unilateral dermatomal distribution that turns to vesicles and crusted.

• A. Varicella
• B. Herpes Simplex
• C. Herpes Zoster
• D. Erythema multiforme

Answer: (C)

Painful, unilateral rash that follows a single nerve path and evolves from red papules into vesicles that crust is classic for herpes zoster (shingles). This pattern comes from reactivation of the varicella-zoster virus in a dorsal root ganglion, so the eruption stays in one dermatome on one side of the body and doesn’t cross the midline. The prodrome often includes pain, burning, or paresthesias before the rash appears, which then progresses to vesicular lesions that crust over over about a week or two. This contrasts with varicella (chickenpox), which typically shows widespread, crops of lesions in various stages across the body; herpes simplex tends to produce grouped vesicles in a localized area (often around the mouth or genitals) rather than a broad dermatomal band; and erythema multiforme presents as target-like lesions with different distribution and mucosal involvement rather than a single dermatomal vesicular pattern.