What could be causing her rash?

This 23-year-old female presented for evaluation of an asymptomatic sparse eruption on her trunk of 2 months duration. She takes no medications and has had her dog for 1 year.

What could be causing her rash? 

A. Pityriasis rosea
B. Nummular eczema
C. Dermatophyte infection
D. Drug reaction
E. Granuloma annulare

(Answer and discussion on next page)

Answer: Pityriasis rosea

This patient has pityriasis rosea. A self-limited eruption typically seen in younger patients that can last weeks to months before spontaneously resolving. Thought to be a post-viral exanthem, it is reported to be pruritic in 50% of cases. Treatment options include topical or systemic steroids, oral erythromycin, and oral acyclovir.

Nummular eczema is typically pruritic and associated with seasonal cold weather and aggressive bathing regimen. Dermatophyte infections typically are on exposed surfaces. There is no history of drug exposure and the paucity of lesions argues against it as well. Granuloma annulare is typically more indurated and without the light scale seen with pityriasis rosea.