What is responsible for this rash?

An 11-year-old female presented for evaluation of a slightly itchy sparse eruption that was slowly spreading on her arms, trunk, and legs over the last 6 months. She is otherwise healthy.

What is responsible for this rash?

A. Scabies
B. Psoriasis
C. Pityriasis rosea
D. Pityriasis lichenoides et varioliformis acuta
E. Follicular eczema

(Answer and discussion on next page)

Answer: Pityriasis lichenoides et varioliformis acuta 

A biopsy confirmed the clinical diagnosis of pityriasis lichenoides et varioliformis acuta (PLEVA). Most patients present during the first 3 decades of life. Studies of children have shown a variable age of onset between 3 to 15 years, with a mean age of 9.3 years. 

This benign condition usually runs a self-limited course over several months. No randomized trials have been reported though anecdotal reports suggest courses of either erythromycin- or tetracycline-based antibiotics can be successful. 

Differential diagnosis. Scabies would be expected to be more widespread and more pruritic. Psoriasis and pityriasis rosea would be scalier. Follicular eczema would show more prominent follicular accentuation than seen here and would be more pruritic