What explains this annular rash?

This 15-year-old boy presented with a new asymptomatic eruption of annular rings sparsely scattered over the trunk and thighs. He denied any exposure history, new medications, or recent illnesses. He was otherwise healthy and was taking no medications.

What explains this annular rash?

A. Insect bite reaction
B. Majocchi purpura
C. Suction purpura 
D. Thrombocytopenia
E. Granuloma annulare

Answer on next page

Answer: Majocchi purpura

This patient had one of the benign pigmented purpuras known as Majocchi purpura, or purpura annularis telangiectodes. They are characterized by annular purpuric lesions that are asymptomatic, and they typically are seen in the younger population, such as in this case.

Insect bites typically are itchy. Suction purpura (colloquially, “hickeys”) is a possibility, although these lesions typically are acquired in more amorous locations. Lesions associated with thrombocytopenia would be more widespread and concentrated on the lower extremities. Granuloma annulare is erythematous with an indurated border, unlike what is seen here.