Curriculum · ENT, Ophthalmology, and Dermatology
Pityriasis rosea
What it is
Pityriasis rosea is an acute, self-limiting eruption of oval, scaly papules and plaques. It tends to affect young adults and young people, and is mainly seen in teenage and young adult females.
Causes and risk
The aetiology is not fully understood, but a viral etiology is probable. Herpes hominis virus 7 is named as an agent that may play a role, and a connection with human herpes virus 6 and human herpes virus 7 is also suggested.
How it presents
It classically starts with a single herald patch, usually on the trunk. The herald patch is an annular erythematous patch of 2-10 cm, which can be anywhere on the body, with peripheral scaling and central clearing. About 1-2 weeks later the secondary eruption appears on the torso as erythematous, oval, scaly patches. The longitudinal diameters of these oval lesions run parallel to the line of Langer, which produces the fir-tree or Christmas tree pattern. The eruption is usually asymptomatic.