I was happy today to have a case of Pitiriasis rosea today in the office to show off to my medical student. The 14 year old girl with the rash was a great sport to let me show her torso rash to my young male 3rd year student. I love diagnoses that are easy, where the condition is not serious, and especially when they have a fun name. Pitiriasis as a general term refers to a flaking or scaling condition and comes from the Greek word for bran. Add to that a differential diagnosis that includes syphilis and a distribution on the skin of the torso compared to a Christmas tree and you’ve got a great teaching case.
Pitiriasis rosea is usually a mild and self limited skin rash felt to be caused by a virus, possibly a Human Herpes Virus of the group 6 or 7 which can cause Roseola infanatum in very young children possibly presenting differently in older children or adults. It is felt to usually be non-contagious, although small outbreaks have been reported. The rash usually first shows up as a large reddish flaky patch, called a herald patch because it heralds the onset of the disease, and followed by multiple smaller reddish patches that are often oval shaped and run with the skin lines of the torso. The skin lines of the torso run diagonally sloping upwards as they run from the mid anterior abdomen outwards, so the distribution is described as a Christmas tree distribution. The rash is sometimes preceded by a minor illness, and the rash sometimes itches mildly to more severely. The good thing is that it resolves without treatment, usually in about 6 weeks or so.
As a medical student we were always drilled to remember that secondary syphilis can present with a similar rash, although I suspect most of us have never actually made a diagnosis of a case of secondary syphilis that presented this way. Still I made sure to quiz my medical student today on this to keep up the tradition of thinking of zebras as well as horses when we hear hoof beats.
Here is a link to several photos of Pitiriasis rosea.