Pityriasis Rosea

In dermatology, quite a few disorders can look a like at first, but then, over time, the diagnosis becomes clearer.  Pityriasis rosea is a classic example.

When examining a patient a few weeks ago, for a routine skin exam, I noticed this patch on her leg.  At first, I thought it was a patch of ringworm, and I started talking to her about treating it as ringworm.  Then, I examined her back and realized I had jumped to conclusions too soon.  She had pitryiasis rosea.

Pityriasis rosea usually begins with a single red scaling patch about one to two inches in diameter.  We call this the “herald patch” because it heralds the arrival of more extensive rash.  Usually the herald patch remains for a few weeks, then eventually fades.  In the meantime, an extensive rash occurs often covering the entire trunk as well as the neck and the thighs.  It is sometimes itchy and occurs in what is described as a “Christmas Tree” pattern on the back.

This is an interesting disorder that usually runs its course in 6-8 weeks.  There continues to be lots of speculation regarding its etiology, but the cause is still unclear.  Treatment is aimed at calming the symptoms by using topical steroids.  Also, many studies have shown that a short course of azithromycin can shorten the duration and minimize the symptoms.

To learn more, visit the AAD’s page about Pityriasis Rosea.