Pityriasis Rosea or Ringworm?

This self-limited eruption is characterized by erythematous, scaling, oval-shaped macules on the trunk and proximal extremities. Most outbreaks begin with a single, large patch-a mother or herald patch-that typically is found on the trunk. Commonly, this lesion is confused with ringworm.

Within the ensuing week or two, many smaller pink patches appear; these are also often mistaken for ringworm. When antifungal agents fail to clear the eruption, add pityriasis rosea and parapsoriasis to the differential. If parapsoriasis remains a clinical concern 6 weeks after disease onset, perform a biopsy to prove the diagnosis.

About half of patients with pityriasis rosea complain of pruritus that can be severe-particularly when they are overheated from exercise or a hot shower. The cause of this condition is unknown, although a preceding viral infection is often revealed in a patient's history.

The typical course of the eruption is several weeks; occasionally, the rash will last for months. Pityriasis rosea is not contagious. Particularly for sexually active patients, secondary syphilis needs to be considered in the differential diagnosis, especially if the palms and soles are involved.

If the patient is asymptomatic, no therapy for the eruption is necessary. Topical corticosteroids can alleviate symptoms; for severe cases, systemic corticosteroids may be helpful.