What Is Pityriasis Rosea?

A Common Rash Commonly Mistaken for Ringworm

Woman itching her arm.
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Pityriasis rosea is a common, self-limiting rash that typically occurs in healthy adolescents and young adults. The cause of the rash is largely unknown, although some studies have suggested that it may be viral or bacterial in nature.

Despite the fact that we know little about the causes of the condition, there are a number of commonalities that researchers have been able to identify

  • The condition tends to occur between the ages of 10 and 35.
  • The outbreak is often preceded by an acute infection and is usually accompanied by fever, fatigue, headache, and sore throat.
  • It occurs more often in the colder months.
  • It occurs in all races equally.
  • Only two percent of people will have a recurrence.

Appearance of a Pityriasis Rosea Rash 

Pityriasis rosea will often appear with a so-called herald patch, a single, round or oval lesion which can develop on any part of the body but primarily the trunk. The circular shape of the lesion is often mistaken for ringworm.

Within a few days to several weeks, smaller lesions will begin to appear and may spread to the arms, legs, and face. On lighter skin type, the lesions will appear salmon-colored; on darker skin, they will be more hyperpigmented (darker or patchy in color). The lesions can sometimes be very itchy.

The erupted lesions are typically oval, with the long axis of the lesion oriented along skin lines.

A fine, tissue-like scale will typically be attached to the border of the lesion (similar to what we see with ringworm).

On average, an eruption can last anywhere from six to eight weeks, although it has been known to persist for five months or more in some cases. 

Variations in Pityriasis Rosea Appearance

Pityriasis rosea can appear differently in different people.

In younger children, pregnant women, and people with darker skin, the rash will appear more bumpy (papular). Vesicles and wheals can sometimes be seen in infants.

While pityriasis rosea typically develops on the trunk and extremities, there have been those in whom the entire body is covered with rash. Lesions in the mouth are also known to occur.

Diagnosis of Pityriasis Rosea

Pityriasis rosea is typically diagnosed based on the appearance of the rash. At the same time, it is commonly misdiagnosed for other conditions such as psoriasis, nummular eczema, and syphilis. Because the cause of the rash is still unknown, identification usually requires the exclusion of all other causes.

To do this, a KOH test and other lab assays will sometimes be performed to rule out ringworm and other communicable skin infection. A screening of sexually transmitted diseases may be used to rule out syphilis. In rare cases, a lesion may need to be biopsied.

Treatment of Pityriasis Rosea

While it is unclear whether pityriasis rosea is contagious, isolation is not considered necessary. Treatment options may be limited, however, given our slim understanding about the condition.

One study did show that high dose erythromycin, given over a period of two weeks, may shorten the course of an outbreak.

Additionally, lesions exposed to direct sunlight tend to resolve faster than those in unexposed areas.

Ultraviolet light B (UVB) therapy may be used in some cases to reduce itching and speed healing, although it generally most beneficial during the first week of an outbreak. Oral antihistamines and topical steroids may also help with the itching.

Sources:

Habif, Thomas. "Pityriasis Rosea" Clinical Dermatology, 4th Edition. Ed. Thomas Habif, MD.; New York; Mosby; 2004: 246-248.

Stulberg, D. and Wolfrey, J. "Pityriasis Rosea." American Family Physician. 2004; 69:87-92.

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