Pityriasis rosea is a mild inflammatory exanthem of unknown cause. The available evidence suggests a viral etiology. Pityriasis rosea affects all age groups but occurs most commonly in patients 10 to 35 years old. It tends to occur in spring and fall but not in epidemics. Pityriasis rosea is not contagious. A pityriasis rosea-like eruption has been associated with some drugs and viruses. Occasionally there are prodromal symptoms including malaise, headache, sore throat, fatigue, and arthralgia.
The rash of pityriasis rosea evolves over a period of several weeks. It begins with a "herald patch," a solitary, erythematous lesion with a raised edematous border most frequently occurring on the chest or back. It is 2 to 6 cm in diameter. About 1 or 2 weeks later, there is a widespread, symmetrical eruption of pink- or salmon-colored maculopapular lesions. The patches are oval and are covered with dry epidermis which desquamates to form a ring of scale at the periphery. The lesions are 0.5 to 1.5 cm in diameter and are at first discrete, but can become confluent. The long axes of the patches frequently run parallel to lines of skin tension, giving rise to the Christmas tree pattern seen on the back. The eruption is generalized and chiefly affects the trunk, although it can occur anywhere. The lesions can be localized. Mucous membranes can be involved with plaques, hemorrhagic punctate spots, or ulcers. Successive crops of skin lesions can occur, and the entire illness can last 3 to 8 weeks. Healing is complete, without sequelae or evidence of organ involvement.
The diagnosis of pityriasis rosea is made by the clinical appearance. It can be confused with viral exanthem, drug eruptions, syphilis, and seborrheic dermatitis. Potassium hydroxide preparation of skin scrapings will serve to distinguish pityriasis rosea from tinea corporis. A serologic test for syphilis must be done to exclude that diagnosis.
Therapy is directed at alleviating symptoms. No treatment has been shown to shorten the duration of the rash. The rash is sometimes very itchy. Oatmeal baths and oral antihistamines will provide temporary relief. Emollients will help dryness and irritation. Secondary infection must be prevented with thorough cleansing.
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