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Pityriasis rosea is an acute, benign, self-limiting process that primarily affects adolescents, but can be seen in patients of all ages from infants to adults. A prodrome of pharyngitis, lymphadenopathy, headache and malaise can precede the onset of the eruption. Pityriasis rosea usually presents initially with a herald patch. The herald patch usually presents as an erythematous, annular, scaly plaque that precedes the remainder of the lesions. The rest of the lesions consist of multiple erythematous macules progressing to small red papules that appear over the trunk. The papules enlarge, become oval, and the long axes of the oval lesions are parallel to each other and follow the lines of skin stress in a "Christmas tree" pattern. A thin layer of trailing scale develops in the center of the oval lesions. The eruption usually ranges from the neck to the knees and involves the trunk and proximal extremities with sparing of the face, palms, and soles. Mild itching is common during the first week of the eruption; but it is mostly asymptomatic after that, and resolves spontaneously in about 4 to 8 weeks.

Differential Diagnosis

The herald patch may be confused with tinea corporis before the appearance of the generalized eruption. A KOH study may help to distinguish the two. It is also confused with nummular eczema. However, nummular eczema is usually crusted whereas the herald patch usually dry and scaly. The generalized lesions may be confused with urticaria, viral exanthems, morbilliform drug eruptions, or guttate psoriasis. An adolescent with "pityriasis rosea" with fever, lymphadenopathy, and palmar lesions should have an RPR (rapid plasma reagin) test to exclude secondary syphilis.

Pathophysiology

It is hypothesized that pityriasis rosea is an infectious process due to a virus, possibly human herpesvirus 7, due to the occasional prodromal symptoms, characteristic disease course, tendency for life-long immunity, seasonal variance, and reports of epidemics. Histologic features are nonspecific with mild edema of the epidermis and dermis, and mild perivascular accumulation of lymphocytes with focal areas of parakeratosis.

Treatment

Most do not require any therapy. Parents should be reassured that despite the long duration of the lesions, they will disappear. Sunshine or ultraviolet B radiation can accelerate the resolution of the lesions. Emollients and antihistamines may be helpful for those who are troubled with pruritus.