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Patient Story
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A 17-year-old is brought to the office by her mom because of a rash that appeared 3 weeks ago for no apparent reason (Figures 137-1 to 137-3). She was feeling well and the rash is only occasionally pruritic. With and without mom in the room, the patient denied sexual activity. The diagnosis of pityriasis rosea was made by the clinical appearance even though there was no obvious herald patch. The collarette scale was visible and the distribution was consistent with pityriasis rosea. The patient and her mom were reassured that this would resolve spontaneously. At a subsequent visit for a college physical, the skin was found to be completely clear with no scarring.

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FIGURE 137-1

Pityriasis rosea in a 17-year-old. Lesions are often concentrated in the lower abdominal area. (Used with permission from Richard P. Usatine, MD.)

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FIGURE 137-2

Scaling lesions seen on the buttocks of the same teen as in Figure 137-1. Note how some of the lesions are annular. (Used with permission from Richard P. Usatine, MD.)

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FIGURE 137-3

Close-up of lesion showing collarette scale. Note how the lesions can be annular with some central clearing. (Used with permission from Richard P. Usatine, MD.)

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Introduction
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Pityriasis rosea is a common, self-limited, papulosquamous skin condition originally described in the 19th century. It is seen in children and adults. Despite the long history, its etiology remains elusive. A number of infectious etiologies have been proposed, but at present, supporting evidence is inconclusive. Pityriasis rosea has unique features including a herald patch in many cases and collarette scale that are useful in distinguishing it from other papulosquamous eruptions.

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Epidemiology
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  • Pityriasis rosea is a papulosquamous eruption of unknown etiology.1

  • It occurs throughout the life cycle. It is most commonly seen between the ages of 10 and 35 years.3

  • The peak incidence is between 20 and 29 years of age.1

  • The gender distribution is essentially equal.1

  • The rash is most prevalent in winter months.4

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Etiology and Pathophysiology
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  • The cause of pityriasis rosea is unknown, although numerous causes have been proposed.

  • It has long been suspected that it may have a viral etiology because a viral-like prodrome often occurs prior to the onset of the rash. Human herpesviruses 6 and 7 have been proposed as causes, but numerous studies have failed to demonstrate conclusive supportive evidence.1,2

  • Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila have been proposed as potential etiologic agents, but studies have not demonstrated any significant rise in ...

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