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PAPULOSQUAMOUS ERUPTIONS
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Pityriasis rosea (PR) is a common, benign, self-limited whole body rash with a seasonal prevalence that is clinically characterized by a solitary “herald patch” lesion followed by a whole body exanthem.
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INSIGHT 
Particularly in patients with darker skin types, pityriasis rosea may be more papular and present in an “inverse pattern” (favoring the body folds such as axillae and inguinal creases).
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SYNONYMS Pityriasis rosea Gibert, roseola annulata (historical).
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AGE 10 to 35 years. Rare in <2 years.
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INCIDENCE Up to 2% of all dermatology visits.
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PREVALENCE Common, especially in fall and spring.
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ETIOLOGY Human herpes viruses HHV6 and HHV7 have been postulated, but not proven.
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A solitary “herald” patch (Fig. 14-1) typically precedes the exanthematous phase by 1 to 2 weeks. The exanthem develops over a period of a week and self-resolves in 6 to 14 weeks without intervention. A generalized prodrome similar to viral infection—upper respiratory symptoms, fevers, myalgias—may be present in more than 60% of individuals.
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HERALD PLAQUE Ovoid patch or plaque with collarette of scale (80%). May rarely have ≥2 herald patches or individual presents for evaluation after patch has faded.
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EXANTHEM Papules and plaques with fine scale.
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SIZE Herald patch: 1 to 10 cm. Exanthem: 5 mm to 3 cm.
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ARRANGEMENT Lesions follow the lines of cleavage in a “Christmas tree” distribution.
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DISTRIBUTION Trunk > proximal arms, legs. Head, face (Fig. 14-2), palms and soles typically spared. Herald patch most often on the trunk but rarely can occur on limbs.
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SITES OF PREDILECTION Axillae, back, inguinal areas.
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Headache, malaise, pharyngitis, or lymphadenitis (5%).
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DIFFERENTIAL DIAGNOSIS
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The diagnosis of PR is made on history of herald patch and clinical findings. PR can be confused with tinea corporis, secondary syphilis, guttate psoriasis, tinea versicolor, parapsoriasis, pityriasis lichenoides (PL), nummular eczema, seborrheic dermatitis, or a drug eruption (gold, ACE inhibitors, metronidazole, isotretinoin, arsenic, β-blockers, barbiturates, sulfasalazine, bismuth, clonidine, imatinib and other tyrosine kinase ...