Review Question - QID 107822

An otherwise healthy child presenting with a large pink, scaly "herald patch" and many surrounding pink papules over the abdomen and back likely has pityriasis rosea. The exanthem is self-limited and will typically resolve without intervention within 3-4 weeks.

Pityriasis rosea is a common, acute exanthem, commonly affecting children and young adults. While the exact etiology of the exanthem is unknown, HHV6 and HHV7 are considered possible viral candidates. It is characterized by an initial herald patch, followed by the development of a diffuse papulosquamous rash. The secondary exanthem is often described as appearing in a "Christmas tree" pattern over the back, as see in Illustration A. There is no confirmatory diagnostic test. While self-resolving, topical or systemic steroids and antihistamines often are used to relieve pruritis.

Stulberg et al provide a general overview of pityriasis rosea. The differential for patients who present with a large, annular lesion and surrounding papulosquamous exanthem includes nummular eczema, secondary syphilis, tinea corporis, pityriasis lichenoides, guttate psoriasis, viral exanthem, lichen planus, and medication reaction. The rash of pityriasis rosea typically lasts about five weeks and resolves by eight weeks in more than 80 percent of patients.

Drago et al conducted a placebo-controlled trial that suggests that acyclovir may be effective in the treatment of pityriasis rosea, especially in patients treated in the first week from onset, when replicative viral activity of HHV is probably very high. Eighty-seven consecutive patients were treated for 1 week with either oral acyclovir (800 mg 5 times daily) or placebo. On the 14th day of treatment, 79% of treated patients fully regressed compared with 4% of the placebo group. The lesions cleared in 18.5 days in treated patients and in 37.9 days in the placebo group.

Figure A illustrates a classic "herald patch" of pityriasis rosea - a large, annular pink plaque and overlying scaling. Illustration A shows the distribution of pityriasis rosea in a classic "Christmas tree" pattern over the back.

Incorrect Answers:
Answer 1 - Guttate psoriasis is characterized by the acute onset of small, drop-like, salmon-pink papules with a fine scale. While in the differential, guttate psoriasis would not resolve without intervention.
Answer 3 - Tinea versicolor is a yeast infection that presents as hypopigmented macules and patches over the abdomen and back.
Answer 4 - Tinea corporis (i.e. ring worm) is a fungal infection that presents with large annular lesions and does not resolve without intervention.
Answer 5 - Urticaria presents acutely with pruritic pink, annular plaques and papules (also called wheels), but would not typically persist for 7 days.