Snapshot A 20-year-old student presents to the school’s health clinic complaining of a scaly rash on his trunk. He recalls having a mild fever and headaches a few weeks prior, but did not think much of it. The lesions do not itch. He loves to play tennis and spends a lot of time outdoors and wear proper attire during activities. On exam, the lesions are primarily on his central trunk. His sun-exposed arms have no lesions on them. Introduction Common, self-limited papulosquamous eruption three stages of disease herald patch secondary eruption spontaneous resolution Epidemiology Children Young adults Rare above 35 years of age ETIOLOGY Pathogenesis idiopathic often associated with URI seasonal pattern suggests viral etiology, though not confirmed potential link to herpesvirus types 6 and 7 Presentation Symptoms prodrome or URI within a month of onset little or no pruritus Physical exam herald patch, a single lesion usually on the trunk plaque with thin collarette of scale inside the border eruption in 1-2 weeks multiple smaller papules appear in “Christmas tree” distribution oriented along Langer (skin cleavage) lines rose-colored or violet common clustering in lower abdominal and pubic area resolution in 4-12 weeks resolves spontaneously without scarring may have post-inflammatory hypo- or hyper-pigmentation Evaluation Diagnosis from clinical exam and history Diagnosis confirmed with skin biopsy potassium hydroxide preparation to exclude Tinea spp. infections (Tinea versicolor and Tinea corporis) If sexually active and palms and soles involved serologic testing for secondary syphilis Differential Tinea corporis Secondary syphilis (esp if palm and soles involved) Tinea versicolor Drug eruption Guttate psoriasis Treatment Observation lesions heal within 4-12 weeks To hasten recovery UVB from natural sunlight or in the dermatology office oral erythromycin If itchy antihistamines topical steroids Complications Post-inflammatory pigmentary changes Relapse Prognosis Very good Typically self-limited and self-resolving in 4-12 weeks