Diagnosis: Pityriasis rosea
Here is demonstrated the axial "centrifugal" distribution of the lesions. (21 days post initial discovery). “Pityriasis rosea usually begins with a large, scaly, pink patch on the chest or back, which. Clinical photograph sourced from Wikimedia Commons (Public domain). Attribution: Aceofhearts1968.
Herald patch: single 2-5cm oval, salmon-colored plaque with collarette of fine scale, usually on trunk. 1-2 weeks later: smaller similar lesions in 'Christmas tree' pattern following Langer's lines on trunk. Spares face/distal extremities (usually).
May have mild prodromal symptoms (malaise, headache, sore throat). Self-limited over 6-8 weeks. Rarely recurs (~2%). More common in spring and fall. May cause mild pruritus. Important to exclude secondary syphilis in sexually active patients.
Usually no treatment needed (self-limited). For pruritus: topical corticosteroids, oral antihistamines. Some evidence for acyclovir/valacyclovir shortening duration if given early. UVB phototherapy for widespread/symptomatic cases.
Secondary syphilis (MUST exclude with RPR/VDRL), Guttate psoriasis, Tinea corporis, Drug eruption, Nummular eczema, Viral exanthem
ALWAYS check RPR/VDRL to exclude secondary syphilis — the 'great imitator.' The herald patch precedes the generalized eruption by 1-2 weeks. Collarette of scale faces INWARD (toward center) — unlike tinea where scale is at the advancing edge.
Tags: pityriasis rosea, papulosquamous, self-limited, viral