A healthy young adult patient presents with an itchy rash in their groin, which has been present for 2 weeks. The rash started as a single lesion (arrow), which then seemed to multiply. The remaining history is unrevealing—no recent illness, no prior medical issues, no new exposures, and no sexual activity.
What’s the diagnosis? What causes it? How do we treat it?
Most cases of PR last 6-8 weeks, then self-resolve. The herald patch is usually oval in shape and 2-5 cm in diameter. It typically becomes scaly and begins to clear centrally, leaving the free edge of the cigarette paper-like scale directed inwards toward the center, a clinical finding known as a “collarette” of scale. The cause is unknown, although associations with human herpesvirus 7 (HHV-7) and human herpesvirus 8 (HHV-8) have been reported.
There are multiple variants of PR, including inversus, marginata, hemorrhagic, urticarial, papular, follicular, vesicular, etc. Estimates vary, but variants may occur up to 20% of the time.
In general, treatment requires reassurance and topical corticosteroids for as-needed symptomatic control of pruritus.