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.
Inversus pityriasis rosea is a variant of pityriasis rosea (PR) with lesions located on flexural areas (e.g., axillae/groin), face, neck, and/or acral areas (e.g., palms/soles), without affecting the trunk. The progression is similar to classic PR, starting with a herald patch followed by multiple similar smaller lesions.
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.
