Genitogluteal porokeratosis: 10 years to make the diagnosis!

Genitogluteal porokeratosis, a relatively rare presentation of porokeratosis of Mibelli, often manifests in an atypical way due to its verrucous appearance that may obscure the characteristic annular keratotic rim. For this reason, misdiagnosis as other common papulosquamous diseases is not uncommon. We report a 44-year-old man with a 10-year-history of slowly progressive pruritic psoriasiform/lichenified plaques over the buttocks. Despite multiple skin biopsies, the lesions were misdiagnosed as psoriasis, lichen simplex chronicus, pityriasis rubra pilaris, and mycosis fungoides, until the last biopsy revealed findings characteristic of porokeratosis. Dermatologists and dermatopathologists should be aware of this rare and unique variant of porokeratosis, which, in addition to the atypical clinical presentation and the occasional misleading histology, may portend a better prognosis in terms of malignant degeneration.