Follicular porokeratosis-a rare variant with a rare anatomic presentation

Summary: Follicular porokeratosis is a rare variant of porokeratosis in which the hallmark histopathological finding, the cornoid lamella, is mainly or exclusively located in the follicular ostia. A 46-year-old woman presented with a pink, scaly, annular plaque involving the left angle of the mouth. The clinical differential diagnosis included tinea faciei, granuloma annulare, and sarcoidosis. The histopathology showed hyperkeratotic and parakeratotic columns localized exclusively to the follicular infundibulum with an underlying diminished granular layer and subtle dyskeratosis. The interfollicular epidermis had mild interface changes with scattered dyskeratotic keratinocytes. The dermis contained dilated vessels, solar elastosis, and a lymphoplasmacytic infiltrate with multinucleated giant cells. Colloidal iron highlighted a normal amount of dermal mucin. Methenamine silver was negative for fungi. Fite and Ziehl-Neelsen stains were negative for mycobacteria. Treponema pallidum was negative for spirochetes. This case of follicular porokeratosis at the angle of the mouth highlights an unusual histopathologic variant of porokeratosis in an uncommon anatomical location. While facial involvement of follicular porokeratosis has been described, peri-oral involvement is a rare phenomenon. Furthermore, this case supports previous studies that the follicular localization of the cornoid lamella is not incidental, and while potentially subtle, is a defining feature of this condition.