Porokeratosis ptychotropica: a lesser-known variant.

We report a case of the rare porokeratosis variant porokeratosis ptychotropica (PP). A circumferential perianal plaque and the characteristic histology of multiple cornoid lamellae with underlying dermal amyloid deposition were seen. Amyloid deposition was seen in the biopsied intertriginous area of the plaque only, which, in concordance with other cutaneous amyloid deposition disorders, may suggest a role for friction in the pathogenesis of this histological finding. We review the literature on PP and summarize the poor response seen to treatments.