Pityriasis rubra pilaris with acantholysis and lichenoid histology.

Acantholytic foci have been reported several times in pityriasis rubra pilaris (PRP). Lichenoid tissue reactions were also mentioned in the literature regarding PRP. We report a 58-year-old patient who, after having colon cancer, had PRP with biopsies showing acantholytic lesions and a heavy lichenoid lymphocytic infiltration. Investigation by serial sectioning of the acantholytic lesion suggested an involvement of the intraepidermal eccrine duct and further investigation with carcinoembryonic antigen (CEA) staining demonstrated a CEA-positive eccrine duct in the acantholytic foci. We suggest that acantholysis in PRP is induced by proteolytic enzymes, urea, and other substances in eccrine sweat in keratin-plugged acrosyringia. This patient had a combination of three relatively rare features of PRP-acantholysis, lichenoid reaction, and a cancer background.