Psoriasis: disease of epidermis or dermis?

Psoriasis is considered a disease of the epidermis. Two lesions of basal cell carcinoma in patches of psoriasis were excised by Mohs microscopically controlled surgery. As healing occurred by second intention, reepithelization of the surface must have taken place from the surface epidermis of the surrounding psoriatic skin. The scarred areas remained free of psoriasis for many years. This emphasizes the role of a dermal factor in the development of psoriasis.