Parapsoriasis, Pityriasis Lichenoides, Pityriasis Rubra Pilaris, and Pityriasis Rosea

In addition to psoriasis, papulosquamous dermatoses include a wide spectrum of inflammatory conditions, which clinically resemble psoriasis and share most of their histopathological features. The main clinical features are scaling papules and plaques typically on an erythematous background. Psoriasiform dermatoses are difficult to diagnose, both clinically and histopathologically, due to their complexity and often overlapping microscopic features. This group of dermatoses includes (among others) parapsoriasis, pityriasis lichenoides, pityriasis rubra pilaris, and pityriasis rosea. Specific histopathological features that are pathognomonic for each disease and clinical correlation are important to distinguish these conditions as the treatment and prognosis differ significantly.