9 - Other Papulosquamous Disorders

Abstract

Parapsoriasis is a poorly defined umbrella term that historically included three different cutaneous diseases – large plaque parapsoriasis, small plaque parapsoriasis, and pityriasis lichenoides. These entities differed clinically and histologically as well as in their pathogenesis and response to treatment. Nowadays, parapsoriasis refers to just two of these disorders, large plaque parapsoriasis and small plaque para­psoriasis. However, there is increasing agreement among experts that large plaque parapsoriasis represents an early, patch stage of mycosis fungoides. Small plaque parapsoriasis and pityriasis lichenoides are chronic, idiopathic, generally benign dermatoses characterized by T cell infiltrates that may exhibit dominant clonality. Pityriasis lichenoides has a spectrum of acute and chronic presentations that varies from papulosquamous to ulcerative and rarely may be associated with mycosis fungoides. Pityriasis rubra pilaris is an idiopathic disorder with six clinical types, including various juvenile and adult forms as well as an HIV-associated subtype; the familial variant is due to CARD14 mutations. Pityriasis rosea is a self-limited eruption more commonly seen in adolescents and young adults with oval papulosquamous lesions following Langer lines. Pityriasis rotunda is a rare condition in which large circular lesions without obvious inflammation are seen. Granular parakeratosis is an uncommon condition where keratotic papules and plaques develop within major body folds, most frequently the axillae of adult women.