Psoriasis, parapsoriasis, pityriasis rosea, pityriasis rubra pilaris, pityriasis lichenoides, lichen planus, and lichen sclerosus are dissimilar disorders grouped together because their primary lesions have similar morphologic characteristics: sharply marginated, scaling papules or plaques without exudates, crusts, or fissures. Lesion appearance and distribution distinguish these diseases from each other.

Last full review/revision October 2012 by Peter C. Schalock, MD