Papulosquamous disease

Abstract Papulosquamous diseases are characterized by well-demarcated areas of papules and scale, typically on an erythematous background. The differential diagnosis includes psoriasis, lichen planus, mycosis fungoides, discoid lupus erythematosus, eczema/dermatitis, drug eruptions, tinea, pityriasis versicolor, secondary syphilis, and pityriasis rosea. The presence of significant pruritus is a useful marker to help with the differential diagnosis: lichen planus and discoid eczema are typically pruritic, whereas others, such as psoriasis, are less so. The distribution is also key to diagnosis, with psoriasis often showing characteristic symmetrical involvement of the extensor surfaces, scalp, and nails. Histology can be essential to reach a diagnosis and plan an appropriate approach to management.