Psoriasis: skin and nails

Psoriasis is seen in many patients with psoriatic arthritis. It forms part of the CASPAR criteria for establishing the diagnosis of psoriatic arthritis (PsA). The psoriasis accompanying PsA may be mild or quite severe, with a very large impact on quality of life. The presence of cutaneous disease may alter the treatment of a patient’s PsA. Psoriasis affects up to 2–3% of the population of Europe, the United States and Canada. The majority of patients have chronic plaque psoriasis (80%). Other clinical phenotypes include guttate psoriasis, erythrodermic psoriasis, inverse psoriasis, sebopsoriasis and pustular subtypes including generalized pustular psoriasis. Nail involvement is a frequent occurrence and indicate an increased risk of developing psoriatic arthritis. In this chapter, the different psoriatic phenotypes are described as well as the histology and, briefly, the pathophysiology of psoriasis. Environmental factors that can impact psoriasis are reviewed.