Psoriasis is a relapsing and remitting inflammatory disease that affects skin and sometimes nails and joints. It has an overall prevalence of about 2% of the world’s population, with important geographical variation that may be attributed to differences in climate, genetic background and antigen exposure.
Psoriasis can take many different forms, the most prevalent of them being plaque psoriasis characterized by skin patches with intense desquamation and loosely adherent silvery-white scales, which preferentially affect the elbows, knees, lower back, buttocks, and scalp. Lesser common forms comprise guttate psoriasis, pustular forms, erythrodermic psoriasis, and lichenified hands.
Psoriatic lesions are very impacting on patients everyday life by causing stigmatization and embarrassment leading to loneliness and the self-imposition of limitations. Established psoriasis can have serious consequences. Population studies have shown that about a third of patients develop psoriatic arthritis, and that severe forms of psoriasis are linked with impacting comorbidities such as cardiovascular disease, Crohn’s disease, type II diabetes mellitus, obesity, dyslipidemia, the metabolic syndrome, and lymphoma.
Skin lesions are due to the dysregulation of immune mediators, leading hyperproliferation and aberrant differentiation of epidermal cells, increased dermal vascularity, and massive infiltration of immune cells. Involved immune mediators include IL-17, IL-23, IL-20, IL-22, IL-1β, IL-6, and TNF-α, which interact as a network in the pathogenesis of psoriasis. The inflammation associated with psoriasis is generally limited to the skin, but can also progress to the joints causing psoriatic arthritis.