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 form is plaque psoriasis, which is being characterized by skin patches with intense desquamation and loosely adherent silvery-white scales and affects mostly the elbows, knees, lower back, buttocks, and scalp. Less common forms include guttate psoriasis, pustular forms, erythrodermic psoriasis, and lichenified hands.
Skin lesions are due to the dysregulation of immune mediators, leading to 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.
Although the inflammation associated with psoriasis is generally limited to the skin, it can also progress to the joints causing psoriatic arthritis. Population studies have shown that about a third of patients develop psoriatic arthritis.Severe forms of psoriasis have also been associated with serious co-morbidities such as cardiovascular disease, Crohn’s disease, type II diabetes mellitus, obesity, dyslipidemia, the metabolic syndrome and lymphoma.