History: Psoriasis is a common, chronic, relapsing, inflammatory skin disorder with a strong genetic basis. The plaque type is the most common, though several distinctive clinical variants of psoriasis exist. Plaque psoriasis most typically is characterized by circular-to-oval red plaques distributed over extensor body surfaces and the scalp. The plaques usually exhibit silvery scaling as a result of epidermal hyperproliferation and dermal inflammation.  Up to 10% of patients with plaque psoriasis also will suffer from psoriatic arthritis. Acute flares or relapses of plaque psoriasis also may evolve into more severe disease, such as pustular or erythrodermic psoriasis.