Psoriasis is a common skin disease, thought to be in the auto immune category. One of the main elements supporting auto immunity is it’s frequent association with an arthritis, which can be severe.
Eczema (atopic dermatitis) is both a skin and an allergic disease, and looks a bit like psoriasis. In my practice I saw many patients with psoriasis, perhaps people confusing allergy and dermatology.
Both psoriasis and eczema have a red inflamed base, with many little silvery scales of skin on top. These patchy areas tend to be on the outside bends of the elbows and knees in psoriasis, contrasting with eczema, where the dermatitis is located on the inside of the bends. Eczema is a lot more itchy.
The cause of the skin lesions in psoriasis is thought to be due to an interleukin called TNF, which calls to the area a number of inflammatory cells which, in addition to the thickened skin area and excess of epithelial cells, leads to a characteristic appearance under the microscope; biopsies are uncommonly needed when there is doubt about the diagnosis.
In its severe form, psoriasis can be very disfiguring, irritating, painful or itchy, and life altering. You have probably seen advertisements on TV.
Psoriasis has accumulated many different treatments, since it has been recognized and treated over such a long period of time. The basis of many effective treatments is “shotgun” systemic immunosuppression, which reduces the autoimmune inflammatory reaction, but with side effects.
Topical Cortisone cream is the cheapest reasonably effective treatment, and works for mild cases. More recent treatments are specifically aimed out the interleukins which cause the disease, like TNF.
Please refer to the mayo clinic article for more pictures, and discussion of treatment.