Psoriasis

Psoriasis is regarded as an autoimmune disease in which genetic and environmental factors have a significant role. The onset of the disease occurs most commonly at about the age of 20 years. Psoriasis is characterized by sharply marginated scaly, erythematous plaques that develop in a relatively symmetrical distribution. The most commonly affected sites are the scalp, elbows, knees, umbilicus, shins and sacrum. Plaques may range in size from a few millimetres to a large part of the trunk or limb. The Köbner phenomenon, in which psoriatic lesions tend to develop at sites of trauma, is sometimes a helpful diagnostic feature. Psoriasis activity fluctuates over a variable timescale of months or years, and may affect larger areas at one time than another. Prolonged remission may occur spontaneously, or may be induced by treatment. Treatment can be topical (emollients, dithranol, tar, deltanoids, corticoids, tacrolimus), systemic (methotrexate, ciclosporin, acitretin, hydroxyurea, fumarates) or with ultraviolet light. Phototherapy and systemic agents should be used only when topical treatments are inadequate. Novel systemic treatments for psoriasis include a rapidly expanding range of biological therapies. These are proteins (usually antibodies) with highly specific actions. Severe forms of psoriasis such as erythrodermic and generalized pustular psoriasis can be life-threatening and may require urgent treatment in hospital.