Psoriasis

Psoriasis affects approximately 1.5% of the population of the UK and is seen mainly in adults, with onset most frequently at around the age of 20. Psoriasis is regarded as an autoimmune disease in which genetic and environmental factors play a significant role. The most commonly affected sites are the scalp, elbows, knees, umbilicus, genitalia, sacrum and shins. 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. Disease activity fluctuates spontaneously over a variable timescale of months or years. The psychological impact and co-morbidity of psoriasis are often underestimated and can greatly impact on quality of life. First-line treatments are topical: emollients, dithranol, tar, deltanoids (vitamin D analogues), retinoids and corticoids (corticosteroids). Second-line treatments have more adverse effects and include phototherapy and systemic drugs: methotrexate, ciclosporin, acitretin, hydroxycarbamide (hydroxyurea) and fumarates. Biological therapies are costly and demonstrate immunosuppressant activity, and are currently reserved for patients unable to benefit from first- and second-line modalities. Severe forms of psoriasis such as erythrodermic and generalized pustular psoriasis can be life-threatening and may require urgent treatment in hospital.