psoriasis

n.

a chronic skin disease in which scaly pink patches form on the elbows, knees, scalp, and other parts of the body. Psoriasis is one of the commonest skin diseases in Britain, affecting about 2% of the population, but its cause is not known. The disorder often runs in families, the commonest time of onset being in adolescence. It sometimes occurs in association with arthritis (see psoriatic arthritis). Occasionally the disease may be very severe, affecting much of the skin and causing considerable disability in the patient. While psychological stress may cause an exacerbation of psoriasis, the only significant event that precipitates the disease is a preceding streptococcal infection. Drugs, such as lithium or beta blockers, may occasionally be responsible.

Although there is as yet no cure, treatment of psoriasis has improved greatly in recent years. Coal tar and dithranol may still be used and topical corticosteroids remain popular. The vitamin D analogues, e.g. calcipotriol, are highly effective, while PUVA is an effective treatment for moderately severe disease. Systemic therapy, such as methotrexate, retinoids, or ciclosporin, is reserved for the worst cases.