PSORIASIS

a chronic, recurrent skin disorder, characterized by reddish, slightly elevated plaques or papules (solid elevations) covered with silvery-white scales. In most cases, the lesions tend to be symmetrically distributed on the elbows and knees, scalp, chest, and buttocks. The lesions may remain small and solitary or coalesce into large plaques that often form geometrical patterns with a central area of normal skin. The nails, frequently involved, become thickened, irregularly laminated, and brittle. The cause of psoriasis is not known, but the lesions are thought to result from abnormalities in both the nonvascular horny outer layer of the skin and its deeper vascular layer. Psoriasis occurs in both sexes with equal frequency, being most prevalent between the ages of 10 and 30. A tendency to psoriasis is inherited. It is most often seen in northern climates, affecting from 1 to 2 percent of the white population. The onset of psoriasis is usually gradual but occasionally explosive. Precipitating factors may include injury to the skin, acute infection, and psychological upsets. Ordinarily, the lesions become less severe and sometimes disappear during the summer, possibly owing to the effect of sunlight. The severe complications of psoriasis are extensive sloughing of the outer layer of the skin, with resulting inflammation, and psoriatic arthritis. Generally, however, individuals with psoriasis are in relatively good health. There is no permanent cure for psoriasis, but the skin symptoms can be treated with locally applied corticosteroids, methotrexate, coal-tar ointment, or ultraviolet light with varying degrees of success.