Introduction to Psoriasis

The prevalence of psoriasis in the U.S. and U.K. populations is about 2%. The prevalence of psoriasis is much lower in Native Americans, African-Americans, and Asians. Most African-Americans trace their ancestry to West Africa where the prevalence of psoriasis is 0.7%. There are between 150,000 and 260,000 new cases of psoriasis per year in the U.S. The sex incidence is equal. The mean age of onset is about 30 years, with the range being from birth to 100 years. Females may be affected earlier in life than males.

The cause of psoriasis remains an enigma.
The most common pattern of psoriasis is that of a symmetric inflammatory papulosquamous disease (see Plate 1, facing p. 34). Recognition of the classic morphology of the skin lesions by an experienced clinician is usually sufficient for confirmation of the diagnosis, but simple diagnostic maneuvers, such as examination of scales for hyphal elements using potassium hydroxide (KOH), serologic testing for syphilis, and skin biopsy, may be necessary to rule out other considerations.