Psoriasis is an autoimmune skin disease that affects 1.5 to 2.0 percent of the Western population, according to Fitzpatrick and colleagues' book on clinical dermatology. It occurs in equal frequency in men and women and tends to occur early in life (average 16 to 22 years) or later on (average 56 years). There are different types of psoriasis, classified by appearance and distribution. Various types of psoriasis give rise to particular symptoms.
Appearance
Psoriasis can be classified broadly by general appearance of the skin lesions. Plaque psoriasis is the most common type, occurring in approximately 80 percent of psoriasis patients, says psoriasis.org. Plaques typically are well-defined raised areas on the skin that are red and are covered by silvery white scales. In guttate psoriasis, skin lesions appear as small, red spots, often occurring suddenly after a trigger such as an infection or other stress. Inverse psoriasis occurs in skin folds; the lesions are smooth and shiny, often irritated by friction and moisture. In pustular psoriasis, the lesions look like pus-filled blisters and are primarily seen in adults. Erythrodermic psoriasis is a quite inflammatory form of the condition in which the skin can be very red over much of the body surface. Skin may shed in sheets rather than in flakes or scales.
Body Distribution
In plaque psoriasis, lesions usually occur on exposed areas that are typically vulnerable to minor trauma such as the scalp, elbows, forearms, low back and knees. Guttate psoriasis typically appears on the trunk or limbs. Inverse psoriasis occurs in skin folds such as in the armpit and groin. Erythrodermic psoriasis affects most of the body surface area. Some forms of pustular psoriasis primarily affect the hands and feet.
Non-Skin Manifestations
Involvement of the nails is common, affecting approximately 25 percent of psoriatic patients as reported by Fitzpatrick and associates. Nail changes include pits on the surface, yellowish discoloration of the nail bed and detachment. Some patients may develop an inflammatory arthritis, or psoriatic arthritis that can affect both the spine and peripheral joints.
Other Symptoms
Itching is relatively common, especially when the condition affects the scalp, genitals or anal area. Psoriasis is usually a chronic condition and lesions can last for months, although they can also present acutely. Trauma such as scratching and rubbing can worsen the lesions, as can stress and certain infections.
References
- "Color Atlas and Synopsis of Clinical Dermatology;" T.B. Fitzpatrick et al.; 1997
- National Psoriasis Foundation
