Psoriasis - Introduction

Highlights	Diagnosis	Managing Psoriasis
Introduction	Treatment	Resources
Causes	Topical Medications	References
Risk Factors	Other Medications
Prognosis	Phototherapy

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Introduction

Psoriasis is a chronic skin disorder marked by periodic flare-ups of sharply defined red patches covered by a silvery, flaky surface. The primary disease activity leading to psoriasis occurs in the epidermis, the top five layers of the skin.

The process starts in the basal (bottom) layer of the epidermis. Here, keratinocytes are manufactured.
Keratinocytes are immature skin cells that produce keratin, a tough protein that helps form hair and nails as well as skin. In normal cell growth, keratinocytes mature and migrate from the bottom (basal) layer to the surface and are shed unobtrusively. This process takes about a month.
In psoriasis, however, the keratinocytes proliferate very rapidly and travel from the basal layer to the surface in only about four days. The skin cannot shed these cells quickly enough so they accumulate in thick, dry patches, or plaques.
Silvery, flaky areas of dead skin build up on the surface of the plaques and are shed. The underlying skin layer, the dermis, is red and inflamed.
The dermis contains nerves and blood and lymphatic vessels, which supply the abnormally multiplying keratinocytes with their blood supply and also transport potent immune factors that cause the underlying inflammation and redness.

Various forms of psoriasis exist. Some can occur independently or at the same time as other variants, or one may follow another. The most common type is called plaque psoriasis.

Plaque Psoriasis

Description of Plaque Psoriasis Patches. Plaque psoriasis is the most common form and causes skin patches with the following characteristics:

The patches start off in small areas, about one-eighth of an inch in diameter. They usually appear symmetrically, that is, in the same areas on opposite sides of the body.
The patches gradually enlarge and develop thick, dry plaque. If the plaque is scratched or scraped, bleeding spots the size of pinheads appear underneath (known as the Auspitz sign).
Some patches may become ring shaped (annular) with a clear center and scaly raised borders that may be wavy and snake-like.
Eventually separate patches may join together to form larger areas as the disorder develops. In some cases, the patches can become very large and cover wide areas of the back or chest (known as geographic plaques because they resemble maps).

Location of Plaque Psoriasis.

Patches most often occur on the elbows, knees, and the lower back.
About half of patients develop psoriasis on the scalp. Many patients have only a few patches in this location. In some cases, however, psoriasis can cover the scalp with thick plaques that may even extend down from the hairline to the forehead. It rarely affects the face in adulthood, however.
Patches also can appear on the palms and soles, in the genital areas of both men and women, above the pelvic bone, and on the thighs and calves.
In children, psoriasis is most likely to start in the scalp and spread to other parts of the body; unlike in adults, it also may occur on the face and ears.