Psoriasis is characterized by the development of erythematous (reddish), well defined, dry, scaly, papules and plaques of sizes ranging from a pin head to palm sized or larger. Lesions have a full rich red (salmon) color in the skin of Caucasians. Rarely, lesions on the legs or trunk may show a violaceous or bluish hue.
Psoriasis usually begins as small, erythematous, scaly papules that gradually enlarge to form well demarcated, raised, erythematous plaque with a scaly surface.
The scales in psoriasis are typically silvery white, dry, brittle and arranged in a lamellated fashion. This silvery white color is due to refraction of light through the air trapped in between the scales. The upper scales fall off in large quantities, while the lower layers of scales are firmly fixed.
Grattage Test: Gentle scraping of the surface of a psoriasis plaque with a glass slide will remove the loosely attached scales and reveal a shiny surface peppered with fine bleeding points. These bleeding points represent the dilated and tortuous capillary blood vessels in the papillary dermis, one of the characteristic pathological events taking place in psoriasis affected skin. This sign is known as Auspitz sign, which is a diagnostic sign of psoriasis.
The number of lesions in psoriasis may be a few or numerous. When multiple, they are arranged in a symmetrical fashion on the body.
The commonest sites for psoriasis are the extensor surfaces of the elbows and knees, low back (sacrum), and the scalp, but any part of the body may be involved.
Nail and joints may also be involved in psoriasis. Progressive painful joint swelling is seen in 10-30% of psoriasis patients.
Another characteristic of psoriasis is the Koebner phenomenon (isomorphic response),whereby new psoriasis lesions appear on areas of skin injury. The injury should reach the level of dermis for the Koebner phenomenon to appear. Superficial scratches involving the epidermis alone will not produce new psoriatic rashes.
Psoriasis derived its name from Sora (Gr), meaning itching. Itching is a prominent symptom in most cases, but varies greatly in intensity from case to case. Some patients do not experience itching at all. In the eruptive stage, when new lesions appear and the present ones progressively enlarge, a warm, burning sensation may be felt by the patient.
Depending upon morphological features, psoriasis may be divided into different clinical types: guttate psoriasis, common plaque psoriasis, inverse or flexural psoriasis, pustular psoriasis and erythrodermic psoriasis.
Depending upon the sites of involvement, psoriasis may be classified as scalp psoriasis, trunk psoriasis, flexural psoriasis, palmo-plantar psoriasis, psoriasis glans and nail psoriasis.
Next: Psoriasis Clinical Types
Reference
Psoriasis, in Rook’s Textbook of Dermatology, 7th Edition, 2004
 |
 |
