Psoriasis

The familiar pink or red lesions with a scaling surface and well defined edge are easily recognised. These changes can be related to the histological appearance:

Auspitz Sign Psoriasis Illustration
Increased epidermal proliferation—nuclei found ... throughout the epidermis

• The increased thickness of the epidermis, presence of nuclei above the basal layer, and thick keratin are related to increased epidermal turnover.

• Because the epidermis is dividing it does not differentiate adequately into normal keratin scales. These are readily removed to reveal the tortuous blood vessels beneath, appearing clinically as "Auspitz sign". The psoriatic plaque can be likened to a brick wall badly built by a workman in too much of a hurry—it may be high but it is easily knocked down.

• The polymorphs that migrate into the epidermis form sterile pustules in pustular psoriasis. These are most commonly seen on the palms and soles.

• The dilated blood vessels can be a main feature, giving the clinical picture of intense erythema.

The equivalent changes in the nail cause thickening and "pits" 0.5-1.0 mm in diameter on the surface; these are thought to be due to small areas of psoriatic changes in the upper layer of the nail plate that then fall out. Onycholysis, in which the nail plate is raised up, also occurs in psoriasis.

Pitting of the nail

Clinical appearance

The main characteristics of psoriatic lesions, which reflect the pathological processes listed above, follow.

Plaques consisting of well defined raised areas of psoriasis. These may be few or numerous, covering large areas of the trunk and limbs. Sometimes there are large confluent lesions.

Small lesions
Lupus Lesions Pictures

Large lesions

Scaling may predominate, giving a thick plaque, which is sometimes likened to limpets on the sea shore, hence the name "rupioid". Scratching the surface produces a waxy appearance—the "tache de bougie" (literally "a line of candle wax").

Erythema may be conspicuous, especially in lesions on the trunk and flexures.

Pustules are rare on the trunk and limbs, but deep seated pustules on the palms and soles are fairly common. In the form of palmo-plantar pustulosis they may occur without psoriasiatic lesions elsewhere.

The size of the lesions varies from a few millimetres to very extensive plaques.

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