Identifying psoriasis requires looking for characteristic skin changes which in many instances have a predilection for specific body parts. Thickening of skin, scaling and redness are all typical changes seen in psoriatic skin. Additionally, psoriasis can affect not just skin, but nails, scalp, and joints as well. In other words, psoriasis has findings typical for both what and where. Key features of Psoriasis include:
What: Skin Plaques
Plaque-type psoriasis is the most common form of the disease, hence the name psoriasis vulgaris. The three hallmarks of a plaque of psoriasis are: thickened skin, red skin and skin scales. The thickness of a plaque (a raised skin lesion more than 1cm in diameter which can be felt) can vary from barely perceptible to several millimeters thick. They range in color from a faint pink to deep beefy red. In patients with darker skin types, there may be less redness and more darkening of the skin. Scales can range from virtually absent to thick oyster-shell like adherent plates known as ostraceous scales.
What: Auspitz's SignWhen adherent psoriatic scales are scraped or picked off, pinpoint bleeding known as Auspitz's sign may occur. The pinpoint areas represent the tops of tiny capillaries which undulate vertically throughout the thickened psoriatic skin.
What: Koebner PhenomenonThe Koebner phenomenon (Koebnerization, isomorphic response) occurs when a new area of psoriasis develops in injured skin. For example, after a surgery, psoriasis may develop around the surgical scar. This phenomenon may also help explain why psoriasis tends to occur on areas of constant low-intensity trauma such as elbows and knees. Koebnerization can occur after non-traumatic skin injury such as a sunburn, or an allergic reaction to a medication. In patients who suffer from dandruff or seborrheic dermatitis of the face and scalp, psoriasis can superimpose itself due to irritation and scratching and a crossover or combination dermatitis known as "sebopsoriasis" develops. Koebnerization is not specific to psoriasis.
What: Guttate, Pustular and Erythrodermic Psoriasis
These less common forms of psoriasis differ dramatically from the typical plaque type. In Guttate (drop-like) psoriasis, tiny papules (lesions which can be felt and are less than 1cm in diameter) appear sprinkled throughout the skin. Pustular psoriasis can occur in smaller areas or involve most of the body with innumerable tiny white pustules. Eythrodermic Psoriasis occurs when the entire body turns bright red and scaly. In this instance, a skin biopsy may be needed to separate erythrodermic psoriasis from other diseases which also can cause a universally red and scaly skin (known as exfoliative erythroderma or "red man").
Where: Typical Locations
Plaque type psoriasis typically involves specific locations on the body including the scalp, elbow, knees, genitals, belly button (umbilicus) and buttocks area (sacrum and intergluteal cleft). In damp areas such as the armpits, under breasts or in the groin, scales become macerated (wet and pasty) and the lesions take on a moist, red and raw appearance closely mimicking a yeast infection in appearance. On the scalp, a severe form of dandruff-like flaking and scaling can be seen.
Where: Hand and Foot Lesions
Psoriasis of the hands and feet can have either a plaque like appearance as seen in other body areas, or a pustular appearance. The presence of pustules is usually attributed to infections, however in psoriasis, pustules form as a part of the inflammatory response. Very thickened plaques on the palms or soles, being somewhat inflexible, may crack with movement. The resulting fissures can be painful and sometimes become secondarily infected. Severe foot lesions can result in disability by limiting your ability to walk.
Where: Finger and ToenailsNail changes commonly seen in psoriasis include thickening, lifting, and pitting of the nails. "Oil spotting" (darkened areas where the nail appears translucent similar to the effect of placing a drop of oil on a sheet of paper) are fairly specific for this disease. Treatment of nail psoriasis can be difficult.
Source: Camisa C. Handbook of Psoriasis, 2nd Ed. Blackwell Publishing, USA 2004.