Psoriasis

With psoriasis, the disease events take place primarily in the topmost skin layer, the epidermis. Here, top skin cells are continually being formed and these move outwards to form horny cells. The normal period of cell regeneration is 28 days. Psoriasis completes this process in only 3 to 4 days; compared to healthy skin (Figure 1) and the formation of new cells is therefore substantially accelerated. Consequently, the cells are unable to develop properly. The cornification of the protecting top horny layer is disrupted and the typical heavy deposits of scaly skin are formed. Extended and more convoluted blood vessels result in a reddening of the skin in the areas affected. Inflammatory cells (leukocytes) can also move into the affected skin areas through these vessels (Figure 2).

Figure 1: Healthy skin

Healthy skin: Horny layer Epidermis Connective tissue Blood vessels

 

Figure 2: Psoriasis plaque

Psoriasis plaque: Scaly skin Thickened horny layer (hyperkeratosis) Loosened spaces containing air Inflammation cells Extended, convoluted blood vessels Increased cell division Extended rete ridges of the epidermis

   

The skin's appearance is characterised by sharply defined, reddened plaques of various shapes and sizes with a characteristic silver-grey skin scaling. Itching is also possible. Psoriasis focus points are predominantly found on the stretching sides of the arms and legs, elbows and knee, in the groin region, on a head full of hair, and behind the ears. Fundamentally, however, every area of the skin surface can be affected, including the nails.

The forms of appearance vary greatly. Often, there are only a few lesions, e.g. in the body areas predominantly affected (see above). Sometimes, however, dot-shaped, coin-shaped or large-area changes resembling a map can be seen. Various forms of psoriasis can be differentiated.

Forms of psoriasis

Psoriasis vulgaris (psoriasis of the plaque type)

The most common form of psoriasis is psoriasis vulgaris which is characterised by thick, silvery, shiny deposits of scaly skin. Psoriasis vulgaris can be divided into two groups. Type 1 mainly includes serious cases that already occur early in life (age 10-25 years). The patients affected have characteristic genetic features. There is a familial prevalence and in most cases the psoriasis can already be triggered by scratching on the skin (Koebner phenomenon). The Type II group includes those patients who do not develop their normally slight psoriasis until after the age of 35 (delayed type). Normally, no other family members are affected. The typical gene markers do not exist here.

Psoriasis guttata

With psoriasis guttata, small, at best lentil-sized focal points are found scattered across the entire skin surface. This form frequently occurs in children and young people, e.g. after an infection with streptococci or when the disease first breaks out. Psoriasis guttata can either ease again or transition to psoriasis vulgaris.

Intertriginous psoriasis

In rare cases, psoriasis lesions appear intertriginously, i.e. in skin folds such as under the armpits, in the abdominal skin fold, under the breast or in the gluteal cleft.

Pustulous psoriasis

This involves a rather seldom, distinct clinical pattern which in turn can manifest itself in different forms. As a basic principle, pustulous psoriasis is accompanied by pustules or blisters that are filled with a whitish to yellowish liquid and surrounded by reddened, inflamed skin. If the entire body is affected, we also talk of a 'generalised' form (von Zumbusch type). The illness is accompanied by a fever and general feeling of illness and can be life-threatening.
Pustulous psoriasis can also only affect the palms of the hands and the soles of the feet. This is then referred to as pustulosis palmoplantaris.