Psoriasis: first-line treatments
Psoriasis is a chronic inflammatory skin disease that affects 2 to 3 per cent of the UK population. Although it can start at any age, the disease usually starts between the second and third decades of life or in the sixth decade. The cause of psoriasis is not known but inheritance appears to play a part — approximately one third of patients have a family history and a number of genetic markers exist.
Types of psoriasis
There are several types of psoriasis.The most common form of psoriasis is chronic plaque psoriasis (also known as psoriasis vulgaris or chronic stable plaque psoriasis), which accounts for approximately 90 per cent of cases.
Chronic plaque psoriasis
Typically, chronic plaque psoriasis presents as well-defined, thickened, red plaques (a plaque is a raised patch on the skin more than 2cm across) covered with silvery scales that are liberally shed (see Figure 1). On black skin the plaques appear dark red and the scale appears greyish. If the scales are scratched or removed, characteristic pinpoint bleeding (Auspitz’s sign) is seen. Chronic plaque psoriasis can occur almost anywhere on the body but the most commonly affected areas are the scalp, the extensor (outside) surfaces of the limbs (typically shins and elbows) and the lower back. The plaques tend to be more or less symmetrical and they can crack and bleed.
The major biological abnormalities in psoriasis include:
- Hyperproliferation of the epidermis, which leads to thickening of the epidermis and scaling — affected skin can be up to 16 times thicker than normal skin (hyperproliferation involves more cells entering the growth phase rather than an acceleration of growth)
- Abnormal differentiation of keratinocytes (cells that make up most of the epidermis) — the cells do not mature in the same way as normal keratinocytes (when the skin in psoriatic plaques is examined microscopically, the granular layer is missing, the stratum corneum is thickened and many of the cells in the stratum corneum still contain nuclei)
- Infiltration of the dermis and epidermis with activated T-lymphocytes and neutrophils
- Stimulation of the cutaneous vasculature, leading to new blood vessel formation in the psoriatic plaques
Cell-mediated immune mechanisms appear to drive these processes and a growing understanding of this area has led to studies of a large number of biological agents as treatments.
Chronic plaque psoriasis can also affect the flexures and intertriginous areas (eg, axillae, groin, perineum and under the breasts) where it appears as red, shiny, moist skin with no scaling. In some countries flexural psoriasis is described as “inverse psoriasis”. A significant proportion of patients find their psoriasis lesions itchy.
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Citation: The Pharmaceutical Journal URI: 10997316
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