Information About Psoriasis

Psoriasis is a chronic skin disease in which itchy, scaly pink patches, usually covered with whitish scales, form on the elbows, knees, scalp and other parts of the body. It is one of the most common skin diseases in Britain, affecting about 2% of the population, but its cause is not known. There does seem to be some hereditary link in psoriasis, but often symptoms may not appear until adulthood. The severity of the condition can vary enormously from person to person and time to time. While psychological stress may cause an exacerbation of psoriasis, the only significant event that precipitates the disease is a preceding streptococcal infection.

When someone is suffering from psoriasis the skin cells in certain parts of the body replicate much faster than normal. Skin cells originate in the deep layers of the skin and usually take about 28 days to come to the surface where they are sloughed off. However, in areas of skin affected by psoriasis this process takes only 8 days or less the new cells accumulate so quickly that they never have a chance to mature.

Clinical Patterns

Although there are various clinical patterns psoriasis tends to be a symmetrical eruption but unilateral lesions do occur too.

Forms Of Psoriasis

Plaque psoriasis - this is the most common form of psoriasis. Characteristically the plaques occur on the extensor surfaces of the knees and elbows. The lesions tend to be discoid or coin shaped. The size may vary from one to several centimetres. Other common sites involved are the scalp, particularly behind the ears, and the sacral region. The face is an uncommon site to be involved.

Guttate Psoriasis

Here the lesions appear suddenly usually over the upper trunk although the limbs, face and scalp may be affected. The lesions are small and tend to vary from one to ten millimetres. Guttate psoriasis is most commonly seen in children and young adults and typically follows a streptococcal upper respiratory tract infection.

Erythrodermic Psoriasis

This term denotes 100% involvement of the skins surface. It may occur in disease other than psoriasis, notably eczema and skin lymphomas. In erythrodermic psoriasis the skin is redder (as the name implies) and the thick, white scaling is not usually present. The scales appear to be shed more rapidly instead of being heaped up and retained, although the surface of the skin is scaly. This form is very rare, and is usually found in young and middle aged adults.

Pustular psoriasis

This form is associated with pustules as part of the morphology. There are two distinct forms of pustular psoriasis, one generalised on different parts of the body and the other localised either on the hands or feet.

Flexural or Intertriginous psoriasis

This form involving the perianal skin and genitalia is a common presentation in children.

Precipitating Factors

There are a number of known precipitating factors in psoriasis. However, not all will precipitate or exacerbate the disease in different individuals. It appears that there are modifying factors in different patients which govern whether lesions will be produced in a given instance.

Infections

Streptococcal infection is probably the most definite known trigger. The pattern of disease produced by streptococcal infections is guttate psoriasis. Patients with established chronic plaque psoriasis may develop an acute flare-up, which is similar to the guttate type eruption, on the trunk and limbs.

Hormonal Factors

Female sex hormones appear to be able to influence psoriasis. An increased incidence of onset has been reported at both puberty and the menopause. Pregnancy usually has a beneficial effect (50% of patients in one trial series reported improvement during pregnancy).

Psychogenic factors

There is no doubt that in a proportion of patients psychogenic stress does appear to precipitate or exacerbate psoriasis. Although it is difficult to measure stress and how different individuals react to it, it is well established that stress does influence the endocrine system, which in turn affects immunological responses, as they occur in psoriasis.

Drugs

Certain drugs in a small proportion of patients affect the condition but this should not be considered as a contraindication to their use. The systemic corticosteroids group of drugs has a beneficial effect on psoriasis, but when the dose is reduced, or the drug stopped, there may be a rebound exacerbation of the disease. For this reason systemic steroids should not be used in the treatment of psoriasis.