Psoriasis is a common skin disorder, affecting approximately 2% of the world’s population. Skin cells on the affected areas of sufferers multiply up to 10 times faster than normal; as they pile up on the surface, they cause raised, silver-scaled patches on a red base. The reason for the rapid cell growth is unknown, but outbreaks are triggered by the immune system. Psoriasis can also affect the nails of sufferers, as well as their joints, causing arthritis.
Psoriasis occurs in different forms
- Plaquepsoriasis is the most common form. Thick patches of psoriasis involve the scalp, elbows, lower back and knees in particular.
- In guttate psoriasis, small drop-like, scaly areas appear on the torso, limbs and scalp. Guttate psoriasis is often triggered by infections like tonsillitis.
- In pustular psoriasis, large and small blisters of non-infectious pus (pustules) form on the palms of the hands and soles of the feet, and sometimes over the entire body.
- Inflexural or inverse psoriasis the skin folds like those in the groin, navel, armpits and under the breasts are involved.
- Very rarely, psoriasis covers the entire body and produces exfoliative erythrodermic psoriasis, where the entire skin becomes inflamed. This form of psoriasis is serious because, like a burn, it keeps the skin from serving as a protective barrier against injury and infection. The patient loses heat and can go into cardiac failure, as it can cause a "high output" state. These patients may require hospitalisation.
- About 7% of people with psoriasis also have joint inflammation that produces symptoms of arthritis. This condition is called psoriatic arthritis.
Recent research indicates that psoriasis is a disorder of the immune system. A type of white blood cell, called a T cell, helps protect the body against infection and disease. It seems that abnormalities in the so-called T helper cells and the way that they interact with skin cells are associated with psoriasis. It is what precipitates the change that is unknown.
Although not contagious, psoriasis tends to run in families. It is undoubtedly a complex genetic disease. People from European descent are particularly susceptible, especially those with a blood relative who suffers from the disorder.
Age of onset is either early (16-22years) or late (57-60 years), and men and women are equally affected.
An episode of psoriasis may result from a number of factors. Emotional stress is one – many patients suffering a flare-up, report a recent emotional stressor, such as a new job or the death of a loved one. Severe sunburn, obesity and certain drugs can aggravate psoriasis. Commonly implicated drugs include the anti-malaria medication chloroquine, lithium, beta-blockers like propranolol and metoprolol, medication taken to treat high blood pressure like ACE-inhibitors, anti-inflammatory drugs and almost any medicated ointment or cream. Streptococcal infections (especially in children), and injured skin (bruises and scratches) can also stimulate the formation of new plaques. Alcohol consumption and smoking clearly make psoriasis worse.
Psoriasis usually starts as one or more small psoriatic plaques – dark-pink, raised patches of skin with overlying silvery flaky scales – usually on the scalp, knees, elbows, back and buttocks. Sometimes the eyebrows, armpits, navel and groin may also be affected. Usually, psoriasis produces only flaking. Even itching is uncommon. On the scalp, flaking may be mistaken for severe dandruff, but the patchy nature of psoriasis, with flaking areas interspersed among completely normal ones, distinguishes the disease from dandruff. Although the first plaques may clear up by themselves, others may soon follow. Some plaques may remain thumbnail-sized, but in severe cases, psoriasis may spread to cover large areas of the body.
When flaking areas heal, the skin may look completely normal and hair growth is unchanged. However, healing psoriasis may leave behind skin changes, particularly pigment changes. Most people with limited psoriasis suffer few problems beyond the flaking, although the skin’s appearance may be embarrassing.
Psoriasis can also involve fingernails and toenails, causing pitting, discolouring and thickening, and sometimes even separating them from underlying tissue.
Patients may also suffer from arthritis.
When to see a doctor
- If you suspect that you have psoriasis, you should see your doctor for prescription of appropriate treatment, and to be screened for arthritis.
- If you have psoriasis that flares up or is not responding to treatment.
- If you have psoriasis and develop symptoms of arthritis.
Psoriasis may be misdiagnosed at first because many other disorders can produce similar plaques and flaking. As psoriasis develops, the characteristic scaling pattern is usually easy for doctors to recognise, so diagnostic tests usually aren’t needed. However, to confirm a diagnosis, a doctor may perform a skin biopsy (removal of a skin specimen and examination under a microscope). This is not usually necessary.
Although psoriasis may be stressful and embarrassing, most outbreaks are relatively benign – early treatment of the plaques will help prevent symptoms becoming more severe, and plaques generally disappear within weeks.
Psoriasis is treated according to the severity of the disease and its responsiveness to initial treatments, including:
- Topical treatment
- Excimer laser
- Systemic treatment
The first stage of treatment is topical (medicines are applied to the skin). When a person has only a few small plaques, psoriasis generally responds quickly.
- Applying an emollient once or twice a day helps your skin retain moisture.
- Some doctors recommend salicylic acid ointment, which smoothes the skin by promoting the shedding of psoriatic scales.
- Ointments containing corticosteroids are effective, and can be made more effective if the area is wrapped in cellophane after applying them (only do this if advised to by your doctor). However, because they can have harmful side effects, you should be careful not to overuse them. This may thin the skin and lose its efficacy.
- Coal-tar ointments and shampoos can alleviate symptoms, but many psoriasis patients seem vulnerable to the side effects – in particular folliculitis, a pimple-like rash affecting the hair follicles.
- Calcipotriol, is a synthetic form of Vitamin D3 (this is not the same as Vitamin D supplements). It controls the excessive production of skin cells, and can help those who can’t tolerate some of the other creams. It works best in conjunction with phototherapy.
- Anthralin (Dithranol) therapy is usually reserved for severe forms of psoriasis. If not properly applied, anthralin can irritate healthy skin and leave stains that can last several weeks. It is therefore not commonly used anymore.
- Tazarotene (a new topical Vitamin A derivative or retinoid), is very useful for plaque and scalp psoriasis. It is applied at night. It may be an irritant and the concurrent use of emollients is recommended.
- Tacrolimus can be used, especially for psoriasis of the face and skin folds.
Topical therapies are often used in combination with each other, or other treatment modalities.
Exposure to ultraviolet light, for example during the summer months, may help exposed regions of affected skin clear up spontaneously. Sunbathing can help to clear up the plaques on larger areas of the body (although this is not recommended due to the risk of developing sun-related skin cancers).
For persistent, difficult-to-treat cases of psoriasis, ultraviolet (UV) light therapy may be prescribed; and is often extremely successful.
- UVB phototherapy is used to treat widespread psoriasis and lesions that resist topical treatment. A light panel or light box is used, either at the doctor’s surgery or at home. Sometimes it is combined with topical treatments.
- PUVA treatment (UVA phototherapy with application or ingestion of substances called psoralens) can be used. Psoralen makes the skin extra sensitive to the effects of ultraviolet light.
There is also a risk of UV-related skin cancers developing after treatment with UV light. It seems that PUVA presents a higher risk.
This modality can be used to treat individual plaques of psoriasis. It can be very expensive.
For more severe forms of psoriasis, a doctor may prescribe internal medications. This is not a decision to be undertaken lightly, as most of these drugs can have severe side effects and require regular blood tests and monitoring.
- Methotrexate: Used to treat some forms of cancer, this drug interferes with the growth and multiplication of skin cells and suppresses the immune system. It can be effective in extreme cases but may cause liver damage or decrease the production of oxygen-carrying red cells, infection-fighting white blood cells and clot-enhancing platelets.
- Acitretin: This is a derivative of vitamin A. It has many side effects, the most concerning of which is that it causes birth defects if taken during pregnancy. In fact, pregnancy should be avoided for at least 2 years after completing treatment with this drug.
- Ciclosporin: This is a drug used to suppress the immune system in patients who have had kidney transplants. It has many side effects, and interacts with many other drugs.
These drugs are a relatively new and exciting development in the treatment of psoriasis. They represent more targeted therapy than the traditional systemic medications. This group includes adalimumab, etanercept, infliximab and usteokinumab. Some result in an increased risk of developing infections. As these are relatively new drugs, we cannot be certain of their long-term effects.
People with psoriasis should try to avoid triggers like alcohol, smoking and stress. Patients with psoriasis are also thought to be more prone to suffering from conditions like strokes and heart attacks, so control of risk factors like blood pressure, diabetes and cholesterol is especially important.
Previously reviewed by Dr Leonore R.J. van Rensburg, MBChB (UCT), M. Med. Dermatology (US)
Updated by Dr B. Tod, MBBCh (Wits), Dermatology registrar, October 2011