Psoriasis is a common, chronic, relapsing inflammatory condition that primarily affects the skin, but which may also involve the finger nails, toe nails and joints.
Worldwide, more than 125 million people live with psoriasis. All ages may be affected, but psoriasis most commonly begins in the teenage and early adult years, before the age of 40.
There is a strong genetic link to psoriasis. It occurs more commonly in people whose parents or siblings are affected. Almost 75% of patients with psoriasis have other members in their family with the condition, and the risk is doubled if a sibling and both parents have psoriasis. The onset of symptoms is often linked to an environmental stressor, such as infection or psychological stress.
The discomfort and unsightly cosmetic appearance of the skin and nails can be a source of acute embarrassment, self-consciousness and frustration.
Types of psoriasis
Plaque psoriasis: This is the most common form (90%), usually occurring over the back of the elbows, front of the knees, on the lower back and around the umbilicus.
Inverse psoriasis: Lesions occur on the joint creases and skin folds and tend not to scale.
Guttate psoriasis: Widely distributed small red, scaly, ‘tear drop’ skin lesions.
Generalised pustular psoriasis: The person is unwell with rapidly progressing tender, sterile pustules and widespread inflammation.
Plaque psoriasis on the front of the knees (Image supplied)
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.
Although there are various forms of the skin condition, the most common form, occurring in 90% of cases, is plaque psoriasis. Skin symptoms of plaque psoriasis include:
- Clearly demarcated patches or ‘plaques’ of thick, red skin, covered with white or silver scales;
- Itching, burning or pain;
- Messy flaking of the scalp;
- Involvement of the finger and toe nails, which may be discoloured and lift from the nail bed.
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.
1. International Federation of Psoriasis Associations (IFPA). World Psoriasis Day. http://www.worldpsoriasisday.com. Accessed 28 September 2015.
2. Telephonic interview with Dr Ayesha Moolla, dermatologist in private practice, Gatesville, Western Cape; 7 July 2015.
3. Laws PM, Young HS. Update of the management of chronic psoriasis: new approaches and emerging treatment options. Clinical Cosmetic and Investigational Dermatology 2010; 3: 25-37.
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