Psoriasis is a chronic, recurring disease that causes one or more raised, red patches that have silvery scales and a distinct border between the patch and normal skin.
The patches of psoriasis occur because of an abnormally high rate of growth of skin cells. The reason for the rapid cell growth is unknown, but a problem with the immune system is thought to play a role. The disorder often runs in families. Psoriasis is common and affects about 1 to 5% of the population worldwide. Light-skinned people are at greater risk, whereas blacks are less likely to get the disease.
Psoriasis begins most often in people aged 10 to 40, although people in all age groups are susceptible.
It usually starts as one or more small patches on the scalp, elbows, knees, back, or buttocks. The first patches may clear up after a few months or remain, sometimes growing together to form larger patches. Some people never have more than one or two small patches, and others have patches covering large areas of the body. Thick patches or patches on the palms of the hands, soles of the feet, or skinfolds of the genitals are more likely to itch or hurt, but many times the person has no symptoms. Although the patches do not cause extreme physical discomfort, they are very obvious and often embarrassing to the person. The psychologic distress caused by psoriasis can be severe. Many people with psoriasis may also have deformed, thickened, and pitted nails.
Psoriasis persists throughout life but may come and go. Symptoms are often diminished during the summer when the skin is exposed to bright sunlight. Some people may go for years between occurrences. Psoriasis may flare up for no apparent reason or as a result of a variety of circumstances. Flare-ups often result from conditions that irritate the skin, such as minor injuries and severe sunburn. Sometimes flare-ups follow infections, such as colds and strep throat. Flare-ups are more common in the winter and after stressful situations. Many drugs, such as antimalarial drugs, lithium, and beta-blockers, can also cause psoriasis to flare up.
Some uncommon types of psoriasis can have more serious effects. Psoriatic arthritis produces joint pain and swelling (see see Joint Disorders: Psoriatic Arthritis). Erythrodermic psoriasis causes all of the skin on the body to become red and scaly. This form of psoriasis is serious because, like a burn, it keeps the skin from serving as a protective barrier against injury and infection. In another uncommon form of psoriasis, pustular psoriasis, large and small pus-filled blisters (pustules) form on the palms of the hands and soles of the feet. Sometimes, these pustules are scattered on the body.
Many drugs are available to treat psoriasis. Most often, a combination of drugs is used, depending on the severity and extent of the person's symptoms.
Topical drugs (drugs applied to the skin) are used most commonly. Nearly everyone with psoriasis benefits from skin moisturizers (emollients). Other topical agents include corticosteroids, often used together with calcipotriene, a vitamin D derivative, or coal tar or pine tar. Tazarotene or anthralin may also be used. Very thick patches can be thinned with ointments containing salicylic acid, which make the other drugs more effective. Many of these drugs are irritating to the skin, and doctors must find which ones work best for each person.
Phototherapy (exposure to ultraviolet light) also can help clear up psoriasis for several months at a time. Phototherapy is often used in combination with various topical drugs, particularly when large areas of skin are involved. Traditionally, treatment has been with phototherapy combined with the use of psoralens (drugs that make the skin more sensitive to the effects of ultraviolet light). This treatment is called PUVA (psoralens plus ultraviolet A). Some doctors are now using narrow-band ultraviolet B (UVB) treatments, which are equally effective but avoid the need to use psoralens and the side effects they cause, such as extreme sensitivity to sunshine.
For serious forms of psoriasis and psoriatic arthritis, drugs taken by mouth are used. These drugs include cyclosporine, methotrexate, and acitretin. Cyclosporine is an immunosuppressant drug that may cause high blood pressure and damage the kidneys. Methotrexate interferes with the growth and multiplication of skin cells. Doctors use methotrexate to treat people whose psoriasis does not respond to other forms of therapy. Liver damage and impaired immunity are possible side effects. Acitretin is particularly effective in treating pustular psoriasis but often raises fat (lipid) levels in the blood and might cause problems with the liver and bones. It can also cause birth defects and should not be taken by a woman who might become pregnant.
Last full review/revision December 2006 by Peter C. Schalock, MD