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.

• A problem with the immune system may play a role, and some people are genetically predisposed to psoriasis.
• Characteristic scales can appear anywhere on the body in large or small patches, particularly the elbows, knees, and scalp.
• This disease is treated with a combination of exposure to ultraviolet light (phototherapy), drugs applied to the skin, and drugs taken by mouth or given by injection.

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 16 to 22 years and aged 57 to 60 years. However, people in all age groups and races are susceptible.

Red Patch in Psoriasis

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, and certain genes are associated with psoriasis.

Symptoms

Psoriasis usually starts as one or more small patches on the scalp, elbows, knees, back, or buttocks. The eyebrows, underarms, navel, the skin around the anus, and the cleft where the buttocks meet the lower back may also be affected. Many people with psoriasis may also have deformed, thickened, and pitted nails. 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.

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 occur after infections, such as colds and strep throat. Flare-ups are more common in the winter, after drinking alcohol, and after stressful situations. Many drugs, such as antimalarial drugs, lithium, angiotensin-converting enzyme (ACE) inhibitors, terbinafine, interferon-alpha, and beta-blockers, can also cause psoriasis to flare up. Flare-ups are also more common among people who are obese, infected with the human immunodeficiency virus (HIV), or smoke tobacco.

Some uncommon types of psoriasis can have more serious effects. Psoriatic arthritis causes joint pain and swelling (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.

Diagnosis

Doctors base the diagnosis on how the scales and plaques look and where they appear on the body. Rarely, doctors take a sample of skin tissue and examine it under a microscope to rule out other disorders (such as skin cancer).

Treatment

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: 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 (also called calcipotriol), which is a form of vitamin D, or coal tar. Tacrolimus and pimecrolimus are used to treat psoriasis that appears on delicate skin (such as on the face or groin or in skinfolds). 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: 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 (psoralen plus ultraviolet A). Many doctors are now using narrowband 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. Doctors can also treat specific patches of the skin directly by using a laser that focuses ultraviolet light.

Systemic Drugs: For serious forms of psoriasis and psoriatic arthritis, drugs taken by mouth or given by injection are used. These drugs include cyclosporine, methotrexate, and acitretin. Cyclosporine is a drug that suppresses the immune system (immunosuppressant) and may cause high blood pressure and damage the kidneys. Methotrexate decreases inflammation in the body and interferes with the growth and multiplication of skin cells. Doctors use methotrexate to treat people whose psoriasis is severe or does not respond to less harmful 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 as well as reversible hair loss. It causes severe birth defects and should not be taken by women who are able to become pregnant. Women should wait at least 3 years after their last dose of acitretin before attempting pregnancy.

People may also be given injections of etanercept, adalimumab, infliximab, alefacept, or ustekinumab. These drugs inhibit certain chemicals involved in the immune system and are called biologic agents. They tend to be the most effective drugs for severe psoriasis, but long-term safety is not clear.

Phototherapy: Using Ultraviolet Light to Treat Skin Disorders
For many years, people have known that exposure to sunlight is helpful for certain skin disorders. Doctors now know that one component of sunlight―ultraviolet (UV) light―is responsible for this effect. UV light has many different effects on skin cells, including altering the amounts and kinds of chemicals they make and causing the death of certain cells that can be involved in skin diseases. The use of UV light to treat disease is called phototherapy. Psoriasis and atopic dermatitis are the disorders most commonly treated with phototherapy. Because natural sunlight exposure varies in intensity and is not practical for a large part of the year in certain climates, phototherapy is nearly always performed with artificial UV light. Treatments are given in a doctor's office or in a specialized treatment center. UV light, which is invisible to the human eye, is classified as A, B, or C, depending on its wavelength. Ultraviolet A (UVA) penetrates deeper into the skin than ultraviolet B (UVB). UVA or UVB is chosen based on the type and severity of the person's disorder. Ultraviolet C is not used in phototherapy. Some lights produce only certain specific wavelengths of UVA or UVB (narrowband therapy), which are used to treat specific disorders. Narrowband therapy helps limit the sunburning associated with phototherapy. Phototherapy is sometimes combined with the use of a psoralen. Psoralens are drugs that may be taken by mouth before treatment with UV light. Psoralens sensitize the skin to the effects of UV light, allowing shorter, less intense exposure. The combination of a psoralen plus UVA is known as PUVA therapy. Side effects of phototherapy include pain and reddening similar to sunburn with prolonged exposure to UV light. UV light exposure also increases the long-term risk of skin cancer, although the risk is small for brief courses of treatment. Psoralens often cause nausea. In addition, because psoralens enter the lens of the eye, UV-resistant sunglasses must be worn for at least 12 hours after undergoing PUVA therapy.

Last full review/revision November 2012 by Peter C. Schalock, MD