Psoriasis is a chronic (long-lasting) skin disease characterized by scaling and inflammation. Scaling occurs when cells in the outer layer of skin reproduce faster than normal and pile up on the skin's surface.

Psoriasis affects 1.5 to 2 percent of the United States population, or almost 5 million people. It occurs in all age groups and about equally in men and women. People with psoriasis may suffer discomfort, restricted motion of joints, and emotional distress.

When psoriasis develops, patches of skin thicken, redden, and become covered with silvery scales. These patches are sometimes referred to as plaques. They may itch or burn. The skin at joints may crack. Psoriasis most often occurs on the elbows, knees, scalp, lower back, face, palms, and soles of the feet. The disease also may affect the fingernails, toenails, and the soft tissues inside the mouth and genitalia. About 10 percent of people with psoriasis have joint inflammation that produces symptoms of arthritis. This condition is called psoriatic arthritis.

What Causes Psoriasis?

Recent research indicates that psoriasis may be a disorder of the immune system. The immune system includes a type of white blood cell, called a T cell, that normally helps protect the body against infection and disease. Scientists now think that in psoriasis, an abnormal immune system produces too many T cells in the skin. These T cells trigger the inflammation and excessive skin cell reproduction seen in people with psoriasis.

In some cases, psoriasis is inherited. Researchers are studying large families affected by psoriasis to identify a gene or genes associated with the disease. (Genes govern every body function and determine inherited traits passed from parent to child.)

People with psoriasis may notice that there are times when their skin worsens, then improves. Conditions that may cause flare-ups include changes in climate, infections, stress, and dry skin. Also, certain medicines, such as the nonsteroidal anti-inflammatory drug indomethacin and medicines used to treat high blood pressure or depression, may trigger an outbreak or worsen the disease.

How Is Psoriasis Diagnosed?

Doctors usually diagnose psoriasis after a careful examination of the skin. However, diagnosis may be difficult because psoriasis often looks like other skin diseases. A pathologist may assist with diagnosis by examining a small skin sample under a microscope. 7

There are several forms of psoriasis. The most common form is plaque psoriasis (its scientific name is psoriasis vulgaris). In plaque psoriasis, lesions have a reddened base covered by silvery scales. Other forms of psoriasis include:

• Guttate Psoriasis: Drop-like lesions appear on the trunk, limbs, and scalp. Guttate psoriasis may be triggered by viral respiratory infections or certain bacterial (streptococcal) infections.

• Pustular Psoriasis: Blisters of noninfectious pus appear on the skin. Attacks of pustular psoriasis may be triggered by medications, sunlight, infections, pregnancy, perspiration, emotional stress, or exposure to certain chemicals.

• Inverse Psoriasis: Large, dry, smooth, vividly red plaques occur in the folds of skin near the genitals, under the breasts, or in the armpits. Inverse psoriasis is related to increased sensitivity to friction and sweating.

• Erythrodermic Psoriasis: Widespread reddening and scaling of the skin is often accompanied by itching or pain. Erythrodermic psoriasis may be precipitated by severe sunburn, use of oral steroids (such as cortisone), or a drug-related rash.

What Treatments Are Available for Psoriasis?

Doctors generally treat psoriasis in steps according to the severity of the disease or responsiveness to initial treatments. This is sometimes called the "1-2-3" approach. In step 1, medicines are applied to the skin (topical treatment). Step 2 involves treatments with light (phototherapy). Step 3 involves taking medicines internally, usually by mouth (systemic treatment).

Over time, affected skin tends to resist some treatments. Also, a treatment that works like magic in one person may have little effect in another. Thus, doctors commonly use a trial-and-error approach to find a treatment that works, then switch treatments every 12 to 24 months to reduce resistance and adverse reactions. Selection of treatment depends on the location of lesions, their size, the amount of the skin affected, previous response to treatment, and patients' perceptions about their skin condition and preferences for treatment. In addition, treatment is often tailored to the specific form of the disorder.

Topical TreatmentTreatments applied directly to the skin are sometimes effective in clearing psoriasis. Doctors find that some patients respond well to sunlight, steroid ointments, medicines made from vitamin D₃, coal tar, or anthralin. Other topical measures, such as bath solutions and moisturizers, may be soothing but are seldom strong enough to clear lesions for a sustained length of time and may need to be combined with more potent remedies.

• Sunlight - Daily, regular, short doses of sunlight without burning clears psoriasis in many people with the disease. However, exposure to sunlight is not recommended for those undergoing ultraviolet light treatments or using certain topical treatments, such as coal tar, which make the skin extra sensitive to the sun's effects.

• Corticosteroids - Available in different strengths, corticosteroids (cortisone) are usually applied twice each day. Short-term treatment is often effective. If less than 10 percent of the body's skin is involved, some doctors will begin treatment with a high-potency corticosteroid ointment (for example, Diprolene^*, Temovate, Ultravate, or Psorcon). High-potency steroids may also be used for treatment-resistant plaques, particularly those on the hands or feet. Long-term use or overuse of high-potency steroids can lead to thinning of skin, internal side effects, resistance to the treatment's benefits, and worsening of the psoriasis. Medium-potency corticosteroids may be used on the torso or limbs; low-potency preparations are used on delicate skin areas.
  

• Calcipotriene - This drug is a synthetic form of vitamin D₃. (This is not the same as vitamin D supplements.) Application of calcipotriene ointment (for example, Dovonex) twice daily controls the excessive production of skin cells in psoriasis. Because calcipotriene can irritate the skin, it is not recommended for the face or genitals. After 4 months of treatment, about 60 percent of patients have a good to excellent response to calcipotriene. The safety of using the drug for psoriasis affecting more than 20 percent of the body's skin is unknown; use on widespread areas of skin may raise the amount of calcium in the body to unhealthy levels.
  

• Coal tar - Coal tar may be applied directly to the skin, used in a bath solution, or used as a shampoo for the scalp. It is available in different strengths, but the most potent form may be irritating. Because coal tar makes skin more sensitive to ultraviolet (UV) light, it is sometimes combined with ultraviolet B (UVB) phototherapy. Compared with steroids, coal tar has fewer side effects but is messy and less effective and thus is not popular with many patients. Other drawbacks include its failure to provide long-term help for most patients, its strong odor, and its tendency to stain skin or clothing.

• Anthralin - Doctors sometimes use a 15- to 30-minute application of anthralin ointment, cream, or paste to treat chronic psoriasis lesions. However, this treatment often fails to adequately clear lesions, it irritates the skin, and it stains skin and clothing brown or purple. In addition, anthralin is unsuitable for acute or actively inflamed eruptions.

• Salicylic acid - Used to remove scales, salicylic acid is usually more effective when combined with topical steroids, anthralin, or coal tar.

• Bath solutions - People with psoriasis may find that bathing in water with an oil added, then applying a moisturizer, can soothe the skin. Scales can be removed and itching reduced by soaking 15 minutes in water containing a tar solution, oiled oatmeal, Epsom salts, or Dead Sea salts.

• Moisturizers - When applied regularly over a long period, moisturizers have a cosmetic and soothing effect. Preparations that are thick and greasy usually work best because they lock water into the skin.

PhototherapyUV light from the sun stimulates production of vitamin D by the skin, which slows the overproduction of skin cells that causes scaling. Daily, short, nonburning exposure to sunlight clears or improves psoriasis in some people. Therefore, sunlight may be included among initial treatments for the disease. A more controlled artificial light treatment may be used in mild psoriasis (UVB phototherapy) or in more severe or extensive psoriasis (psoralen and ultraviolet A [PUVA] therapy).

• UVB Phototherapy - Artificial sources of UVB light are similar to sunlight. Some physicians will start with UVB treatments instead of topical agents. UVB phototherapy also is used to treat widespread psoriasis and lesions that resist topical treatment. This type of phototherapy is normally administered in a doctor's office by using a light panel or light box, although with a doctor's guidance, some patients can use UVB light boxes at home. UVB phototherapy also may be combined with other treatments. One combined therapy program, referred to as the Ingram regime, involves a coal tar bath, UVB phototherapy, and application of an anthralin-salicylic acid paste, which is left on the skin for 6 to 24 hours. A similar regime, the Goeckerman treatment, involves application of coal tar ointment and UVB phototherapy.

• PUVA - This treatment combines oral or topical administration of a medicine called psoralen with exposure to ultraviolet A (UVA) light. Psoralen makes the body more sensitive to UVA light. PUVA is normally used when more than 10 percent of the body's skin is affected or when rapid clearing is required because the disease interferes with a person's occupation (for example, when a model's face or a carpenter's hands are affected by psoriasis). Compared with daily UVB treatment, PUVA treatment taken two to three times per week clears psoriasis more consistently but less quickly. However, it is associated with more side effects, including nausea, headache, fatigue, burning, and itching. Long-term treatment is associated with irregular skin pigmentation. Researchers have found that PUVA is effective and relatively safe when combined with some oral medications (retinoids and hydroxyurea) but appears to be associated with skin cancer when combined with other oral medications (for example, methotrexate or cyclosporine). In rare cases, patients who must travel long distances for PUVA treatments may, with a physician's close supervision, be taught to administer this treatment at home.

Systemic Treatment Doctors sometimes prescribe medicines that are taken internally for more severe forms of psoriasis, particularly when more than 10 percent of the body is involved.

• Retinoids - These drugs are derived from vitamin A and include etretinate (Tegison) and isotretinoin (Accutane). Etretinate is most effective against pustular and erythrodermic psoriasis. Isotretinoin is also helpful against pustular psoriasis. Both drugs can cause birth defects and are not recommended for women of childbearing age. At high doses, etretinate can affect liver function. Therefore it is often combined with UVB phototherapy or PUVA so that a lower, less toxic, dose can be taken.

• Methotrexate - This treatment, which can be taken by pill or injection, slows down cell production and suppresses the immune system. Patients taking methotrexate must be closely monitored because this drug can cause liver damage or decrease the production of oxygen-carrying red blood cells, infection-fighting white blood cells, and clot-enhancing platelets. As a precaution, doctors do not prescribe the drug for people with long-term liver disease or anemia. Also, methotrexate should not be used by pregnant women, by women who are planning to get pregnant, or by their male partners.

• Hydroxyurea (Hydrea) - Compared with methotrexate, hydroxyurea is less toxic but also less effective. Hydroxyurea is sometimes combined with PUVA or retinoids. Possible side effects include anemia and a decrease in white blood cells and platelets. Like methotrexate, hydroxyurea must be avoided by pregnant women or those who are planning to get pregnant.

• Antibiotics - Although seldom used in routine treatment, antibiotics may be employed when an infection such as streptococcus has triggered the outbreak of psoriasis, as in certain cases of guttate psoriasis.

What Are Some Promising Areas of Psoriasis Research?

Researchers continue to search for genes that contribute to the inheritance and causes of psoriasis. Scientists are also working to improve our understanding of what happens in the body to trigger this disease. In addition, much research is focused on developing new and better psoriasis treatments. Some of these experimental treatments, such as cyclosporine and agents that are directed at T cells, work by suppressing the immune system.

How Can People Contribute to Psoriasis Research?

The National Psoriasis Tissue Bank, which is supported by the National Psoriasis Foundation, is helping researchers worldwide to study the inherited tendency toward psoriasis by collecting white blood cells from over 250 families affected by the disease. Tissue specimens may also be collected from some patients. There is particular interest in large families in which psoriasis is both common and spans two or more generations. More recently, the tissue bank has begun research involving families that have at least two siblings with psoriasis. A living parent also must be available for examination. People seeking more information or families interested in participating in a study should contact:

National Psoriasis Tissue Bank
Baylor University Medical Center
Suite 656, Wadley Tower
3600 Gaston Avenue
Dallas, TX 75246
214/820-2635
Fax: 214/820-1296

Where Can People Get More Information About Psoriasis?

The National Psoriasis Foundation provides physician referrals and publishes pamphlets and a newsletter that includes information on support groups, research, and new drugs and other treatments. The foundation also promotes community awareness of psoriasis. For information, contact:

National Psoriasis Foundation
6600 S.W. 92nd Avenue
Portland, OR 97223
503/244-7404, or
800/723-9166
World Wide Web address: http://www.psoriasis.org

Acknowledgments

The National Arthritis and Musculoskeletal and Skin Diseases Information Clearinghouse (NAMSIC) is a public service sponsored by the NIAMS that provides health information and information sources. The NIAMS, a part of the National Institutes of Health (NIH), leads the Federal medical research effort in arthritis and musculoskeletal and skin diseases. The NIAMS sponsors research and research training throughout the United States as well as on the NIH campus in Bethesda, MD, and disseminates health and research information. JW 7/96
Updated 1/97
Office of Scientific and Health Communications