Psoriasis is a skin disease that occurs when skin cells regenerate at an exceptionally fast rate. Normally, skin cells regenerate about every 28 days. In areas affected by psoriasis, inflammation causes the skin cells to regenerate every two to four days. Thus, new cells form at a faster pace than old ones can be shed, causing an accumulation of skin cells in the form of thick, red patches with white or silver scales. The degree of symptoms and amount of skin area involved vary from person to person. Patients often go through periods of remission and exacerbation of symptoms.
There are several forms of psoriasis. The most common is plaque psoriasis. Patients develop sharply defined scaly plaques, most commonly on the elbows, knees, scalp, and groin. Many patients also have nail involvement, characterized by a yellow discoloration, thickening, pitting, and lifting of the nail plate. In guttate psoriasis, patients develop multiple patches of red, scaly skin on the extremities. This form most commonly occurs after a bout of streptococcal pharyngitis. In erythrodermic psoriasis, the entire skin surface is affected. As a result, the skin loses some of its natural protective function, causing fluid loss, electrolyte imbalances, problems with body temperature regulation, or infection. Pustular psoriasis is characterized by the development of pus-filled lesions. In some patients the lesions are confined to the soles and palms of the hands. In others, the condition can affect the entire body and may be life threatening.
Psoriasis is the second most common skin condition in the U.S. According to the American Academy of Dermatology, it affects 6-7 million Americans. About 150,000 to 260,000 new cases are diagnosed every year. Symptoms of psoriasis appear to be triggered by inflammation, such as after a cut, scratch, sunburn, infection, or sore throat. Symptoms are often worse in the winter, when the weather is drier, and people have less exposure to sunlight. About 10 to 30 percent of people with psoriasis develop a form of arthritis, called psoriatic arthritis. The disease most commonly affects the small joints of the hands and feet.
There is no cure for psoriasis. The type of treatment used depends upon the degree and severity of symptoms. Mild cases can often be treated with topical preparations, such as corticosteroids, coal tar, anthralin, retinoids, and vitamin D creams. Exposure to sunlight seems to improve symptoms for many patients and doctors may recommend light therapy. When symptoms are more widespread, or don't respond to other treatments, PUVA (photochemotherapy) may be used. Patients are given a drug, called Psoralen, and then exposed to ultraviolet A light. The treatment suppresses the rate of skin cell turnover. However, PUVA treatment is associated with an increased risk for skin aging and skin cancer. Severe psoriasis may also be treated with oral medications, such as methotrexate, retinoids, or cyclosporine.
Some doctors are using another treatment for severe psoriasis, called Remicade® (infliximab, Centocor, Inc.). Remicade is currently used to manage other inflammatory diseases, such as Crohn's disease and rheumatoid arthritis. Doctors who gave the drug to treat joint problems in psoriatic arthritis noticed patients' skin symptoms also went away or improved. The effects were only temporary. However, researchers noted a single infusion could lead to the disappearance of most treatment-resistant plaques for an average of three to four months. Remicade is given in an intravenous infusion over about a two- to three-hour period. Currently, doctors are trying to determine the lowest effective dose to reduce the risk of side effects, especially an increased susceptibility to infection. After the initial dose, patients will get a series of infusions – one at two weeks, a third about a month later, and then once every two to four months.
For general information on psoriasis:
American Academy of Dermatology, www.aad.org
National Institute of Arthritis and Musculoskeletal and Skin Diseases, www.niams.nih.gov
National Psoriasis Foundation, 6600 SW 92nd Ave., Suite 300, Portland, OR 97223-7195, www.psoriasis.org