Psoriasis is yet another common skin disease with no known cause, although the current theory is that it is an autoimmune disease, a condition in which the body’s immune system attacks one of the normal tissues in the body. It is usually chronic, with spontaneous cycles of improvement and worsening. Treatments — and there are now many — may bring about improvement and remission, but a cure has yet to be found.
About 1.5 percent of the U. S. population has psoriasis. It is rare in Africans and uncommon in African Americans. It is also rare in Native Americans. The condition is, at least partly, genetically based. About a third of the close relatives of someone with psoriasis will also have the disease, and in identical twins, about 70 percent will both have the disease if one of them has it. It appears to involve an immune stimulation, which leads to an overgrowth of skin cells that fail to mature completely. The disease is not infectious or sexually transmitted. It cannot be passed between husbands and wives.
Psoriasis can appear at any age, but becomes less common in older people. It tends to appear at a later age in men than in women. The younger someone is when it appears, the more severe the condition usually proves to be.
The typical lesion of psoriasis is a red, slightly raised plaque with fine silvery scales on it which can be flaked off. People with extensive plaques, especially on the scalp, can have an enormous amount of flaking. The plaques are found most commonly on the elbows, knees, scalp, and lower back, but there are many variations, such as plaques around the buttocks, anus, and genitalia or involving the soles of the feet and palms of the hands. Changes commonly occur in the fingernails and toenails, most commonly ridging and pitting.
With the exception of a form of arthritis called psoriatic arthritis, which resembles rheumatoid arthritis, psoriasis is not associated with any serious or fatal condition. Many sufferers live to a ripe old age, battling their psoriasis every year of their lives.
Some infections, including strep sore throat and HIV, can worsen the psoriasis in someone who already has it. Many commonly used drugs, including beta blockers, lithium, anti-malarials, and indomethicin (Indocin), may also cause flare-ups.
People with few small plaques often need no treatment or can use a steroid, cortisone-type cream. These work better if applied under a so-called occlusive dressing. Some come in a tape which carries the drug and provides the occlusion, or plastic wrap can simply be taped over the cream.
Sunlight is very effective in keeping the plaques under control, and many people with psoriasis maintain a year-round tan for this reason. Modern variations of this include the PUVA treatment, in which a sensitizing agent is taken by mouth and then the person sits in a tanning booth exposed to UVA. These treatments have been shown to increase the risk of skin cancer and should only be used under the close supervision of an expert. The anti-cancer drugs, methotrexate and hydroxyurea, and the immunosuppressive drug cyclosporine have also been shown to improve the condition. These drugs should only be administered by experts to people with severe psoriasis.