Psoriasis affects between 1 and 2 percent of the United States population, or about 5.5 million people. Although the disease occurs in all age groups and about equally in men and women, it primarily affects adults. People with psoriasis may suffer discomfort, including pain and itching, restricted motion in their joints, and emotional distress.
In its most typical form, psoriasis results in patches of thick, red skin covered with silvery scales. These patches, which are sometimes referred to as plaques, usually itch and may burn. The skin at the joints may crack. Psoriasis most often occurs on the elbows, knees, scalp, lower back, face, palms, and soles of the feet but it can affect any skin site. The disease may also affect the fingernails, the toenails, and the soft tissues inside the mouth and genitalia. About 15 percent of people with psoriasis have joint inflammation that produces arthritis symptoms. This condition is called psoriatic arthritis.
What Causes Psoriasis?
Recent research indicates that psoriasis is likely a disorder of the immune system. This 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 causes activity by T cells in the skin. These T cells trigger the inflammation and excessive skin cell reproduction seen in people with psoriasis.
In about one-third of the cases, psoriasis is inherited. Researchers are studying large families affected by psoriasis to identify a gene or genes that cause the disease. (Genes govern every bodily function and determine the 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 flareups include changes in climate, infections, stress, and dry skin. Also, certain medicines, most notably beta-blockers, which are used to treat high blood pressure, and lithium or drugs used to treat 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 can look like other skin diseases. A pathologist may assist with diagnosis by examining a small skin sample (biopsy) under a microscope.
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--Small,
drop-like lesions appear on the trunk, limbs, and scalp. Guttate psoriasis
is most often triggered by bacterial infections (for example, Streptococcus).
- Pustular psoriasis--Blisters
of noninfectious pus appear on the skin. Attacks of pustular psoriasis
may be triggered by medications, infections, emotional stress, or exposure
to certain chemicals. Pustular psoriasis may affect either small or
large areas of the body.
- Inverse psoriasis--Large,
dry, smooth, vividly red plaques occur in the folds of the skin near
the genitals, under the breasts, or in the armpits. Inverse psoriasis
is related to increased sensitivity to friction and sweating and may
be painful or itchy.
- 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.
