Psoriasis: Wayward White Blood Cells, Remission and Reactivatio

by Food and Drug Administration (FDA)

It's not easy living in Leah Bird's skin. "The worst thing is when people just stare," says Bird. "I almost like it better if someone comes up to me and asks me what it is."

Then she'll tell them, "I have psoriasis. It's not contagious."

Bird, 51, of suburban Boston, has had flare-ups of this chronic skin disease since she was a teen-ager. The dry, red, scaly patches of skin that characterize psoriasis have covered as much as 85 percent of her body, she says. "It alarms people. It looks very scary to people who don't know what it is."

But psoriasis is more than cosmetic. "This disease is common, chronic, and costly, both in monetary terms and in quality of life," says Jonathan Wilkin, M.D., director of the Food and Drug Administration's Division of Dermatologic and Dental Drug Products.

More than 5 million Americans have psoriasis, and they spend between $1.6 billion and $3.2 billion each year to treat the disease, according to the National Psoriasis Foundation (NPF). Between 150,000 and 260,000 new cases are diagnosed each year, including 20,000 in children younger than 10.

"Psoriasis can be painful and can be profoundly disruptive to a person's life," says Jill Lindstrom, M.D., an FDA dermatologist. "People who don't have it don't understand how burdensome the disease can be. There is constant shedding of scales. There can be functional impairment, itching, and pain." And health complications, such as arthritis, accompany some cases.

There is no cure for psoriasis, but a broad range of treatments is available to reduce the symptoms, clear up the skin, and send the disease into remission. FDA-approved treatments range from creams rubbed into the skin, to lasers that aim ultraviolet rays at the skin, to the newest treatments — injectable drugs made from living cells.

What is Psoriasis?

Psoriasis is an inflammatory skin disease in which skin cells replicate at an extremely rapid rate. New skin cells are produced about eight times faster than normal — over several days instead of a month — but the rate at which old cells slough off is unchanged. This causes cells to build up on the skin's surface, forming thick patches, or plaques, of red sores (lesions) covered with flaky, silvery-white dead skin cells (scales).

Rarely life-threatening, at its mildest, psoriasis can be itchy and sore. At its worst, it's painful, disfiguring, and debilitating. About two-thirds of the people with psoriasis have a mild form of the disease, says the NPF. About one-third have moderate or severe psoriasis. Psoriasis can affect people at any age, but it most often strikes those between the ages of 15 and 35.

There are five forms of psoriasis. Plaque psoriasis is the most common — affecting 4 out of 5 people who have psoriasis, says the NPF. Plaque psoriasis may start with small red bumps and progress to larger lesions.

The plaques of psoriasis occur most frequently on the elbows, knees, other parts of the legs, scalp, back, face, palms, and soles of the feet. Psoriasis can also affect the fingernails and toenails, causing pitting, discoloration, or tissue buildup around the nails. According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, about 15 percent of people with psoriasis also get psoriatic arthritis, which can be progressively disabling if untreated.

Wayward White Blood Cells

Scientists believe that certain white blood cells called T lymphocytes (T cells) play an important role in psoriasis. "And the disease has a genetic component," says Lindstrom. In about one-third of psoriasis cases, there is a family history of the disease.

T cells circulate throughout the body, orchestrating the immune system's response to foreign invaders like bacteria or viruses. In people with psoriasis, the defective T cells are overactive and migrate to the skin as if to heal a wound or ward off an infection. This process leads to the rapid growth of skin cells, triggering inflammation and the development of lesions.

Both the environment and genetics may play a role in the development of psoriasis. "In genetically predisposed children, psoriasis can be triggered by a strep or other infection," says Lindstrom. That's what happened to author John Updike. After an attack of measles at the age of 6, Updike developed psoriasis "in all its flaming scabbiness from head to toe," as he later described it in his memoir, Self-Consciousness.

Remission and Reactivation

While the disease never goes away, the symptoms of psoriasis subside for a while (remission) and then return (flare-up, or reactivation). Remission can last for years in some people; in others, flare-ups occur every few weeks. Certain triggers, such as stress and seasonal changes, can reactivate psoriasis. "Certain drugs may also exacerbate it," says Lindstrom, including lithium, prescribed for bipolar disorder (also called manic-depressive illness), beta-blockers used to treat high blood pressure, and antimalarial drugs.

About the Author

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