Psoriasis: More Than Skin Deep

Harvard Health Letters

The first accurate medical discussion of psoriasis dates back to 1801, but the disease itself is much older. In fact, its very name is borrowed from an ancient Greek word meaning an itchy or scaly condition. About 7 million Americans are plagued by psoriasis, and many of them have serious complications involving other organs. Although psoriasis is classified as a dermatologic disease, it doesn't start in the skin, and its damage may be more than skin deep.

BENEATH IT ALL

At a basic level, psoriasis is a disorder of the immune system. White blood cells called T-helper lymphocytes become overactive, producing excess amounts of cytokines, such as tumor necrosis factor, interleukin-2, and interferon-gamma. In turn, these chemicals trigger inflammation in the skin and other organs.

In the skin, the inflammation produces three characteristic findings: widened blood vessels, accumulation of white blood cells, and abnormally rapid multiplication of keratinocytes, the main cells in the outer layer of the skin. In healthy skin, keratinocytes take about a month to divide, mature, migrate to the skin surface, and slough off to make way for younger cells. But in psoriasis, the entire process is speeded up to as little as three to five days. The result is thickened, red skin that sheds silvery scales of keratinocytes that have matured before their time.

In contrast with normal skin, people with psoriasis develop characteristic scaly, red patches when new skin cells are produced at a more rapid rate and don't mature normally. Inflammation and the growth of new blood vessels redden the affected areas.

BEHIND IT ALL

Scientists have learned that abnormal activity of the immune system gets the blame for psoriasis, but why does the immune system veer off target?

In about a third of cases, psoriasis runs in families. At least nine genetic abnormalities have already been associated with psoriasis, and more are likely. But environmental factors also play a role; psoriasis has been linked to psychological stress, obesity, smoking, alcohol, strep throat, viral infections, lack of sunlight, and certain medications (antimalaria drugs, lithium, beta blockers, and others).

CLINICAL FEATURES

Psoriasis is a chronic condition that strikes both males and females at any time from childhood to old age. It ranges from mild to severe. In general, the earlier it starts, the more likely it is to involve large areas of skin and to have serious consequences.

Psoriasis comes in many forms. About 90 percent of patients have the plaque type, with sharply demarcated salmon-pink plaques of inflamed skin covered by silvery scales. In most cases, the plaques develop symmetrically on both sides of the body. Plaques are most common on the elbows, knees, and scalp, especially at the hairline. Other common locations include the genitals, the crease between the buttocks, the ear canals, and the belly button.

About half of all patients with psoriasis have nail involvement, and some people have nail psoriasis without skin inflammation. Nail problems range from tiny pits to yellowing of the nail surface and accumulation of debris under the nails. Nail psoriasis is often linked to arthritis.

The second most common form of the disease is called guttate psoriasis. Latin scholars have a head start in understanding this variety, since the name comes from "gutta," meaning "droplet." Patients have numerous small, red, scaly spots scattered on the arms and legs. In children and adolescents, guttate psoriasis can develop abruptly several weeks after a strep throat or viral infection. In that situation, it can resolve on its own in three to four months, but it may also convert to plaque psoriasis.

These common forms of psoriasis may be mild, but can also be very distressing. Itching is troublesome, but the unsightly skin changes can cause even more unhappiness, especially when large areas of skin are involved and scales accumulate on clothing and furniture. And other forms of the disease are even worse. These include erythrodermic psoriasis, which can cause severe inflammation of the entire skin surface, and pustular psoriasis, which can look as if there are innumerable small boils all over the body. Fortunately, these life-threatening forms of psoriasis are rare.

COMPLICATIONS

Psoriasis shows up in the skin and nails, but immune system abnormalities cause the disease, and they can damage internal organs, as well.

Arthritis.

Up to 25 percent of patients with psoriasis develop joint inflammation. In some cases, the arthritis can precede the skin involvement. There is a strong link between nail psoriasis and arthritis, and some arthritis patients have nail disease without any skin inflammation.

Psoriatic arthritis, as it's called, can strike the small joints of the fingers, one or two larger joints elsewhere in the body, or the spine. It is a painful, chronic inflammatory arthritis, but tests for rheumatoid arthritis and other forms of autoimmune arthritis are negative. Some patients improve with nonsteroidal anti-inflammatory drugs, but others require powerful medications to quiet down the immune system.

Cardiovascular disease.

Research has established a link between psoriasis and heart attacks. The risk of cardiovascular complications is highest in patients with severe psoriasis that developed at a relatively young age. The association remains valid even after scientists account for risk factors that are common to both psoriasis and heart disease, such as smoking, obesity, and stress. Psoriasis patients are also at high risk for peripheral artery disease and stroke. Researchers believe that inflammation is the thread that ties psoriasis to atherosclerosis.

Psychosocial disorders.

Like other chronic diseases, psoriasis can cause emotional distress and disrupt social interactions and productivity. Physical discomfort and disfigurement combine to make severe psoriasis a disabling disease.

Other conditions.

Patients with psoriasis have an increased risk of diabetes, high blood pressure, Crohn's disease, and the metabolic syndrome, a dangerous constellation of risk factors involving blood pressure, insulin resistance, obesity, and abnormal blood lipids. Patients who receive aggressive psoriasis therapy may also have a heightened risk of certain cancers.

TREATMENT

People with very mild psoriasis may be able to get help from self-treatment with little more than a skin moisturizer, an antidandruff shampoo, and some sunlight. But most patients require medically supervised therapy. Although no treatment will cure psoriasis, many medications can control the disease.

Topical therapy.

These ointments, gels, and lotions are the mainstay of treatment, especially for mild-to-moderate disease. In the past, coal tar and anthralin were widely recommended; because they stain skin and clothing, they've been replaced by topical treatments that are more convenient and more effective.

Many corticosteroid preparations are available; they vary in potency but all can reduce inflammation and control itching. Corticosteroids act rapidly, but long-term use of strong steroids can produce skin thinning and damage. Newer topical therapies that are proving very effective include two forms of vitamin D, calcipotriene (Dovonex) and calcitriol (Vectical), and the vitamin A relative tazarotene (Tazorac); all are prescription drugs.

Phototherapy.

At one time, it involved two to four weeks of sunbathing or, for those who could afford it, "climatotherapy" with naturally filtered sunlight at the Dead Sea. Now, though, doctors use carefully controlled exposure to ultraviolet (UV) radiation to treat moderate to severe psoriasis. UVB can be administered alone or in combination with tar or other topical agents; some patients can use UVB at home. UVA is usually reserved for extensive psoriasis that has not improved with other treatments. It is used with a photosensitizing drug in the so-called PUVA regimen.

Systemic therapy.

The toughest cases of psoriasis call for the toughest treatments. Options include the oral vitamin A-like drug acitretin, the antimetabolite methotrexate, and the immunosuppressant drug cyclosporine. Biologic agents that target specific steps in the immune system include alefacept, etanercept, and infliximab.

All of these systemic therapies can produce serious side effects, and all require careful monitoring by experienced physicians. Still, systemic therapies offer new hope to patients who are disfigured and disabled by severe psoriasis. It demonstrates how modern science has made inroads against a disease that has plagued man for thousands of years.

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