What Is Psoriasis?

Psoriasis has been recognized for centuries, possibly as early as 900 B.C. However, the first medically accurate description of this condition was made in 1808 by an English dermatologist named Robert Wilan. Today, Mosby's Medical Dictionary gives us the modern definition: "a common, chronic skin disorder characterized by circumscribed red patches covered by thick, dry, silvery, adherent scales that are the result of excessive development of epithelial (skin) cells."

Put simply, psoriasis is caused by too many skin cells developing at once. This results in patches of reddened skin with silvery scales on the surface.

The most common places for psoriasis to appear first are the knees, elbows, lower back, and scalp. Sometimes, however, it may initially appear, or evolve from a previous form, as:

• one or a few solitary patches that come and go

• widespread guttate (drop-like) lesions that seem to suddenly appear

• erythrodermic psoriasis, a general redness all over the body, often with scaling

• pustules — pus-filled lesions — on the palms of the hands and soles of the feet

• lakes of pus, with definite physical symptoms (This form is sometimes fatal.)

• psoriasis-linked arthritis, commonly of the lower back or of the hand and foot joints

• the Koebner phenomenon, in which lesions appear in places where the skin has been injured

Whatever form psoriasis takes, usually the skin erupts symmetrically — that is, lesions appear in similar places on each side of the body. When symptoms do appear, some people experience severe itching, while others have none at all.

Who Gets Psoriasis?

It is estimated that 2 percent of the world population has psoriasis, although this disease is relatively uncommon in parts of Asia and Africa. In the United States, psoriasis affects approximately 2.5 to 7 million people. Of these, more than 1 million have moderate to severe forms of psoriasis.

The condition affects people of all ages, from newborns to the elderly. Usually it starts in early and middle adulthood, although 10 to 15 percent of cases start before age ten. Males and females suffer from psoriasis equally.

How Is a Diagnosis Made?

Unless the psoriasis takes an unusual form, most dermatologists can make a diagnosis easily. When it is difficult to tell at first glance, several clues may indicate its presence. These include:

• family history of psoriasis

• fingernails/toenails that are pitted, or appear lifted off the nail beds

• a pinkish rash in the crease or cleft of the buttocks

• skin patches with sharp margins

When psoriasis is suspected but not confirmed, a skin biopsy may also prove useful.

How Does the Disease Progress?

Psoriasis pursues an unpredictable course. It may be limited to a few lesions that seem to come and go with stress, or it may be more widespread. Some individuals have only scalp involvement. The most commons form consists of generalized, symmetrical, red, scaly patches involving the scalp, knees and elbows, and the trunk. This form varies in intensity and may persist for life.

Sometimes, acute psoriasis is brought on by an infection like strep throat. In this case it appears in drop-like form. Although treating the bacterial infection may help clear the skin, once this kind of psoriasis appears it tends to be stubborn, and other treatments are often necessary.

Rarely, generalized redness occurs, or lakes of pus appear. These outbreaks may suddenly occur in people with the more limited lesions, perhaps associated with illness, medication, or even a bad sunburn. Or the disease may be confined to the palms of the hands and/or soles of the feet, with or without pustules. In each of these cases, targeted and intensive therapy may help, but relapses are frequent and a maintenance treatment program is usually required.

On rare occasions, psoriasis clears spontaneously, not to return for many years. Until a cure is found, however, most will need to continue some form of therapy for the rest of their lives.

What Aggravates the Disease?

In a susceptible individual, many diverse factors can bring on or aggravate psoriasis. These include:

• emotional stress

• physical injury

• allergies

• infections, particularly strep throat and HIV

• a toxic reaction to ultraviolet light (UVL)

In addition, some drugs have been shown to play a role. Medications like lithium, corticosteroids, beta-blockers, antimalarials, and nonsteroidal anti-inflammatory drugs are all possible triggers. Excessive consumption of alcohol, too, may not only worsen psoriasis but also increase the risk of mortality in moderate to severe cases.

Finally, pregnancy has been associated with psoriasis as well, but the news here is mixed. Of those with psoriasis, 50 percent improve with pregnancy, but 25 percent get worse and 25 percent are unchanged.

When Psoriasis Causes Arthritis

Generally, psoriasis only affects the skin. However, about 10 percent of people with psoriasis develop psoriatic arthritis. In this condition, psoriasis usually precedes the arthritis. Inflammation may worsen as the psoriasis intensifies. The reverse is true as well; clearing of the skin can partially or completely relieve the arthritis symptoms. This is particularly true after a Goeckerman regimen treatment (described in chapter 6) where multiple factors, rest, tar and ultraviolet light may play a role. How does the doctor decide you may have psoriatic arthritis?

• the blood factor that would indicate rheumatoid arthritis tests negative

• it affects the finger and toe joints nearest the nails

• pain and stiffness is present in the lower back

• the nails appear pitted and separated from the nail beds

• x-rays will show inflammation

Psoriatic arthritis may first affect a joint that suffered a prior injury. Rarely a severe and destructive form of the disease occurs, bringing with it deformities and disability.

Generally, managing severe psoriatic arthritis with both a dermatologist and a rheumatologist is recommended. Treatment for resistant cases of psoriatic arthritis involves the use of several of the systemic drugs discussed in chapter 7.

What Is the Underlying Cause of Psoriasis?

The exact cause of psoriasis is still not completely known, although there have been many advances in our understanding during the past decade.

For a long time, psoriasis was considered a genetically transmitted disease. Therefore, patients were frequently asked to give a family history of the condition. Indeed,...