What is psoriasis? |

Causes and Symptoms

Psoriasis is a common skin problem that afflicts approximately two of every hundred people, affecting males and females with relatively equal frequency. Although it affects all races, it is most prevalent among northern Europeans. This stubborn, chronic, and as yet incurable disease most commonly appears in one’s teens or twenties, although it can appear in early childhood. While 70 percent of those who develop psoriasis do so by the age of twenty, there is another common danger period in the fifties and sixties, with a large number of patients developing their first symptoms at that time.

There are several different types of psoriasis, making diagnosis difficult. By far the most widespread is the plaque type; because it accounts for 95 percent of all cases, this type is also called common psoriasis. Plaque-type psoriasis gets its name from the appearance of the patches of affected skin. Each patch resembles a plaque or small disk stuck to the body’s surface. These dull, wine-colored patches of abnormal skin are often rounded or oval; they may be very irregular in shape when several nearby patches join together. The surface of each thickened patch is rough and scaly, with the scales ranging in color from red to white to the most typical silvery gray. These psoriatic plaques can be small (the size of coins) or become palm-sized and larger. Whatever their final size, they generally begin as purple or reddened areas the size of a pinhead. The original areas expand in size, usually for a few weeks, until they reach a stable phase and stop expanding. The average size of a plaque in the stable phase is between two and three inches. A patch of stable psoriasis may eventually grow pale, become less scaly, and disappear completely, or it may begin to enlarge for no apparent reason. Even those plaques that have disappeared may be reactivated and reappear in the same place at some later time.

Certain parts of the body seem most prone to psoriatic
lesions, namely the elbows, the knees, the scalp, and the lower back. The patches may appear elsewhere, including the genitals and the buttocks, but the face, hands, and feet are rarely affected. Severe cases may cover the entire chest or back. In a few cases, psoriasis is symmetrical, appearing in the same area on the left and right sides of the body simultaneously. The patches are, however, more likely to develop in a random, scattered manner. Almost 50 percent of patients with psoriasis have lesions on their scalps. When these plaques are very large and widespread, they are difficult to treat and very difficult to hide. Although very uncomfortable, scalp psoriasis does not affect the growth of hair or cause baldness. It can cause a temporary thinning of the hair, but the hair grows normally again once the disease is controlled by medication. About one-third of psoriasis patients have affected fingernails and toenails. The diseased nails show pits or pinpoint indentations, loosening, thickening, and a yellowish discoloration. Surprisingly, in some people the condition remains on the nails alone, never developing elsewhere.

In addition to psoriasis of the nails, there are several rare and unusual types of psoriasis that are quite different from the common or plaque type. These include flexural or inverse, guttate, pustular, and erythrodermic psoriasis. Flexural psoriasis appears in folds and creases on the body and is often found on people who are particularly overweight and who are in their mid-forties or older. The patches tend to be very moist rather than scaly and are particularly sore and uncomfortable. Guttable psoriasis consists of an enormous number of highly scattered but minute plaques. It is extremely rare and occurs between the ages of eight and sixteen. Although the spots usually clear up in a few weeks, they sometimes recur or change into the large lesions of common psoriasis. Pustular psoriasis is the only form of the disease that occurs on the palms of the hands or the soles of the feet. It was named for the yellow or white pus-filled spots that form on the skin and eventually drop off. These spots form when enormous numbers of white blood cells invade the skin even though there is no infection present and, therefore, no need for these infection-killing cells. Erythrodermic psoriasis literally means “red skin.” This very rare condition is so named because the entire body is covered by flaming red patches that do not turn scaly. Since the extensive nature of this condition makes internal temperature control very difficult and dehydration inevitable, it can be very dangerous and may require hospitalization.

Common psoriasis, by comparison, is not dangerous or life-threatening. It is usually not painful and does not even cause itching in most patients. It is, however, very annoying because of its unsightly appearance and its tendency to flare up repeatedly. Once the disease has appeared, it stays with the person for life, improving or worsening periodically. After periods of relative quiet, during which the skin may appear quite normal, patients with psoriasis experience new eruptions and scaling for no apparent reason. Plaques continue to form for an unpredictable amount of time, until the condition spontaneously quiets down again.

The source of the plaques is a failure in the mechanism by which normal skin renews itself. Ordinarily, the cells at the base of the epidermis reproduce themselves at a slow and steady rate. They then move upward in about twenty-eight days, changing chemically, dying, and detaching from the surface, the stratum corneum. In psoriatic skin, however, there is a huge increase in the number of basal cells in the epidermis, which reproduce so rapidly that they push upward to the surface in only four days, forming thick disks of sticky, abnormal cells. Below the epidermis, the dermis of a patient with psoriasis is also abnormal. Its normally fine blood vessels are wide and extremely twisted, which results in the red appearance of the plaques and causes bleeding to occur easily when the skin is bumped or scratched. An unusually high number of the white blood cells called neutrophils and T lymphocytes are also present. They move up into the epidermis, creating inflammation and swelling within the plaques.

Long before modern dermatology discovered these disturbing facts about the structure and the functioning of psoriatic skin, it was noted that the disease does seem to run in families. If one parent has the problem, there is a one-in-three chance that a child will eventually be afflicted; if both parents have the disease, the risk for their offspring is one in two. With nonidentical twins, there is a 70 percent chance that if one has psoriasis, they both will; with identical twins, the figure can be as high as 90 percent, according to some studies. Investigators suspect that psoriasis is not handed down by a simple pattern, such as with eye color inheritance. It seems more likely that the condition results from a combination of several genetic factors from each parent, much like the manner in which height and intelligence are inherited.

Treatment and Therapy

More than 90 percent of psoriasis patients can be cleared significantly of their lesions or even made lesion-free by the medicines and methods developed by modern technology. For minor outbreaks, limited to a small area of the body, the first choice for treatment is a corticosteroid cream or ointment applied directly to the plaques.
Corticosteroids are hormones, produced by the adrenal glands, that are able to reduce inflammation. Corticosteroids are produced in the laboratory and combined with other chemicals to reduce inflammation even more effectively by decreasing blood flow to the psoriatic lesions. Dermatologists have a large variety of such preparations ranging from mild to extremely potent. They must find one that is strong enough to suppress the inflammation but not so strong that it causes unwanted side effects.

There are two major undesirable side effects of corticosteroid therapy. Psoriatic skin absorbs all substances more easily than normal skin; the excess hormones enter the bloodstream and can change the output of hormones by the pituitary and adrenal glands, dangerously altering the body’s chemical balance. The other danger is to the skin itself, which becomes abnormally thin, easily damaged, and prone to infections. Another drawback to the use of corticosteroids is the tendency for the psoriatic plaques to reappear soon after the creams or ointments are discontinued.

Many patients find relief from a completely different class of medications, those which contain tar. This thick, black, oily liquid is produced from coal. It contains thousands of chemical substances, and biochemists do not know which of those substances actually help to heal the skin. Tar-containing ointments, creams, gels, shampoos, and bath additives are useful for removing the scales without worrisome side effects. A major drawback, however, is their tendency to stain clothing, bedding, bathroom tiles, and bathtubs. Some staining can be avoided by covering the treated skin area with bandages, cotton underwear, or a shower cap. In addition to the staining, many patients find the tar odor quite unpleasant; pharmaceutical companies are constantly trying to improve this aspect of these quite effective products.

A third type of preparation is particularly effective for removing very thick scales. These medications contain a compound called salicylic acid. Like the corticosteroids, salicylic acid ointments and gels are most effective when they are in contact with the plaques for a long period of time. After treatment, it is often recommended that patients cover their lesions with plastic gloves, plastic bags (for the feet), or taped-down plastic wrap for four to eight hours.

Patients with psoriasis have noted for years that exposure to the sun is very helpful in clearing their lesions. Daily sunlight exposure is effective for as many as 80 percent of patients. This treatment is relatively accessible for at least part of the year and inexpensive compared to the various medications available. Given the increased risk of skin cancer, it is strongly recommended that patients have repeated but brief sun exposures and avoid sunburn by using creams and lotions. Although sun exposure is helpful to most patients with common psoriasis, it rarely helps and can even worsen the pustulate and erythrodermic types. Since too much exposure to sunlight will damage rather than help any skin, even plaque-type patients are advised to stop their sun exposure once the psoriasis has improved.

For patients in many climates, sunbathing is possible for only a few months of the year. The development of sunlamps for use at home or in a dermatologist’s office, hospital, psoriasis care center, or tanning parlor has made this therapy possible all year round. Because of the danger of severe sunburns, sunlamp treatments remain controversial. To reduce their danger, a dermatologist must carefully determine the amount of time of each treatment, the precise distance from the lamp, and the appropriate frequency of treatments for each individual patient to achieve maximal and safe results.

The curative effect of sunlight depends on the presence of the very short wavelength part of the light, called ultraviolet. It is ultraviolet B (UVB) waves that help heal psoriasis, possibly by slowing down the high growth rate of cells in the epidermis. Both natural sunlight and sunlamps contain UVB and, therefore, have the potential to help psoriasis. They also have the potential, however, to burn the skin.

Patients with severe psoriasis may require the use of ultraviolet A (UVA) waves from a special kind of sunlamp. The patient is given a dose of a psoralen, a substance that makes the skin more light-sensitive, and is then exposed to UVA inside a full-body light cabinet. Thirty treatments may be required to completely clear the skin. The psoralen is often given in tablet form, although some patients suffer fewer side effects if it is painted onto the skin or if they bathe in it. The early side effects of PUVA (psoralen plus UVA) treatment include nausea, itching, colored blotches on the skin, and occasional worsening of the psoriasis. More worrisome are the possible later side effects: skin cancer and the development of cataracts in the eyes. The danger of developing cataracts also exists from natural sunlight and UVB sunlamps; patients using any light therapy must use excellent sunglasses that block out all rays harmful to the eyes.

For the patient with widespread psoriasis who is not responsive to corticosteroids, tar preparations, or the various light therapies, the drug methotrexate is effective in more than 80 percent of patients. This powerful drug was originally developed to treat various kinds of cancer because it slows down the process of cell multiplication. Thus the psoriatic epidermal cells are prevented from reproducing and forming the scaly plaques. Often methotrexate must be taken for six months or a year, in pill form or by injection, to have a significant impact on an extensive case. Such a dosage poses a risk of numerous and serious side effects, including persistent feelings of sickness, indigestion, and diarrhea. Frequent tests are necessary to monitor the condition of the blood, since methotrexate can interfere with the bone marrow’s production of normal blood cells. Most important, periodic liver biopsies, the removal of sample liver cells by means of a special needle, are necessary because methotrexate can cause irreversible damage to this crucial organ. It is very important that a pregnant woman never take methotrexate or that a woman never
become pregnant while taking it. The drug’s ability to interfere with cell growth can cause many abnormalities in a developing embryo or fetus. Similar fetal abnormalities can be caused by the drugs called retinoids.

For patients with pustular and erythrodermic psoriasis, the retinoids etretinate and acitretin can be very useful, if side effects are carefully monitored. Some dermatologists have been especially successful combining PUVA and etretinate therapies; the improvement in the psoriasis is greater than with either alone, while the lower dosage of each minimizes risk and side effects.

Another medication effective in treating severe psoriasis is cyclosporine. It has brought dramatic improvement to patients with lifelong disabling symptoms. Many people, however, can tolerate the drug only for short periods. Because of its potential to cause high blood pressure and kidney damage, as well as an increased risk of cancer, this medicine is prescribed only with extreme caution.

All the many therapies described can bring partial or total clearing of lesions and even result in the remission of the disease for a period of time. Until the cause of psoriasis is completely understood, however, it is likely that no permanent cure will be developed.

Perspective and Prospects

Descriptions of psoriasis are found in the records of the earliest known civilizations. The term “psora” comes from the ancient Greek language. Psoriasis was considered a form of leprosy in biblical times. Despite this ancient history and extensive modern research, however, the exact cause of psoriasis is still unknown. Unlike many human diseases, psoriasis does not afflict any animals; therefore, it cannot be studied through controlled laboratory testing.

Early work on psoriasis by dermatologists centered on differential diagnosis. This is the ability to distinguish psoriasis from various rashes caused by fungi, such as ringworm, and from the many forms of eczema or dermatitis caused by allergies. Skin biopsies developed by oncologists can now determine that the condition is not a cancer; the portion of skin removed, when placed under a microscope, will clearly show the dermal and epidermal appearance characteristic of psoriatic skin.

While skin scientists have proven that psoriasis is not contagious, it has been known since the 1930s that many cases develop soon after strep throat and other upper respiratory infections. The bacteria involved are not the cause of the psoriasis, however, but rather a trigger for the development of a condition for which the patient is genetically predisposed. Another trigger, excessive scratching or rubbing of the skin, can precipitate outbreaks in susceptible people; this is named the Koebner phenomenon, for its discoverer. With the help of neurologists and psychologists, it has been proven that the disease is not caused by “nerves,” yet stress of all kinds is definitely able to make its symptoms worse, and patients must be helped to lower their stress levels if they are to keep the disease under control.

Nutritionists have searched for ways to use diet to help psoriatics, but to no avail. Although no particular foods either help or hinder the course of the disease, most dermatologists now recognize that drinking alcohol can both precipitate and aggravate the disfiguring plaques.

Immunologists have been very involved in the study of psoriasis even though it is not an allergic reaction to any substance in one’s environment. In the late twentieth century, they pursued many possible connections between the streptococci bacteria that cause strep throat, the white blood cells called T lymphocytes that seek to destroy them, and the development of psoriasis. They believe that, in predisposed people, chemicals from the bacteria cause the T lymphocytes to give off substances that trigger the skin’s uncontrolled and excessive production of epidermal cells.

Geneticists have been searching diligently for the source of the predisposition to psoriasis. Among the genes children receive from their parents are those that build particular proteins on their white blood cells called human leukocyte antigens (HLAs). Out of the hundreds of different HLAs that one can possibly inherit, those who develop psoriasis always seem to possess similar combinations. The identification of the genes responsible for HLAs and the role of those genes in precipitating psoriasis may bring about major improvements in the treatment and possibly a cure for this disease afflicting millions of people throughout the world.

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