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Psoriasis - The Unscratchable Itch

By: Kenneth Gordon, MD & Mark Lebwohl, MD

The word "psoriasis" is derived from the Greek word for "itch," but unlike some pesky prickle, psoriasis can't be scratched away. More than seven million Americans suffer with psoriasis, a chronic skin disease characterized by an overproduction of skin cells that result in flaky and patchy raised areas on the skin's surface.

Below, two experts in psoriasis offer a full introduction to this chronic disease.

Let's start with the basics. What is psoriasis?

MARK LEBWOHL, MD: Psoriasis is a disorder of the skin in which an abnormality of the immune system triggers the release of substances that cause the cells of the skin to multiply too quickly. Ordinarily, skin cells on the superficial area of the skin regenerate about every 28 days. In those with psoriasis, that same portion of the skin may be made over every two to four days, and that skin comes up as thick, scaly, red plaques.

Are there some parts of the body that are more susceptible to psoriasis than others?

KENNETH GORDON, MD: Typically traumatic areas are more susceptible, like elbows and knees, and the lower part of the back. But the important thing to remember is, psoriasis can happen anywhere on the body. Anywhere there's skin you can have psoriasis.

Are there many different types?

MARK LEBWOHL, MD: Classically, there are four types. The most common type is plaque psoriasis, which is characterized by large, red, scaly patches that, as you've already heard, affect the elbows and knees, but can affect any part of the body. There are severe cases in which patients are covered, 80 to 100% of their body surface, with plaques. That accounts for the majority of patients with psoriasis.

Around 10% of patients have something called guttate psoriasis, which are smaller, red, scaly lesions-1 or 2 cm-that cover large areas of the body. Typically, these patients will develop a lot of little spots all over after strep throat. That's the second most common type.

The two most dangerous types are called erythrodermic psoriasis and pustular psoriasis.

Erythrodermic psoriasis patients' entire skin surface turns bright red and scaly, and they lose all of the protective functions of their skin. They literally can't control body temperature. They lose nutrients and fluid through their skin and they're susceptible to infection. The skin barrier against infection is lost, and that is a life-threatening form of psoriasis. Patients have actually died from that form of psoriasis.

The other form, pustular psoriasis, occurs in two ways. One of them is generalized pustular psoriasis, in which, again, patients lose all of those protective functions of the skin, and this becomes a life-threatening instance where patients can die from their psoriasis. And there is a localized form which, while it is not life-threatening, is just as debilitating. It is a localized pustular psoriasis of the palms and soles. Patients simply can't use their hands or feet. They can't walk, they can't handle anything with their hands, because it's very painful.

How common are these more serious forms of psoriasis?

MARK LEBWOHL, MD: Fortunately they are rare. They're most commonly triggered by systemic steroids, or withdrawal of systemic steroids.

If someone has a very chronic case of psoriasis, are other parts of the body affected by it?

MARK LEBWOHL, MD: The one particular part of the body that can routinely be affected in patients with psoriasis are the joints. It turns out that roughly 7%, or a little less than one out of ten patients who have psoriasis, will have significant psoriatic arthritis, meaning inflammation of the joints. There are several different forms of that, and it can range in severity from fairly mild to quite severe and debilitating.

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Who gets psoriasis? How common is it?

MARK LEBWOHL, MD: It affects a little over 2.5% of the population, and it can affect anyone. Ordinarily, about a third of patients have a family history of the disease. Two-thirds of patients don't know of someone else in the family had the disease. Nevertheless, it can affect anyone, and it can actually start at any age. There have been patients who were born with psoriasis. There are patients who develop psoriasis for the first time after the age of 100. An average age would be somewhere around 30 years old. But, again, it can affect any age.

Is it contagious?

KENNETH GORDON, MD: It is not contagious at all.

Why does psoriasis happen?

KENNETH GORDON, MD: A patient who is genetically predisposed to developing the disease will have some kind of immune challenge. That challenge will cause the immune cells, the lymphocytes, to respond and go to the skin and release cytokines, which induce the skin cells to change. The problem is, we don't know exactly what causes those lymphocytes to behave in that manner, and that's why we don't fully understand the etiology. But we do know that the lymphocytes that cause those problems are necessary for the disease, and the elimination of their activity can help to treat the disease.

How significantly does this disease affect patients?

KENNETH GORDON, MD: The effects of psoriasis are very far-ranging in both patients' health and the way they view themselves. Patients with psoriasis view their disease as something as disabling as diabetes or congestive heart failure. And it's important to remember that these people have a very visible disease on their skin. They're sometimes not allowed in a swimming pool because of the myth that psoriasis is contagious. Disease that affects only the palms or soles might be very debilitating because of pain on walking or holding a pencil. Patients will go a long way to try to get treatment because of the both mental and physical disabling properties of the disease.

So quite a severe psychological toll can be exacted, as well?

KENNETH GORDON, MD: There are surveys that show that the psychological toll of psoriasis is the equivalent of depression, which is about as severe as you can get.

What hope is there out there for patients who have it now?

MARK LEBWOHL, MD: I would say if you looked over the past 20 or 30 years at drugs that have been introduced for a variety of dermatologic conditions, an enormous proportion have been introduced for psoriasis. A lot of that is due to the patient advocacy groups, like the National Psoriasis Foundation, that have been pushing for new treatments. Also, there are a number of drugs on the horizon that will be approved for psoriasis that I think are both safer and as effective, or more effective, than many of the treatments we use today.