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Psoriasis As An Autoimmune Disorder

By Rosalyn Carson-DeWitt

Updated April 13, 2009

(LifeWire) - Psoriasis causes a variety of symptoms that range from merely irritating to actually debilitating. The symptoms can include thick, red patches on the skin; pitted, ridged fingernails; scaly, itchy scalp and hair loss; and stiff, painful joints.

Why do some people, but not others, get this frustrating condition in the first place? Arriving at an answer to this question relies partly on knowing that psoriasis is an "autoimmune disorder" — [i]auto[/i] meaning self and [i]immune[/i] referring to the body's complex immune system.

What is an Autoimmune Disorder?

Your body's immune system is responsible for fighting what is perceived to be foreign invaders threatening your body's health: bacteria, viruses and fungi are just a few examples. Your good health depends partly on two important features of the immune system:

  1. It should be able to recognize all tissues and organs within your body as "self" and therefore exempt them from attack by the immune system.
  2. It should be able to identify foreign invaders as "other" to participate in their destruction and mobilize other parts of the immune system to participate in this attack.

Unfortunately, when you have an autoimmune disease, your body's immune system mistakenly confuses what is "self" with what is "other." Instead of protecting your body, the immune system produces cells and chemicals that attack your own body, causing damage and disease. Rheumatoid arthritis; some types of thyroid diseases; and anemia, lupus, celiac disease and type 1 diabetes are also autoimmune diseases.

Why is Psoriasis an Autoimmune Disorder?

As part of its defense against foreign invaders, your body's bone marrow and thymus gland collaborate to pump out specialized white blood cell warriors called "T cells." Under normal circumstances, T cells are programmed to identify and coordinate an attack on enemy combatants.

When you have psoriasis, T cells mistakenly identify your skin cells as "other" and attack them. This attack injures the skin cells, setting off a cascade of responses in your immune system and in your skin, resulting in skin damage (that is, swelling, reddening and scaling).

In an effort to heal, your skin cells begin reproducing rapidly. Activities that should take a month take place in only days, and abnormally large numbers of new skin cells push their way to the surface of your skin. This occurs so quickly that older skin cells and white blood cells aren't shed quickly enough. These discarded cells pile up on the surface of the skin, creating thick, red plaques with silvery scales on their surface: the hallmark of the classic form of plaque psoriasis.

Why Do People Get Psoriasis?

Both genetic and environmental factors are believed to be responsible for whether or not a person will get psoriasis. The theory is that those who develop the disease are born with a particular genetic makeup that causes vulnerability to psoriasis, and those who actually develop the disease are exposed to something in the environment that triggers the disorder.

How Do Environmental Triggers Affect Psoriasis?

Encountering certain environmental triggers seems to jump-start the machinery of the body's immune system in vulnerable individuals. When you have an autoimmune disease, such as psoriasis, the machinery doesn't confine its attack to a real invading enemy. Once the immune system gets rolling, it assaults the tissues and organs of the body with the equivalent of friendly fire.

Some of the environmental factors that seem to be able to trigger psoriasis or to cause a flare-up of the condition in someone who already has the disorder include:

  • Infections - Psoriasis often starts or worsens after you've had some kind of infection, especially one caused by streptococcus bacteria (as in "strep throat").
  • Medications - Lithium, antimalaria drugs, high blood pressure medicines (called "beta blockers") and the anti-inflammatory drug Indocin (indomethacin) are some of the drugs that seem to be possible triggers
  • Skin injury - Overly dry skin, sunburn, cuts and scratches sometimes seem to be able to add the insult of psoriasis to the original injury
  • Stress - Some studies suggest that stress can serve as a trigger

How are Autoimmune Disorders Treated?

A number of medications can be used to try to quiet down the immune system; two common examples are Trexall (methotrexate) and Sandimmune (cyclosporine). Other possibilities belong to the pharmaceutical class known as "biologic drugs," which are made from human or animal protein, including Enbrel (etanercept), Remicade (infliximab) and Humira (adalimumab).

Sources:

Ferri, F.F. "Psoriasis." Ferri's Clinical Advisor 2008. 2008. Habif, T.P. "Psoriasis and Other Papulsquamous Diseases." Clinical Dermatology. 2004.

Lowes, M.A. "Current Concepts in the Immunopathogenesis of Psoriasis." Dermatological Clinics. 22(2004): 349-69.

Luba, K.M. "Chronic Plaque Psoriasis." American Family Physician. 73(2006): 636-44. <http://www.aafp.org/afp/20060215/636.html>.

"Psoriasis." aad.org. 2007. American Academy of Dermatology. 23 June 2008. <http://www.aad.org/public/publications/pamphlets/common_psoriasis.html>.

Shaw, J.C. "Psoriasis and Other Papulosquamous Diseases." Textbook of Primary Care Medicine. 2001.

LifeWire, a part of The New York Times Company, provides original and syndicated online lifestyle content. Rosalyn Carson-DeWitt, MD, works as a medical writer, editor, and consultant in Durham, N.C. She served as editor in chief for two multivolume MacMillan encyclopedias: The Encyclopedia of Drugs, Alcohol, and Addictive Behavior and Drugs, Alcohol and Tobacco: Learning About Addictive Behavior. She worked on the 18th edition of the Merck Manual of Diagnosis and Therapy and has written thousands of print and online articles for healthcare providers and consumers.
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