(LifeWire) - Psoriasis is a chronic skin condition that causes thick, reddened, scaly, itchy or sore areas. Affected areas may become so dry that they crack and bleed. Nails may become thick and discolored, with pits and ridges. You can develop psoriasis anywhere, although knees and elbows are most often affected. Other frequently affected areas include the scalp, palms of the hands and soles of the feet, legs, back, face, fingernails and toenails. Psoriasis can also cause a type of arthritis called "psoriatic arthritis." Symptoms of psoriasis come and go over time and can range in severity from being a simple annoyance to causing true disability.
Although you may have heard of psoriasis, you may not know that there are actually five different types. You can have more than one type of psoriasis at the same time, or you may start out with symptoms of one type that morph over time into symptoms of another type. The five types of psoriasis share certain features (such as an origin in the malfunctioning of the immune system and the tendency to run in families), but each also has unique characteristics.
This is the classic form of psoriasis, and the one with which most people are familiar; about 80% to 90% of all psoriasis is this type. In plaque psoriasis, patches (plaques) of skin are thick, red, swollen, inflamed and covered with a crusty silver scale. Plaques may be tender and/or itchy. While plaque psoriasis can crop up anywhere on the body, the most commonly affected areas are the knees, elbows, scalp, or trunk. Once a plaque appears, it can be present for years.
In this form of psoriasis, small, light pink or red, teardrop-shaped areas appear on the trunk, limbs and/or scalp, often after a bout of strep throat. Other triggers for guttate psoriasis include upper respiratory tract infection, skin injury, stress and drugs (such as antimalaria medications and beta-blockers). This form of psoriasis tends to affect individuals under the age of 30. It may occur as a one-time episode, or it may recur, triggered (for instance) by future respiratory infections.
In pustular psoriasis, the skin becomes red, and tender, pus-filled blisters emerge. Sometimes, just the palms of the hands and soles of the feet are involved. Other times, lesions appear all over the body. Pustular psoriasis can also include systemic symptoms like fever, chills, weight loss, nausea, headache, joint pain and fatigue. (When this cluster of symptoms occurs, the result is called von Zumbusch-type psoriasis.) In some cases, pus accumulates underneath the fingernails, unseating them (a phenomenon known as acrodermatitis continua). Pustular psoriasis can be triggered by a reaction to medications (like steroids or lithium), other chemicals, stress or infections. Although pustular psoriasis most commonly affects adults, there is a very rare form that strikes children. Pustular psoriasis can be an acute, short-lived condition, or a long-term, chronic condition.
Unlike other forms of psoriasis, inverse psoriasis gives rise to smooth areas of redness and swelling. These patches appear most often in the folds of skin at the groin, under the breasts, and in the armpits. Because these patches are located in warm, moist areas, there is a high likelihood of complications due to infection by yeast or fungi. Sweating and friction may worsen symptoms. Inverse psoriasis tends to affect overweight individuals in particular.
This is the least common form of psoriasis, and it can have very serious complications. In erythrodermic psoriasis, large areas of skin (and sometimes the whole body) develop bright red, swollen, peeling skin. The affected areas itch and/or burn severely. Because the body responds to inflammation by increasing blood flow to affected areas, and because the areas of erythrodermic psoriasis are so large, the heart may actually become strained by the extra work involved. People with erythrodermic psoriasis have an increased risk of infection, fever and dehydration, which may require hospitalization. An episode may be triggered by medications (including steroid use), undertreated psoriasis or bad sunburn.
Sources:
"About Psoriasis." Psoriasis.org. Dec. 2005. National Psoriasis Foundation. 16 May 2008.
<http://www.psoriasis.org/about/psoriasis/pustular.php>
Habif T.P. "Psoriasis and Other Papulosquamous Diseases." Clinical Dermatology. Fourth ed. St. Louis: Mosby, 2004. 209-239.
"Psoriasis." Ferri's Clinical Advisor 2008. First ed. Ed. Fred Ferri. Philadelphia: Mosby Elsevier, 2008. 374-5.
"Questions and Answers About Psoriasis." National Institute for Arthritis and Musculoskeletal and Skin Diseases. May 2003. National Institutes for Health. 15 May 2008. <http://www.niams.nih.gov/Health_Info/Psoriasis/psoriasis_qa.pdf>
"What Is Psoriasis?" Skincarephysicians.com. 10 Apr. 2007. American Academy of Dermatology. 31 May 2008. <http://www.skincarephysicians.com/psoriasisnet/phototherapy.html#1>