September 5, 2013 Psoriasis is an autoimmune disease that causes raised, red, scaly patches to appear on the skin. Dr. Lawrence Jaeger of New York is an expert in the diagnosis and treatment of skin conditions and is board certified in dermatology and dermatologic surgery. It typically affects the outside of the elbows, knees or scalp, though it can appear on any location. Some people report that psoriasis is itchy, burns and stings. Psoriasis is associated with other serious health conditions, such as diabetes, heart disease and depression. If you develop a rash that doesn’t go away with an over-the-counter medication, you should consider contacting your doctor. How is psoriasis diagnosed? There are no special blood tests or tools to diagnose psoriasis. A dermatologist (doctor who specializes in skin diseases) or other health care provider usually examines the affected skin and determines if it is psoriasis. Your doctor may take a piece of the affected skin (a biopsy) and examine it under the microscope. When biopsied, psoriasis skin looks thicker and inflamed when compared to skin with eczema. What type of psoriasis do I have? There are five types of psoriasis. Plaque Psoriasis Plaque psoriasis is the most common form of the disease and appears as raised, red patches covered with a silvery white buildup of dead skin cells. These patches or plaques most often show up on the scalp, knees, elbows and lower back. They are often itchy and painful, and they can crack and bleed. Guttate Guttate [GUH-tate] psoriasis is a form of psoriasis that appears as small, dot-like lesions. Guttate psoriasis often starts in childhood or young adulthood, and can be triggered by a strep infection. This is the second-most common type of psoriasis, after plaque psoriasis. About 10 percent of people who get psoriasis develop guttate psoriasis. Inverse Inverse psoriasis shows up as very red lesions in body folds, such as behind the knee, under the arm or in the groin. It may appear smooth and shiny. Many people have another type of psoriasis elsewhere on the body at the same time. Pustular Pustular [PUHS-choo-lar] psoriasis in characterized by white pustules (blisters of noninfectious pus) surrounded by red skin. The pus consists of white blood cells. It is not an infection, nor is it contagious. Pustular psoriasis can occur on any part of the body, but occurs most often on the hands or feet. Erythrodermic Erythrodermic [eh-REETH-ro-der-mik] psoriasis is a particularly severe form of psoriasis that leads to widespread, fiery redness over most of the body. It can cause severe itching and pain, and make the skin come off in sheets. It is rare, occurring in 3 percent of people who have psoriasis during their life time. It generally appears on people who have unstable plaque psoriasis. Individuals having an erythrodermic psoriasis flare should see a doctor immediately. This form of psoriasis can be life-threatening.