Diagnosing Psoriasis

Dermatologists at NYU Langone diagnose people with psoriasis, a skin condition that can affect people of any age. Usually, a person with psoriasis has thick, red, scaly skin patches, also called plaques. These plaques have well-defined edges and may be covered with a layer of skin that looks white or silver.

For some people, plaques are intensely itchy. They can affect skin on any part of the body, but they most often appear on the outside of the elbows and knees, the lower back, the face, and the scalp. Psoriasis can also affect the palms of the hands and the soles of the feet, and may cause fingernails and toenails to become thick and white. The condition may also affect genital skin.

Plaque psoriasis is the most common type, but there are a few other main types. Guttate psoriasis causes skin lesions that appear as numerous small, red circles. Pustular psoriasis causes red skin patches covered with white bumps, or pustules, that may coalesce into “lakes” of pus—a substance containing white blood cells—or appear to be crusted. Inverse psoriasis causes red patches that affect folds of skin, such as the underarms, the backs of knees, and the groin, and may not be scaly. Dry skin, including dry scalp or dandruff, may also occur as a result of psoriasis.

Psoriasis is considered mild to moderate if lesions cover less than 10 percent of the body. Severe psoriasis affects 10 percent of the body or more.

Up to 30 percent of people with psoriasis also experience swelling, stiffness, or pain in their joints, including the spine, a condition called psoriatic arthritis. If you experience joint stiffness or pain, NYU Langone dermatologists and rheumatologists, who specialize in conditions that cause painful swelling in joints and muscles, collaborate to determine if you have psoriatic arthritis. If you do, they help you manage symptoms.

The cause of psoriasis is unknown, but researchers theorize that it occurs when an overactive immune system response leads to inflammation. This inflammatory reaction speeds up skin cell production, resulting in excessive amounts of skin cells. These accumulate into the various skin lesions—most commonly thick, scaly plaques—that doctors recognize as psoriasis.

It’s possible that some people are born with a genetic predisposition to psoriasis or that it runs in some families. In addition, researchers have linked certain triggers to the development of psoriasis in those predisposed to it. These include stress, skin injuries, and certain medications such as lithium.

NYU Langone dermatologists can identify psoriasis lesions and diagnose the condition during a physical exam. Occasionally, your doctor may recommend a biopsy—in which he or she removes a small amount of skin for laboratory testing—to distinguish psoriasis from another cause of a rash, such as eczema.

Physical Examination

A dermatologist examines your skin and notes the location, distribution, size, shape, and appearance of lesions. During a physical exam, he or she may also ask about your symptoms and medical history, including whether someone else in your family has been diagnosed with psoriasis.

Your doctor also asks for details about when skin lesions first appeared, whether they come and go or are itchy or painful, and if you have pain or swelling in your joints. If you have been diagnosed and treated for psoriasis before, tell your doctor what treatment you tried, so that he or she can recommend the most appropriate treatment options.

Telling your doctor about any other conditions you have been diagnosed with and if you are taking medication also helps in diagnosing psoriasis. Some conditions, such as HIV and AIDS, may weaken the immune system and increase the risk of psoriasis.

Skin Biopsy

Most of the time, your dermatologist can diagnose psoriasis just by examining your skin. But if he or she needs more information to confirm the diagnosis and rule out other causes of symptoms, such as eczema or cutaneous lupus, a skin biopsy may be performed.

A biopsy is a test in which a pathologist examines skin cells under a microscope to determine whether psoriasis is the cause of symptoms. Dermatologists usually perform what’s known as a punch biopsy. The “punch” name describes the technique: your doctor uses a device the size and shape of a pencil to puncture the skin and remove a small tissue sample. The round incision is closed with one or two stitches.

The results of a skin biopsy are available in about a week.