How Is Psoriasis Diagnosed?

Psoriasis is an autoimmune disease that speeds up the growth of skin cells and causes inflamed patches on the body. These patches are called "plaques" and can be itchy and painful. More than 7.5 million people over the age of 20 live with psoriasis in the United States.

However, this number may be higher as psoriasis can sometimes be difficult to diagnose; it can look like other skin conditions (e.g., eczema) and is often underdiagnosed in people with darker skin tones.

If you think you may have symptoms or are at risk of developing psoriasis, it is a good idea to a healthcare provider. At your appointment, your healthcare provider—often a dermatologist, a medical doctor who specializes in skin conditions—will typically ask you about your medical history and use a physical examination to look at any plaques, rashes, or scales on your skin. In some cases, they may also order a skin biopsy to reach a more accurate diagnosis.  

Medical History

During your appointment, your healthcare provider will usually ask you about you and your family’s medical history, your lifestyle, and any changes or stressors. Some questions may include:

• What symptoms do you have?
• How long have you had symptoms?
• Does anyone in your family have psoriasis?
• Have you experienced any major life changes or stressors recently? 

Your provider might also ask if you're experiencing pain, swelling, or stiffness in your joints. This may sound like a strange question, but studies show that one in three people with psoriasis can also develop psoriatic arthritis—a condition that causes inflammation on the skin and in the joints.

Physical Exam

After your medical history questionnaire is completed, your healthcare provider or dermatologist will take a look at any plaques, scales, or rashes on your body. 

Many dermatologists can diagnose psoriasis by simply looking at your skin, nails, or scalp. They may also use a dermatoscope, which is a tool with a light that zooms in on your skin to help your provider examine and identify your plaques. 

Not all plaques look the same. People with darker skin tones can have plaques that are purple or brown, accompanied by scales that are gray. People with lighter skin tones may have plaques that appear pink or red, with scales that look white.

While psoriasis is more common in white people and those of European descent, it has also been underdiagnosed in people with darker skin tones. This is mostly because research on psoriasis has typically been done on those with lighter skin. This can make it more difficult for people with darker skin to get an accurate diagnosis; therefore, more research is needed.

A qualified dermatologist will generally know what to look for in different skin tones. However, the National Psoriasis Foundation has developed a Skin of Color Resource Center to provide you with additional resources on how to receive a second opinion and a proper diagnosis. 

Skin Biopsy 

Psoriatic plaques can resemble other skin conditions like eczema and contact dermatitis. To reach a proper diagnosis for psoriasis, your healthcare provider may also order a skin biopsy—a procedure that uses a device to take a small sample of your skin. Once the sample has been taken, your provider will send it to a lab to get the skin tested. 

There are three main ways to perform a biopsy: 

• Shave biopsy: This procedure uses a razor blade to remove a sample of your skin. It is typically only done if you have small plaques on the top layers of your skin. 
• Punch biopsy: If your plaques are formed in deeper layers of your skin, your provider will use a round blade to take a sample of your skin. 
• Excisional biopsy: Thick plaques will usually require this type of biopsy which uses a small knife called a scalpel to remove a larger skin sample.

Before performing the biopsy, your healthcare provider will likely clean the area where the skin will be removed and give you a form of anesthesia to numb the pain.  

While most skin biopsies for psoriasis are harmless, some people may experience slight bruising, bleeding, or soreness in the area the skin sample was taken. The good news: side effects of the biopsy usually don’t last for more than a few days. 

Screening for Related Conditions 

Your healthcare provider may use additional testing methods like patch testing and imaging tests to rule out or test for other conditions. Eczema and psoriatic arthritis are some conditions that are frequently associated with psoriasis.

Patch Testing

Plaques and scales are symptoms of a variety of skin-related concerns. Though it's not needed to diagnose psoriasis, your healthcare provider may use an exam called patch testing to determine if you have other skin conditions.

Dermatologists often use patch tests to examine the cause of rashes, itchiness, and potential allergic reactions. Unlike a medical history questionnaire or physical exam, which can be done during one doctor’s visit, a patch test can take up to one week to complete over the course of a few appointments. 

During a patch test, your provider will place several different allergens on your back and then tape those allergens with a patch. Generally, these patches must be left on your skin for 48 to 72 hours. The purpose of these patches is to see if your skin reacts to any of the allergens.

At your next appointment, your provider will remove the patches to make a note if any of the allergens gave you a skin reaction. If your skin had a reaction, your provider will be able to tell you whether you have an allergy, atopic dermatitis (a common type of eczema), or other skin condition. 

Imaging Tests

Imaging tests, like X-rays and MRIs, are not used to diagnose psoriasis. However, if you receive a psoriasis diagnosis, you may be at risk of developing psoriatic arthritis. In fact, nearly a third of people with psoriasis also have psoriatic arthritis. This is known as a comorbid or co-occurring condition.

Your healthcare provider will likely use imaging tests such as X-rays or MRIs to take a closer look at your joint tissue. Imaging tests take detailed images of your joints and can help your provider look for any changes or damage to your tissue or bones. Generally, your provider will order imaging tests for your hands, knees, and feet because psoriatic arthritis generally affects the smaller joints in your body in the early stages.  

If your provider notices damage or concerns with your joint tissue, they will consult with a rheumatologist (a doctor who specializes in the joints and muscles) and a dermatologist to help you create a treatment plan that is right for you. 

A Quick Review

Psoriasis is an autoimmune skin condition that can cause inflamed skin patches. There is no one test that your healthcare provider will use to diagnose you with this condition. Instead, your provider will use a variety of tests including a medical history questionnaire, physical exam, and skin biopsy. You may also be asked to take a patch test or undergo imaging tests to potentially detect other skin conditions associated with psoriasis. 

Psoriasis symptoms can be painful and uncomfortable. If you notice changes to your skin, you may find it beneficial to visit your healthcare provider for an examination. Receiving an early diagnosis can help you better manage symptoms and prevent further irritation or discomfort to your skin.