How Plaque Psoriasis Is Diagnosed

plaque psoriasis diagnosis
 © Verywell, 2018

The diagnosis of plaque psoriasis is usually straightforward. It is a relatively common condition that most health providers see frequently—you can see your regular physician to receive your diagnosis. Pediatricians, internal medicine doctors, and family practice physicians all have experience with the condition.

Unlike some other medical conditions that are more difficult to classify, plaque psoriasis is often promptly diagnosed. If your plaque psoriasis is for some reason difficult to diagnose or to treat, your regular physician might refer you to a dermatologist.

Plaque psoriasis is almost always diagnosed clinically. That means that your physician will usually be able to tell you that you have plaque psoriasis with only your medical history and a physical exam.

Self-Check and At-Home Testing

Don’t try to diagnose your psoriasis at home or just using the internet. It’s fine to research your symptoms. However, many different types of medical conditions can cause rash and skin irritation. If you self-treat what you think is psoriasis, you might only make your skin condition worse. Instead, get the help of a health professional that you trust.

However, it can be helpful to think about your symptoms before you see your healthcare professional. This can help you make sure you don’t leave out any important details when you describe your condition.

Medical History

To diagnose you, your doctor will take your medical history. This will include asking about your symptoms and how they might have changed over time.

Your doctor will also ask about your other medical conditions and about your family’s medical history. Some of these questions might not seem to have anything to do with psoriasis, but they can help to arrive at the correct diagnosis.

Physical Exam

Your doctor will also perform a careful medical exam. This will include a close examination of your skin.

Plaque psoriasis tends to have a specific appearance with patterns that your doctor can use to help diagnose your condition. For example, the affected reddish areas of skin typically appear with silvery scales. Your doctor will check other parts of your body that psoriasis can affect as well, like your joints, your nails, or your scalp.

Labs, Tests, and Imaging

There is no blood test that can be used to help diagnose plaque psoriasis. Medical imaging is also not a part of the diagnostic process.

Rarely, a physician might need to take a skin biopsy to definitively diagnose your plaque psoriasis. You would receive a local anesthetic to numb the area. Then someone would remove a small area of skin where you have symptoms. An expert then examines your skin under the microscope. This lets the professional get a closer look at the specific changes happening in your skin. This may help rule out other skin conditions that can appear similar to plaque psoriasis.

Your doctor might also need certain laboratory tests if you are beginning medications for plaque psoriasis. However, this is not part of the diagnostic process.

Severity Evaluation

As part of your diagnosis, your physician may want to evaluate the severity of your condition. This can help you keep track of your progress, and is done by evaluating how much of your body is affected.

Your doctor might mention that you have mild, moderate, or severe psoriasis, based on the intensity of your symptoms. Most people who have psoriasis have only mild disease. That is disease that affects less than 5 percent of your body surface area, and which doesn't affect the genitals, face, hands, or feet.

In some cases, your doctor might want to get an even more exact assessment of your plaque psoriasis severity. For example, your doctor might mention the percentage of your body surface that appears to be affected. This may help you and your doctor better keep track of how well your body is responding to psoriasis treatment.

Differential Diagnoses

As part of the diagnosis, your doctor will tell you the specific type of psoriasis that you have. For example, pustular psoriasis and guttate psoriasis have somewhat different symptoms compared to plaque psoriasis.

  • Inverse psoriasis (a less scaly rash affecting mainly the skin folds of the body)
  • Erythrodermic psoriasis (with a widespread red rash)
  • Pustular psoriasis (with raised pus-filled blisters on your palms and soles)
  • Guttate psoriasis (tiny red rashes, usually scattered on the trunk, which may be more common in children than adults)

Your doctor will also need to make sure that you have psoriasis and not some other skin condition. Other skin conditions can sometimes resemble psoriasis in appearance. Some conditions that may appear similar include:

Your doctor will consider these and other skin conditions when diagnosing you with plaque psoriasis. Rarely, you might initially receive a different diagnosis before eventually being diagnosed with psoriasis. Or you might be first diagnosed with psoriasis before eventually receiving a different, correct diagnosis.

Because the diagnosis is a clinical one, mistakes will occasionally happen. That is one reason it is important to keep working with a health professional to see how your symptoms respond. If you have any questions about your diagnosis, don’t hesitate to ask your medical provider.

Diagnosing Comorbidities

Some people with plaque psoriasis have medical comorbidities related to their condition. For example, some also have psoriatic arthritis. So as part of your medical history and exam, your doctor will look for signs of this as well.

Other problems such as cardiovascular disease and depression are also more common in people with psoriasis, so your health care provider may also need to screen you for these other conditions as a part of your diagnosis.

In some cases, you may need additional tests to diagnose comorbidities. For example, if you have symptoms of joint pain, your doctor might want specific blood tests. These can help rule out other causes of joint pain, like rheumatoid arthritis.

But not everyone with psoriasis will need to have such tests. Your medical provider will let you know if any of these additional tests might be necessary.

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