What Tests Are Needed for a Psoriatic Arthritis Diagnosis?

If you have psoriasis, there’s a 1 in 4 chance you may develop psoriatic arthritis (PsA). Psoriatic arthritis is a chronic autoimmune condition that can cause inflammation in the joints, tendons, and spine. This is in addition to skin rashes and nail changes from psoriasis.

Psoriatic arthritis is typically diagnosed by a rheumatologist — a type of physician who specializes in autoimmune conditions. But there’s no single test for psoriatic arthritis, so getting a diagnosis can sometimes be tricky. In this article, we explain how a rheumatologist uses different clues to make a psoriatic arthritis diagnosis.

How does a rheumatologist diagnose psoriatic arthritis?

Psoriatic arthritis is called a “clinical diagnosis.” This means there’s no single test to diagnose it. Instead, rheumatologists use old-school diagnostic tools to figure out what’s going on. The main tools are your medical history and a physical examination.

The medical history involves your symptoms — when they started, how often you have them, and how they affect you. Common symptoms of psoriatic arthritis include:

• Swollen, tender joints — especially in your hands and feet

• Back pain and stiffness, especially if it’s worse in the morning but better with exercise

• A swollen finger or toe that looks like a sausage (this is called dactylitis)

• Psoriasis rashes or nail changes

The physical examination allows the rheumatologist to look for specific signs of psoriatic arthritis (more on that below).

This is why rheumatologists are often thought of as “medical detectives.” They carefully listen, observe, and piece together clues to solve the mystery of what’s causing your symptoms.

What PsA symptoms and signs will a doctor look for?

The rheumatologist will check you from head to toe. To make sure nothing is missed, you might be asked to put on a gown. This exam will be very thorough, so don’t be surprised if it takes longer than a regular check-up. 

Your rheumatologist will check your heart, lungs, and abdomen. They’ll also check for signs of psoriatic arthritis, including:

• Psoriasis rashes (these can be hidden on your scalp, in your armpits, under your breasts, or between your buttocks) 

• Changes in your fingernails or toenails

• Joint tenderness and swelling

• Swollen fingers or toes (dactylitis)

• Eye inflammation

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What tests may be needed to diagnose psoriatic arthritis?

Your medical history and physical exam are really the most important parts of diagnosing psoriatic arthritis. But sometimes, other tests can help — especially when the diagnosis isn’t clear. Remember, there’s no single test that can diagnose psoriatic arthritis.

Extra tests that may be ordered include:

• Blood tests: These can help rule out other conditions, like rheumatoid arthritis.

• X-rays: If you’ve had psoriatic arthritis for over a year, X-rays may show joint changes that are associated with untreated psoriatic arthritis.

• Magnetic resonance imaging (MRI): This is an imaging test that gives a more detailed view of your joints than basic X-rays. And it can help detect joint inflammation or damage in people with subtle symptoms. If your healthcare professional sees swollen joints during an exam, this test isn’t needed.

• Ultrasound: This is a less expensive, quick imaging test. It can also detect joint inflammation and damage that X-rays can’t. Some rheumatologists can perform an ultrasound in their office. But typically it’s done at an imaging center.

• Skin biopsy: In most cases, a rheumatologist or dermatologist can diagnose psoriasis just by looking at a rash. But in rare cases, a skin biopsy might be needed to confirm it. This involves removing a small piece of skin and looking at it under the microscope.

Which criteria must be met for a psoriatic arthritis diagnosis?

Rheumatologists use your symptoms, exam results, and other tests to make a diagnosis. Certain criteria may also be helpful. For example, having three or more of the following supports a diagnosis of psoriatic arthritis:

• Current psoriasis, evidence of psoriasis in the past, or a family history of psoriasis

• Nail changes typical of psoriasis

• A negative rheumatoid factor in the blood test

• Current or past dactylitis

• Specific changes in your hands or feet on X-rays

Can I self-diagnose psoriatic arthritis?

There’s no at-home test for psoriatic arthritis, and you can’t generally self-diagnose the condition. A rheumatologist is the best person to make this diagnosis. But you and your primary care provider or dermatologist can look out for symptoms, in an effort to catch psoriatic arthritis early. This is especially important if you have psoriasis, since about 1 in 4 people who have psoriasis develop psoriatic arthritis. 

If you have psoriasis, you can take an online screening test called the Psoriasis Epidemiology Screening Tool (PEST). It helps spot early symptoms of psoriatic arthritis and determine if you need to see a rheumatologist.

What conditions could be mistaken for psoriatic arthritis?

Many different autoimmune conditions can cause inflammatory arthritis (swollen and painful joints). But if you also have psoriasis, psoriatic arthritis is the most likely culprit. 

If multiple treatments for psoriatic arthritis have failed to improve your symptoms — or if new symptoms develop — your rheumatologist may take a step back. (When new evidence comes to light, it’s important to look at the case again, just like a real detective.)

These are some conditions that could be mistaken for psoriatic arthritis: 

• Rheumatoid arthritis

• Reactive arthritis

• Spondyloarthritis (ankylosing spondylitis)

• Lupus

• Viral infection (which can cause worsening of psoriasis rashes and painful, swollen joints)

There are rarer autoimmune conditions that can also cause inflammatory arthritis. But they usually come with other symptoms, too. If you develop new or different symptoms, let your rheumatologist know. They’ll be able to determine if more testing is needed.

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Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

Reviewed by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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