How Psoriatic Arthritis Is Diagnosed

To diagnose psoriatic arthritis (PsA), healthcare providers consider your medical history and examine you for signs of the condition. These can include joint swelling and tenderness, and red, scaly patches of skin. They also order tests and imaging studies to look for evidence of inflammation in the blood and abnormalities in the joints.

Still, a psoriatic arthritis diagnosis is never truly confirmed. Rather, it's decided on by ruling out other possibilities.

This article explains the diagnostic process, how to do a self-check at home, and what conditions may have similar symptoms. It also looks at the importance of family history and how race can affect both how PsA is experienced and diagnosed.

Physical Examination

Psoriatic arthritis is so named because of its two main components: psoriasis and arthritis.

Psoriasis causes damage to the epidermis, the outer layer of the skin, while arthritis is inflammation of the joints.

Given this, your healthcare practitioner will ask you about a variety of symptoms and look for signs such as the following:

• Painful, swollen joints, especially the fingers and toes
• Pain in the lower back, ankles, and feet
• Psoriasis symptoms on your skin, including redness, dryness, flaking, and scaling
• Psoriasis symptoms on your nails, such as pitting and pulling away from the nail bed
• Swollen fingers and toes
• Pain where connective tissues attach to bones in your heels, soles, elbows, and other locations (known as enthesitis)

They will also ask where you hurt and what makes your pain better or worse.

Medical History

Be sure to tell your provider about any other diagnoses, especially psoriasis. While PsA can occur on its own, around 85% of cases are preceded by psoriasis.

Also mention if you have a family history of PsA or psoriasis. PsA is more common if you have a family member with one or both of these conditions. You may, in fact, develop PsA without having psoriasis first.

Labs and Tests

No specific test can confirm a psoriatic arthritis diagnosis. But blood tests that can detect signs of body-wide inflammation can help support one. Some tests can also help rule out other forms of arthritis.

You may have blood tests for:

• Rheumatoid factor (RF): RF is found in around 80% of people with rheumatoid arthritis (RA), another inflammatory disorder that affects the joints. Higher levels of RF point to RA. No RF or low levels hint at PsA instead.
• Anti-cyclic citrullinated peptide (anti-CCP) antibodies: These immune-system cells attack your joints. They're common in RA. Only about 5% of people with PsA test positive for anti-CCP.
• Inflammatory markers: Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) can indicate systemic inflammation. Blood tests may reveal high levels with PsA but even higher ones with RA.

These tests may be ordered by a primary care doctor or a rheumatologist, a doctor who specializes in arthritis and similar diseases. If you haven't been previously diagnosed with psoriasis, you may be sent to a dermatologist, who specializes in skin conditions, for that.

You may have additional tests done, depending on what other diagnoses your provider is exploring. These may include:

• Urinalysis: People with PsA may have excess protein in their urine.
• Biopsy: A tissue sample (e.g., skin) is removed and examined under a microscope.
• Bacterial culture: This is performed on skin lesions.
  
• Antinuclear antibody (ANA) test: This blood test looks for proteins tied to autoimmune disorders.

Imaging

X-rays and/or magnetic resonance imaging (MRI) are common in PsA diagnosis.

X-rays use electromagnetic waves to take pictures of the inside of your body. They show your bones and joints. MRIs use radio waves and strong magnetic fields to show soft tissue damage.

Findings that point to PsA include:

• Enthesitis
• A joint on one side of the body is affected, but not the other (asymmetric joint involvement)
• Only part of the spine is affected (asymmetrical spinal involvement)
• Involvement of finger and toe joints closest to the tip
• "Pencil-in-a-cup" deformity, which is when a bone in the finger becomes sharp (like a pencil point) and wears down the adjacent bone so it looks like a cup

Around 77% of people with psoriatic arthritis have joint abnormalities that are seen on X-ray. Moreover, up to 47% of those with a new diagnosis will experience the wearing away of bone within two years.

Differential Diagnoses

The term differential diagnosis is medical jargon for "other things it could be."

Because no tests confirm PsA, it's important to test for similar conditions so they can be excluded. These conditions and their distinguishing features include:

• Rheumatoid arthritis: Positive RF factor blood test, damage on hand X-rays, joints on both sides of the body are affected
• Reactive arthritis: Soft tissue swelling, mainly in weight-bearing joints
• Ankylosing spondylitis: MRI shows symmetrical inflammation of the sacroiliac (SI) joint (at the base of your spine) and the ilium (the bone that forms the upper part of the pelvis)
• Osteoarthritis: Negative for inflammatory markers, excess wear in the central portion of a bone seen on an X-ray ("gull-wing deformity")
• Gout: Uric acid crystals in joint fluid
• Lupus: Diagnosed based on an ANA test and biopsy of the skin or a kidney
• Fibromyalgia: Tender-point exam to check for widespread pain or questionnaires based on symptoms and severities
• Mycobacterial tenosynovitis: Lab culture shows bacterial infection
• Sarcoid dactylitis: Complication of the inflammatory disease sarcoidosis that causes lumps of cells called granulomas; X-ray shows bone cysts, tissue biopsy detects granulomas

It can take several rounds of testing before you find out what's causing your symptoms. This process can be frustrating, but it's the only way to ensure a proper diagnosis and determine the right treatment.

Racial Disparities in PsA

Serious racial disparities exist when it comes to psoriatic arthritis severity and treatment. For example, Black people tend to have more severe:

• Skin involvement
• Psychological impact
• Impaired quality of life

Despite that, they're less likely than White people to be put on immunosuppressant drugs—the preferred treatment for PsA.

Studies suggest psoriatic arthritis is diagnosed less often in:

• Black people
• People of Asian descent
• Latinx people

Disparities mean a higher disease burden and lower quality of life for people with PsA who are in these groups.

Some studies show implicit, often unconscious biases against people of color throughout the healthcare community. This is believed to negatively affect treatment decisions and outcomes.

Some facilities have found that poverty plays a role. But when comparing Black and White people of the same socioeconomic status, outcomes remained worse for Black people.

Researchers have called for more investigation into these disparities and their impact, as well as better education for eliminating bias.

Summary

The PsA diagnostic process involves a review of your medical and family history, a physical exam, blood tests, and imaging. No test can diagnose PsA alone. Conditions with similar symptoms must be ruled out first.

If you suspect you have PsA, see a healthcare provider. If you are a person of color, know that there are documented disparities when it comes to PsA treatment. If you don't feel like you are receiving the care that you need, seek another healthcare practitioner.