About 1 in 3 people with psoriasis also have psoriatic arthritis (PsA), but some haven’t been diagnosed yet. Joint pain, swelling, stiffness, or back pain in someone with a history of psoriasis — whether you or your child — is a reason to see your healthcare provider. If you have PsA, an early diagnosis can help prevent long-term joint damage.

Although no single test can confirm a diagnosis of PsA, dermatologists and rheumatologists can review the results of several tests to look for signs of PsA, determine how severe it is, and recommend effective treatment options.

Diagnosing PsA early can help prevent long-term joint damage.

Psoriatic Arthritis and Psoriasis

PsA is a long-term inflammatory disease that causes joint pain, swelling, and stiffness. PsA is diagnosed using a range of clinical tools, including medical history, physical examination, blood tests, and imaging studies. In some cases, doctors may take a biopsy of a skin lesion or joint fluid to help rule out other types of arthritis.

In approximately 80 percent of people with PsA, psoriasis appears before joint symptoms begin. PsA symptoms can look similar to other types of inflammatory arthritis, like rheumatoid arthritis and ankylosing spondylitis. They can also resemble gout, a form of arthritis that causes sudden joint pain, swelling, and redness. Because of these similarities, people are sometimes misdiagnosed. According to an article in Rheumatology and Therapy, PsA affects men and women equally.

Medical History and Examination

Rheumatologists typically diagnose and treat PsA. They start by taking a medical history. Approximately 40 percent of people with PsA have at least one close family member with psoriasis or PsA. Your healthcare provider will likely ask if anyone in your family has psoriasis or another autoimmune disease. (An autoimmune disease is a condition that develops when the immune system mistakenly attacks the body’s own tissues.) If you’re not sure, talk to your relatives before your appointment so you can provide that information.

You’ll have a physical exam to check your skin, nails, and joints for possible symptoms of PsA or psoriasis. Your doctor may ask when the symptoms first started, how often they appear, how severe they are, and any factors that make them better or worse.

Your doctor may also check your hands and feet for PsA symptoms. They’ll look for:

• Nail changes — Pitting, crumbling, or ridging of fingernails and toenails, including separation from the nail bed, are an early sign of PsA.
• Swollen fingers or toes — This condition is called dactylitis or “sausage digits.”
• Enthesitis — You may experience pain and swelling of tendons and ligaments where they attach to bone.
• Other typical symptoms of PsA — These may include joint pain, stiffness, and fatigue.

By gently pressing on certain areas, your doctor can check for pain, tenderness, swelling, or warmth to assess the health of your joints. You may be asked to perform simple physical activities that show range of motion, stiffness, and overall mobility.

If you have back pain, fatigue, or any other potential PsA symptoms, tell your doctor during the physical exam. The more information you provide, the more likely you’ll get an accurate diagnosis.

Some people can have PsA even if they don’t have visible psoriasis. Doctors might find hidden plaques (on the scalp, belly button, or buttocks).

What Tests Confirm Psoriatic Arthritis?

No single test or marker can say for sure if someone has PsA. However, your doctor can use a few different blood tests to measure inflammation levels and rule out other types of arthritis. ​If you have questions about blood tests for PsA, schedule an appointment with your healthcare provider.

No single test can say for sure if someone has PsA. However, your doctor can use a few different blood tests to measure inflammation levels and rule out other types of arthritis.

C-Reactive Protein

This test measures amounts of C-reactive protein (CRP), a molecule made by the liver and released into the bloodstream when you have high levels of inflammation. High CRP levels indicate inflammation. A CRP test can’t confirm a PsA diagnosis on its own. However, when used with other blood tests and imaging studies, a CRP test can help your doctor make an accurate diagnosis by providing more information.

Erythrocyte Sedimentation Rate

An erythrocyte sedimentation rate (ESR) test detects levels of inflammation by measuring the rate at which red blood cells (erythrocytes) fall or settle in a tall, vertical tube. Sedimentation happens when red blood cells collect at the bottom of a test tube. A higher amount after one hour usually means more inflammation in the body. Like the CRP test, the ESR test alone doesn’t diagnose a specific illness, but it can be used with other tests to help narrow down the cause of your symptoms.

Rheumatoid Factor

This blood test is routinely used to diagnose or rule out rheumatoid arthritis. It measures levels of rheumatoid factor (RF), a protein that causes the immune system to mistakenly attack healthy tissues.

People with PsA usually test negative for rheumatoid factor (RF). If the RF test result is positive, it may point to rheumatoid arthritis instead of PsA.

Anti-Cyclic Citrullinated Peptide

Anti-cyclic citrullinated peptide (anti-CCP) is another type of protein that attacks healthy tissues in the body. An anti-CCP test is primarily used to diagnose or rule out RA.

Human Leukocyte Antigen B27

Human leukocyte antigen B27 (HLA-B27) is a gene linked to several autoimmune diseases, including PsA. A blood test for HLA-B27 may help your doctor find the cause of your joint pain. A positive HLA-B27 test result is also connected to conditions like ankylosing spondylitis (a type of inflammatory arthritis that affects the spine) and inflammatory bowel disease.

Imaging Tests for the Diagnosis of Psoriatic Arthritis

In addition to lab tests for PsA, diagnostic imaging is frequently used to confirm a PsA diagnosis. Below are examples of imaging tests your doctor might order.

X-Rays

Standard X-rays are most effective at diagnosing later-stage PsA. They can show serious bone damage — like the “pencil-in-cup” sign — that helps doctors tell PsA apart from other joint diseases. If your X-ray shows pencil-in-cup, it means the end of one bone has worn down into a sharp point, like a pencil, and fits into a nearby bone that’s hollowed out like a cup.

Ultrasound

Ultrasound uses sound waves to capture images inside the body. This test is more effective at showing early signs of PsA, compared to X-rays. This imaging test is good at detecting enthesis, which is commonly found in people with PsA.

MRI

MRI uses large magnets and radio waves to create images of organs and structures inside the body, like soft tissues that may be damaged by PsA. MRI scans are better than X-rays at detecting inflammation.

Biopsies for the Diagnosis of Psoriatic Arthritis

To learn more about a possible PsA diagnosis, your doctor may take a sample of fluid from a swollen joint or a small skin sample to check for signs of psoriasis. If you’ve got psoriasis on the skin, it’s a strong sign that joint symptoms could be caused by PsA.

Arthrocentesis

Arthrocentesis is a procedure used to rule out certain types of arthritis. Your doctor collects synovial fluid from your joints using a needle and syringe. Synovial fluid is a thick liquid found in your joints. It cushions your joints and reduces friction.

The fluid is then examined for several factors, such as uric acid, a natural waste product that can build up in the joints. High levels of uric acid indicate gout, a type of inflammatory arthritis that frequently affects the big toe. People with PsA may be at risk of developing gout.

Skin Biopsy

To confirm psoriasis and rule out other skin conditions, like eczema, your doctor may perform a punch biopsy. They use a pencil-shaped device to remove a small tissue sample to examine under a microscope, and then close the incision with a couple of stitches.

If you have questions about blood tests, imaging, biopsies, or how to test for PsA based on your symptoms, a doctor specializing in rheumatology can help.

Psoriatic Arthritis Classification Criteria

The Classification Criteria for Psoriatic Arthritis (CASPAR) are often used to define PsA. The CASPAR criteria require that a person already have some form of inflammatory arthritis and at least three points from the following list to be diagnosed with PsA:

• Active psoriasis — 2 points
• Family history of psoriatic disease — 1 point
• Nail psoriasis — 1 point
• Negative RF factor — 1 point
• Bone damage — 1 point
• Dactylitis — 1 point

What Is the Prognosis for Psoriatic Arthritis?

Although there is currently no cure for PsA, a growing range of treatments can help prevent the disease from progressing and causing permanent joint damage. Early diagnosis is important to protect your joints from irreversible damage. With the right treatment plan, many people are able to manage symptoms well and maintain a good quality of life. Regular checkups can help your doctor make changes to your treatment if needed.

Talk With Others Who Understand

On MyPsoriasisTeam, the social network for people with psoriasis and psoriatic arthritis, members come together to ask questions, give advice, and share their stories with others who understand life with psoriatic arthritis.

Have you been diagnosed with psoriatic arthritis? What was your experience with getting a diagnosis? Share your thoughts in the comments below, or start a conversation by posting on your Activities page.