Medical Tests Used to Diagnose Psoriatic Arthritis

Psoriatic arthritis (PsA) is a type of inflammatory arthritis that affects the joints and entheses (the connective tissue between bone and tendons or ligaments). Common symptoms of PsA are joint pain, swelling, and morning stiffness. According to the National Psoriasis Foundation (NPF), PsA affects up to 30% of people with the autoimmune skin condition psoriasis.

Both PsA and psoriasis are autoimmune diseases, conditions where the immune system malfunctions and attacks healthy tissues. With PsA, those attacks are on the joints and entheses, leading to severe inflammation and swelling. With psoriasis, those attacks are on the skin, causing the body to make new skin cells more often, which pile up on the skin’s surface.  

This article covers the symptoms of PsA, tests for diagnosing the condition, and when to see a healthcare provider.

Psoriatic Arthritis Symptoms

PsA can affect any joint in the body. It can be asymmetrical (affecting joints on one side of the body) or symmetrical (involving the same joints on both sides).

Symptoms of PsA can start gradually and slowly worsen. They can also come on suddenly and become painful and severe quickly.  

Symptoms of PsA include:

• Dactylitis or painful swelling of the fingers and toes: This symptom is sometimes called “sausage digits” because it causes the fingers and toes to become so swollen that they resemble small sausages. It affects about half of the people with PsA and is often the first symptom of the condition, lasting for months or years.
• Enthesitis: This symptom refers to pain and inflammation of the entheses. It is common in early PsA and can significantly affect a person’s function and quality of life.
• Joint symptoms: These include pain, stiffness, swelling, and warmth
• Reduced range of motion: PsA joint swelling can make it harder to raise your arms, bend your knees or back, and twist the wrists and ankles. It can also make it harder to use your hands for activities like typing or opening a jar.
• Back, hip, and shoulder pain: PsA is a type of spondyloarthropathy, a condition that strikes the spine and nearby joints, leading to back, hip, and shoulder pain. According to the Spondylitis Association of America, spine involvement in PsA, called psoriatic spondylitis, affects about 20% of people with PsA.
• Skin symptoms: These appear as thick, red patches of skin called plaques. They can be dry, itchy, and sore.
• Nail symptoms: These include nail pitting (small dents), ridging, thickening, crumbling, nail bed separation, discoloration, and a buildup of skin cells under the nail.
• Chest and rib pain (costochondritis): This is due to cartilage inflammation in the area linking the breastbone to the ribs.
• Eye inflammation from uveitis: Symptoms might include blurry vision, floating spots in the line of sight, eye pain, eye redness, and light sensitivity.
• Fatigue: This is an early sign of PsA that causes extreme tiredness and exhaustion, leading to a lack of energy or motivation to function in your daily life.

PsA Disease Complications  

PsA can lead to other severe health conditions. These conditions are caused by the same inflammatory processes that attack the joints and skin. PsA treatment can prevent these complications.  

PsA disease complications might include: 

• Life-threatening infections
  
• Heart disease
• Interstitial lung disease (scarring of the lungs)
• Depression
• Inflammatory gastrointestinal diseases, such as inflammatory bowel disease
• Arthritis mutilans: A rare but severe, destructive form of PsA that attacks the joints of the fingers and toes
• Psoriatic spondylitis

Psoriatic Arthritis Tests

There is no single test that can confirm a diagnosis of PsA. Your healthcare provider will rely on blood work, imaging, bone density scans, joint fluid testing, and more in determining the source of your symptoms.

Blood Tests

Blood tests can help confirm PsA and rule out other types of inflammatory arthritis.

• Erythrocyte sedimentation rate (sed rate or ESR): This blood test measures inflammation in the body. It looks at how fast red blood cells will settle to the bottom of tube. The faster they fall, the more severe the inflammation.
• C-reactive protein (CRP): CRP is another indicator of inflammation in the body. High CRP levels are typical in PsA. However, a CRP blood test is not enough to confirm a diagnosis because other types of inflammatory arthritis like rheumatoid arthritis (RA) also cause high levels of CRP.
• Rheumatoid factor (RF) and CCP antibody testing: RF and anti-CCP testing can rule out RA. People with RA have higher levels of RF and CCP in their blood, and these tests are generally negative in PsA.
• HLA-B27 genetic blood markers: Researchers have identified a genetic marker linked to PsA called human leukocyte antigen B27 (HLA-B27). HLA-B-27 is located on the surface of white blood cells. The prevalence of HLA-B27 ranges from 20% to 35% in people with PsA and is often linked to spine inflammation.
• Serum uric acid: Elevated uric acid levels are sometimes found in people with PsA. They are also linked to gout, high blood pressure, and heart disease. 

Imaging Tests

If your healthcare provider suspects PsA, they will request imaging studies, including X-rays, magnetic resonance imaging (MRI), and ultrasound.

According to a 2018 report in the journal Arthritis & Therapy, PsA imaging is vital even early in the disease process. PsA can cause bone erosion (loss of normal bone) and joint destruction even before you notice symptoms. These changes are specific to PsA and rarely seen with other types of inflammatory arthritis.

The different types of imaging that look for signs of PsA are:  

• X-rays: X-rays can show bone changes, including bone erosions and bony growths. They can also identify joint spacing—a sign of cartilage or soft tissue damage.
• Magnetic resonance imaging (MRI): MRI scans offer a more detailed picture than X-rays. They can better visualize bone and surrounding tissues. They can also show inflammation and its effects on the entheses and sacroiliac (SI) joints (the joints that link the pelvis and lower spine).
• Ultrasound: Ultrasound imaging can show inflammation at the synovium—the linings of the joints. They can also look for early signs of bone erosion and bone spurs. Ultrasound tends to be more helpful in early PsA because it is sensitive enough to detect the initial stages of joint damage.

Joint Fluid Test

Arthrocentesis, or a joint fluid test, takes a small amount of fluid from the knee or another joint. If uric acid crystals are found in the fluid, your healthcare provider might look into further testing for gout.  

Anemia Tests 

People with inflammatory diseases like PsA can develop anemia (low number of healthy red blood cells). Symptoms of anemia include exhaustion, dizziness, and shortness of breath.

Chronic inflammation is generally the cause of anemia in PsA. This type of anemia is treated by getting inflammation under control. Tests for anemia include a complete blood count and may include tests for iron levels to rule out other types of anemia.

Other Diagnostic Tools

Additional diagnostic tools that aid your healthcare provider in a PsA diagnosis are your medical and family history and a physical examination.

Medical History

Your healthcare provider will ask when your symptoms started and the specific symptoms you have experienced. They will also want to know if you have a personal medical history of psoriasis or a family history of PsA or psoriasis.  

If you are experiencing more severe symptoms of PsA, including eye problems and gastrointestinal symptoms, you should let your healthcare provider know. These symptoms might be an indication that PsA is quickly progressing.  

Physical Examination

Your healthcare provider will want to examine the joints, entheses, skin, and nails if they suspect PsA.  

• Joints: When examining the joints, your healthcare provider will do so by touch to look for tenderness and swelling. They will examine the fingers and toes, hands, wrists, elbows, shoulders, hips, ankles, sternum, and jaws.
• Entheses: Your healthcare provider is looking for signs of enthesitis, which classically affects the heels and soles of the feet. It can also affect the rib cage, spine, pelvis, elbows, and knees. Any inflamed area will be sore and tender.
• Skin and nails: Your healthcare provider will examine the skin to look for signs of psoriasis, especially skin plaques. They will also check the nails for signs of nail involvement, such as pitting and ridging. 

When to See a Healthcare Provider

PsA is a progressive condition that will worsen over time and lead to severe, life-threatening complications if left untreated. It is, therefore, crucial to get a timely diagnosis and start treatment before joint and bone damage starts.

A timely diagnosis is critical if you have psoriasis or a family history of PsA or psoriasis. But you can still get PsA without risk factors.  

Regardless of risk factors, reach out to your healthcare provider if you experience any of the following:  

• Stiffness, pain, and swollen joints that last two or more weeks
• Morning joint stiffness or stiffness after periods of inactivity that stays for a half-hour or longer
• Finger or toe swelling with no known cause that lasts more than a few days and doesn’t resolve with home treatment or returns weeks or months later
• Nail or skin symptoms common in PsA
• Severe fatigue that lasts two or more weeks 

The sooner you receive a PsA diagnosis and start treating, the better your chance of avoiding joint and bone damage.

Summary

Psoriatic arthritis is an autoimmune disease where the immune system malfunctions and attacks healthy tissues, mainly the joints and entheses. Common signs of the condition are joint pain, morning stiffness, swollen fingers and toes, skin rash, and pitted nails.  

No one test can confirm PsA, so healthcare providers must rule out other conditions that cause similar symptoms, including rheumatoid arthritis and gout. A diagnosis may require a medical and family history, physical examination, blood work, lab testing, and imaging.

A Word From Verywell

Psoriatic arthritis is a lifelong condition without a cure. But the outlook for the condition is improving and will continue to improve as researchers look for new and more advanced treatment options. The many currently available treatment options can relieve your symptoms, slow down disease progression, and even lead to remission.

It is OK to be hopeful about the future with a chronic condition like PsA. Choose to keep doing the things that make you happy and stay connected with friends and family as much as you can. If you think you are depressed or just struggling to cope, find a therapist you can trust.