Getting the right diagnosis for peripheral spondyloarthritis can take time, but it’s an important first step toward managing symptoms and protecting your joints. Since many of the symptoms overlap with other conditions, doctors use a combination of your medical history, physical examination, and specific tests to confirm the diagnosis.

Who Should Consider Getting Tested for Peripheral Spondyloarthritis

If you’re experiencing peripheral spondyloarthritis, which is a type of inflammatory arthritis that primarily affects the joints in your arms and legs rather than your spine, you might notice certain symptoms that should prompt you to see a doctor. This condition is part of the larger family of spondyloarthritis diseases, but unlike the axial form that mainly affects the spine, peripheral spondyloarthritis causes inflammation in joints away from the center of your body.^[1]

You should consider seeking medical evaluation if you have painful swelling in your knees, ankles, wrists, or other joints in your arms and legs that doesn’t seem to be getting better. This is especially true if the pain lasts for more than a few weeks and isn’t the result of an obvious injury. One characteristic feature to watch for is inflammation where your tendons and ligaments attach to your bones, a condition called enthesitis. This often causes heel pain or discomfort around your knees.^[1]

Another telltale sign is when your fingers or toes become swollen and puffy, taking on what doctors describe as a “sausage-like” appearance. This swelling, called dactylitis, can make your digits look noticeably larger than normal and can be quite painful.^[4]

Young adults are particularly at risk, as spondyloarthritis often begins in people before the age of 45, frequently starting in the teens or twenties. If you’re in this age group and experiencing these symptoms, it’s especially important not to dismiss them as just normal aches and pains.^[2]

You should also pay attention to other symptoms that might seem unrelated to your joint problems. People with peripheral spondyloarthritis sometimes develop eye inflammation, skin problems like psoriasis, or digestive issues such as diarrhea. These extra symptoms, called extra-articular manifestations, can be clues that help doctors make the right diagnosis.^[4]

How Doctors Diagnose Peripheral Spondyloarthritis

Diagnosing peripheral spondyloarthritis can be challenging because there isn’t a single test that can definitively confirm the condition. Instead, doctors look at the complete picture of your symptoms, medical history, examination findings, and test results together. This comprehensive approach helps distinguish peripheral spondyloarthritis from other conditions that might cause similar symptoms, such as rheumatoid arthritis or other forms of joint disease.^[3]

Medical History and Physical Examination

Your doctor will typically begin by asking detailed questions about your symptoms. They’ll want to know exactly which joints hurt, how long you’ve had the pain, and what makes it better or worse. They’ll also ask about any family history of arthritis, psoriasis, inflammatory bowel disease, or eye problems, since these conditions are connected to spondyloarthritis.^[4]

During the physical examination, your doctor will carefully check all of your joints for swelling, tenderness, and range of motion. They’ll pay special attention to areas where tendons and ligaments attach to bones, particularly around your heels, knees, and other common sites of enthesitis. They’ll also look for swollen fingers or toes and examine your skin and nails for signs of psoriasis.^[4]

Blood Tests

Blood tests play an important role in the diagnostic process, though they can’t diagnose peripheral spondyloarthritis on their own. Your doctor will likely order tests to measure markers of inflammation in your body, such as C-reactive protein or erythrocyte sedimentation rate. These tests show whether inflammation is present, but they don’t tell doctors exactly what’s causing it.^[4]

Another common blood test checks for a gene called HLA-B27. Many people with spondyloarthritis carry this gene, though not everyone who has it develops the disease. Similarly, some people with spondyloarthritis don’t have the gene at all. This means a positive test can support the diagnosis, but a negative test doesn’t rule it out.^[1]

Importantly, people with spondyloarthritis typically test negative for rheumatoid factor, an antibody that’s commonly found in people with rheumatoid arthritis. This is why spondyloarthritis is sometimes called “seronegative,” meaning that this particular blood marker is negative. This distinction helps doctors differentiate spondyloarthritis from rheumatoid arthritis.^[1]

Imaging Studies

Imaging tests help doctors see what’s happening inside your joints and bones. The specific type of imaging your doctor orders will depend on your particular symptoms and which joints are affected.^[4]

X-rays are often the first imaging test performed. For peripheral spondyloarthritis, doctors commonly order X-rays of the hands and feet to look for signs of joint damage or inflammation. If you have symptoms in larger joints like the knees or hips, those might be X-rayed as well. X-rays can show changes in the bone and joint structure, though early in the disease these changes might not yet be visible.^[11]

If X-rays don’t provide enough information or if your doctor suspects inflammation that isn’t yet visible on X-rays, they might recommend an ultrasound or MRI scan. Ultrasound is particularly useful for detecting inflammation in tendons and ligaments, which is common in peripheral spondyloarthritis. MRI scans can show inflammation in soft tissues and bones in great detail, making them valuable for catching problems early.^[11]

Your doctor might also order imaging of your sacroiliac joints—the joints that connect your spine to your pelvis. This is because some people with peripheral spondyloarthritis also have inflammation in these central joints, even if their main symptoms are in their arms and legs. Finding inflammation in the sacroiliac joints can help confirm the diagnosis.^[11]

Tests Used to Qualify for Clinical Trials

When researchers design clinical trials to test new treatments for peripheral spondyloarthritis, they need to make sure that everyone enrolled in the study truly has the condition. This requires standardized testing and criteria that all participants must meet.

Most clinical trials for peripheral spondyloarthritis use classification criteria developed by the Assessment of SpondyloArthritis International Society, known as ASAS. These criteria look at a combination of symptoms, examination findings, blood tests, and imaging results to determine whether someone has peripheral spondyloarthritis. To meet these criteria, patients typically need to have arthritis, enthesitis, or dactylitis as their main symptoms, plus one or more additional features of spondyloarthritis.^[3]

Clinical trials usually require participants to have blood tests showing inflammation, such as elevated C-reactive protein or erythrocyte sedimentation rate. These measurements help researchers confirm that participants have active disease and also provide a way to track whether the experimental treatment is reducing inflammation over time.^[11]

Imaging studies are also standard requirements for enrollment in clinical trials. Depending on the study, participants might need to have X-rays, ultrasound, or MRI scans showing evidence of inflammation or damage in their peripheral joints. For some studies, participants must have imaging of the sacroiliac joints as well, even if peripheral symptoms are the main concern.^[11]

Trials may also test for the HLA-B27 gene, though having or not having this gene usually doesn’t determine whether someone can participate. Instead, researchers often collect this information to better understand how genetic factors might affect treatment response.^[13]

Some clinical trials require participants to have symptoms for a certain length of time—either a minimum duration to ensure the condition is chronic, or a maximum duration to focus on people with early disease. For example, one study of peripheral spondyloarthritis specifically enrolled people who had experienced symptoms for fewer than 12 weeks, focusing on very early disease.^[13]

Trials testing different types of treatments may have additional specific requirements. Studies of medications called disease-modifying antirheumatic drugs or DMARDs typically focus on people with joint inflammation in multiple locations. Studies of newer medications called biologics might require that participants have already tried standard treatments without sufficient improvement.^[8]

Importantly, clinical trials often exclude people who have certain subtypes of peripheral spondyloarthritis, particularly psoriatic arthritis. This is because treatments for psoriatic arthritis are already well-studied and approved, so researchers want to focus on people with non-psoriatic forms of peripheral spondyloarthritis, where treatment options are more limited.^[3]