A common diagnostic dilemma in spondyloarthritis—and how to approach it in the clinic
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Axial psoriatic arthritis involves the trunk, spine, and pelvis, and can cause chronic back pain and stiffness… Over time, [it] can permanently limit posture and spine mobility.
—Stella Bard, MD, rheumatologist
A patient presents with spine and joint pain. They have eye inflammation, irritable bowel syndrome (IBD), and changes to the nail bed, but no skin lesions.[] At first glance, this looks like axial spondyloarthritis. But psoriatic arthritis (PsA), including axial PsA (axPsA), can present the same way. If you’re stumped, you’re not alone.
Spondyloarthritis is an umbrella term referring to a group of chronic inflammatory diseases including axSpA and PsA, among other conditions.[] So how do you distinguish between them? Several clinical clues can help guide your diagnosis.
PsA's clinical clues
PsA itself has a unique presentation. According to researchers writing in RMD Open, inflammatory back pain is the leading clinical symptom in axSpA, but in PsA, oligoarthritis or polyarthritis, along with enthesitis, are the most common musculoskeletal symptoms, although axial manifestation may also be present.[] These symptoms can occur together with skin and nail involvement.
Another useful clue: 68% of PsA patients will see skin involvement before arthritis sets in.[] There’s also PsA sine psoriasis—in which rheumatological manifestations precede the onset of the skin lesions. This occurs in 13% to 25% of patients with PsA.[] Patients with PsA sine psoriasis tend to be HLA-Cw6 positive, have dactylitis, and experience pain in the hand’s distal interphalangeal joints.[]
Axial disease complicates the picture
To make matters more complicated, PsA symptoms may also involve axial pain. This is where axPsA—a disease that still lacks a clear definition—comes into play.
According to Stella Bard, MD, a rheumatologist at NY Arthritis, axPsA involves the trunk, spine, and pelvis, and it can cause chronic back pain and stiffness. "Over time, [it] can permanently limit posture and spine mobility,” she says. “Osteolysis is perhaps the scariest complication, causing bone erosion and bone destruction.”
Authors of a 2025 review in Therapeutic Advances in Musculoskeletal Disease note that increased understanding of the similarities and differences between axSpA and axPsA has revealed that, “besides their existing commonalities, there are significant pathophysiological discrepancies.”[]
Differentiating between axPsA and axSpA
Despite overlapping symptoms, several features can help differentiate axPsA from axSpA:
axPsA tends to affect older patients, and women and men equally; it isn’t as strongly associated with HLA-B27 as is axSpA.
axPsA also involves peripheral arthritis and enthesitis; spinal disease symptoms alone can occur.
Imaging looks a bit different: axPsA often shows unilateral and asymmetrical sacroiliac involvement, compared with symmetrical for axSpA.
axPsA may affect the spine without clear sacroiliitis—a pattern that’s uncommon in axSpA. In axSpA, patients tend to experience bilateral sacroiliitis.
Uveitis and IBD are more common in axSpA than axPsA.
The good news: “Over the last several years, there have become many treatment options and possibilities for both psoriasis and psoriatic arthritis,” Amy Kehl, MD, board-certified rheumatologist at Providence Saint John’s Health Center in Santa Monica, tells MDLinx. “The decision to use biologics specifically depends on the degree of disease activity. We consider the number of joints involved, or how much skin involvement there is, and the impact on the patient’s quality of life when weighing the risks and benefits of biologic medications,” she says.