From the Journals

AS inflammatory back pain criteria fall short in PsA

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Findings reinforce the value of imaging for AxPsA

Identifying psoriatic arthritis with axial disease (AxPsA) is important because it changes the treatment selection and also may be associated with a more severe disease course. In a recent paper by Yap et al, the investigators underscore the challenges in identifying the prevalence of axial disease in PsA. Many of our patients with PsA report back pain at some point in their disease course, and as the rheumatologist, we must grapple with whether their symptoms represent inflammatory disease that requires a change in therapy.

Dr. Alexis R. Ogdie

In this study, the authors examined the correlation of three definitions of inflammatory back pain (IBP) with both the rheumatologist’s assessment of whether the patient has IBP and with the presence of imaging findings such as x-ray or MRI abnormalities in the sacroiliac joints or lumbar spine. Of the 171 patients studied, 38% were reported to have IBP per the rheumatologist, 18% were thought to have noninflammatory back pain, and 32% had imaging findings consistent with AxSpA. The agreement between the rheumatologist and the inflammatory back pain criteria was reasonable (kappa 0.6-0.7). Rheumatologists and IBP criteria had moderate sensitivity (0.73-0.82) for having x-ray or MRI changes consistent with axial disease but low specificity (0.33-0.46). Surprisingly, HLA markers were not good markers of having axial disease in this population, aside from HLA-B38, which was protective but relatively uncommon.

The bottom line is that using IBP criteria or our general gestalt is still not as good as getting appropriate imaging and further underscores the potential need to screen patients with PsA, particularly those reporting back pain, for axial involvement.

Alexis R. Ogdie, MD, is director of the Penn Psoriatic Arthritis Clinic at the University of Pennsylvania, Philadelphia, and is a member of the steering committee for the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis.



Established criteria for identifying inflammatory back pain in people with ankylosing spondylitis do not perform well in identifying axial involvement in people with psoriatic arthritis and neither does clinical judgment, a study shows.

radiograph of ankylosing spondylitis feellife/Thinkstock

There’s reason to believe that the natural history of patients with psoriatic arthritis (PsA) who have axial disease could differ from those without it, and there are differences in how well criteria that are currently used to identify inflammatory back pain (IBP) in people with ankylosing spondylitis (AS) perform in people with PsA, study first author Kristy S. Yap, MBBS, and her colleagues at the University of Toronto Psoriatic Arthritis Clinic wrote in Annals of the Rheumatic Diseases.

“Axial involvement in PsA is a marker of disease severity, and those with axial disease often have worse outcomes, compared with peripheral arthritis alone,” they wrote.

This is backed up by European League Against Rheumatism recommendations that advise clinicians to consider prescribing tumor necrosis factor inhibitors for people with PsA who have active axial involvement.

“Thus, an important question when evaluating a patient with PsA is to determine if axial PsA is present,” they wrote, noting that it was currently unclear whether the three sets of criteria that exist for defining inflammatory back pain in AS – Calin, Rudwaleit, and Assessment of Spondyloarthritis International Society (ASAS) – were useful for screening for axial involvement in people with PsA.

The researchers therefore set out to determine the agreement between rheumatologist judgment of the presence of IBP as well as the presence of IBP according to the three criteria in 171 patients with PsA (52% male, average age 46.6 years), 96 of whom reported chronic back pain, including 65 with IBP and 31 with nonspecific back pain.

Radiology data from these patients showed that 27 with baseline x-rays fulfilled the New York radiographic criteria for AS, and 45 had radiographic sacroiliitis not satisfying NY criteria (excluding grade 1) and/or syndesmophytes. Nine out of 31 patients with no axial disease on x-ray had evidence of axial disease on MRI. Eighteen out of 54 patients had axial involvement without back pain.

Results showed that agreement (kappa coefficient) between rheumatologist judgment of IBP and IBP criteria in patients with back pain was moderate and was highest for the Calin criteria (0.70; 95% confidence interval, 0.56-0.85), followed by the ASAS criteria (0.61; 95% CI, 0.46-0.76) and the Rudwaleit criteria (0.59; 95% CI, 0.44-0.74).

When x-ray or MRI change was considered “gold standard” for axial involvement for all patients, the specificity was high for rheumatologist judgment of IBP as well as Calin, Rudwaleit, and ASAS criteria, but their sensitivity was low, the researchers reported.

When the investigators compared positive likelihood ratios (LRs) for the presence of back pain, the Rudwaleit criteria (2.17) performed the best in ruling in axial disease, whereas the LRs were 1.75 for Calin and 1.86 for ASAS criteria. Rheumatologist-reported back pain (0.68) performed the best for ruling out axial disease when comparing negative LRs.

“The low positive LRs of the Calin, Rudwaleit, and ASAS criteria as well as that of rheumatologist report of back pain or judgment of IBP for [axial] PsA defined as any axial radiological change found in our study suggests that none of these criteria performed well in detecting axial disease in patients with PsA,” the study authors wrote.

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