AS inflammatory back pain criteria fall short in PsA

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.