Rheumatologist-assessed inflammatory back pain (IBP) or the criteria for IBP developed for ankylosing spondylitis might not perform well when determining axial involvement in psoriatic arthritis, according to a study published in Annals of the Rheumatic Diseases.
To assess the agreement between rheumatologist-judged IBP and IBP criteria (ie, Calin, Rudwaleit, and Assessment of Spondyloarthritis International Society criteria), researchers calculated likelihood ratios using the kappa coefficient to evaluate 171 patients (average age, 46.6 years) with chronic BP or IBP. Of the 171 study participants, 96 reported chronic BP, 65 patients had IBP, and 54 patients (32%) had evidence of radiologic changes in the spine.
Agreement between rheumatologist judgment of IBP and IBP criteria was found to be moderate and highest for the Calin criteria (kappa coefficient, 0.70), followed by the Assessment of Spondyloarthritis International Society criteria (kappa coefficient, 0.61) and the Rudwaleit criteria (kappa coefficient, 0.59). For the presence of radiologic axial involvement, the positive likelihood ratio was highest for the Rudwaleit criteria (kappa coefficient, 2.17).
With the exception of higher Bath Ankylosing Spondylitis Disease Activity Index scores and lower prevalence of human leucocyte antigen-B38 in participants with BP, there were no differences among patients with axial psoriatic arthritis.
The researchers reported several limitations to these findings, including that they did not perform spinal magnetic resonance imaging in all patients, they did not complete parallel comparison to a group of patients with axial spondyloarthritis, and they used a small number of patients in subgroup analyses.
“In order to stratify patients with poorer prognosis, rheumatologists should consider conducting axial imaging in all patients with psoriatic arthritis regardless of the presence or the nature of back pain,” concluded the study authors.
Yap KS, Ye JY, Li S, Gladman D, Chandran V. Back pain in psoriatic arthritis: defining prevalence, characteristics and performance of inflammatory back pain criteria in psoriatic arthritis [published online August 4, 2018] Annals of the Rheumatic Diseases. doi: 10.1136/annrheumdis-2018-213334