Objective We aimed to determine the agreement between rheumatologist-judged inflammatory back pain (IBP) and criteria defining IBP in patients with psoriatic arthritis (PsA) and predictive value of IBP in identifying axial involvement in PsA.
Methods Using prospectively collected data, we investigated the agreement between rheumatologist judgement of IBP and IBP criteria (Calin, Rudwaleit and Assessment of Spondyloarthritis International Society) using the kappa coefficient. We also determined the sensitivity, specificity and likelihood ratios of the presence of back pain, rheumatologist-judged IBP and the three IBP criteria for detecting axial PsA (AxPsA). Finally, we compared the clinical and genetic markers in patients with PsA with axial radiological changes with and without back pain.
Results 171 patients (52% male, mean age 46.6 years) were identified. Ninety-six (56.13%) patients reported chronic back pain. Sixty-five (38.01%) had IBP. 54 (32%) patients had evidence of radiological change in the spine. The agreement between rheumatologist judgement of IBP and IBP criteria was highest for the Calin criteria (0.70). Positive likelihood ratio for the presence of radiological axial involvement was highest for Rudwaleit criteria (2.17). No differences between patients with AxPsA with or without back pain were found, except for higher Bath Ankylosing Spondylitis Disease Activity Index and lower prevalence of human leucocyte antigen-B*38 in those with back pain.
Conclusion Rheumatologist-judged IBP or the criteria for IBP developed for ankylosing spondylitis may not perform well when ascertaining axial involvement in PsA.
- likelihood ratio
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Handling editor Josef S Smolen
Contributors All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. All authors were likewise involved in the study conception and design, acquisition of data as well as analysis and interpretation of data. VC had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Funding The Psoriatic Arthritis Program is supported by the Krembil Foundation.
Competing interests KSY was supported by a Ken Muirden Scholarship from Arthritis Australia.
Patient consent Not required.
Ethics approval University Health Network Research Ethics Board.
Provenance and peer review Not commissioned; externally peer reviewed.
Presented at This paper is based on work previously presented at the 2016 ACR/ARHP Annual Meeting and was published as a conference abstract.