Background/Purpose: Patients with psoriasis, iritis, or colitis and back pain represent a high-risk population for the presence of axial spondyloarthritis (axSpA). Clinicians rely on the elicitation of features of inflammatory back pain (IBP) to discriminate between more common non-specific back pain and inflammatory conditions. Different criteria have been developed for classification purposes, but these have been developed and validated in patients with established idiopathic ankylosing spondylitis. It is unknown how these criteria, namely ASAS, Berlin and Calin criteria, perform in patients presenting with back pain and extra-articular features of axSpA. To address the circularity between elicitation of IBP and clinical diagnosis, we used not only rheumatologist diagnosis as benchmark, but also imaging. We aimed to assess the diagnostic utility of all available criteria for IBP in an inception cohort of patients with psoriasis, iritis, or inflammatory bowel disease (IBD) referred to a rheumatologist with undiagnosed back pain, using the final rheumatologist diagnosis and imaging as the benchmarks.

Methods: The multicenter Screening for Axial Spondyloarthritis in Psoriasis, Iritis, and Colitis (SASPIC) Study is aimed at early detection of axial SpA in consecutive patients presenting with undiagnosed back pain to the rheumatologist. Consecutive patients ≤45 years of age with ≥3 months undiagnosed back pain with any one of psoriasis, acute anterior uveitis (AAU), or IBD diagnosed by the relevant specialist undergo routine clinical evaluation by a rheumatologist for axial SpA. The rheumatologist determines the presence or absence of axial SpA at 3 consecutive stages: 1. After the clinical examination; 2. After the results of labs (B27, CRP) and radiography; 3. After the results of local MRI evaluation. Imaging was also assessed centrally by 3 expert readers. Majority central reader evaluation of presence/absence of MRI indicative of axSpA and final diagnosis by the rheumatologist were used as external standards to test the performance (sensitivity, specificity, positive and negative likelihood ratios (LR+/LR-)) of the following criteria for IBP: ASAS, Berlin, Calin, rheumatologist global for likelihood of IBP >5 (0-10 scale).

Results: 246 patients were included, of whom 47.6% were diagnosed with axSpA by the local rheumatologist. The diagnosis of axSpA was confirmed in 45.7%, 61.6% and 40.2 % of patients with undiagnosed back pain and psoriasis, iritis, and IBD. The diagnostic utility for all IBP criteria was equally poor, especially showing a lack of specificity (Table 1). MRI was considered indicative of axSpA by central readers in 21.2%, 43.5% and 19.7% of patients with psoriasis, iritis, and IBD. When using MRI as external reference (Table 2), all IBP criteria performed even worse.

Conclusion: All IBP criteria, as well as rheumatologist global assessment, have poor diagnostic utility for diagnosis of axSpA in patients with undiagnosed back pain and extra-articular features. This should be a reminder to not rely only on the concept of IBP in daily routine, and also reinforces the desirability of less subjective assessment tools, especially imaging. 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-relative-diagnostic-utility-of-inflammatory-back-pain-criteria-in-an-inception-cohort-of-patients-with-psoriasis-iritis-and-colitis-presenting-with-undiagnosed-back-pain/