Diagnostic accuracy of inflammatory back pain for axial spondyloarthritis in rheumatological care

Abstract

ObjectiveInflammatory back pain (IBP), the key symptom of axial spondyloarthritis (axSpA), including ankylosing spondylitis, has been proposed as a screening test for patients presenting with chronic back pain in primary care. The diagnostic accuracy of IBP in the rheumatology setting is unknown.MethodsSix rheumatology centres, representing secondary and tertiary rheumatology care, included routinely referred patients with consecutive chronic back pain with suspicion of axSpA. IBP (diagnostic test) was assessed in each centre by an independent (blinded) rheumatologist; a second (unblinded) rheumatologist made the diagnosis (axSpA or no-axSpA), which served as reference standard.ResultsOf 461 routinely referred patients, 403 received a final diagnosis. IBP was present in 67.3%, and 44.6% (180/403) were diagnosed as axSpA. The sensitivity of IBP according to various definitions (global judgement, Calin, Berlin, Assessment of SpondyloArthritis international Society criteria for IBP) was 74.4%–81.1 % and comparable to published figures, whereas the specificity was unexpectedly low (25.1%–43.9%). The resulting positive likelihood ratios (LR+) were 1.1–1.4 and without major differences between sets of IBP criteria. The presence of IBP according to various definitions increased the probability of axSpA by 2.5%–8.4% only (from 44.6% to 47.1%–53.0%).ConclusionsThe diagnostic utility of IBP in the rheumatology setting was smaller than expected. However, this was counterbalanced by a high prevalence of IBP among referred patients, demonstrating the effective usage of IBP in primary care as selection parameter for referral to rheumatology. Notably, this study illustrates potential shifts in specificity and LR+ of diagnostic tests if these tests are used to select patients for referral.

Low specificity but high sensitivity of inflammatory back pain criteria in rheumatology settings in Europe: confirmation of findings from a German cohort study

“…IBP and individual IBP parameters are commonly seen in patients with and without an axSpA diagnosis. Our data confirm results from Germany, in which similar sensitivity (73.9–88.9) and specificity (22.7–39.5) for IBP according to the ASAS criteria are described 6. These studies show that approximately every second patient seen by a rheumatologist fulfils the IBP criteria but does not have axSpA.…”

“…A recent study in German chronic back pain patients with a suspicion of axSpA report on the performance of, among others, the Assessment of Spondyloarthritis international Society (ASAS) IBP criteria and individual IBP parameters. Data showed high sensitivity of the criteria and individual IBP parameters, however specificity was low 6. Important findings like low specificity indicate that in the German rheumatology setting diagnostic utility of IBP criteria was lower than expected.…”

Non-radiographic versus radiographic axSpA: what’s in a name?

“…Remarkably, r-axSpA presents an earlier age at disease onset [ 19 ], and this has been shown to be significant in a recent meta-analysis [ 12 ]. The characteristics of the presenting low back pain between both subgroups have not been thoroughly studied, yet percentages of inflammatory back pain are similar in a referral study [ 20 ]. Focusing on peripheral manifestations, there are conflicting results depending on the inclusion criteria used by the two meta-analyses available [ 12 , 21 ], with the largest study reporting a higher prevalence of peripheral arthritis, enthesitis and dactylitis on the nr-axSpA population, which may have reflected a selection bias as argued by the authors [ 12 ].…”

Classification vs diagnostic criteria: the challenge of diagnosing axial spondyloarthritis

“…In a recent systematic evaluation of the diagnostic performance of inflammatory back pain, the sensitivity for the diagnosis of axial SpA ranged 74.4%–81.1% across the different criteria set, whereas the specificity was rather low, with a range 25.1%–43.9% [ 16 ]. These data were recently confirmed in an independent cohort [ 17 ].…”