Correspondence on ‘No efficacy of anti-IL-23 therapy for axial spondyloarthritis in randomised controlled trials but in post-hoc analyses of psoriatic arthritis-related ‘physician-reported spondylitis’?’

We read with interest the Viewpoint article by Braun and Landewe1 regarding post- hoc analysis of back pain in trials of interleukin (IL)-23 inhibitor therapy in patients with peripheral psoriatic arthritis (PsA). Indeed, we share their concerns regarding study design, the use of outcome measures developed for axial spondyloarthritis (axSpA) and, most importantly, the attribution of the diagnostic label ‘physician-reported spondylitis’ in these patients. In addition to the issues eloquently outlined in the article, it is important to be aware that the pre-test probability of inflammatory disease being directly responsible for back pain is likely much lower in patients with PsA who are older and therefore more likely to have mechanical or non-specific back pain than people presenting with axSpA. In other words, even before doing any test, a middle-aged person with PsA, as represented in most phase III PsA clinical trials, is more likely to have non-inflammatory than inflammatory back …