Objective: Inflammatory back pain (IBP) is an important clinical symptom in patients with axial spondyloarthritis (SpA) and relevant for classification and diagnosis. Here we report about a new approach for the development of IBP classification criteria.
Methods: Rheumatologists (n=13) who are experts in SpA took part in a two day international workshop to investigate 20 patients with back pain and possible SpA. Each expert documented the presence/ absence of clinical parameters typical for IBP, and judged whether IBP was considered present or absent, based on the evoked information. This expert judgement was used as the dependent variable in a logistic regression analysis in order to identify those individual IBP parameters that contributed best to IBP. The new set of IBP criteria was validated in a separate cohort of patients (n=648).
Results: Five parameters explained best IBP according to experts. These were: 1) improvement with exercise (odds ratio (OR) 23.1); 2) pain at night (OR 20.4); 3) insidious onset (OR 12.7); 4) age at onset <40 years (OR 9.9); and 5) no improvement with rest (OR 7.7). If at least 4 out of these 5 parameters were fulfilled the criteria had a sensitivity of 77.0% and specificity of 91.7% in the workshop patients, and 79.6% and 72.4%, respectively, in the validation cohort.
Conclusion: This new approach with real patients defines a set of IBP definition criteria using the expert’s overall judgement on IBP as gold standard. The IBP experts criteria are robust, easy to apply and have a good face validity.